JP2007136163A - Panoramic imaging device, and image processing method in panoramic imaging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a panoramic imaging device, in which a panoramic image needs to be taken only once along a desired sectional surface along a tooth line of a patient to display images of inner structure of the tooth line with the optimum focal point as desired in accordance with the positions using obtained image data. <P>SOLUTION: This panoramic imaging device is provided with an X-ray source 31, and a detector 32 to output electric signals of digital quantity corresponding to an incidental X-ray at a specific frame rate. The device is also provided with a means 24 to move the pair of the X-ray source and the detector around the patient as they face each other through the patient, a means 54 to store output signals of the detector in order as frame data, a means 56 to generate panoramic images of a desired cross section based on the frame data, and means 56, 57, and 58 to generate a partial sectional image with the focal point set to a desired position in an imaging space in a designated partial range of the panoramic image along the desired cross section based on the frame data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a panoramic image photographing apparatus for photographing a panoramic image of a specific part of a subject, for example, a dentition, and an image processing method in the panoramic photographing, and in particular, an X-ray source and a digital X-ray arranged to face each other. A pair of X-ray detectors arranged so that the subject is interposed between the X-ray source and the X-ray detector, and in that state, along the predetermined trajectory around the subject, the X-ray source and the X-ray detector; The X-rays irradiated from the X-ray source and transmitted through the subject are detected by the X-ray detector every predetermined time while moving the pair of the X-rays, and the digital transmission X-ray data detected by the X-ray detector is detected. The present invention relates to a panoramic image photographing apparatus that uses a panoramic image of a subject and an image processing method in panoramic photographing.

  With the recent changes in food culture and lifestyle, the number of people receiving dental treatments is increasing, and dental specialists frequently require regular dental examinations and early treatment. Has been recommended. In the case of treating teeth, in many cases, X-ray imaging is performed to check the state of teeth (dentition) and gums. Conventionally, this X-ray imaging has often obtained a local projection image of the gum part using an X-ray film. However, as an alternative method or a combination thereof, an X-ray CT scanner or a dedicated dentistry is used. A dental panoramic image photographing apparatus is used.

  The X-ray CT scanner simply applies a generalized CT imaging method to the imaging of the jaw part, and the resolution of the panoramic image along the dentition reconstructed from the acquired image by this scanner is so high Instead, it is only used to examine the entire dentition.

  On the other hand, the dental panoramic imaging apparatus positions the pair of the X-ray source and the X-ray detector so as to sandwich the jaw part of the subject, and moves the pair around the jaw part to collect the X-ray transmission data, A panoramic image along a predetermined cross section for the dentition is generated from this data. As an example of this dental panoramic image photographing apparatus, an apparatus described in the cited document 1 is known.

  This cited document 1 shows an example of a digital panoramic image photographing apparatus (name of the invention is “digital panoramic X-ray photographing apparatus”). The panoramic image photographing apparatus includes a turning drive unit that integrally turns an X-ray source and an X-ray image detection unit that are arranged to face each other with a subject interposed therebetween. The X-ray source includes an X-ray tube and a collimator that narrows the X-rays emitted from the X-ray tube into a slit beam shape. The X-ray image detection unit includes an X-ray detector such as an X-ray CCD sensor that outputs a digital amount of an electrical signal corresponding to the incident X-ray dose. Further, this panoramic image photographing apparatus sequentially stores image information collected by the X-ray detector as a frame image, and sequentially reads out the image information at a predetermined time interval from the storage means, Image processing means for adding the read image information while shifting the image information by a predetermined distance with respect to the direction in which the image moves, and forming a panoramic image having an arbitrary cross section according to the read interval of the image information and the shift amount. . Accordingly, a panoramic image of a cross section along the patient's dentition can be provided as a diagnostic image on a monitor such as a personal computer without using an X-ray film.

JP-A-4-144548

  However, even with digital panoramic imaging by the above-described dental panoramic image capturing apparatus, panoramic images that sufficiently satisfy the requirements of the dentist are not necessarily provided.

  For example, in order to obtain a panoramic image optimal for diagnosis, it is necessary to set an imaging position in an optimal cross section along the dentition of the patient, but this is difficult. The reason is that it is not easy to set a cross section focusing on the site to be diagnosed. When trying to set such a cross-section for optimum focus, many have to rely on the photographer's shooting skills. When a diagnosis is performed using an out-of-focus image, that is, a blurred image, the diagnostic burden on the dentist increases accordingly.

  Further, in the case of a conventional dental panoramic image photographing device, each tooth and gum in the depth direction of the dentition (gum) (that is, the longitudinal direction of the dentition, that is, the thickness direction of each tooth) from the captured panoramic image. It is not possible to obtain the structural information inside of the information together with the position information or by specifying the position. That is, it is not possible to specify the position freely and obtain structural information inside the teeth and gums at that position. In addition, it is quite impossible to specify a three-dimensional position and obtain internal information on the dentition and gum structure at that position. That is, information on structures other than the dentition cross-section reflected in the panoramic image is hardly provided. On the other hand, the shape of teeth and the angle of how they grow are different in each individual's dentition, and there are naturally individual differences. For this reason, even if the interpreting doctor wants to examine the back part or the front part a little, wants to examine the cross section along the diagonal tooth, or wants to examine the cross section along the thickness direction of the tooth, I can't see it freely. Therefore, there is a tendency to lack information on which part of the tooth has decayed teeth and alveolar pyorrhea and what is the positional relationship between the gums, blood vessels and nerves.

  Therefore, in order to make up for such a lack of information, it is necessary to perform another photographing that complements the panoramic image. As the complementing method, there are, for example, a method in which intraoral imaging is separately performed while paying attention only to a region of interest, and a method in which X-ray tomography is separately performed using a panoramic image imaging apparatus or another apparatus. Thus, the captured panoramic image alone cannot be sufficiently used for diagnosis, and information supplement is necessary. This increases the time and effort until diagnosis and decreases patient throughput, but there is X-ray exposure based on re-imaging, which is not preferable for the patient.

  The present invention has been made in view of the situation of the conventional digital panoramic imaging described above, and it is only necessary to perform X-ray imaging of a panoramic image once along an arbitrary cross section along a patient's dentition. By using the image data collected by the above, the focal tomographic plane in the depth direction of the dentition and gums can be provided freely and with high resolution along with the distance information, and therefore a panoramic image photographing device easy to use for interpretation is provided. That is its main purpose.

  In order to achieve the above-described object, according to one aspect of the present invention, an X-ray source that emits X-rays and a detector that outputs a digital signal corresponding to the incident X-rays at a constant frame rate And a movement drive means for moving the X-ray source and the detector around the object in a state where the X-ray source and the detector are opposed to each other with the object interposed therebetween, and the movement drive means includes the X-ray source and the detection Based on the frame data stored in the storage means and the storage means for sequentially storing the electrical signals output by the detector at the frame rate as the frame data as the detector is moved around the subject. A panoramic image generating means for generating a panoramic image of a desired tomographic plane specified in advance, and the movement driving of a specified partial region of the panoramic image using the frame data. A partial cross-sectional image generating means for generating a partial cross-sectional image focused on a desired position in a space in which the X-ray source and the detector are moved by a stage; An imaging device is provided.

  Further, according to another aspect of the present invention, the detector is moved along with the X-ray source / detector pair moving around the object in a state of facing the object. Electrical signals output at a constant frame rate are sequentially stored as frame data, a panoramic image of a tomographic plane designated in advance is generated based on the stored frame data, and the panorama image is used using the frame data. A panorama generating a partial cross-sectional image focused on a desired partial area of an image according to a desired position in a space in which the X-ray source and the detector are moved. An image processing method for photographing is provided.

  According to the present invention, a panoramic image is only X-rayed once along an arbitrary cross section along a patient's dentition, and image data acquired by the imaging can be used to obtain a depth direction of the dentition and gums. The internal structure can be provided freely and with high resolution along with the distance information, and therefore a panoramic image photographing apparatus that is easy to use for interpretation can be provided.

  The best mode (embodiment) for carrying out the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
A first embodiment of a panoramic image photographing apparatus according to the present invention will be described with reference to FIGS.

  FIG. 1 shows an external appearance of a panoramic image photographing apparatus 1 according to this embodiment. As shown in the figure, the panoramic image photographing apparatus 1 includes a housing 11 that collects gray-level original image data for generating a panoramic image from a subject (patient) P in a standing posture of the subject, for example. For controlling the collection of data performed by the housing 11, generating the panorama image by capturing the collected data, and performing post-processing of the panorama image interactively with the operator (doctor, engineer), And a control / arithmetic unit 12 composed of a computer.

  The housing 11 includes a stand unit 13 and a photographing unit 14 that can move up and down with respect to the stand unit 13. The stand unit 13 includes a base 21 that is fixedly placed on the floor and a support column 22 that is erected on the base 21. In this embodiment, the support column 22 is formed in a prismatic shape, and the photographing unit 14 is attached to one of its side surfaces so as to be movable up and down within a predetermined range.

  Here, for convenience of explanation, an XYZ orthogonal coordinate system is set in which the longitudinal direction of the support column 22, that is, the vertical direction, is the Z axis. Note that, for a two-dimensional panoramic image described later, the horizontal direction is expressed as an x-axis and the vertical direction is expressed as a y-axis.

  The imaging unit 14 includes a vertical movement unit 23 having a substantially U-shape when viewed from the side, and a rotation unit 24 supported by the vertical movement unit 23 so as to be rotatable (rotatable). The vertical movement unit 23 can move in the Z-axis direction (vertical direction) over a predetermined range in the height direction via a drive mechanism 31 (for example, a motor and a rack and pinion) installed in the column portion 22. It has become. A command for this movement is issued from the control / arithmetic unit 12 to the drive mechanism 31.

  As described above, the vertical movement unit 23 is substantially U-shaped when viewed from one side surface thereof, and includes an upper arm 23A and a lower arm 23B on each of the upper and lower sides, and upper and lower arms 23A and 23B. The connecting vertical arm 23C is integrally formed. The vertical arm 23 </ b> C is supported by the column 22 described above so as to be movable up and down. Of these arms 23A to 23C, the upper arm 23A and the vertical arm 23C cooperate to define an internal space. A rotation drive mechanism 30 (for example, an electric motor and a reduction gear) for rotation drive is installed inside the upper arm 23A. The rotation drive mechanism 30 receives a rotation drive command from the control / arithmetic unit 12. The output shaft of the rotation drive mechanism 30, that is, the rotation shaft of the electric motor is arranged so as to protrude downward (downward in the Z-axis direction) from the upper arm 23A, and the rotation unit 24 can be rotated around this rotation shaft. Is bound to. That is, the rotation unit 24 is suspended by the vertical movement unit 23 and is rotated by being energized by the drive of the rotation drive mechanism 30.

  On the other hand, the lower arm 23B is extended to have a predetermined length in the same direction as the upper arm 23A, and a chin rest 25 is formed at the tip thereof. A mouthpiece 26 is detachably attached to the chin rest 25. The subject P holds the mouthpiece 26. For this reason, the chin rest 25 and the mouthpiece 26 serve to fix the oral cavity of the subject P.

  The rotating unit 24 has an appearance that is formed in a substantially U shape when viewed from one side surface in the state of use, and is rotatable to the motor output shaft of the upper arm 23A so that its open end can be rotated downward. It is attached. Specifically, a horizontal arm 24A that rotates (rotates) in the horizontal direction, that is, substantially parallel in the XY plane, and left and right vertical arms (first axis) extending downward (Z-axis direction) from both ends of the horizontal arm 24A. Vertical arm, second vertical arm) 24B, 24C. The horizontal arm 24 and the left and right first and second arms 24B and 24C play an important role in data collection, and the mechanisms and parts necessary for this are provided in the internal space defined by the arms 24A to 24C. It is equipped and is driven and operated under the control of the control / arithmetic unit 12.

  Specifically, an X-ray tube 31 as a radiation source is provided at the lower end inside the first vertical arm 24B, and X-rays can be exposed from the exit window toward the second vertical arm 24C. It has become. On the other hand, a digital X-ray detector 32 in which X-ray detection elements as radiation detection means are arranged in a two-dimensional slit shape (for example, a 64 × 1500 matrix shape) at the lower end inside the second vertical arm 24C. It is equipped and detects X-rays incident from this entrance window. As an example, the detector 32 includes a CdTe line detector (for example, 6.4 mm wide × 150 mm long). The detector 32 is arranged in the vertical direction with its vertical direction coinciding with the Z-axis direction. At the entrance IW of the detector 32, the scattered X-rays to the detector 32 are blocked, and the incident X-rays are actually collected through a window (for example, a window having a width of 3.5 mm; therefore, the lateral direction of the detector 32). Is provided with a slit-like collimator 33 (corresponding to the incident surface 32A of the detector 32). Thus, for example, incident X-rays can be collected as image data of a digital electric quantity corresponding to the amount of X-rays at a frame rate of 300 fps (one frame is, for example, 64 × 1500 pixels). Hereinafter, this collected data is referred to as “frame data” (also referred to as original frame data).

  For this reason, at the time of imaging, the pair of the X-ray tube 31 and the detector 32 is positioned so as to face each other across the oral cavity of the subject P and is driven so as to rotate around the oral cavity as a unit. Is done. At this time, the pair of the X-ray tube 31 and the detector 32 has a predetermined focus on a desired cross section (more precisely, a standard plane (standard tomographic plane) described later) along the dentition of the oral cavity, and the standard. It is rotationally driven to follow the surface. The shape of this standard surface when viewed from the Z-axis direction is substantially horseshoe-shaped. When following this standard plane, the X-ray tube 31 and the detector 32 do not necessarily rotate at the same angular velocity, but as a superordinate concept, the rotation can also be called “movement along an arc”. The standard surface is a surface parallel to the detection surface 32A (see FIG. 2) of the detector 32. In the present embodiment, the detection surface 32A is positioned so as to coincide with the Z-axis direction.

  FIG. 2 shows an electrical block diagram for control and processing of this panoramic image photographing apparatus. As shown in the figure, the X-ray tube 31 is connected to the control / arithmetic apparatus 12 via a high voltage generator 41 and a communication line 42, and the detector 32 is connected to the control / arithmetic apparatus 12 via a communication line 43. ing. The high voltage generator 41 is provided in the support column 22, the vertical movement unit 23, or the rotation unit 24. It is controlled according to the shooting conditions and the sequence of exposure timing.

  The control / arithmetic unit 12 is constituted by, for example, a personal computer capable of storing a large amount of image data in order to handle a large amount of image data, for example. That is, the control / arithmetic unit 12 has, as its main components, interfaces 51, 52, 62, a buffer memory 53, an image memory 54, a frame memory 55, which are connected to each other via an internal bus 50. An image processor 56, a controller (CPU) 57, and a D / A converter 59 are provided. An operation device 58 is communicably connected to the controller 57, and a D / A converter 59 is also connected to a monitor 60.

  Of these, the interfaces 51 and 52 are connected to the high voltage generator 41 and the detector 32, respectively, and communicate control information and collected data exchanged between the controller 57 and the high voltage generator 41 and the detector 32. Mediate. Another interface 62 connects the internal bus 50 and a communication line, and the controller 57 can communicate with an external device. As a result, the controller 57 can capture the intraoral image captured by the external intraoral X-ray imaging apparatus, as well as a panoramic image captured by the present imaging apparatus and a focus optimized image (described later) based on the image, for example. According to the DICOM (Digital Imaging and Communications in Medicine) standard, it can be sent to an external server.

  The buffer memory 53 temporarily stores digital frame data received from the detector 32 via the interface 52.

  The image processor 56 is placed under the control of the controller 57 and interactively generates a panoramic image of the standard surface along the patient's dentition and the subsequent use of the panoramic image with the operator. Has the function to execute. A program for realizing this function is stored in the ROM 61 in advance. In this embodiment, the standard plane is a tomographic plane selected from a plurality of prepared tomographic planes. That is, the position of the standard surface can be changed within a certain range in the depth direction of the dentition. The post-processing for generating and interpreting the panoramic image is one of the core features of the panoramic image photographing apparatus, and will be described in detail later.

  Frame data and image data processed by the image processor 56 or being processed are stored in the image memory 54 so as to be readable and writable. For the image memory 54, a large-capacity recording medium (nonvolatile and readable / writable) such as a hard disk is used. The frame memory 55 is used to display the generated panoramic image data and / or post-processed panoramic image data. The image data stored in the frame memory 55 is called by the D / A converter 59 at a predetermined cycle, converted into an analog signal, and displayed on the screen of the monitor 60.

  The controller 57 controls the overall operation of the constituent elements of the apparatus in accordance with a program responsible for overall control and processing stored in the ROM 61 in advance. Such a program is set so as to interactively receive operation information on predetermined items from the operator. For this reason, as will be described later, the controller 57 generates parameters that are necessary for reconstruction (which will be described later) that is responsible for generating a panoramic image of the standard plane and optimizing the focus of the panoramic image (that is, processing that reduces blurring of the image). Gain) setting, frame data collection (scanning), and operation information of the operator output from the operating device 58 can be taken into account and interactive control can be performed.

  For this reason, as shown in FIG. 1, the patient places the jaw at the position of the chin rest 25 in the standing or sitting posture, holds the mouthpiece 26, and presses the forehead against the headrest 28. As a result, the position of the patient's head (jaw) is fixed at substantially the center of the rotation space of the rotation unit 24. In this state, under the control of the controller 57, the rotation unit 24 rotates around the patient's head along the XY plane and / or along an oblique plane on the XY plane (see arrows in FIG. 1). .

  During this rotation, under the control of the controller 57, the high voltage generator 41 supplies a high voltage for irradiation (specified tube voltage and tube current) to the X-ray tube 31 in a pulse mode of a predetermined cycle. Then, the X-ray tube 31 is driven in a pulse mode. As a result, pulsed X-rays are emitted from the X-ray tube 31 at a predetermined cycle. The X-rays pass through the patient's jaw (dental portion) located at the imaging position and enter the line sensor type detector 32. As described above, the detector 32 detects incident X-rays at a very high frame rate (for example, 300 fps), and sequentially outputs the two-dimensional digital data (for example, 64 × 1500 pixels) of the corresponding electric quantity. This digital data is handled as the frame data described above, and is temporarily stored in the buffer memory 53 via the communication line 43 and the interface 52 of the control / arithmetic apparatus 12. The temporarily stored frame data is then transferred to the image memory 53 and stored.

  For this reason, the image processor 56 generates a panoramic image along the standard surface along the dentition by reconstruction using the frame data stored in the image memory 53, and the region of interest designated on the panoramic image. A focus-optimized image is generated by reconstruction using the frame data forming (ROI). It should be noted here that the panoramic image itself is an entire cross-sectional image of the standard surface generated with the intention of optimizing the focus. However, in actuality, there is a difference in the shape of each dentition of the subject, so the image with the least out-of-focus (in-focus, that is, the focus is optimized) for each region on the standard surface alone Hard to get. For this reason, in this embodiment, based on a panoramic image of a standard surface (a cross-sectional image covering at least the entire dentition), a cross-sectional image showing the internal structure more clearly (with less blur and in focus) Reconfiguration to get. In many cases, the post-reconstruction is usually performed on a partial area of the panoramic image as a base, and the cross-sectional image of the partial area is referred to as a focus optimized image here.

  Thus, both the generation of the panoramic image and the generation of the focus optimized image involve a process called reconstruction. As will be described in detail later, this reconstruction is simply a process of superimposing and adding frame data (pixel values) to each other. Note that the region of interest set on the panorama image is normally specified on the panorama image as a local region that forms a part of the panorama image, but the entire panorama image can also be set as the region of interest. . Of course, the focus optimization image is generated when a doctor or the like desires.

  The panorama image and / or the focus optimized image is stored in the image memory 54 and displayed on the monitor 60 in an appropriate manner. Among these, at least the selection of the standard surface, the setting of the region of interest, the change of the cross-sectional position, the display mode, and the like reflect the operator's intention given from the operating device 58.

  The panoramic image capturing and interpretation using the panoramic image capturing apparatus 1 is generally as described above, but the concept called “gain” is used to generate the panoramic image of the standard plane and the focus optimized image of the designated area. Has been introduced. In this embodiment, the “gain” is set in advance by calibration, and the gain data is stored in a predetermined area of the image memory 54 in advance as a lookup table LUT.

  Therefore, including the above-described concept of “gain” and “setting of gain using phantom”, panorama image generation of the entire dentition and focus optimization image of the designated region executed by the panorama image photographing apparatus 1 are performed. Details necessary for generation will be described for each item.

(Gain concept)
In this panoramic image photographing apparatus 1, panoramic images of a standard plane (desired tomographic plane) along a specified (or selected as will be described later) panoramic image are frame data (elongated, for example, 300 fps). A two-dimensional slit shape, which is actually a set of X-ray transmission data regarded as a line shape) is generated by overlapping each other while shifting the position. This superposition addition is a process that forms the core of “reconstruction”. In other words, it is utilized that the degree of contrast of pixel values increases due to overlay addition, and structures (teeth, gums, etc.) are rendered at a higher density than other parts. Here, when a plurality of sets of frame data are overlapped and added to each other, the “amount indicating the degree of overlap” that indicates how much the frame data of each set is shifted and overlapped is called a gain.

  When this gain is small, the degree of superposition is dense, and when the gain is large, the degree of superposition is coarse. The manner of superimposing the frame data is schematically shown in FIGS. FIG. 6A shows superposition when the gain is small, and FIG. 4B shows superposition when the gain is large. As described above, the concept of the degree of superposition (dense / dense) accompanying the magnitude of the gain is opposite to that of a normal electric circuit. As will be described later, this is a coordinate with the horizontal axis as the position where the frame data is the horizontal axis and the frame data are mutually added in the memory space (mapped position, that is, the pixel position of the reconstructed panoramic image). This is due to the “equivalent to the slope” of the upper curve (called the speed curve). This speed curve will be described later.

  Furthermore, as described above, when the gain, that is, the amount of overlap of frame data is adjusted, the image density changes between images to be generated. In other words, if the cross-section to be reconstructed is changed, the shade changes between images as it is, making it difficult to interpret. For this reason, it is necessary to multiply the pixel value of the reconstructed image by a coefficient proportional to or directly proportional to the gain to be used, so that the apparent shading is the same between the images.

  An example of this gain will be described using the simplified model of FIG. As shown in the figure, the X-ray tube 31 and the detector 32 have distances D1 and D2 with respect to each other object OB (patient's jaw dentition) (X-ray tube being scanned at each point of the dentition, respectively). If the relative ratio of the direction along the straight line (hereinafter referred to as the depth direction) connecting the detector and the detector is kept constant and the relative motion speed is kept at a certain value, the object OB The amount (gain) of overlay of frame data that is not blurred (that is, in focus) is determined.

  In other words, when scanning is performed as described above, a focal plane (a continuous cross-section in focus) is determined based on the relative operation speed and gain. Since this focal plane corresponds to the ratio of the distances D1 and D2, the focal plane is located on a plane translated from the detector 32 in each depth direction.

  In general, as the gain decreases, the focal position becomes closer to the X-ray tube 31 in each depth direction Ddp, and as the gain increases, the focal position moves away from the X-ray tube 31 in each depth direction Ddp. For this reason, using a phantom (to be described later) that quantitatively understands the distance interval between the X-ray tube 31 and the detector 32 in each of the depth directions, a quantitative measurement (setting of how much the gain is focused) ) Is performed in advance for each position on a straight line along each depth direction. That is, the relationship between each position (each distance from the standard surface) and the gain is measured in advance, and the relationship information may be held as, for example, a lookup table LUT as described above.

  This pre-measurement scan is performed by placing a phantom at the position of the chin rest 25 and rotating the pair of the X-ray tube 31 and the detector 32. The trajectory and speed of this rotation are based on actual imaging of the subject P ( It is set to be the same as that of scanning.

  Further, from the characteristics of the gain, the gain in the vertical direction, that is, the direction (Z-axis direction) parallel to the detection surface 32A of the detector 32 (the surface on which X-rays are incident: see FIG. 2) is constant for each position on the XY plane. It is. That is, when the detector 32 is at a certain position, the gain at each position (in the XY plane) in the depth direction passing through the detector 32 is different for each position, but is parallel to the detection surface 32 passing through the position. The same value is taken in all directions (Z-axis direction).

  Of course, in addition to the method based on the above-described table reference, the relationship between the values may be held by an arithmetic expression, and the gain may be obtained by calculation each time a position in the depth direction is given. In addition, the gain is obtained for each position in the depth direction, but finally, using this obtained gain, the gain of the scan space (the space including the dentition) including the whole of the position is converted into polar coordinates and It may be converted into a value expressed in rectangular coordinates, and this conversion gain may be used.

  Therefore, by referring to the lookup table LUT, it is possible to obtain the gain of each mapping position along the tomographic plane when focusing on a tomographic plane different from the standard plane to be reconstructed first. By superimposing the frame data on each other using this gain, the pixel value of the panoramic image at each mapping position on the standard plane can be obtained. Such a plane is basically a plane perpendicular to the XY plane, but may be an oblique plane oblique to the XY plane (and the YZ plane and / or the XZ plane).

(Phantom used for pre-measurement)
As described above, in order to quantitatively measure the relationship between the distance in the depth direction and the gain in advance, a phantom is used in this embodiment.

  Generally, since the tooth arrangement, that is, the dentition is a horseshoe shape, it is divided into a plurality of scan regions (anterior tooth region or back tooth region) according to the curvature, and the horseshoe shape while changing the distances D1 and D2 described above. Scan to follow the set standard plane along Thus, using the phantom, the distance and gain in each depth direction at predetermined intervals in the direction along the dentition (for example, the distance between the i-th and i + 1-th in the depth direction in FIG. 4 is 10 mm). It is desirable to quantitatively measure this relationship.

  Examples of phantoms used for this preliminary measurement are shown in FIGS. 5 and 6 illustrate the first phantom FT1. The phantom FT1 is preferably a base 71 (see FIG. 6), which is a strong plate with little X-ray absorption, such as a lead plate, and has a substantially horseshoe shape, and a predetermined angle from one end of the base 71. A plurality of measurement plates 72 (see FIG. 5) made of an acrylic plate or the like extending obliquely upward with θ (for example, 45 degrees), a chin rest fixing portion 73 extending downward from the other end of the base portion 71, and On one surface of the measurement plate 72 over a predetermined distance (horizontal plane (XY plane)) over a predetermined distance in the longitudinal direction (a distance corresponding to a predetermined distance range R1 (for example, 20 mm) on the horizontal plane (XY plane)). And a plurality of phantom bodies 74 made of lead balls or the like arranged at a distance of a minute distance R2 (for example, a distance corresponding to 5 mm).

  Among these, the angle θ of the measurement plate 72 with respect to the base 71 is an angle for inclining by the angle θ with respect to the X-ray projection direction. In addition, the plurality of measurement plates 72 are arranged along the tooth row so as to virtually cross the tooth row (see the dotted line L1 in FIG. 6), and a predetermined distance between them is near the back teeth. The pitch is set to about P1 (for example, 10 mm). (See FIG. 6). The phantom body 74 is smaller than the minute distance R2 and has a diameter (for example, a diameter of 1 mm) that allows sufficient visual observation of blur. For this reason, the minute distance R2 is a process between the center positions of the two adjacent phantom bodies 74. Further, the predetermined processing range R1 is set to a range to be observed as a horseshoe cross section of the dentition.

  It should be noted that the mounting position of the measurement plate 72 with respect to the base 71 is preferably adjustable by the adjusting mechanism AD in the depth direction by shifting the screwing position.

  FIG. 7 illustrates another phantom FT2. In this phantom FT2, instead of the phantom body 74 disposed on the measurement plate 72 of the phantom FT1, a strip-like and thin-film phantom body 74A made of hard lead is disposed. The size of the phantom body 74A is, for example, a width of 5 mm, a length of 21.2 mm (predetermined distance range R1), and a thickness of about 0.5 mm. Each position in the longitudinal direction of the phantom body 74A can be determined based on linearity if the distance between one end face of the phantom body 74A and one end face of the measurement plate 72 is known. Other structures are the same as those shown in FIGS.

  Even when any of these phantoms FT1, FT2 is used, it is possible to measure the focal blur and distance. That is, in the case of the first phantom FT1, the degree of blurring of the lead ball image forming the plurality of phantom bodies 74 on each measurement plate 72 is visually observed from the panoramic image collected by the scan for the pre-measurement. In the case of the other second phantom FT2, the degree of blur between the strip-shaped lead plate forming the phantom body 74A on each measurement plate 72 and the end face of the measurement plate 72 itself is visually observed from the same panoramic image. Based on this observation result, if there is a blur for each phantom body 74 of each measurement plate 72 or the longitudinal direction of the phantom body 74A of each measurement plate 72, the gain is adjusted by trial and error. The image is observed, and the gain when the blur is the least is determined as the focus optimization gain at that position in the depth direction. In other words, this gain is about the superposition of frame data providing an image with the least blur. The image processor 56 recognizes the degree of superposition at the position of each phantom body, and passes an amount indicating the degree to the controller 57 as a gain.

  The phantom FT may be configured by periodically arranging objects that do not transmit plate-like X-rays along the dentition. In the case of this structure, it is made of a material that does not transmit the distance guide in the depth direction. In this case, a method of searching for a gain in which the appearance of the boundary between the non-transmitting plate material and the transmitting portion is sharply blurred is adopted.

(Lookup table)
As described above, the focus optimization gain at each position (distance) in the depth direction intersecting each position of the dentition is stored in a predetermined area of the image memory 54 as a lookup table LUT in this embodiment. . If the lookup table LUT is held in this way, an arbitrary cross section along the dentition can be reconfigured with the degree of freedom of the lookup table LUT.

  By the way, the position where the above-mentioned pre-measurement is performed is defined as a distance from the standard plane on a straight line connecting the X-ray tube and the detector during scanning, that is, in each depth direction during scanning. For this reason, in order to create a look-up table LUT adapted to a three-dimensional voxel space, the above-described gain of each sample point in this voxel space may be created by interpolation from known gains in the vicinity (calibration). ) As a result, as shown in FIG. 8, the gain is set by the horseshoe-shaped three-dimensional voxel corresponding to the range R1 of the predetermined distance along the horseshoe-shaped dentition, for example, at equal intervals in the same horseshoe section on the XY plane. Gain is set. As described above, the gain value in the Z-axis direction (vertical direction) is the same at each sample position (for example, the position of (N−1, SD)), and therefore the calculation for that amount may be omitted. it can. Therefore, the look-up table LUT has information indicating the correspondence relationship between the position shown in FIG. 8 (position as a distance from the standard surface) and the gain corresponding to the position.

  For this lookup table LUT, how to determine the optimal number of gains of detailed sample points (finely the pitch between sample points) is determined from the viewpoint of achieving both image quality and calculation time. is important. Basically, it is preferable to have a sample point gain as detailed as possible, and to perform two-stage cross-sectional reconstruction using this gain. In the first stage, the panoramic image of the standard surface is reconstructed with a relatively coarse gain so that the entire dentition can be observed quickly. In the second stage, the region of interest is extracted from the entire panoramic image. For example, it is possible to specify manually, and a panoramic image of the region of interest is reconstructed with a preset detailed gain. Thereby, the gain can be set by the interpolation calculation with higher accuracy, and then the local region based on the high accuracy gain after the overall observation can be observed in more detail.

  Even when this two-stage reconstruction method is employed, it is important to obtain a panoramic image (entire dentition image) at a more appropriate cross-sectional position in the first stage. This is to prevent the oversight by grasping a site such as a lesion from the beginning. For this reason, it is important to specify the dentition cross section (standard surface) that matches the shape and size of each patient's dentition as much as possible.

(Speed curve)
Next, a method for reconstructing a cross-sectional image along a horseshoe-shaped dentition using the above-described gain will be described. The basic idea is the speed curve shown in FIG.

  In FIG. 9, the horizontal axis indicates the frame number (for example, 1 to 4096) of the frame data, and the vertical axis indicates the position where the frame data is added in the memory space. A curve CA indicates the position in the memory space mapped after the panoramic image reconstruction with respect to the frame number of the frame data in the cross section designated as the standard plane output from the detector 32 according to the present embodiment. This is a standard pattern of dotted speed curves.

As can be seen from this graph CA, in the standard surface, the inclination (that is, gain) of the graph is different between the side surface (back tooth portion) of the dentition and the front surface, and the inclination of the side surface is about −1.5, It is designed at about -0.657.
This standard pattern is preset in advance, and in the case of a desired collection position of a human dentition, an image that is not optimally focused can be obtained due to individual differences in tooth profile or variations in the desired position. There is sex. For example, in order to obtain an image in which the focus is optimized in an individual, as shown by a curve CB in FIG. 9, it is only necessary to collect while slightly changing the speed depending on the scanning position. It becomes complicated. Therefore, in this embodiment, instead of such complicated scan control, the degree of superimposition (that is, gain) of collected frame data is adjusted. The basis of this is the speed curve described above. A panoramic image reconstruction equivalent to changing the actual collection speed along the cross-section represented by the designated desired curve, such as the curve CB, can be performed as post-processing for the overlay amount of the frame data.

(Basic idea of focus optimization)
First, as shown in FIG. 10, a panoramic image (base image) of a standard surface along a dentition, which is standardly prepared by designating or selecting on the apparatus by an image interpreter, is basic. This image interpreter uses this panoramic image to grasp the entire state of the dentition. While observing the panoramic image, the image interpreter selects an ROI (region of interest: hereinafter referred to as “ROI”) as a local region of interest on which the focus is more desired (focus optimization is desired). Set as). FIG. 10 shows two ROIs (ROI1, ROI2).
ROI1 specifies a smaller area that covers only the portion that is truly desired for both the x-axis and the y-axis. The size of this ROI 1 can be set to almost the same value as that of the X-ray film used in the conventional intraoral photographing method. In addition, in the case where the side teeth are imaged by the intraoral imaging method, the dentition is set so as to enter the X-ray film moderately. It is also preferable to rotate (tilt) the cross-section designated by (2) from the plane of the panoramic image parallel to the x-axis and the y-axis. Cross sections from various directions and angles having the size of this small region (translated cross section, inclined (rotated) cross section, cross section of those translated and inclined (rotated) appropriately combined, As will be described later, an image of a curved cross section matching the curved shape of each tooth is subjected to a focus optimization process.
On the other hand, ROI2 exemplifies a larger range specification that is specified when the focus is optimized over the entire dentition. In any case, since the region to be processed can be limited by specifying the ROI in this way, the amount of calculation for optimizing the focus, which will be described later, can be reduced and the processing time can be shortened. it can.
In addition, when specifying ROI <ROI1, RO2> on the base image in this way, it is desirable to limit the range of the ROI in the y-axis (vertical) direction. The reason is that data in the vertical direction that does not need to be optimized is excluded from the calculation for the focus optimization to reduce the calculation amount, thereby increasing the calculation speed.

  As described above, after the ROI is designated, various cross sections having sizes determined by the ROI are designated interactively. The apparatus applies only the image of the cross-section so designated to the focus optimization process. This process is automatically performed in response to a command from the operator for taking a cross section. As a result, the local cross-sectional image corresponding to the ROI can be displayed on the monitor 60 with its focus optimized, and can be used for detailed observation.

  In addition, when displaying this optimized ROI image, that is, a local cross-sectional image, on the monitor 60, a display method that reduces a sense of discomfort due to the conventional X-ray film intraoral imaging method is preferable. Specifically, it is convenient to display the vertical and horizontal sizes of such local cross-sectional images according to the actual distance.

(Overview of focus optimization)
This focus optimization process is executed by the image processor 56 as shown in FIG.

  When receiving a focus optimization command, the image processor 56 reads the speed curve CA of the standard plane, and refers to the speed curve CA and the designated ROI, and the horizontal direction of the ROI (time series direction of the frame data). In this case, the frame data FDc which is the center of the frame is specified as schematically shown in FIG. 12 (step A1). Next, the image processor 56 specifies a plurality of frame data FDb ′ to FDe ′ corresponding to the entire region of ROI from the speed curve CA around the frame data FDc as schematically shown in FIG. 12 (step A2). . At this time, since the detector 32 has a usable effective width, it is desirable to add frame data FDb and FDe for the effective width to the left and right of the group of the frame data FDb ′ to FDe ′, respectively.

  Next, the image processor 56 superimposes and adds (reconstructs) the frame data FDb to FDe specified according to the speed curve CA of the standard surface (step A3). That is, each of the frame data FDb to FDe is mapped to each mapping position (vertical axis in FIG. 12) in the ROI according to the speed curve CA (see mapping directions P1 and P2). At the time of mapping, the pixel value at the center position of each frame data is set to zero (0), and the offset of the pixel value at the time of superposition is eliminated. The mapping position is actually a two-dimensional position, but will be described in one dimension for easy understanding.

  By such mapping, data from a plurality of frame data is superimposed on each mapping position (pixel position), and these data are added. Thereby, the pixel value at each mapping position is calculated, and a partial cross-sectional image (in this case, a part of the panoramic image of the standard plane) is generated. As a result, the gradient of the speed curve CA, that is, the shade corresponding to the gain is formed in each pixel forming the ROI, and the dentition structure appears on the panoramic image.

  Next, the image processor 56 interactively determines whether or not to change the position information to be reconstructed (in this case, not only the position in the depth direction of the region defined by the designated ROI but also its angle is included) ( Step A4). If there is a position change, the gain corresponding to the changed position information is read from the lookup table LUT (step A5). This read gain is integrated in the direction of the center pixel of the frame data to calculate a corrected speed curve CB (step A6).

  At this time, since the size of the ROI is a fixed value, the number of frames of frame data necessary for reconstruction of a new position is different. Therefore, the frame data necessary for reconstruction of the area is specified so that the frame data FDc as the center specified in step A1 described above also becomes the center position in the area at the correction position (step A7). Note that the number of frame data may be increased or decreased according to the correction position so that the size of the new area at the correction position is the same as the size of the first ROI.

  When this preparation is completed, the image processor 56 is changed in the same manner as described above (see step A3) based on the speed curve CB obtained in step A6 and the plurality of frame data specified in step A7. The cross-sectional image of the partial area is reconstructed (step A8). At this time, the speed curve CB used at the time of reconstruction is represented as shown by, for example, a virtual line in FIG.

  Further, a coefficient proportional to or directly proportional to the gain (corresponding to the cross-sectional position) used for reconstruction is multiplied by each pixel value of the cross-sectional image generated by the reconstruction (step S9). Thereby, it is possible to almost eliminate the difference in apparent shading between images, and even if the cross-sectional image changes, it is easy to see and the interpretation work can be facilitated.

  The cross-sectional image generated in this way is not a part of the panoramic image along the standard plane, but is a cross-sectional image at a partial position changed based on the ROI specified on the panoramic image. If the cross-sectional image is desired by the interpreting doctor, the image data of the cross-sectional image and the position information (depth direction position and angle information) of the image are stored (steps A10 and A11). If not, the process returns to step A4 (step A10).

  Next, an example of processing related to gain pre-measurement, panorama shooting, and image interpretation executed by the panoramic image photographing apparatus 1 according to the present embodiment will be described with reference to FIGS.

(Gain pre-measurement)
First, referring to FIG. 13, gain pre-measurement (when the gain has already been set, gain calibration will be described).

  As described above, the gain is an amount that means “the degree of superposition” when frame data are overlapped and added to each other, and the gain for achieving an optimal focal position without blur is the tooth It changes according to each position (distance) in each depth direction intersecting the column. As the gain decreases, the focal position becomes closer to the X-ray tube 31 in each depth direction, and as the gain increases, the focal position moves away from the X-ray tube 31 in each depth direction.

  In order to set and hold the gain in advance, the controller 57 of the control / arithmetic apparatus 12 interactively performs the process schematically shown in FIG. 13 with the operator.

  In the prior gain measurement, the phantom FT is fixed at the position of the chin rest 25 (see FIG. 1) instead of the subject. The position of the fixed phantom FT corresponds to a spatial position determined as a standard position of the dentition when the dentition of the subject P is actually photographed, as will be described later. As the phantom FT, the one shown in FIG. 5 or 7 is used as described above. In accordance with the position of the phantom FT in the Z-axis direction, the vertical movement unit 23 is arranged so that the cross-section of the X-ray tube 31 irradiated X-ray collimated by the collimator is positioned in the slit beam. The height is adjusted.

  When the fixed arrangement of the phantom FT is completed, the control / arithmetic unit 12 receives an X-ray irradiation condition (tube voltage, tube current, scan time, etc.) from the operator (step S1).

  When the condition setting is completed, the rotary unit 24 (that is, the pair of the X-ray tube 31 and the detector 32) is moved (scanned) around the phantom FT along the XY plane in response to a command from the operator. While the X-ray tube 31 is irradiated with X-rays, the detector 32 detects transmission X-rays of a high-speed frame, and frame data is collected (step S2). That is, as an example, frame data is output from the detector 32 at a high frame rate of 300 fps, and the frame data is transferred to the image memory 54 via the buffer memory 53 and stored.

  Next, the controller 57 instructs the image processor 56 to reconstruct a panoramic image of the dentition cross section (predetermined surface) at a predetermined spatial position using the collected frame data (step S3). As shown in FIG. 14, the predetermined plane is along the center line ST of the subject's standard dentition (that is, a dentition in which each tooth is aligned on a horseshoe-shaped locus of a standard size). This predetermined plane is made to coincide with a reference plane among a plurality of standard planes prepared so as to be selectable in actual photographing described later.

  The gain G for each position Pn on the predetermined plane (that is, the position where each depth direction Ddp intersects the standard plane) is determined in advance as the slope of the speed curve of the standard plane indicated by the curve CA in FIG. ing. Therefore, the image processor 56 calls all the collected frame data from the image memory 54 as described above, and adds the frame data to the mapping position determined according to the speed curve CA (that is, overlapped and added). The standard plane panoramic image is reconstructed.

  Next, the controller 57 displays the reconstructed panoramic image of the standard plane on the monitor 60 (step S4). An example of this display is shown in FIG. As shown in the figure, five left end measurement plates 72L, a left intermediate measurement plate 72LC, a central measurement plate 72C, a right intermediate measurement plate 72RC, and a right end installed on the phantom FT at a predetermined inclination angle of 45 degrees. A panoramic image of the standard surface on which the measurement plate 72R is reflected is displayed. A plurality of phantom bodies 74 are transferred on each measurement plate, but although only schematically shown in the figure, the spatial position of the central region in the plate longitudinal direction (depth direction) corresponding to the standard surface 1 or a plurality of phantom bodies 74 in a state where the blur is the least, that is, a state where the focus is most focused.

  Here, the longitudinal direction of the plate is roughly divided into five types: the outermost peripheral region Rotm, the outer peripheral region Rot, the central region Rc, the inner peripheral region Rin, and the innermost peripheral region Rinm, for the convenience of gain pre-measurement. (See FIG. 15), the standard plane is set to belong to the central region. That is, in the example of the phantom FT1 shown in FIG. 5 described above, the region of the predetermined distance range R1 (for example, 20 mm) projected onto the base 71 (XY plane) is divided into five regions. The predetermined distance range R1 is a range in the depth direction in which the section of the dentition is freely moved to be examined.

  Here, two regions, that is, two cross sections, can be set before and after the standard plane in the depth direction, and five types of cross sections can be measured together with the standard plane. This is schematically shown in FIG. The outermost virtual line is the outermost peripheral section OTM, the next inner virtual line is the outer peripheral section OT, the inner virtual line is the standard plane ST, and the inner virtual line is the inner peripheral section IN. , And the innermost imaginary line indicates the innermost circumferential section INM. The distance in the depth direction between the cross sections is set to 4 mm, for example.

  For this reason, the reason why the depth direction is roughly divided into 5 regions is sufficient if the cross-sectional area of about 20 mm can be secured in the depth direction of the dentition, and it is sufficient to withstand the use. Interpolate the gain. Therefore, when a compromise is made between the calculation amount and the calculation time, it is sufficient to collect five points (gains in five regions) in each depth direction as the gain base data at this stage.

  Next, the operator shifts to an interactive setting operation of gains of cross sections (positions) before and after the depth direction other than the standard plane while visually observing and observing the panoramic image. Specifically, first, the operator selects the first measurement plate 72 in the phantom FT and displays an enlarged image of the measurement plate 72 (step S5; see FIG. 16). This enlarged display is for making the plurality of phantom bodies 74 on the measurement plate 72 easier to see and setting the gain as accurately as possible. This enlarged display will be described using the central measurement plate 72C as an example. The order of the enlarged display for each measurement plate is arbitrary.

  Next, the controller 57 receives operation information from an operator viewing the enlarged central portion measurement plate 72C, and designates a region other than the central region in the longitudinal direction on the central portion measurement plate 72C. (Step S6). In response to the area designation, the controller 57 calculates the position of the designated area in the depth direction and stores the position coordinate information (step S7). Through the processes of steps S6 and S7, first, for example, the outermost peripheral area Rotm of the central measurement plate 72C, that is, the outermost peripheral cross section OTM in the depth direction along the direction in which the central measurement plate 72C is placed. The position of is specified.

  Next, the controller 57 receives the operation information from the operator, and the one or more phantom bodies 74 belonging to the outermost peripheral area Rotm that is currently being observed have no blur (there is almost no blur or the least blur) In other words, it is determined whether or not it is in the best focus as long as it is visually observed (in the optimum focus state) (step S8). Now, since the phantom body 74 is a round lead ball, the operator can determine that it is in an optimally focused state when it is round and its outline clearly appears. In that case, a button (not shown) indicating the optimum focus state on the monitor screen may be pressed. When it can be determined that the optimal focus state has not yet been reached, the operator presses a button indicating the non-optimal focus state on the monitor screen, and in response, a gain change (gain increase, gain) that appears on the monitor screen is displayed. (Step S9).

  When this gain change is performed, a panorama image corresponding to the changed cross-section, that is, the changed position in the depth direction is reconstructed using the changed gain G (step S10). At this time, the calculation time can be shortened by reconstructing only the portion of the center measurement plate 72C related to the currently enlarged display (the region is designated). This newly reconstructed panoramic image is displayed again (enlarged display image) (step S11).

  Thereafter, the process of the controller 57 is moved to step S8, and the presence or absence of blurring of the phantom body 74 belonging to the outermost peripheral area Rotm of the central measurement plate 72C is determined in the same manner as described above. When this determination is NO, there is still room for optimum focusing, so the controller 57 changes the gain in accordance with an instruction from the operator, and reconstructs and displays a panoramic image (steps S9 to S11). . When the gain is changed through trial and error in this way and a panoramic image without blur is obtained (YES in step S8), the operator gains the gain along the depth direction of the center measurement plate 72C. It can be recognized that this is a gain for obtaining an optimum focus at the position of the outermost peripheral section OTM. Therefore, the controller 57 stores the gain at this time in the image memory 54 in response to the operation of the operator, assuming that the gain is the focus optimization gain (step S12).

  Next, the controller 57 shifts the process to step S <b> 13 and determines whether or not the gain measurement has been completed for all the regions in the longitudinal direction on the current measurement plate 72. When this determination is NO (step S13, NO), the controller 57 returns to step S6 and executes another region in the same manner as described above. Thereby, for example, it is possible to measure the focus optimization gain at the position of the outer peripheral section OT corresponding to the outer peripheral region Rot along the depth direction of the central measurement plate 72C.

  If YES is obtained in step S13, the controller 57 further determines whether or not the same focus optimization gain has been measured for all the measurement plates (step S14). If the determination is NO, since the measurement plate to be measured still remains, the controller 57 returns the processing to step S5 and performs the same processing as described above for another measurement plate, for example, the right intermediate measurement plate 72RC. Apply. Thereby, the gain at the position of the cross section corresponding to the region other than the central region Rc in the longitudinal direction of the measurement plate is measured. On the other hand, when the determination of YES is made in step S14, the gain and reference plane in total of 20 points of the cross-sectional positions of the outermost circumference, outer circumference, inner circumference, and innermost circumference using all five measurement plates 72 are used. Thus, gains at a total of 25 positions (positions of black circles in FIG. 17) based on the five gains are obtained as reference data.

  Next, the controller 57 has a total of 25 points mapped to a two-dimensional area (see the hatched portion in FIG. 17) centered on the standard plane ST on the XY plane and having a predetermined distance range R1 along the plane ST. An appropriate interpolation method is applied to the reference gain to calculate gain data (positions marked with x in FIG. 17) for filling the space between the positions having the reference data spatially (step S15). When this interpolation is completed, the gain values of the respective points (positions of black circles and crosses) in the two-dimensional area forming the horseshoe shape are stored in the image memory 54 as a lookup table LUT (step S16). This look-up table LUT includes positions that intersect the standard plane ST, positions that are scattered along the depth direction passing through the positions, and gain values at the positions.

  The gain value in the vertical direction (Z-axis direction) orthogonal to the two-dimensional region has the same value at each point as described above. Therefore, the two-dimensional lookup table LUT indicates a lookup table for a three-dimensional gain.

  As described above, through the series of processes shown in FIG. 13, the gains at the respective positions of the three-dimensional area having the horseshoe-shaped two-dimensional area determined by the predetermined distance R1 in the depth direction centered on the standard surface ST are measured. become. It is sufficient that this gain pre-measurement is performed at the time of factory shipment or at the time of installation of the apparatus, but it may be performed as a calibration at the time of starting the apparatus not only at regular or irregular maintenance management. . In the case of calibration, the contents of the lookup table LUT held so far are updated to new gain data each time.

  The more phantoms used for this pre-measurement and calibration, the more detailed the gain data that can be measured, the more it can measure the gain data. The number of measurement plates and the arrangement position may be determined by comparing the accuracy of the measurement.

(photograph)
Next, imaging, that is, actual data collection will be described with reference to FIG.

  At the time of photographing, the operator inputs patient information such as patient ID, patient name, photographing date and time to the control / calculation device 12 (step S21). In response to this input, the controller 57 records the patient information in a predetermined area of the image memory, and associates it with frame data to be collected later using, for example, the patient ID as key information.

  Next, the subject P (patient) is positioned as described in FIG. That is, the operator adjusts the height of the vertical movement unit 13 and then takes a predetermined image of the oral cavity of the subject using the chin rest 25 and the headrest 28 with the subject P holding the mouthpiece 26. Position to position. This positioning may be performed before the patient information is input, or may be performed after setting the X-ray irradiation conditions described later.

  The controller 57 sets the standard plane used for actual photographing interactively based on the operation information from the operator (step S22). This standard plane is set by selecting several standard planes prepared in advance in the apparatus. This will be described later.

  Furthermore, the controller 57 sets X-ray irradiation conditions (X-ray tube voltage, tube current, scan time, scan trajectory, and the like) based on operation information from the operator, as in the case of gain pre-measurement described above. (Step S23).

  When the preparation is completed in this way, the controller 57 responds to the command from the operator and moves the rotating unit 24 (that is, the pair of the X-ray tube 31 and the detector 32) along the XY plane of the oral cavity of the subject P. While moving (scanning) around, the X-ray tube 31 is irradiated with X-rays, while the detector 32 detects transmission X-rays in a high-speed frame. Thereby, collection of frame data is performed (step S24). That is, as an example, frame data is output from the detector 32 at a high frame rate of 300 fps, and the frame data is transferred to the image memory 54 via the buffer memory 53 and stored.

  Note that image data captured by an external intraoral X-ray imaging apparatus may be received and stored in the image memory 54 before or after the above-described collection of frame data, if necessary.

  After this scan is completed, the subject P is released from the apparatus.

(Interpretation (observation))
When the collection of the frame data is completed by the above-described scan, the doctor can perform interpretation using the frame data as post-processing.

  A series of processes of the controller 57 used for the interpretation are shown in the flowcharts of FIGS. 19 to 20, and an operation example associated with the interpretation is shown in FIGS. 21 to 25.

  As shown in FIG. 19, the controller 57 receives an input of a patient, that is, an interpretation target, in response to a command from the operator (step S31). Thereby, for example, when information for specifying an interpretation target such as a patient ID and photographing date / time is input, the controller 57 conveys the information to the image processor 56, so that the image processor 56 identifies the subject P specified by the information. Is read from the image memory 56 to its own work area (step S32).

  Next, the controller 57 instructs the image processor 56 to reconstruct the panorama image of the standard plane and display the panorama image on the monitor 60 (steps S33 and S34). Thereby, as schematically shown in FIG. 21, a panoramic image of the standard surface of the dentition of the subject P is displayed on the monitor 60. This panoramic image depicts a cross-sectional structure along the standard plane in the same manner as the X-ray transmission image.

  These processes are the same as the processes at the time of the prior gain measurement (see steps S3 and S4 in FIG. 13). The processing up to this point corresponds to the preparation stage of the interpretation work.

  Next, the controller 57 waits while determining whether or not the ROI information to be set for the panoramic image of the standard surface has been given by the operator, that is, the interpretation doctor (step S35). As described above, this ROI is information specifying a local region of interest in the panoramic image of the standard plane, and the interpretation doctor wants to interpret the local region from various angles and cross sections. Used for. This ROI can be specified as a rectangular small region in this embodiment, and its vertical and horizontal sizes are arbitrary, but its maximum size is smaller than that of a panoramic image.

  This ROI setting method is illustrated in FIG. ROI: R1 shown in FIG. 22 (A) is a region of interest designated when a specific tooth in the upper dentition alone is desired to be focused and examined. In FIG. 22 (B), It is a comparatively large region of interest designated when a plurality of teeth in each of the upper and lower dentitions are collectively focused and examined. In any case, it is preferable to minimize the size of the panoramic image in the vertical direction (Z-axis direction) as much as possible in order to shorten the calculation time of image processing to be described later.

  Note that the size of this ROI can be set to the same value as that of the X-ray film used in the conventional intraoral radiography as described above. In addition, the cross-section designated by the ROI can be rotated (tilted) from the plane of the panoramic image so that the side teeth fit within the ROI.

  If the determination in step S35 is YES, the ROI is superimposed and displayed on the panoramic image using the designated ROI information (step S36). This superimposed display state is assumed to be represented in FIG. The controller 57 confirms the position and size of the displayed ROI according to the operation information from the operator (step S37), and if necessary, accepts the position and / or size change information, The ROI is changed and superimposed (step S38).

  When the ROI is specified in this way, the controller 57 specifies the frame number range (that is, the frame data range) of the frame data providing the pixel specified by the ROI on the panoramic image (step S39). . As will be described later, this specification is performed for inclining (rotating) a section having the size of the region of interest specified by the ROI and observing the region of interest as another section. That is, as described with reference to FIG. 11, the range of frame numbers corresponding to the size of the designated ROI in the horizontal direction (X (Y) axis direction) is determined with reference to the speed curve of the ROI standard surface. As described above, the panoramic image is cut in accordance with the size of the designated ROI in the vertical direction (Z-axis direction).

  Next, since the effective width of the detector 32 is known in advance, the controller 57 specifies the final frame number to which this effective width is added (step S40).

  Thereafter, the controller 57 shifts to a process for observing a cross section of the region of interest specified in the ROI in various manners (steps S41 to S54).

  Specifically, first, for the region of interest on the panoramic image of the standard plane specified by the ROI, it is determined based on the operation information whether or not the image as it is is enlarged (step S41). If display is instructed, the image is enlarged at a desired enlargement ratio and superimposed (step S42). An example of this enlarged / superimposed display is shown in FIG. At this time, the enlargement ratio may be a default value or may be arbitrarily selected within a predetermined range.

  Further, in response to the operation information from the interpretation doctor, the controller 57 translates the cross section having the size of the region of interest on the panorama image of the standard plane designated by the ROI in the depth direction, and moves the translation. The process of examining the image along the cross section is performed interactively (steps S43 to S46). FIG. 24 illustrates the concept of parallel movement of the cross section. Since a part of the cross section along the standard plane selected in advance is displayed, the parallel movement means that the cross section is shifted to the front side or back side of the standard plane. become. The range in which this translation is possible is determined according to the above-mentioned predetermined distance range R1 (for example, 20 mm: see FIG. 5). That is, if the movement is within the predetermined distance range R1, since the gain for focus optimization has already been measured, the cross-sectional image can be reconstructed using the gain. When a pathologically suspicious part is found in the panoramic image of the standard surface, it is possible to know the progress of the disease and the state of the gums in the thickness direction of the tooth by translating the cross section.

  For this reason, it is determined based on the operation information whether or not it is necessary to examine the parallel movement section (step S43), and if that is necessary, a movement indicating in which direction the section is moved by which distance. Information is input from the interpretation doctor (step S44). If the movement distance = 0 is specified here, a partial cross section of the panoramic image itself is specified.

  Next, a new section corresponding to the movement information (for example, 4 mm parallel translation to the back side), that is, the position of the translated section is specified, and the gain G determined by the position of the section is read from the look-up table LUT. By superimposing and adding as described above using the gain G from which the frame data is read, a local cross-sectional image designated by the ROI and translated is reconstructed (step S45). That is, a focus optimized image with little or no defocus is obtained.

  The image reconstructed in this way is displayed in a predetermined or desired manner (step S46). Among these, the display according to a predetermined mode is a display method determined by default, and is superimposed and displayed as a part of the panoramic image at a predetermined position of the currently displayed panoramic image. On the other hand, the display in a desired mode can be specified by selecting a desired display method from among preset display methods, as will be described later, for the convenience of interpretation. .

  Further, when the controller 57 confirms the determination of NO (that is, not to translate) in step S43 described above, the controller 57 interactively determines whether or not the vehicle is tilted (rotated) (step S42). That is, the controller 57 inclines (rotates) the cross section having the size of the region of interest on the panoramic image of the standard plane specified by the ROI in response to the operation information from the interpretation doctor, and the inclination. The process of examining the image along the (rotated) cross section is performed interactively (steps S48 to S50).

  Note that this tilt (rotation) processing means that the projection direction is changed obliquely by an amount corresponding to the tilt (rotation) of the cross section. The angle for tilting (rotating) is usually several degrees to several tens of degrees.

  FIG. 25 explains the concept of the inclination (rotation) of the cross section designated by this ROI. Note that the inclination of these cross sections is determined by the position of the central axis, the inclination direction, and the inclination angle. For this reason, it can be said that the “inclination” of the cross section is “rotation (rotation)” about the central axis of the cross section, and therefore, the term “inclination” will be represented below. 25 (A) to 25 (C) incline the cross section by a desired angle around the center position, the upper end position, and the lower end position in the vertical direction (Z-axis) direction of the cross section specified by the ROI. Is. In addition, the states shown in FIGS. 25D to 25F are obtained by inclining the cross section by a desired angle around the center position, the left end position, and the right end position in the horizontal direction (x direction) of the cross section specified by the ROI. It is something to be made. The limit for inclining the local cross section designated by the ROI is within the range in the depth direction in which the gain is preset for the cross section. As a result, the meaning of image interpretation comes out.

  Therefore, if it is determined in step S47 that the display is tilted, the controller 57 then obtains the position of the central axis, the tilt direction, and the tilt angle as operation information (step S48). For this reason, the controller 57 sets a new section corresponding to the tilt information (for example, tilts clockwise by 10 degrees with the longitudinal center position of the local section specified by the ROI as the central axis), that is, the tilt. The position of the cross section is specified, the gain G determined by the position of the cross section is read from the lookup table LUT, the frame data contributing to the image reconstruction of the cross section is specified, and the specified frame data is read By adding using G as described above, an image of a local cross section designated by the ROI and inclined is reconstructed (step S49).

  The image reconstructed in this way is displayed in a predetermined or desired manner (step S50). This display method is the same as the processing in step S46 described above.

  Further, when the controller 57 confirms the NO determination (ie, does not tilt (rotate)) in step S47 described above, the controller 57 interactively determines whether or not “parallel movement + tilt (rotation)” (step S51). That is, the controller 57 translates the cross section having the size of the region of interest on the panoramic image of the standard plane specified by the ROI in the depth direction in response to the operation information from the interpretation doctor, and regarding the depth direction. The process of diagnosing (rotating) and examining the image along the moved cross section is performed interactively (steps S52 to S54). In this case, as a method for determining the position of the moved cross section, it may be tilted (rotated) after being translated, or may be performed in the reverse order. For this reason, information specifying the above-described two types of movement (translation + tilting (rotation)) of the local section specified by the ROI is input, the focus of the section is optimized, and the focus is optimized. An image is displayed.

  When the optimized ROI image, that is, the local cross-sectional image is displayed on the monitor 60, as described above, the vertical and horizontal sizes of the local cross-sectional image can be displayed in accordance with the actual distance.

  If NO is also determined in step S51 described above, the process proceeds to step S55. In this step S55, the controller 57 determines whether or not the interpretation end is instructed by the radiogram interpreter. If the interpretation is still continued (NO), the process returns to the above-described step S35, and the above-described process is performed. repeat.

  On the other hand, when the interpretation end (YES) is determined, the controller 57 reads the image data (panorama image, cross-sectional image specified by the ROI, etc.) and the accompanying information (patient). It is determined interactively whether or not the (information) data is stored in the recording medium (step S56). If the determination is YES, that is, if it is decided to save the data, the data is saved in the image memory 54 (step S57). Further, the controller 57 determines whether or not to transfer such data to an external DICOM server based on a request from the interpreter (step S58). If the determination is YES, that is, if the transfer is a transfer, the data is DICOM. After conversion into the specification, the data is transmitted to an external communication line via the communication interface 62. The DICOM server is a server that satisfies the DICOM (Digital Imaging and Communications in Medicine) standard.

  Further, the controller 57 determines whether or not to print the target image data based on the operation information from the radiogram interpreter (step S60). A print command for the image data is issued (step S61).

(Standard surface selection process)
Here, with reference to FIGS. 26 and 27, the standard plane selection process (step S22) in the above-described shooting will be described.

First, the controller 57 displays, as an initial screen, a schematic diagram Tst of the standard dentition and a curved line SC1 superimposed along the standard dentition Tst on the monitor 60 as shown in FIG. 27 (FIG. 26). , Step S22 ₁ ).

  The line SC1 indicates a first standard surface (standard cross section) set along the standard tooth row Tst. The first standard surface SC1 is a cross section having a standard size based on the standard dentition Tst statistically derived from the majority of people. Accordingly, if the dentition of the subject P matches the standard dentition Tst with respect to the size and the arrangement position of each tooth, the first standard surface SC1 is sufficient. That is, the X-ray tube 31 and the detector 32 are moved (rotated) so that the X-rays emitted from the X-ray tube 31 are always focused on the first standard surface SC1, so that the first standard surface SC1 itself is An optimum focal section is obtained, and an image of this section is projected as a panoramic image. As described above, this projection image is collected at high speed as frame data (line data) by the detector 32. In such a case, it is not necessary to select another cross section.

  However, since the subject P is an adult or a child, and the shape (dental shape) of the dentition varies among individuals, the first standard surface SC1 often does not match. On the other hand, if the panoramic image as the base image is matched to the actual dentition shape of the subject P as much as possible, more accurate image information can be obtained, and more accurate diagnosis and interpretation can be performed. Can do. Further, the subsequent specification of a local region for interpretation based on the base image, that is, the panoramic image of the entire dentition, becomes more accurate. From this point of view, this standard plane selection process is executed.

The controller 57 asks the operator whether or not to select the first standard surface SC1 displayed on the initial screen (step S22 ₂ ). The operator determines whether or not the standard surface should be changed to another cross section in consideration of the size of the tooth profile of the subject P and the shape of the dentition. As other standard surfaces that can be selected, second and third standard surfaces SC2 and SC3 are prepared (see FIG. 27). The second standard surface SC2 is set to a horseshoe shape having a smaller rate than the first standard surface SC1, and the third standard surface SC3 is set to a horseshoe shape having a greater rate than the first standard surface SC1.

Therefore, when the operator considers the size and shape of the dentition of the subject P to be diagnosed and determines that the first standard surface SC1 is in time, the operator performs the operation to that effect and performs the first standard. The surface SC1 is determined (step S22 ₃ ). On the other hand, if it is determined that the first standard surface SC1 is excessive or insufficient, the second or third standard surface SC2, SC3 is selected (step S22 ₄ ). The selected section SC2 (SC3) is displayed on the monitor screen shown in FIG. 27 with a different color, for example, for confirmation (step S22 ₅ ).

  In this way, from the beginning, a standard plane that matches the shape and size of the dentition of each subject P is selected as much as possible, and a panoramic image along the standard plane is taken as a base image.

(Display mode selection process)
Furthermore, with reference to FIGS. 28 to 31, the display mode selection processing (steps S <b> 46, S <b> 50, S <b> 54) related to the display in the above-described interpretation will be described.

  The image data to be displayed is a panoramic image that was first taken as a base image, an original image of a local area specified by the ROI on this panoramic image (part of the base image), and specified by the ROI. It is a focus optimization image of a local region (ie, an image focused on a translated section, an inclined section, or a translated and tilted section: steps S45, S49, S53).

  Therefore, the controller 57 first determines whether or not the panoramic image and the focus optimized image are divided and displayed based on operation information from the image interpreter (step S61). If YES in this determination, that is, if the divided display is performed, the controller 57 displays the panoramic image and the focus optimized image on the monitor 60 as shown in FIG. 29, for example (step S62). According to this example, the panoramic image Ppano is displayed on the lower side of the monitor screen, and the focus optimization image Popt is displayed on the upper side thereof. In the panoramic image Ppano, for example, a rectangular ROI designating a local area is displayed superimposed.

  Thereafter, the controller 57 stands by while determining whether or not an operation for terminating the display has been performed (step S63).

  On the other hand, when the divided display is not performed (NO in step S61), the controller 57 next determines whether or not the superimposed display is performed based on the operation information (step S64). When superimposing display is performed based on this determination, it is determined from the operation information whether or not to enlarge at least one of the original image and the focus optimized image, and if specified, the enlargement process is executed (step S1). S65, S66).

  Thereafter, the controller 57 causes the monitor 60 to superimpose and display the original image Pori and the focus optimized image Popt on the panoramic image Ppano so as to compare left and right, for example, in the manner shown in FIG. 30 (step S67). Thereafter, the process proceeds to step S63.

  Furthermore, if the determination in step S64 described above is NO, that is, if superimposed display is not performed, the controller 57 further determines whether or not to display only the focus optimized image (step S68). If YES is determined in step S68, the controller 57 displays only the focus optimized image on the monitor 60 as schematically shown in FIG. 31, for example (step S69).

  These displayed images are always attached with position information of a cross section that provides the images. For example, as indicated by reference numeral PI in FIGS. 29 to 31, the position information of the standard plane is specified for the panoramic image Ppano, and the position information on the panoramic image specified by the ROI for the original image Pori is the focus optimized image. In Popt, information on the position of the local cross section that provides the image (position on the panoramic image, distance from the standard plane when moved, angle / direction when tilted (rotated), information on the distance and angle, etc.) ) Is attached.

  Since various display modes can be selected in this way, the radiogram interpreter can display the interpretation result in a convenient mode.

  As described above, the digital dental panoramic image photographing apparatus according to this embodiment can provide a panoramic image that sufficiently meets the demands of a dentist, unlike the conventional one.

  Specifically, using the same frame data collected by one imaging, an image obtained by translating a cross-section of a local part to be diagnosed diagnostically or changing the projection direction by tilting (rotation) is used. It can be reconfigured any number of times. The interpretation doctor can quantitatively specify the distance to move the cross section in parallel and the angle to tilt (rotate) it. That is, the image interpretation doctor can move the local cross section interactively while viewing the displayed panoramic image of the standard surface, and observe the image of the tooth or gum on which the cross section is displayed. Thereby, for example, information such as whether the further back side of one tooth hurts or how far the lesion extends to the gum can be obtained three-dimensionally. In addition, the standard plane panorama image that serves as the base image that determines the position of the cross-section of the local part also matches the actual dentition of the subject from several preset standard cross-sections as much as possible. The cross section can be selected as the standard plane.

  For this reason, even if it is important to set the imaging position (cross section) to an optimal cross section along the patient's dentition, it does not need to be so nervous. That is, it is only necessary to select the best one from several types of standard surfaces prepared in advance and start shooting. As described above, the subsequent interpretation can be freely performed using the frame data collected by this photographing. As a result, the operator's burden on the setting of the optimum cross section, which has been pointed out in the past, is remarkably reduced, and the skill level required of the operator is alleviated.

  As described above, the image of the local cross section specified on the panoramic image of the cross section (standard plane) collected with the appropriate optimization and the image of another cross section obtained by repositioning the cross section three-dimensionally are always used. Then, it is reconstructed as an optimally focused image with less blur using a gain that has been measured in advance and stored. Therefore, since there is little blur, the structure information of teeth and gums is abundant and accurate. The diagnosis burden on the dentist is reduced accordingly.

  In addition, an image of a cross section designated by ROI interactively is displayed together with position information. For example, position information indicating that the cross section designated by the ROI is a cross section translated 5 mm behind the standard plane, and the cross section designated by the ROI is on the lower side around an axis passing through the center in the vertical direction. The position information indicating that the section is tilted (rotated) by 20 degrees is displayed. For this reason, the image interpretation doctor can perform image interpretation while grasping the distance (feel) of the internal structure of the teeth and gums. In this way, the interpreting physician considers individual differences such as the shape of the dentition, `` I want to examine the part slightly behind or the front part '', `` I want to examine the cross section along the oblique teeth '', `` `` I want to examine the cross section along the thickness direction of the teeth '', etc., which allows cross-section observation that was almost difficult in the past, and can obtain more information useful for diagnosis, and the accuracy of diagnosis Greatly contributes to improvement.

  In this way, the internal information of the dentition can be easily and abundantly obtained using the frame data collected in one imaging, so that there is almost no need for another imaging to complement the panoramic image as in the past. Become. Therefore, the time and effort required for diagnosis are reduced, patient throughput is improved, and increase in the patient's X-ray exposure can be suppressed.

As for the computer 12, another computer may be used in a stand-alone format or an online format for a portion having a function of post-processing the panoramic image.

(Second Embodiment)
Subsequently, a second embodiment of the panoramic image photographing apparatus according to the present invention will be described with reference to FIGS.

  The panoramic image photographing apparatus according to this embodiment is an image related to a two-dimensional area designated by the ROI, that is, an image of an original area (original image) on the panoramic image specified in step 39 (FIG. 19). ), Processing for enhancing contrast in the enlarged original image enlarged in step S42 (FIG. 20) and the focus optimized image displayed in steps S46, S50, and S54 (FIG. 20) (contrast enhancement processing) It is characterized by implementing. Other configurations and processes are the same as or similar to those of the first embodiment. For this reason, the same code | symbol is used for the component same as the thing of 1st Embodiment.

  Note that this contrast enhancement is not necessarily limited to the two-dimensional area specified by the ROI. For example, as described in the above-described embodiment, the contrast enhancement is performed on the entire panoramic image reconstructed on the standard plane. May be. However, the contrast enhancement process usually increases the calculation load and decreases the processing speed. For this reason, considering the reduction in computation load, the increase in processing speed, and the fact that it is sufficient to increase the contrast of a necessary partial area in actual interpretation, as described above, such contrast enhancement is specified by the ROI. It is desirable to implement in a two-dimensional area.

  This contrast enhancement process can be executed by the image processor 56 or the controller 57. In the present embodiment, the image processor 56 is responsible for the contrast enhancement processing.

  Now, it is assumed that such contrast enhancement processing is performed in the focus optimization / display of the local section to be translated according to steps S45 to S46. In this case, the image processor 56 executes contrast enhancement processing between the focus optimization processing in step S45 and the display processing in step S46. In the image memory 54, a gray level two-dimensional digital image is stored in advance as a reconstructed image having a focus optimized in a local area. Using this two-dimensional digital image as an original image, contrast enhancement processing is performed on the original image.

  FIG. 32 shows a flow of a series of processing for contrast enhancement executed by the image processor 56.

  This contrast enhancement processing is roughly performed by inputting frame data (gray level image data) that is original image data (step S101), pre-processing called density value shift applied to the original image data (step S102), Wavelet transform as multi-resolution decomposition applied to density-shifted original image data (step S103), weighting processing for contrast enhancement on the coefficient obtained by this conversion (step S104), and re-processing applied to the weighted coefficient Inverse wavelet transform (step S105) as a configuration process, and display and storage of a contrast-enhanced image obtained by the inverse wavelet transform (step S106) are included. Hereinafter, this processing will be described in detail.

(Original image input)
First, the image processor 56 reads gray level digital image data (frame data) to be subjected to contrast enhancement processing from the image memory 54 into its work memory in response to an operator's command given through the operation device 58 ( Step S101).

(Density value shift)
Next, the image processor 56 automatically executes preprocessing called density value (shift) on the read image data (step S102).

  This density value shift is pre-processing for shifting the density value of the entire image on the density gradation so that the average density value of the image is at the center of the density gradation (scale: gray level scale in the present embodiment). is there. By performing this density value shift, it is possible to effectively apply the dynamic range (monitor 60) of the image display device and appropriately apply contrast enhancement to the original image to be processed. That is, contrast enhancement can be reliably performed while suppressing the number of pixels to be scaled out.

  Now, for example, assuming that the density value of an original image having a density gradation of 8 bits (256 gradations) is f (x, y), the value to be shifted = offset is

  For this reason, the image processor 56 specifically performs the processing shown in FIG. First, the image processor 56 calculates the shift value offset using the density value f (x, y) of each pixel (x, y) based on the equation (1) (step S102A). Next, the image processor 56 designates the pixel position (x, y) by a predetermined algorithm (step S102B). Thereby, for example, the pixel in the first row and the first column of the two-dimensional original image is designated.

  Thereafter, the image processor 56 determines whether or not the above processing has been completed for all the pixels (x, y) (step S102H). If this determination is NO, the process returns to step S102B, and the processes of steps S102B to S102G described above are repeated for the next pixel (x, y). If the determination in step S102H is YES, the density value shift process ends.

  By executing the density value shift as the pre-processing as described above, the curve is shifted on the density histogram as illustrated in FIG. Like the histogram curve A, the number of pixels to be scaled out before the density value shift is very large, but after the density value shift, the entire histogram curve moves to the center of the scale, and the pixels to be scaled out are eliminated or decreased.

(Multi-resolution decomposition)
Referring back to FIG. 32, the image processor 56 then executes multiresolution decomposition processing on the original image shifted in density value, for example, by performing wavelet transform (step S103). As an example, the wavelet transform is sequentially executed from the level j = 1 to 8. This level j indicates the degree of multi-resolution decomposition, and the lower the numerical value of level j, the higher the resolution (therefore, the resolution is highest when level j = 1).

This wavelet transform is a means for expressing an arbitrary signal belonging to this function L ² (R) with a function belonging to the square integrable function L ² (R) as a basis, and a wavelet (short wave: Wave-lets). It is the inner product of the basis function obtained by shifting or scaling the function on the time axis and the signal of the processing target.

  Note that wavelet transform is useful for this multi-resolution analysis, but other appropriate transforms can also be used. Further, even when the wavelet transform is used, it is not always necessary to use the wavelet transform based on the Dobesy function, and for example, a transform using a Haar wavelet or the like may be used.

FIG. 35 shows a coefficient image (FIG. 35B) obtained when wavelet transform of level j = 1 is performed on the original image S ⁽⁰⁾ (see FIG. 35A) having n × m pixels. The coefficient image when the wavelet transform of level j = 2 is applied to the image S ⁽¹⁾ of the expansion coefficient of the low frequency component of this coefficient image (FIG. 5C), and the coefficient of the low frequency component of this coefficient image A coefficient image ((d) in the figure) when the wavelet transform of level j = 3 is applied to the image S ⁽²⁾ is schematically shown.

(Weighting process)
When the wavelet transformation is thus completed, the image processor 56 automatically executes a weighting process for contrast enhancement on the coefficient obtained by the transformation (step S104). This weighting process is another feature of the present invention. An outline of this weighting process is shown in FIG. This weighting process is performed according to the feature (attribute) of the density value of the original image.

<Automatic setting of reference weight>
First, reference weight setting (designation) automatically performed by the image processor 56 will be described (step S104A).

  By the above-described wavelet transform, the subband low frequency component coefficient s and high frequency component coefficient w are obtained under each level j (j = 1 to 8 in this embodiment). Since the density gradient information of the image is included in the high frequency component, contrast enhancement (or adjustment) is performed by manipulating the high frequency component. For this purpose, the high-frequency component of each level j subband is weighted. This weight is expressed as α (j).

  How to calculate and adjust the weight α (j) (automatic weight setting) will be described.

The inventor researched the relationship between the weight α (j) and the density histogram and found several features. For example, if the value of the weight α (j) is set to the same value without depending on the value of the level j, the range that the pixel density value can take in proportion to the value of the weight α (j). Is to increase. However, it has also been found that if the weight α (j) is set too large, the number of pixels to be scaled out from the range of density values 0 to 255 increases. Therefore, in this embodiment, the weight α (j) is automatically set from the ratio of the number of pixels to be scaled out to the total number of pixels. For this purpose, first, a reference weight α ₀ (= α (1)) value is determined as follows.

This reference weight α ₀ is given in order to give the highest priority to the image with the highest frequency (high resolution) among the contrast-enhanced images (image of level j = 1), and this image has the largest weight. (= Reference weight α ₀ ).

The value of the reference weight alpha ₀ will vary depending on the conditions set, as an example, take 3-4 degree value.

<Setting of weight function>
As described above, when the reference weight α ₀ is determined from the density histogram of the original image to be processed, that is, the attribute of the original image, the image processor 56 uses the reference weight α ₀ to respond to a plurality of predetermined patterns. A weight function is automatically set (step S104B).

That is, the image processor 56 changes the contrast enhancement effect by changing the weight α (j) for each subband. Therefore, in the present embodiment, the determined reference weight α ₀ is applied to the following arithmetic expression. Compute the kind of weight function. The function values of the five types of weighting functions thus set are stored and stored in a table, for example, for each level j.

Among these, the weighting function set based on the equation (8) is always based on the weight α having a constant value α ₀ (= reference weight) regardless of the value of the level j, as shown by the straight line A in FIG. Take (j). The weight α (j) = α ₀ is a weight given to the image component with the highest frequency (high resolution) among the images to be emphasized.

Further, as shown by the straight line B1 in FIG. 37, the weight function set based on the equation (10) becomes weight α (j) = reference weight α ₀ when the level j = 1, and from this value, the level j As the value increases, the value decreases linearly, and when the level j = 8, the value of the weight α (j) = 1 is taken. The image component of the highest level j = 8 giving this weight α (j) = 1 means the average density value of the whole original image, and in this embodiment, density value shift is performed as preprocessing. This means that the average density value = 128.

As shown by a curve B2 in FIG. 37, the weight function set based on the equation (9) is weight α (j) = reference weight α ₀ when level j = 1, and level j increases from this value. As the level j = 8, the value of weight α (j) = 1 is taken. Specifically, while drawing a weight curve that gently swells downward as level j rises from 1, it is finally possible to look at a weight curve that gently swells upward at level j = 4 in the middle. Level j = 8 and weight α (j) = 1.

Furthermore, as shown by a curve B3 in FIG. 37, the weight function set based on the equation (11) becomes weight α (j) = reference weight α ₀ when level j = 1, and from this value, level j However, the rate of decrease while the level j is small is low, and a weight curve is drawn in which the level j rapidly decreases in the latter half. On the other hand, the weight function set based on the equation (12) is weight α (j) = reference weight α ₀ when level j = 1, as shown by a curve B4 in FIG. The weight decreases as the level j increases from the value, but the decrease rate is high while the level j is small, and a weight curve is drawn in which the decrease rate is saturated in the latter half of the level j.

  Among these plural types of weight functions, the weight functions represented by the straight lines A and B1 and the curves B2 to B4 can be classified as monotonous non-increasing functions, and the weight functions represented by the straight line B1 and the curves B2 to B4. Can be classified as a monotonically decreasing function.

  The weighting functions indicated by the straight line B1 and the curves B2 to B4 are weighting functions (monotonic non-increasing functions) that take non-constant weights according to the level j, and among these, the weighting functions indicated by the curves B2 to B4 are nonlinear weights. It is a function. Incidentally, the straight line A is a linear weight function having a constant value. The weight function of the straight line B1 is also a linear weight function.

  In this way, a plurality of types of weighting functions are set, regardless of what image content (density value attribute) the original image to be processed has to select appropriate contrast enhancement according to the image content. This is to widen the width.

  Here, general forms of various weight functions shown in FIG. 37 are exemplified. This weight function is a power function for variable j,

α (1) = α ₀ and α (8) = 1, and j = 1 to 8 can be expressed as a monotonically non-increasing function. By setting the real coefficients a _n , a _n−1 ,..., A ₀ to appropriate values, the weight function can be changed as in the curves B1 to B4 shown in FIG. The function represented by the straight line A does not satisfy the condition of α (8) = 1, but is used as a case where all weights for emphasis are constant.

It should be noted that what value the maximum level j will be depends on the size of the image (matrix size). For example, when the image matrix size = 256 × 256, the highest level j = 8, and when the image matrix size = 1024 × 1024, the highest level j = 10. For this reason, when a weight function up to the maximum level j = 10 is required, the weight α (j) = α _{0 is obtained} at the level j = 1, and the weight α (j) = 1 is reduced at the level j = 10. A weight function is used.

<Select weight function>
Next, the arithmetic processor 13 selects (designates) an optimum weight function corresponding to the attribute of the density value of the original image from a plurality of types of weight functions automatically set according to the reference weight α ₀ as described above (step). S104C-S104J).

  As described above, in this embodiment, the high-frequency component weight α (j) is controlled to perform reconstruction (inverse wavelet transform) to generate a contrast-enhanced image. According to the research conducted by, the degree of contrast enhancement as a result differs depending on how the weight α (j) is given.

  To explain this, generally, when the weighting function is set to a uniform weight as shown by the straight line A (Equation (9)) in FIG. 37 and the contrast enhancement is performed, the scale-out becomes conspicuous. This is because the weight α (j) is constant without depending on the value of the level j, so that the dynamic range is widened, but the selected density value is limited. In addition, when the weight function is set nonlinearly as shown by the curve B4 (Equation (12)) in FIG. 37, the degree of contrast enhancement is low because the weight α (j) at a high level j is small.

  In contrast, the non-constant weight function represented by the curve B2 (formula (9)), straight line B2 (formula (10)), or curve B3 (formula (11)) in FIG. When it is adopted, it is possible to emphasize well the fine features of the contents of the original image while suppressing the scale-out.

  However, it is also known that the non-constant weight α (j) is not universal. For example, in the case of an original image having a part with a lot of specific density values such as “sky” in the image, it is also known that if a non-constant weight function is applied, an artifact is generated in the part. . In the case of such an original image, it is safer to adopt a constant weight function from the viewpoint of artifact suppression.

  In other words, whether the original image has many areas with a constant density value such as “sky”, whether there are areas where the density value changes sharply, such as the roof or wall of a “house”, or the density of a person image. It is necessary to select a weighting function in consideration of the distribution of the density histogram of the original image, such as whether there are many changes in value. In other words, it is important to determine the characteristics of the density value of the original image to be processed and select (switch) an appropriate weight function.

  Therefore, in this embodiment, the ratio of the high frequency component to the low frequency component included in the density value of the original image is adopted as a basic index as an index for appropriately selecting the weight function. This is based on the finding that such a ratio can be an index for discriminating the characteristics of the original image. Furthermore, as another index, the maximum slope obtained from the cumulative histogram is also effective. In the case of the present embodiment, as a method for discriminating the characteristics of the original image, the above-mentioned “ratio of high frequency components” and “maximum slope of cumulative histogram” are used in combination to enhance the discrimination. In the case where importance is attached to simplification of processing, it is possible to perform determination using only “ratio of high frequency components” without using information of “maximum slope of cumulative histogram”.

  Based on the above, the description will return to FIG. The image processor 56 calculates, for each level j, the ratio R of the sum of the absolute values of the high frequency components to the sum of the absolute values of the low frequency components from the coefficient information of the multiresolution decomposition by wavelet transform at each level j (step S104C). ). Thereby, for example, seven ratios R from level j = 1 to 8 are calculated.

Then, the image processor 56 determines whether the threshold _{R th} hereinafter this ratio R is determined in advance (step S104D).

This determination is YES, that is, when the following R ≦ _{R th,} the image processor 56 calculates the maximum inclination _{INC max} of the cumulative density histogram (step S104E). The maximum slope of the cumulative density histogram refers to the maximum slope of the curve obtained by integrating the density histogram (see FIG. 38).

When the maximum inclination INC _max is obtained, the image processor 56 determines whether or not the maximum inclination INC _max ≧ threshold INC _th (step S104F). Here, the threshold INC _th is a desired value set in advance. If YES in this determination, that is, if the condition of maximum gradient INC _max ≧ threshold INC _th is satisfied, the image processor 56 selects a function of the constant weight α (j) based on Expression (8) as the weight function (step S104G). .

On the other hand, when NO is determined in step S104F, that is, when the maximum inclination INC _max <INC _th is satisfied, and when NO is determined in step S104D described above, that is, when the ratio R> R _th is satisfied, as an example, equation (9) Is selected (see curve B2 in FIG. 37) (step S104H). In step S104H, an appropriate weight α (j) based on equations (9) to (12) may be selected.

The processing from step S104D to S104H is repeatedly executed for each of a predetermined number of levels j (for example, j = 1, 2) determined in advance according to the size of the original image (step S104I). For example, in the case of a two-dimensional image having 256 × 256 pixels, it is determined whether or not the ratio R ≦ R _th for each of the levels j = 1 and 2, and the above-described processing is repeated. In the case of a two-dimensional image having 1024 × 1024 pixels, it is determined whether or not the ratio R ≦ R _th for each of the levels j = 1, 2, and 3, and the above-described processing is repeated.

In this way, by increasing the number of levels j to be determined as the number of pixels increases, it is possible to discriminate the attribute / feature possessed by the density value of the original image in detail. However, this ratio R ≦ R _th is not executed for all levels j = 1 to 8. Normally, when the level j becomes higher, the ratio R becomes less meaningful, so that an appropriate level is considered in consideration of the calculation amount. It is hard to keep it down to j.

  For this reason, when the discrimination and selection of the weighting function are performed up to an appropriate level j = 1, 1, the image processor 56 can estimate the tendency of the weighting function for the entire level j = 1-8. The weight function for the remaining levels j = 3 to 8 is selected (step S104J).

  As a result of the determination for level j = 1, 2, a nonlinear weight function based on equation (9) may be selected for both levels j = 1, 2, or a constant value weight function based on equation (8) may be selected. Sometimes selected. Further, a non-linear weight function based on Expression (9) is selected at level j = 1, but a constant value weight function based on Expression (8) may be selected at level j = 2. Therefore, in step S104J, as an example, the weight function selected at level j = 2 may be applied to levels j = 3-8. Note that weighting can be omitted for the higher level j (that is, weight = 1 is set).

  When the optimum weight function corresponding to the attribute / feature of the density value of the original image is thus automatically set for each level j, the image processor 56 refers to the function value (table) of the weight function. To set the value of the weight α (j) (step 104K).

  Thereafter, the image processor 56 shifts the process to step S105 of FIG. 32 described above, and performs image reconstruction processing in which the set weight α (j) is given to the high frequency component. This process is performed by inverse wavelet transformation based on the following equation.

  This image is displayed on the display 17 in step S105, and the image data is stored in the image data storage device 12, for example.

  In the above-described series of processing, in the original image, a density shift target area (area where the density average value is calculated), multi-resolution decomposition is performed, and the target area, image characteristics (density value characteristics) are identified, and Each area required for setting the weighting function is preferably the same area.

(Function and effect)
As described above, the above-described contrast enhancement processing can be applied to a local region designated on the panoramic image. Thereby, in addition to the effect in 1st Embodiment mentioned above, the various predominances based on this contrast emphasis process can be enjoyed.

  First, since the density value shift of the original image is performed as pre-processing, the dynamic range of the density gradation can be used effectively, and the contrast enhancement processing performed thereafter can be made appropriate.

  Further, since the value of the weight α (j) is changed for each level j, the reconstructed image uses a plurality of density levels, suppresses block artifacts while suppressing scale-out, and has a structure of low frequency components. While showing an object, it is possible to appropriately emphasize the fine features of the original image, to obtain excellent gradation expression, and to always properly emphasize the contrast of a wide density range as the entire image.

  Furthermore, unlike various conventional image contrast enhancement methods, the present embodiment uses a combination of “the ratio of the absolute value of the high frequency component to the absolute value of the low frequency component” and “the maximum slope of the cumulative histogram”. Therefore, contrast enhancement is performed by automatically and accurately grasping image characteristics. For this reason, artifacts can be significantly suppressed in the contrast-enhanced image, and the image quality regarding the panoramic image can be improved.

  As described above, according to the contrast enhancement method according to the present embodiment, the contrast enhancement according to the characteristics of the original image is performed without over-emphasizing noise in an area where the change in density value is small and maintaining the texture of the entire image. Can be done. For this reason, a panoramic image effective for dental interpretation can be provided.

  Furthermore, as described above, since the density shift is performed, it is possible to provide a sharp image by effectively using the dynamic range, and it is possible to reliably suppress the occurrence of block artifacts by setting a smooth weighting factor. The image quality can be improved.

  Furthermore, unlike the contrast enhancement methods according to some conventional methods, only the weighting process is applied to the coefficients of the high frequency components after the multi-resolution decomposition, so the amount of calculation is not so much and the calculation load increases. Can be suppressed. In addition, this weighting always matches the feature of the image, and depending on the content of the image, excessive contrast enhancement and the occurrence of block-like artifacts are significantly reduced.

  By the way, in this embodiment, a series of contrast enhancement processing typically shown in FIG. 32 is automatically executed by the image processor 56. For this reason, the operator only has to instruct the execution of processing through the operation device 58. Moreover, this automated contrast enhancement is performed based on the characteristics of the original image as described above. For this reason, it is possible to save work for the operator and to obtain an image in which contrast is accurately enhanced.

  Note that the contrast enhancement processing applicable to this panoramic image photographing apparatus is not necessarily limited to the above-described one, and may be performed by a conventionally well-known method. For example, Histogram Equalization (HE) method that operates histogram, Contrast Limited Adaptive Histogram Equalization (CLAHE) method that gives locality to contrast enhancement and suppresses excessive contrast enhancement, image density gradient There are methods using information. For this reason, references for these contrast enhancement processes are listed below.

W.K.Pratt: Digital image processing, John Wiley & Sons, New York, 1978 S.M.Pizer, et al.:"Adaptive histogram equalization and its variations, "Comput. Vision, graph.image proc., Vol.39, pp.355-368, 1987. S.G.Mallat, S.Zhong: ”Characterization of signals from multiscale edges,” IEEE Trans. PAMI, vol. 14, pp.710-732, 1992 J. Lu, et al .: “Contrast enhancement via multiscale gradient transformation,” IEEE Int'l Conf Imag. Proc. (ICIP), pp.482-486, 1994. J.J.Heine, et al .: “Multiresolution statistical analysis of high-resolution digital mammograms,” IEEE Trans. Medical Imaging, vol.16, pp.503-505, 1997 K.V.Velde: “Multi-scale color image enhancement,” IEEE Int Conf Image Proc (ICIP), vol.3, pp.584-587, 1999 US Pat. No. 5,467,404 US Pat. No. 5,960,123 (Third Embodiment) Next, with reference to FIGS. 39 and 40, a third embodiment of the panoramic image photographing apparatus of the present invention will be described. Note that the same reference numerals are used for hardware components similar to those described above.

  The panoramic image photographing apparatus according to this embodiment is not ideal for the patient's dentition, and even when teeth are overlapping in the dentition, the overlapping state and the front-rear relationship of the portion are appropriately adjusted. It has a function that can be interpreted. When teeth overlap with each other in this way, there is a problem in that the overlapping portion appears white in the panoramic image and cannot be interpreted or cannot be interpreted with high accuracy.

  This problem can be solved by performing effective width control processing, which will be described later, at an appropriate timing during the interpretation processing shown in FIGS. 19 and 20 at the time of interpretation, or subsequently after the interpretation processing. .

  In this effective width control process, the controller 57 controls the effective width in the lateral direction of the detection surface 32A of the detector 32 as a software process. Specifically, the effective width of the X-ray incidence of the detector 32 in the horizontal direction in which the detector 32 is moved and the position of the effective width are freely controlled for panoramic image data. Therefore, the function of generating a partial cross-sectional image (partial cross-sectional image specified by ROI) functionally realized by the controller 57 has the function of this effective width control process. This effective width control process can be executed in each of the first embodiment and the second embodiment described above.

  39 (A) and 39 (B) schematically show how the adjacent teeth 1 and 2 overlap each other. Therefore, the normal effective width W1 of the X-ray incidence of the detector 32, for example, 3.5 mm is reduced (for example, W2 = 2 mm), and the X-ray with the reduced effective width is transverse to the incident surface 32A of the detector 32. (The direction in which the detector 32 is moved during scanning) is moved to the right end and / or the left end. The controller 57 causes the controller 57 to execute this effective width reduction and movement process. In other words, since the X-ray tube 31 and the detector 32 both straddle both teeth 1 and 2 in the portion where the teeth overlap, the image interpreter is small enough to avoid the effective width of the detector. Set to a value and move the part of its effective width. Thereby, the overlapping of teeth on the image can be avoided as much as possible. For example, FIGS. 39A and 39B show a state in which the X-ray tube 31 and the detector 32 are at the same position on the movement trajectory for scanning, but the effective width W of the detector 32 is Because of the narrowness, the influence of the tooth overlap on the image is less in the case of FIG. 5B than in the case of FIG.

  For this reason, taking advantage of this property, the degree of overlap between teeth can be grasped on the image by performing the process outlined in FIG. 40 below between the radiogram interpreter and the controller 57.

  As described above, the portion where the teeth overlap is reflected in white on the panoramic image as described above. For this reason, the controller 57 receives the ROI information from the radiogram interpreter, and specifies the overlapping portion of the teeth and the partial region including the overlapping portion (step S150). Next, the controller 57 moves the effective width of the detector 31 to the left end of the detection surface 31A only by the overlapping portion, and reconstructs the image of the partial area in the moved state by operating the image processor 56. (Step S151). For example, a filter with function values of 1 and 0 may be used for the corresponding frame data for the movement of the effective width. Further, the above-described gain is used for reconstruction. Thereafter, the controller 57 moves the effective width of the detector 31 to the right end of the detection surface 31A by such an overlapping portion, and reconstructs an image of the partial region in the moved state (step S152). In this way, two types of images with the effective width shifted to the left and right are generated, and these images are displayed on the monitor 60 in a comparative manner. For this reason, it is easy for a radiogram interpreter to make a diagnosis as to how adjacent teeth 1 and 2 overlap each other by visually comparing the two reconstructed images displayed. In addition, since any one of the reconstructed images can obtain an image with little influence of the overlapping portion, the accuracy of diagnosis is improved.

As another accompanying effect, it is preferable that the effective width (horizontal width) and the position of the detector 32 can be preset from the outside of the apparatus, that is, from the operation device 58. As a result, if the lateral width and position of the detector 32 are controlled equivalently in a place where tooth overlap is observed on the conventional panoramic tomographic orbit, the geometry of the X-ray tube 31 and the detector 32 becomes the tooth shape. By setting the overlap so as to be avoided as much as possible, it is possible to reduce the overlap on the panoramic image of the overlapping portion of the tooth, which has been difficult to diagnose in the past, as much as possible, and also facilitate the diagnosis.

(Fourth embodiment)
Next, with reference to FIGS. 41 to 44, a fourth embodiment of the panoramic image photographing device of the present invention will be described. Note that the same reference numerals are used for hardware components similar to those described above.

  Similarly to the third embodiment, the panoramic image photographing apparatus according to this embodiment can reliably display the structure between teeth by avoiding the overlap even if the teeth overlap in the depth direction. It can be done.

  In order to realize this, the panoramic image photographing apparatus according to the present embodiment includes a digital semiconductor detector 82 having an X-ray incident surface 82A shown in FIG. As shown in the figure, the X-ray incident surface 82A of the detector 82 has a substantially cross shape when viewed from the X-ray incident direction, and has a wider first angle of incidence extending in the lateral direction (X direction). K1 and a second incident region K2 extending in the vertical direction (Y direction). Among these, the size of the first incident region K1 is, for example, about 2.5 to 7.5 cm (lateral length LA) × 10 cm (longitudinal length LB), and is not an area sensor but an area sensor. It has a two-dimensional pixel region that falls into the category of. In particular, it is desirable that the lateral length LA is as large as possible within the range of the conventional line sensor. The longitudinal length LB is set so as to sufficiently cover the upper and lower regions of the patient's gums (see virtual line H).

  On the other hand, the second incident region K2 has a line-shaped pixel region with a small width in the lateral direction so that the region other than the gums can be covered to some extent. The reason why the second incident region K2 is formed in an elongated shape is to reduce the amount of signal processing and arithmetic processing by reducing pixel regions that are not so necessary. If the amount of processing is not a problem, the incident area of the detector 82 may be a rectangular shape that covers the first and second incident areas K1 and K2.

  This detector 82 can output a detection signal having a digital amount corresponding to the intensity of the transmitted X-ray from each pixel in the first and second incident areas K1 and K2, similarly to the detector 32 described above. it can.

  As shown in FIG. 42, the detector 82 is arranged opposite to the X-ray tube 31 and, as described above, around the mouth and jaw of the subject P so as to scan with a preset standard plane as a focus. Move the rotation. As a result, since the first incident region K1 of the detector 82 is wide in the lateral direction, that is, the moving direction by scanning, the viewing direction of the X-ray path passing through the dentition is widened, and some X-ray paths therein are It also permeates through the gaps between the overlapping teeth (gap between teeth). That is, transmitted X-rays along the X-ray path viewed from the direction where the teeth do not overlap also enter the first incident region K1.

  For this reason, the controller 57 reconstructs and displays the panorama image Ppano of the standard plane using the frame data collected using the detector 82 in the same manner as described above (see FIG. 43, steps S161 and S162: FIG. 44). ). Next, the controller 57 designates a partial visual field area in the panoramic image Ppano by ROI based on the operation information of the operator. (Step S163: FIG. 44) It is preferable that the partial visual field region is designated as a portion where teeth are overlapped in the depth direction on the panoramic image Ppano or suspected. Next, the controller 57 specifies the partial region RG of the first incident region K1 of the detector 82 corresponding to the size of the partial visual field region (step S164: see FIG. 44). The partial region RG is specified as an initial region, and is specified as, for example, one of the first incident regions K1 in the lateral end region. The controller 57 then reconstructs and displays an image in the same manner as described above using a part of the frame data collected in the initial region of the detector 82 (step S165). As a result, as shown in FIG. 44, the image Pa is displayed in the partial visual field area (ROI) designated on the panoramic image Ppano.

  Next, if the reconstruction and display are not terminated (NO in step S166), the controller 57 does not change the size of the partial visual field region (ROI), and corresponds to the first visual field region. The partial region RG on K1 is automatically shifted by a predetermined amount in the direction of the other end (step S166). This corresponds to changing the projection direction of the X-ray path without changing the position of the partial visual field region (ROI). Next, the controller 57 reconstructs and displays an image in the same manner as described above using the data (other partial data of the frame data) collected in the moved partial area of the detector 82 (step S165). . Thereby, the image Pa of the partial visual field area (ROI) designated on the panoramic image Ppano is displayed at another projection angle.

  Hereinafter, similarly, the controller 57 reconstructs and displays the partial field-of-view image (that is, the partial image at a fixed position) while automatically shifting the partial region by the first incident region K1. Are repeatedly executed in succession (steps S165 to S167). As a result, the partial visual field image on the panoramic image Ppano is automatically displayed with the projection angle continuously changed while sequentially shifting the partial area on the first incident region K1.

  For this reason, the operator simply designates a partial visual field area of medical interest as ROI once on the panoramic image Ppano, and does not change the position of the visual field area, and the partial image with a different projection angle. Can be obtained as a video. Therefore, the operator can find an image with little or no tooth overlap (gap) in the continuously displayed partial images.

  If the operator obtains an image with little or no overlap between the teeth (YES in step S166), the operator performs the focus optimization process on the image to obtain an image Popt with less defocus. (Step S168: See FIG. 44).

  Thus, even if there is overlap in the depth direction between the teeth, the adoption of the detector 82 with a wider field of view, creation of an image while shifting the projection angle, search for the projection angle without overlapping of teeth, and A focus optimization image depicting the structure of the gap between teeth can be obtained by combining the focus optimization processing when finding a projection angle at which teeth do not overlap.

  It should be noted that the degree of overlap between the observable teeth is determined by the degree of the visual field (wide angle size) of the first incident region K2 of the detector 78. The wider the visual field range of the first incident region K2, the more observable even if the teeth overlap each other.

  In this series of processing, since the focus is on the overlapping of teeth, the vertical direction of the second incident region K2 does not need to be so wide. For this reason, the first incident area A1 is set to be narrow for the purpose of reducing the calculation load. When the projection angle is at the center of the allowable projection angle, the partial field image extends in the vertical direction. The structure of the part is also displayed for reference.

  Further, the search for the projection angle without the gap between the teeth described above may be automatically repeated until the operator gives a stop instruction.

  It should be noted that the present invention is not limited to the configurations shown in the above-described embodiments and modifications, and can be implemented with appropriate modifications without departing from the spirit of the present invention described in the claims. These modifications are also included in the concept of the present invention.

1 is a schematic perspective view showing an appearance of a panoramic image photographing apparatus according to the present invention. 1 is a schematic block diagram showing an electrical configuration of a panoramic image photographing apparatus according to the present invention. The figure explaining the view of the gain with respect to a focus introduced by this invention. The figure explaining the relationship between a dentition and a depth direction. The figure explaining an example of a phantom. The figure explaining another example of a phantom. The figure explaining another example of a phantom. The figure explaining the dentition and the range of the depth direction which sets a gain. The graph which illustrates the speed curve showing the gain introduced by this invention. The figure which illustrates the kind of ROI set on the panorama image of a standard surface. 4 is a schematic flowchart illustrating basic processing for focus optimization according to the present invention. The figure explaining the superposition addition of the frame data for the focus optimization which concerns on this invention. The flowchart explaining the outline | summary of the process of the gain prior measurement which a controller performs. The figure explaining the relationship between the several cross section of a dentition, and the direction (depth direction) which connects an X-ray tube and a detector. The figure explaining the measurement of the optimal gain of each position in each depth direction. The figure explaining the measurement of the optimal gain of each position in each depth direction. The figure explaining the three-dimensional distribution of the gain to measure. The flowchart explaining the outline | summary of the imaging | photography process centering on a controller. The flowchart which illustrates the outline | summary of the interpretation process centering on a controller. The flowchart which illustrates the outline | summary of the image interpretation process centering on a controller with FIG. The figure of the screen which shows the panoramic image of a standard surface typically. The figure of the screen which illustrates various ROI designated on a panorama image. The figure of the screen which shows the example of a display of the enlarged view of the part (cross section) of ROI designated on the panoramic image. The figure explaining the concept to translate the cross section by ROI designated on the panoramic image in the depth direction. The figure explaining the concept which inclines (rotates) the cross section by ROI designated on the panoramic image. The flowchart explaining the outline | summary of the selection process of the standard surface centering on a controller. The figure explaining the concept of selection of a standard surface. The flowchart which illustrates the selection process of the display mode when displaying the image of the cross section designated by ROI. The figure of the screen which shows the example of a display of the image of the cross section designated by ROI. The figure of the screen which shows another example of a display of the image of the cross section designated by ROI. The figure of the screen which shows another example of a display of the image of the cross section designated by ROI. 9 is a flowchart showing an outline of an automated contrast enhancement process executed by an image processor in the second embodiment of the panoramic image photographing apparatus according to the present invention. 4 is a schematic flowchart showing density value shift executed by an image processor in cooperation with a controller. The figure explaining the relationship between scale-out and density value shift. The schematic diagram explaining the wavelet transformation as multiresolution analysis about each level. 4 is a schematic flowchart showing an automated weighting process executed by an image processor. The graph which illustrates two or more weight functions with respect to the high frequency component of each level obtained by wavelet transformation. The figure explaining the relationship of the maximum inclination of a density histogram and a cumulative density histogram qualitatively. The figure explaining the pros and cons of the control of the effective width of the detector which a controller performs in cooperation with an image processor in 3rd Embodiment of the panoramic image imaging device which concerns on this invention. 10 is a flowchart illustrating an outline of a control process for an effective width of a detector that is executed by a controller in cooperation with an image processor in a third embodiment. The figure explaining the two-dimensional X-ray incident area | region of the detector employ | adopted by 4th Embodiment of the panoramic image imaging device which concerns on this invention. The figure explaining the relationship between the overlap of teeth and an X-ray path. The flowchart explaining the outline | summary of the process which searches the clearance gap between the overlapping parts of the teeth performed by the controller in 4th Embodiment. The figure explaining the image displayed by the process which searches the clearance gap between the overlapping parts of the teeth in 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Panorama image imaging device 11 Case 12 Computer 14 Image pick-up part 23 Vertical movement unit 24 Rotation unit 30 Rotation drive mechanism 31 X-ray tube 32 Detector 41 High voltage generator 53 Buffer memory 54 Image memory 55 Frame memory 56 Image processor 57 Controller 58 Controller 60 Monitor 82 Detector P Subject FT Phantom

Claims (35)

An X-ray source that emits X-rays;
A target that outputs a digital electrical signal corresponding to incident X-rays at a constant frame rate, and a pair of the X-ray source and the detector facing each other across the target. Moving drive means for moving around,
Storage means for sequentially storing, as frame data, electrical signals output by the detector at the frame rate as the movement driving means moves the X-ray source and the detector around the object;
Panorama image generating means for generating a panoramic image of a desired tomographic plane designated in advance based on the frame data stored in the storage means;
Using the frame data, a specified partial area of the panoramic image is focused according to a desired position on the space where the X-ray source and the detector are moved by the movement driving means. And a partial cross-sectional image generating means for generating a partial cross-sectional image. The panoramic image photographing device according to claim 1,
Variable on coordinates determined by the position in the space, a plurality of frame data stored in the storage means, and the mapping position when the frame data is mapped on the memory space to reconstruct a panoramic image A pre-measurement means for presetting correspondence information between a gain defined as a slope of a simple curve and
The panoramic image generation means is means for generating the panoramic image by referring to the correspondence information according to the position of the desired tomographic plane in the space,
The partial cross-sectional image generation unit is a panoramic image photographing device that is a unit that generates the partial cross-sectional image by referring to the correspondence information according to a position of the partial region in the space. The panoramic image photographing device according to claim 2,
The movement drive means is means for moving the pair of the X-ray source and the detector so that the desired tomographic plane is in focus,
The pre-measurement means includes
Means for setting the correspondence information of the desired tomographic plane from the frame data read from the storage means;
Means for calculating the correspondence information of each position in the space as three-dimensional information from the correspondence information of the desired tomographic plane;
A panoramic image photographing apparatus. The panoramic image photographing device according to claim 3,
The detector is a line detector having a line-shaped detection surface on which the X-rays are incident,
The panorama image photographing apparatus in which the gain takes the same value for each position at a position parallel to the detection surface of the detector in the space. The panoramic image photographing device according to claim 2,
The panoramic image photographing apparatus, wherein the movement driving means is a means for moving the pair of the X-ray source and the detector along the desired tomographic plane. The panoramic image photographing device according to claim 5,
The rotation driving means is configured to provide a distance ratio between the distance between the X-ray source and the object and the distance between the object and the detector and the X so that the desired tomographic plane is always in focus. A panoramic image photographing apparatus which is means for adjusting the moving speed of a pair of a radiation source and the detector. The panoramic image photographing device according to claim 3,
The panoramic image photographing apparatus, wherein the desired tomographic plane is a tomographic plane designated according to the shape and size of the object. The panoramic image photographing device according to claim 5,
The panoramic image photographing apparatus, wherein the desired tomographic plane is a tomographic plane designated according to the shape and size of the object selected from a plurality of tomographic planes designated in advance. The panoramic image photographing device according to claim 2,
The panoramic image generating means
Panoramic image display means for displaying a panoramic image of the desired tomographic plane;
The partial cross-sectional image generating means
A region of interest setting means capable of interactively setting a partial region of interest in the panoramic image displayed by the panoramic image display means as the partial region;
Receiving means for interactively receiving the gain of the cross section defined by the region of interest as information on the specified distance;
Gain acquisition means for acquiring a gain according to the cross-section conversion information with reference to the correspondence information from the desired cross-section conversion information;
A panoramic image photographing apparatus comprising: a partial cross-sectional image calculating unit that calculates an image corresponding to the cross-sectional conversion information as the partial cross-sectional image based on the gain acquired by the gain acquiring unit and the frame data. The panoramic image photographing device according to claim 9, wherein
The partial cross-sectional image calculating means includes means for adjusting the number of frames of the frame data corresponding to the gain variation and maintaining the specified size of the region of interest when calculating the partial cross-sectional image. Panoramic image shooting device. The panoramic image photographing device according to claim 9, wherein
A panoramic image photographing apparatus comprising: a partial cross-sectional image display unit that displays the partial cross-sectional image calculated by the partial cross-sectional image calculation unit superimposed on the panoramic image. The panoramic image photographing device according to claim 11,
The panoramic image photographing apparatus, wherein the partial cross-sectional image display means is a means for displaying the partial cross-sectional image along with the image of the region of interest. The panoramic image photographing device according to claim 11,
The partial cross-sectional image display means has means for enabling at least a part of the cross-section conversion information to be displayed, stored and read out together with the panoramic image and the partial cross-sectional image. The panoramic image photographing device according to claim 1,
The panoramic image photographing apparatus characterized in that the partial cross-sectional image display means sets and displays the size of the partial cross-sectional image to the same value as the film size used in the intraoral photographing method. The panoramic image photographing device according to claim 1,
The panoramic image photographing apparatus characterized in that the partial cross-sectional image display means displays the size of the partial cross-sectional image so as to substantially match the actual size of the actual photographing part of the object. The panoramic image photographing device according to claim 1,
The partial cross-sectional image display means tilts the designated partial area from a cross-sectional position parallel to the vertical direction and the horizontal direction of the panoramic image, and sets the desired part of the object to fit in the designated partial area. A panoramic image photographing device. The panoramic image photographing device according to claim 9, wherein
The panoramic image photographing apparatus, wherein the cross-section conversion information is information for translating a cross section defined by the region of interest along a distance direction connecting the X-ray source and the detector. The panoramic image photographing device according to claim 9, wherein
The cross-section conversion information is centered on at least one of the two axes orthogonal to each other perpendicular to the direction of the distance connecting the X-ray source and the detector. A panoramic image photographing apparatus which is information rotated around an axis parallel to this axis. The panoramic image photographing device according to claim 9, wherein
The cross-section conversion information translates a cross-section defined by the region of interest along a linear direction connecting the X-ray source and the detector, and connects the X-ray source and the detector. A panoramic image photographing apparatus that is information that is rotated around at least one of two axes perpendicular to each other and perpendicular to the distance direction, or around an axis parallel to this axis. The panoramic image photographing device according to claim 17,
The partial cross-sectional image display means has means for enabling at least a part of the cross-section conversion information to be displayed, stored and read out together with the panoramic image and the partial cross-sectional image. The panoramic image photographing device according to claim 2,
The pre-measurement means includes
A pre-imaging means for photographing the panoramic image by placing a phantom device provided with a phantom for measuring a distance in a linear direction connecting the X-ray source and the detector at a position where the object is placed;
Means for setting the desired gain for each of the distances while the photographer visually observes the phantom reflected in the panoramic image photographed by the preliminary photographing means;
A panoramic image photographing device comprising: means for storing the set correspondence information of the distance and the gain in a memory. The panoramic image photographing device according to claim 21,
The phantom device is a panoramic image photographing device including a base member, an inclined substrate inclined at a predetermined angle with respect to the base member, and a plurality of phantoms arranged at regular intervals on the inclined substrate. The panoramic image photographing device according to claim 22,
The plurality of phantoms is a panorama apparatus that is a granular object formed of a material that does not transmit the X-rays. The panoramic image photographing device according to claim 21,
The phantom device includes a base member, an inclined substrate inclined at a predetermined angle with respect to the base member, and a strip-shaped phantom placed on the inclined substrate along the inclined substrate over a certain distance. A panoramic image photographing device. The panoramic image photographing device according to claim 1,
A panoramic image photographing apparatus provided with contrast enhancing means for enhancing the contrast of the partial sectional image on the partial sectional image generated by the partial sectional image generating means. The panoramic image photographing device according to claim 1,
A panorama image photographing apparatus provided with contrast enhancement means for enhancing the contrast of the panorama image to the panorama image generated by the panorama image generation means and passing the enhanced panorama image to the partial cross-sectional image generation means. The panoramic image photographing device according to claim 25,
The contrast enhancing means includes
Decomposition means for subjecting the data of the partial cross-sectional image generated by the partial cross-sectional image generation means to multi-resolution decomposition to decompose into coefficient data composed of coefficients of a low frequency component and a high frequency component;
Weighting means for assigning weights according to characteristics of the density values of the partial cross-sectional images to the coefficients of the high-frequency components for each level of some or all of the multiple resolution decomposition levels;
A panoramic image photographing apparatus comprising: reconstruction means for reconstructing the coefficient data having the weighted high-frequency component coefficients into a new image. The panoramic image photographing device according to claim 27,
The decomposition means includes means for estimating whether the vertical and horizontal sizes of the region of the partial cross-sectional image area are not powers of 2; Means for decomposing the original image into subbands having the coefficient data by performing the multi-resolution decomposition of the plurality of levels by a wavelet transform on a partial cross-sectional image set in a power region;
The panoramic image photographing apparatus, wherein the reconstruction means is means for reconstructing the new image by performing inverse wavelet transform on the subbands weighted by the weighting means. The panoramic image photographing device according to claim 1,
The panoramic image photographing apparatus according to claim 1, wherein the desired tomographic plane is a tomographic plane along a dentition having a substantially horseshoe shape. The panoramic image photographing device according to claim 1,
The partial cross-sectional image generating means can effectively control the effective width of the X-ray incident on the detector in the lateral direction in which the detector is moved and the position of the effective width with respect to the panoramic image data. A panoramic image photographing apparatus having width control means. The panoramic image photographing device according to claim 1,
The detector has an incident region having a two-dimensional region portion having a width in the moving direction, which is a region in which the X-ray is incident.
The partial cross-sectional image generating means is collected from means for designating the partial field of view on the panoramic image and a part of the incident area of the detector corresponding to the size of the partial field of view. A means for specifying a part of the frame data, a means for reconstructing and displaying an image using the specified data, and an image of the partial field of view corresponding to the partial field of view. And means for continuously repeating the reconstruction and display of the image based on the other data using the other data of the frame data collected from the other areas of the incident area of the detector. A panoramic image photographing device. The panoramic image photographing device according to claim 31,
The incident area of the detector has a substantially cross-shaped area having an area intersecting with the two-dimensional area portion. An X-ray source that emits X-rays;
A detector that outputs a digital amount of an electrical signal corresponding to incident X-rays at a constant frame rate;
Moving drive means for moving the X-ray source and the detector around the object in a state of being opposed to each other with the object interposed therebetween;
Storage means for sequentially storing, as frame data, electrical signals output by the detector at the frame rate as the movement driving means moves the pair of the X-ray source and the detector around the subject; ,
Panorama image generating means for generating a panoramic image of a desired tomographic plane designated in advance based on the frame data stored in the storage means;
A partial image defined in a partial designated area of the panoramic image generated by the panoramic image generating means is used as the X-ray source and the detector by the movement driving means using the frame data. A panoramic image photographing apparatus comprising: a partial cross-sectional image visualizing unit that converts into a partial cross-sectional image focused according to a desired position in a moved space and visualizes the partial cross-sectional image. An electrical signal output by the radiation detector at a constant frame rate as the X-ray source and detector pair are moved around the object in a state where the X-ray source and the detector are opposed to each other with the object sandwiched therebetween. As sequentially
Based on the stored frame data, a panoramic image of a tomographic plane designated in advance is generated,
Using the frame data, a partial cross-sectional image in which a specified partial area of the panoramic image is focused according to a desired position on a space in which the X-ray source and the detector are moved is obtained. An image processing method in panoramic photography, characterized in that: A program stored in memory and readable by a computer,
The electrical signals output by the radiation detector at a constant frame rate are sequentially stored as the X-ray source and detector pair are moved around the object in a state of facing each other with the object interposed therebetween. In the program that processes the frame data obtained
In the computer,
Generating a panoramic image of a desired tomographic plane specified in advance using the stored frame data;
Using the frame data, the designated partial area of the panoramic image of the desired tomographic plane is focused according to a desired position on the space where the X-ray source and the detector are moved. Generating a partial cross-sectional image;
A program characterized by being executed functionally.

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