JP2016036671A - Radiographic apparatus and deviation calculation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiographic apparatus capable of creating a clear tomographic image with no deviation even if no marker is photographed.SOLUTION: According to the X-ray photographing apparatus of the present invention, a clear tomographic image with no deviation can be created even if no marker is photographed. In the structure of the present invention, in order to calculate a correction value for canceling the deviation of a subject image, the subject image itself is used. Different from a marker, a subject image is not photographed clearly on an X-ray image. This is because a subject has a thickness and the inner structure of the subject is photographed on an X-ray image, with the inner structure folded and piled up. Thus the present invention is configured such that a provisional tomographic image is created to determine how the subject image is deviated, and a correction value calculation unit 13 calculates the direction and intensity of the deviation of the subject image on the basis of the tomographic image.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radiography apparatus and a blur calculation method for generating a tomographic image based on radiographs taken continuously while changing an imaging direction, and in particular, radiography having a configuration capable of imaging other than tomography. The present invention relates to an apparatus and a blur calculation method.

  A medical institution is equipped with a radiation imaging apparatus that acquires an image of a subject with radiation. As shown in FIG. 27, the radiation imaging apparatus having such a conventional configuration includes a bed that supports the top plate 52 on which the subject is placed, a radiation source 53 that is suspended from the ceiling of the examination room, and a bed. And a radiation detector 54 for detecting the emitted radiation. Such an apparatus is configured to be capable of various photographing such as spot photographing and long photographing.

  Some apparatuses shown in FIG. 27 are configured such that the radiation source 53 and the radiation detector 54 can move synchronously so that a tomographic image by tomosynthesis can be acquired. Imaging by tomosynthesis is a specific method in which the radiation source 53 and the radiation detector 54 are moved in opposite directions with respect to the subject M on the top plate 52, and the radiographic images continuously taken between them are superimposed. This is a method for obtaining a tomographic image when the subject M is cut in a plane.

  By the way, the radiation tomography apparatus for exclusive use which performs imaging | photography regarding tomosynthesis comprises the radiation source 53 and the radiation detector 54 integrally. According to such an apparatus, the positional relationship between the radiation source 53 and the radiation detector 54 is constant. Therefore, such a dedicated device can generate a relatively clear tomographic image.

  However, since the general-purpose apparatus described with reference to FIG. 27 has a configuration in which the bed can be moved with respect to the radiation source 53, the imaging system 53 including the radiation source 53 and the radiation detector 54. , 54 is difficult to move as ideal. If the movement mode of the imaging systems 53 and 54 deviates from the ideal, the tomographic image will be blurred accordingly. There is a limit to eliminate this blur by positioning the bed with respect to the radiation source 53.

  Therefore, according to the conventional configuration, a series of radiographic images are captured in a state where the marker is captured together with the subject in the field of view, and the imaging systems 53 and 54 are moved based on the marker image captured in each radiographic image. It recognizes how much the style is from ideal and corrects the image based on this recognition (see, for example, Patent Document 1). As a result, a clear tomographic image can be acquired even with a general-purpose radiation imaging apparatus.

  The marker and the subject are simultaneously photographed with the above-described configuration. Certainly, only the marker is taken continuously to recognize how far the movement mode of the imaging systems 53 and 54 deviates from the ideal, then the subject is taken continuously instead of the marker, and the obtained subject image is copied. It is a way of thinking to correct a series of images. However, if this is done, if there is a change in the manner of movement of the imaging systems 53 and 54 between the imaging of the marker and the imaging of the subject, this cannot be dealt with. Therefore, according to the configuration of Patent Document 1, the subject and the marker are imaged at the same time, and the movement mode of the imaging systems 53 and 54 for this imaging is known.

JP 2013-17675 A

  However, in the conventional radiographic apparatus, only a tomographic image in which a marker is reflected together with the subject image can be obtained. The marker on the tomographic image hinders observation of the subject.

  In imaging related to tomosynthesis, it is usual to narrow the field of view for the purpose of suppressing exposure of the subject. A tomographic image obtained by such imaging is an image in which a cross-sectional image of the subject is fully reflected. Regardless of where the marker image is placed in the tomographic image, the marker image overlaps the cross-sectional image of the subject. That is, a part of the subject image on the tomographic image is hidden behind the marker image.

  However, in order to take an image so that the marker image does not overlap the subject image on the tomographic image, it is necessary to considerably increase the field of view when taking a series of radiographic images. When such imaging is performed, not only unnecessary exposure of the subject increases, but also the image quality of the tomographic image decreases as the scattered radiation increases.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a radiation imaging apparatus capable of generating a clear tomographic image without blurring without imaging a marker. .

The present invention has the following configuration in order to solve the above-described problems.
That is, a radiographic apparatus according to the present invention includes a radiation source that irradiates a subject with radiation, a detection unit that detects radiation transmitted through the subject, a radiation source moving unit that moves the radiation source relative to the subject, and a detection A detector moving means for moving the means relative to the subject, an image generating means for generating a radiographic image based on the output of the detecting means, and a series of images continuously taken while the radiation source and the detecting means are moved in opposite directions. The tomographic image generating means for generating a tomographic image based on the radiation image of the above and the actual moving direction of the detecting means differ from the assumption of the tomographic image generating means, and the inclination of the actual detecting means with respect to the moving direction of the detecting means Based on the tomographic image of the subject in the tomographic image, the direction and intensity of the blurring of the subject image in the tomographic image generated due to a difference from the assumption of the image generation means Based on the calculation result of the calculation means, and a position correction means for correcting the position of the subject image reflected in the series of radiographic images so as to cancel the blur of the subject image seen on the tomographic image, The image generating means generates a tomographic image for diagnosis in which a subject image without blur is reflected based on a series of corrected radiographic images.

[Operation / Effect] According to the radiation imaging apparatus described above, a clear tomographic image without blurring can be generated without imaging a marker. In the conventional configuration, by grasping the marker reflected in the radiographic image, it is possible to know how far the subject image in the series of radiographic images deviates from the ideal, and by correcting this misalignment, the tomographic image blur is corrected. Is preventing. On the other hand, according to the configuration of the present invention, the blur direction and intensity of the subject image are grasped based on the actual subject image. That is, in the configuration of the present invention, the subject image itself is used to calculate a correction value that cancels the blurring of the subject image.
Unlike the marker, the subject image is not clearly reflected on the radiation image. This is because the subject has a thickness, and the internal structure of the subject is reflected in the radiation image. Therefore, in the configuration of the present invention, a tomographic image is provisionally generated for the purpose of knowing the blurring mode of the subject image, and the calculation means calculates the direction and intensity of blurring of the subject image based on this tomographic image. The tomographic image includes information regarding blurring of the subject image.
Therefore, according to the present invention, it is possible to provide a radiation imaging apparatus capable of generating a tomographic image without blurring without providing a marker. As a cause of blurring of the subject image, the actual moving direction of the detecting means is different from the assumption of the tomographic image generating means, and the actual inclination of the detecting means with respect to the moving direction of the detecting means is different from the assumption of the tomographic image generating means. There is.

  Further, in the above-described radiographic apparatus, the calculating unit captures a tomographic image obtained by reconstructing a radiographic image belonging to a group that has been captured first in a series of radiographic images and a later in the series of radiographic images. The image of the subject is blurred based on the displacement of the subject image that is obtained by reconstructing the radiographic images belonging to the selected group and is reflected in each of the subsequent tomographic images having the same cut surface as the previous tomographic image. Is more desirable.

  [Operation / Effect] The above configuration more specifically shows the radiation imaging apparatus of the present invention. The tomographic image obtained by reconstructing the radiographic image belonging to the group that was captured earlier in the series of radiographic images is the first halfway through the process of subject image blurring on the tomographic image. Represents. On the other hand, a post-tomographic image obtained by reconstructing a radiographic image belonging to a group taken later in a series of radiographic images is the last halfway through the process in which the subject image is blurred on the tomographic image. Represents. Accordingly, the blur of the subject image can be calculated by examining the displacement of the position of the subject image reflected in each of the tomographic image and the rear tomographic image.

  Further, in the above-described radiographic apparatus, the calculation unit shifts the detection unit in the moving direction based on the front tomographic image and the rear tomographic image generated by superimposing a series of radiographic images without shifting each other. It is more desirable to calculate the resulting blur of the subject image.

  [Operation / Effect] The above configuration more specifically shows the radiation imaging apparatus of the present invention. When the calculation unit generates a front tomographic image and a rear tomographic image by directly superimposing a series of radiographic images without shifting each other, the subject images on both images are not displaced by the inclination of the detection unit. Therefore, the blur of the subject image due to the shift in the moving direction of the detecting means is accurately based on the front tomographic image and the rear tomographic image generated by the calculation means superimposing the series of radiation images without shifting each other. Can be calculated.

  Further, the radiographic apparatus according to the present invention provides a subject caused by the inclination of the detection unit based on the front tomographic image and the rear tomographic image generated by the calculation unit superimposing a series of radiographic images while shifting each other. The image blur is calculated.

  [Operation / Effect] The above configuration more specifically shows the radiation imaging apparatus of the present invention. When the calculation unit generates a front tomographic image and a rear tomographic image by directly superimposing a series of radiographic images without shifting each other, the subject images on both images are not displaced by the inclination of the detection unit. Therefore, in order to calculate the blur of the subject image due to the inclination of the detection means, it is necessary to generate a front tomographic image and a rear tomographic image by superimposing a series of radiographic images while shifting each other.

  Further, in the radiographic apparatus described above, the calculation means is caused by the inclination of the detection means based on a tomographic image based on a series of radiographic images corrected to cancel out the blur of the subject image caused by the moving direction of the detection means. It is more desirable to calculate the blur of the subject image.

  [Operation / Effect] The above configuration more specifically shows the radiation imaging apparatus of the present invention. When a series of radiographic images are superimposed while being shifted from each other to generate a front tomographic image and a rear tomographic image, and a correction value is calculated based on these images, the correction value includes correction and detection related to displacement in the moving direction. The correction related to the inclination of the means overlaps and cannot be separated from each other. Then, it can operate only on the cut surface for which the correction value is obtained. Therefore, the influence of the shift in the moving direction is removed from the series of radiographic images before generating the front tomographic image and the rear tomographic image by superimposing the series of radiographic images while shifting each other. By configuring in this way, it is possible to reliably acquire a correction value indicating only the correction relating to the detection means.

  Moreover, in the above-described radiation imaging apparatus, it is more desirable that the radiation source is supported by being suspended in the examination room.

  [Operation / Effect] The above configuration more specifically shows the radiation imaging apparatus of the present invention. In a general-purpose radiographic apparatus in which the radiation source is suspended and supported in the examination room, the detection means is likely to be displaced in the moving direction and the detection means is inclined with respect to the moving direction of the detecting means. Therefore, the present invention is particularly effective when applied to such an apparatus.

This specification also discloses a method invention corresponding to the above-described radiographic apparatus.
That is, the blur calculation method according to the present invention includes a radiation source that irradiates a subject with radiation, a detection unit that detects radiation transmitted through the subject, a radiation source moving unit that moves the radiation source relative to the subject, and a detection Detector moving means for moving the means relative to the subject, and tomographic image generating means for generating a tomographic image based on a series of radiographic images continuously taken while the radiation source and the detecting means are moved in opposite directions. A blur calculation method for calculating a blur direction and intensity of a subject image in a tomographic image generated by a provided radiography apparatus, wherein an actual detection unit moving direction is based on a series of radiographic images. Subject in a tomographic image that occurs due to a difference from the assumption of the tomographic image and the inclination of the actual detection means with respect to the moving direction of the detection means differs from the assumption of the tomographic image generation means It is characterized in that calculated on the basis of the direction and intensity of the vibration on the tomographic image of the subject fancy-through on the tomographic images.

  Further, in the blur calculation method described above, a tomographic image obtained by reconstructing a radiographic image belonging to a group captured earlier in a series of radiographic images and a group captured later in a series of radiographic images. If the blur of the subject image is calculated based on the displacement of the subject image that is obtained by reconstructing the radiation image to which it belongs and is reflected in each of the subsequent tomographic images having the same cut surface as the previous tomographic image More desirable.

  According to the radiation imaging apparatus of the present invention, a clear tomographic image without blurring can be generated without imaging a marker. In the configuration of the present invention, the subject image itself is used to calculate a correction value that cancels out blurring of the subject image. Unlike the marker, the subject image is not clearly reflected on the radiation image. This is because the subject has a thickness, and the internal structure of the subject is reflected in the radiation image. Therefore, in the present invention, a tomographic image is tentatively generated for the purpose of knowing the blurring mode of the subject image, and the calculation means is configured to calculate the blurring direction and intensity of the subject image based on the tomographic image. ing.

1 is a functional block diagram illustrating an overall configuration of an X-ray imaging apparatus according to Embodiment 1. FIG. FIG. 3 is a schematic diagram illustrating a tomographic imaging principle according to the first embodiment. FIG. 3 is a perspective view illustrating removal of the FPD according to the first embodiment. 1 is a perspective view illustrating an FPD according to Embodiment 1. FIG. FIG. 6 is a schematic diagram for explaining a shift in the movement direction of the FPD according to the first embodiment. FIG. 6 is a schematic diagram for explaining a shift in the movement direction of the FPD according to the first embodiment. 6 is a schematic diagram illustrating blurring of a tomographic image caused by a shift in the movement direction of the FPD according to Embodiment 1. FIG. 6 is a schematic diagram illustrating blurring of a tomographic image caused by a shift in the movement direction of the FPD according to Embodiment 1. FIG. FIG. 6 is a schematic diagram illustrating calculation of blurring of tomographic images caused by a shift in the movement direction of the FPD according to the first embodiment. FIG. 6 is a schematic diagram illustrating calculation of blurring of tomographic images caused by a shift in the movement direction of the FPD according to the first embodiment. 6 is a schematic diagram illustrating a correction value related to a shift in the movement direction of the FPD according to Embodiment 1. FIG. FIG. 6 is a schematic diagram illustrating correction related to a shift in the movement direction of the FPD according to the first embodiment. FIG. 3 is a schematic diagram for explaining the properties of the reference cut section according to the first embodiment. FIG. 3 is a schematic diagram for explaining the properties of the reference cut section according to the first embodiment. FIG. 3 is a schematic diagram for explaining the properties of the reference cut section according to the first embodiment. 3 is a schematic diagram illustrating the inclination of the FPD according to Embodiment 1. FIG. FIG. 6 is a schematic diagram for explaining blurring of a tomographic image due to the inclination of the FPD according to the first embodiment. FIG. 6 is a schematic diagram for explaining blurring of a tomographic image due to the inclination of the FPD according to the first embodiment. FIG. 6 is a schematic diagram for explaining blurring of a tomographic image due to the inclination of the FPD according to the first embodiment. FIG. 6 is a schematic diagram for explaining blurring of a tomographic image due to the inclination of the FPD according to the first embodiment. FIG. 6 is a schematic diagram conceptually illustrating suppression of tomographic image blurring caused by the inclination of the FPD according to the first embodiment. 6 is a schematic diagram illustrating calculation of blurring of a tomographic image caused by the inclination of the FPD according to Embodiment 1. FIG. 6 is a schematic diagram illustrating calculation of blurring of a tomographic image caused by the inclination of the FPD according to Embodiment 1. FIG. FIG. 10 is a schematic diagram for explaining a correction value for blurring of a tomographic image caused by the inclination of the FPD according to the first embodiment. 6 is a schematic diagram illustrating correction of blurring of a tomographic image caused by the inclination of the FPD according to Embodiment 1. FIG. 3 is a flowchart for explaining the operation of the X-ray imaging apparatus according to Embodiment 1; It is a schematic diagram explaining the X-ray imaging apparatus which concerns on a conventional structure.

  The configuration of the X-ray imaging apparatus according to the present invention will be described. X-rays correspond to the radiation of the present invention. FPD is an abbreviation for flat panel detector. Further, the X-ray imaging apparatus according to the present invention is a general-purpose apparatus capable of imaging tomographic images based on the same principle as a digital tomosynthesis apparatus as well as spot imaging. Since the present invention is characterized by tomographic image capturing, the following description will explain the configuration and operation related to tomographic image capturing. The subject M corresponds to the subject of the present invention. The subject in the present invention does not include a marker.

<Overall configuration of X-ray imaging apparatus>
As shown in FIG. 1, the X-ray imaging apparatus 1 according to the first embodiment receives a top plate 2 on which a subject M in a supine position is placed, and X-rays provided on the upper side (one surface side) of the top plate 2. An X-ray tube 3 that irradiates the specimen M, and an apparatus that is placed on the top 2 and disposed below the subject M, detects X-rays that have passed through the subject M, and outputs a detection signal. Output FPD4. The FPD 4 is a rectangle having four sides along either the body axis direction A or the body side direction S of the subject M. One of the FPDs 4 is used at the time of imaging, and is arranged between the subject M and the top board 2 in the case of imaging related to the supine position. The detection surface for detecting X-rays of the FPD 4 faces the X-ray tube 3 and the subject M side. The X-ray tube 3 irradiates the quadrangular pyramid-shaped X-rays toward the FPD 4. Therefore, the FPD 4 receives X-rays on the entire detection surface.

  The support column 5 extends from the ceiling of the examination room toward the floor surface, and supports the X-ray tube 3. The X-ray imaging apparatus 1 having such a support 5 is called a radiation source suspended type. The X-ray tube 3 is supported by being suspended in the examination room. The X-ray tube 3 corresponds to the radiation source of the present invention, and the FPD 4 corresponds to the detection means of the present invention.

  The X-ray tube controller 6 shown in FIG. 1 is provided for the purpose of controlling the X-ray tube 3 with a predetermined tube current, tube voltage, and pulse width.

  The X-ray tube moving mechanism 7a is configured to move the column 5 with respect to the ceiling of the examination room. The X-ray tube moving mechanism 7a can move the support column 5 along the body axis of the subject M or can move it along the body side of the subject M. When the column 5 is moved, the X-ray tube 3 suspended and supported by the column 5 moves following the column 5. Thus, the X-ray tube 3 can be moved with respect to the subject M on the top 2 by the X-ray tube moving mechanism 7a. The X-ray tube movement control unit 8a is provided for the purpose of controlling the X-ray tube movement mechanism 7a. The X-ray tube moving mechanism 7a corresponds to the radiation source moving means of the present invention. In the configuration of the first embodiment, it is assumed that the X-ray tube moving mechanism 7a operates only on the body axis of the subject M.

  The FPD moving mechanism 7 b is configured to move the FPD 4 relative to the top plate 2 below the top plate 2. The FPD moving mechanism 7b can move the FPD 4 along the body axis of the subject M. In this way, the FPD 4 can move relative to the subject M on the top 2 by the FPD moving mechanism 7b. The FPD movement control unit 8b is provided for the purpose of controlling the FPD movement mechanism 7b. The FPD moving mechanism 7b corresponds to the detector moving means of the present invention.

  The X-ray tube moving mechanism 7a and the FPD moving mechanism 7b are configured to move the X-ray tube 3 and the FPD 4 in synchronization with the subject M. The X-ray tube moving mechanism 7a and the FPD moving mechanism 7b are linear trajectories (longitudinal of the top plate 2) parallel to the body axis direction A of the subject M according to the control of the X-ray tube moving control unit 8a and the FPD moving control unit 8b. The X-ray tube 3 is moved straight along (direction). The moving direction of the X-ray tube 3 and the FPD 4 coincides with the longitudinal direction of the top 2. The directions of the synchronous movement of the X-ray tube 3 and the FPD 4 realized by the X-ray tube moving mechanism 7a and the FPD moving mechanism 7b are opposite to each other. Therefore, when the X-ray tube 3 moves from the head of the subject M toward the toes, the FPD 4 moves from the toes of the subject M toward the head.

  During the synchronous movement of the X-ray tube 3 and the FPD 4, the cone-shaped X-ray beam irradiated by the X-ray tube 3 is always irradiated toward the region of interest of the subject M. That is, the irradiation angle of the X-ray beam is changed from, for example, an initial angle of −20 ° to a final angle of 20 ° by changing the angle of the X-ray tube 3. In other words, the apparatus according to the present invention is devised so that the X-ray tube 3 is inclined so that the X-ray beam irradiated by the X-ray tube 3 is always received by the entire surface of the X-ray detection surface of the FPD 4. . Such an X-ray irradiation angle change is performed by the X-ray tube tilting mechanism 9. The X-ray tube tilt control unit 10 is provided for the purpose of controlling the X-ray tube tilt mechanism 9.

  When the X-ray imaging apparatus according to the present invention generates a tomographic image, the X-ray tube 3 and the FPD 4 are indicated by an alternate long and short dash line through a position indicated by a broken line with the position of the solid line shown in FIG. 1 as an initial position. Move counter to position. At this time, the X-ray tube 3 irradiates the pulsed X-ray beam 74 times while moving synchronously with the FPD 4.

  The image generation unit 11 acquires an X-ray detection signal output by the FPD 4 every time X-ray irradiation is performed, and generates 74 X-ray images P1, P2, P3,. The generated image generation unit 11 is sent to the tomographic image generation unit 12. The image generation unit 11 corresponds to the image generation unit of the present invention, and the tomographic image generation unit 12 corresponds to the tomographic image generation unit of the present invention.

  The tomographic image generator 12 superimposes a series of X-ray images P1, P2, P3,... P74, which are continuously shot while the X-ray tube 3 and the FPD 4 are moved in opposite directions, on the basis of the filter back projection method. Thus, a tomographic image D obtained when the subject M is cut along a certain cross section is generated.

<Principle of the filter back projection method>
FIG. 2 illustrates the principle of the filter back projection method used by the tomographic image generation unit 12. For example, a virtual plane (reference cut section MA) parallel to the top plate 2 (horizontal with respect to the vertical direction) will be described. As shown in FIG. The FPD 4 is synchronized with the opposite direction of the X-ray tube 3 in accordance with the irradiation direction of the cone-shaped X-ray beam B by the X-ray tube 3 so as to be projected onto the fixed points p and q of the X-ray detection surface of the FPD 4. A series of X-ray images P are generated by the image generation unit 11 while being moved.

  In the series of X-ray images P, the projected image of the subject M is reflected while changing the position. Then, when this series of X-ray images P is reconstructed by the tomographic image generation unit 12, images (for example, fixed points p and q) positioned on the reference cut surface MA are accumulated and imaged as X-ray tomographic images. Will be.

  On the other hand, the point I not located on the reference cut surface MA is reflected as a point i in a series of subject M images while changing the projection position on the FPD 4. Unlike the fixed points p and q, such a point i is blurred without forming an image when the tomographic image generation unit 12 superimposes the X-ray projection images. In this way, by superimposing a series of projection images, an X-ray tomographic image in which only an image positioned on the reference cut surface MA of the subject M is reflected is obtained. In this way, when the projected images are simply superimposed, a tomographic image at the reference cut surface MA is obtained.

  Furthermore, the tomographic image generation unit 12 can obtain a similar tomographic image even at an arbitrary cut surface horizontal to the reference cut surface MA. During shooting, the projection position of the point i moves in the FPD 4, but this moving speed increases as the separation distance between the point I before projection and the reference cut surface MA increases. By utilizing this, reconstruction is performed while shifting the acquired series of subject M images in the body axis direction A at a predetermined pitch, and a tomographic image at a cutting plane parallel to the reference cutting plane MA is obtained. That is why.

  The correction value calculation unit 13 calculates the blur of the subject image based on the displacement of the position of the subject image reflected in each of the front tomographic images D2 and D2a and the rear tomographic images D73 and D73a. There are two blurs of the subject image: the actual movement direction of the FPD 4 is different from the assumption of the tomographic image generation unit 12, and the actual inclination of the FPD 4 with respect to the movement direction of the FPD 4 is different from the assumption of the tomographic image generation unit 12. Caused by a factor. The correction value calculation unit 13 calculates individual correction values for these two factors. The correction value calculation unit 13 corresponds to calculation means of the present invention.

  The tomographic images D2 and D2a are obtained by the tomographic image generation unit 12 reconstructing a series of X-ray images P1, P2, P3,. The rear tomographic images D73 and D73a are obtained by the tomographic image generation unit 12 reconstructing a series of X-ray images P1, P2, P3,. The front tomographic image D2 and the rear tomographic image D73 are for the same reference cut surface MA, and the front tomographic image D2a and the rear tomographic image D73a are for a common cut surface below the reference cut surface MA. It is.

  The correction unit 14 corrects the position of the subject image reflected in the series of X-ray images so as to cancel out the blurring of the subject image seen on the tomographic image based on the calculation result of the correction value calculation unit 13. The tomographic image generation unit 12 according to the present invention is a diagnostic tomographic image in which a subject image without blur is reflected based on a series of X-ray images P1, P2, P3,. D is generated. The correction unit 14 corresponds to the position correction unit of the present invention.

<Removal of FPD>
The FPD 4 in the present invention can be removed from the top plate 2. FIG. 3 illustrates the top plate 2 of the X-ray imaging apparatus 1 of the present invention. The top plate 2 is provided with a drawer 2a as shown in FIG. The drawer 2a can be taken in and out in the body side direction S with respect to the top plate 2 main body. When the FPD 4 is set under the top plate 2, the FPD 4 is accommodated in the drawer 2a. The FPD moving mechanism 7b realizes the movement of the FPD 4 by moving the FPD 4 along the body axis of the subject M together with the drawer 2a.

  As shown in FIG. 4, the FPD 4 accommodated in the drawer 2 a has a connection terminal that is connected to the X-ray imaging apparatus 1. When the FPD 4 is set below the top plate 2, this connection terminal is connected to a connector provided inside the drawer 2a. By this connection work, the FPD 4 can obtain power from the apparatus main body and can transmit and receive signals to and from the apparatus main body. The present invention can also employ an FPD configured to exchange information with the X-ray imaging apparatus 1 wirelessly.

  The main control unit 25 is constituted by a CPU, and realizes the respective units 7b, 8b, 10, 11, 12, 13, and 14 by executing various programs. Further, it may be realized by dividing each of these units into individual control devices in charge. The storage unit 23 stores all parameters necessary for the operation of the X-ray imaging apparatus 1 of the first embodiment, such as correction values. The console 26 is used to input an operator's instruction. The display unit 27 is provided for the purpose of displaying a tomographic image D for diagnosis.

<Image blurring that causes problems when tomographic images are taken with a general-purpose device>
The X-ray imaging apparatus according to the present invention is a general-purpose imaging apparatus, not a dedicated apparatus that captures only tomographic images. The dedicated apparatus has a configuration suitable for photographing a tomographic image, and the obtained tomographic image is clear and free from blurring. In other words, the dedicated device is devised so that the X-ray tube 3 and the FPD 4 are moved in an integrated manner by moving the X-ray tube 3 and the FPD 4 integrally.

  However, the general-purpose apparatus according to the present invention has a configuration in which the moving mechanisms of the X-ray tube 3 and the FPD 4 are independent from each other. Even in such a device, if the X-ray tube 3 and the FPD 4 are controlled to move synchronously, the X-ray tube 3 and the FPD 4 can be moved simultaneously and stopped simultaneously. it can.

  However, in a general-purpose apparatus, the position of the top plate 2 can be adjusted with respect to the X-ray tube 3 and the column 5 that suspends the X-ray tube 3. If the position of the top plate 2 changes with respect to the X-ray tube 3, the positional relationship between the X-ray tube 3 and the FPD 4 also changes. Further, the FPD 4 of the general-purpose device is configured to be housed in the drawer 2a of the top plate 2 as described with reference to FIG. Each time the FPD 4 is set in the drawer 2a, the positional relationship between the FPD 4 and the top plate 2 changes slightly. If the position of the FPD 4 changes with respect to the top plate 2, the positional relationship between the X-ray tube 3 and the FPD 4 also changes.

  If the X-ray image P is continuously shot while the positional relationship between the X-ray tube 3 and the FPD 4 is not as ideal, the subject image reflected in the X-ray image P is affected by the positional shift. receive. That is, when an X-ray image P photographed in a state where the positional relationship between the X-ray tube 3 and the FPD 4 is ideal and an X-ray image P photographed in a state not ideal are compared, The positions of the subject images to be inserted are shifted from each other. Moreover, the intensity and direction of image misalignment among the 74 X-ray images P is not constant. While an image on a certain X-ray image P is slightly shifted from an ideal position, an image shift greatly occurs in another X-ray image P. As described above, the image misalignment pattern varies among the 74 X-ray images P.

  The tomographic image generation unit 12 operates on the assumption that the X-ray image P was captured in a state where the positional relationship between the X-ray tube 3 and the FPD 4 is ideal. Therefore, the tomographic image generation unit 12 executes generation of a tomographic image ignoring that the images on the 74 X-ray images P are deviated from the ideal positions. If all 74 images of the X-ray image P are reflected in the ideal position, the tomographic image generation unit 12 can acquire a clear tomographic image. However, as described above, if the images of the 74 X-ray images P are reflected while being shifted in a slightly different manner from the ideal position, the tomographic image generator 12 cannot superimpose the images on the tomographic image. The image is blurred.

  Such blurring of the image on the tomographic image occurs because the positional relationship between the X-ray tube 3 and the FPD 4 is not ideal. In the present invention, the positional relationship between the X-ray tube 3 and the FPD 4 is considered to be divided into two factors, and it is devised so that a clear tomographic image can be generated by removing these influences individually.

<Cause of blurring of tomographic image: shift in moving direction>
The first cause of image displacement on the tomographic image is displacement of the FPD 4 with respect to the moving direction of the X-ray tube 3. As described above, in order to generate the tomographic image D, it is necessary to move the X-ray tube 3 and the FPD 4 in opposite directions as shown in FIG. This is because the tomographic image generation unit 12 operates assuming such movement. The x direction in FIG. 5 means the direction along the body axis of the subject M for the X-ray tube 3. The X-ray tube 3 completes 74 times of X-ray irradiation while moving in the x direction, and does not move in the y direction perpendicular to the x direction and the vertical direction. Ideally, the X-ray detection is completed while the FPD 4 also moves in the x direction as shown in FIG.

  However, with the general-purpose device according to the present invention, it is difficult to accurately move the FPD 4 in the x direction. This is because it is difficult to arrange the top plate 2 so that the longitudinal direction is horizontal in the x direction. Therefore, in actual continuous shooting, as shown in FIG. 6, the FPD 4 moves both in the x direction and in the y direction. This FPD4 movement is in contrast to the movement of the X-ray tube 3 which moves only in the x direction. This difference in movement causes a shift in the image on the tomographic image.

  Then, what kind of influence does the deviation of the FPD 4 with respect to the moving direction of the X-ray tube 3 have on the X-ray image P? The answer to this question can be understood by generating a tomographic image of the subject M on the reference cut surface MA shown in FIG. FIG. 7 shows X-ray images P1, P2, P3,... P74 and a tomographic image D obtained in an ideal state where the FPD 4 is moving in the moving direction (x direction) of the X-ray tube 3. At this time, it is considered how an image on the reference section of the subject M is reflected in the tomographic image D. Such an image is actually a cross section of the bone of the subject M or other soft tissue, but in FIG. 7, for convenience of explanation, an object having a rectangular cross section on the reference cross section. It represents as.

  The rectangles on the reference cut section are reflected in the X-ray images P1, P2, P3,. That is, the rectangle is reflected in the same position of each X-ray image P1, P2, P3,. However, each X-ray image P1, P2, P3,... P74 also overlaps with the subject image on the cutting plane other than the reference cutting plane, so look at each X-ray image P1, P2, P3,. However, it is difficult to visually recognize the rectangle on the reference section.

  The tomographic image D generated by the tomographic image generation unit 12 based on the X-ray images P1, P2, P3,... P74 in FIG. This is because the X-ray images P1, P2, P3,.

  FIG. 8 shows X-ray images P1, P2, P3,... P74 and a tomographic image D obtained in a state deviating from an ideal state in which the FPD 4 does not move in the moving direction (x direction) of the X-ray tube 3. At this time, it is considered how a rectangular image on the reference section of the subject M is reflected in the tomographic image D. The rectangles on the reference cut section are reflected in the X-ray images P1, P2, P3,. That is, the rectangle is reflected in the X-ray images P1, P2, P3,. However, it is recognized that the rectangle is displaced in the y direction between the X-ray images P1, P2, P3,. This is because continuous shooting was performed while the FPD 4 moved in the y direction with respect to the X-ray tube 3.

  In the tomographic image D generated by the tomographic image generation unit 12 based on the X-ray images P1, P2, P3,... P74 in FIG. Even though the X-ray images P1, P2, P3,... P74 are superimposed without shifting, a rectangular image is reflected between the X-ray images P1, P2, P3,. Because. Therefore, in the tomographic image D, the rectangle is reflected as if it were extended in the y direction.

  The blur direction and size of the image seen in the tomographic image D in FIG. 8 are as follows: the position of the rectangle that appears in the X-ray image P1 taken at the beginning of continuous shooting and the X-ray image taken at the end of continuous shooting If it is compared with the position of the rectangle reflected in P74, it is likely to be actually measured. In practice, however, such a comparison is almost impossible. Since each X-ray image P1, P74 also has a subject image on a cutting plane other than the reference cutting plane, the rectangle on the reference cutting plane is visible even when viewing each X-ray image P1, P74. Because it is difficult.

  Therefore, according to the present invention, X-ray images P1, P2, P3,... Continuously shot at the start of imaging and X-ray images P74, P73, P72,. By generating two tomographic images, the positions of the rectangles are compared. FIG. 9 shows three consecutive X-ray images P1, P2 including the first X-ray image P1 captured after 74 X-ray images P1, P2, P3,. , P3 are overlapped without shifting, and the tomographic image D2 is generated. In this way, since the tomographic image D2 is composed of only three images, the rectangle on the reference cross section is not so clearly reflected, but the image quality sufficient to achieve the purpose of knowing the position of the rectangle is sufficient. It shall have.

  However, in practice, it is insufficient to extract a rectangle simply by superimposing three consecutive X-ray images P1, P2, and P3. Therefore, as an actual operation related to acquisition of the tomographic image D2, it is better to generate the tomographic image D by superimposing the 30 X-ray images P1, P2, P3,. Such circumstances also apply to the later tomographic image D73 described later. The reason why the number of images to be superimposed is three is for the sake of concise explanation.

  Similarly, FIG. 10 shows three consecutive X-ray images including the last imaged X-ray image P74 after the 74 X-ray images P1, P2, P3,. A state is shown in which the tomographic image D73 is generated by superimposing P72, P73, and P74 without shifting. In this way, since the rear tomographic image D73 has only three images superimposed, the rectangle on the reference cross section is not so clearly reflected, but the image quality sufficient to achieve the purpose of knowing the position of the rectangle is sufficient. It shall have.

  The 74 X-ray images P1, P2, P3,... P74 in FIG. When the X-ray images P1, P2, P3,... P74 are viewed in order, the rectangle that has been reflected near the center of the X-ray image P1 moves gradually upward. That is, among the 74 X-ray images P1, P2, P3,... This is related to the way in which the FPD 4 moves in the y direction with respect to the X-ray tube 3 is linear.

  Since the tomographic image D in FIG. 8 is generated by superimposing all the 74 X-ray images P1, P2, P3,... P74, the rectangle on the tomographic image D is greatly blurred. Compared to this, the tomographic image D2 generated by superimposing the X-ray images P1, P2, and P3, which are similar to each other in the positions where the rectangles are reflected, shows the rectangles relatively without blurring. Such a situation is the same for the rear tomographic image D73. The tomographic image generation unit 12 generates such tomographic images D2 and D73.

  Then, which rectangle of the three X-ray images P1, P2, P3 represents the position of the rectangle in the tomographic image D2. Given that the number of X-ray images taken before the X-ray image P2 and the number of X-ray images taken after that are the same, the tomographic image D2 is the X-ray image. It is better to see that it represents the position of the rectangle reflected in P2. The position of the rectangle reflected in the X-ray image P2 indicates the average of the positions of the rectangles reflected in the three X-ray images P1, P2, and P3, and is considered to correspond to the position of the rectangle reflected in the tomographic image D2. Because it is. Such a situation is the same for the rear tomographic image D73. It is better to see that the rear tomographic image D73 represents a rectangular position that appears in the X-ray image P73.

  If only the first tomographic image D2 and the rear tomographic image D73 can be acquired, it is possible to know how the subject image is reflected while being shifted over a series of X-ray images P1, P2, P3,. That is, if the positions where the rectangles are captured are compared between the front tomographic image D2 and the rear tomographic image D73, how much the rectangle is between the X-ray image P2 and the X-ray image P73 being captured. You can know which direction you moved.

  The correction value calculation unit 13 actually performs such an operation. The correction value calculation unit 13 searches for the subject image reflected in the tomographic image D2 from the rear tomographic image D73 by pattern matching processing, and how much the subject image is between the tomographic image D2 and the rear tomographic image D73. Find in which direction you moved. That is, the correction value calculation unit 13 is caused by a shift in the moving direction of the FPD 4 based on the front tomographic image D2 and the rear tomographic image D73 generated by superimposing a series of X-ray images without shifting each other. The blur of the subject image to be calculated is calculated.

  Further, as long as this moving direction and moving amount are known, the rectangles reflected in the other X-ray images P1, P3, P4,... P72, P74 also move in what direction from the position reflected in the X-ray image P2. You can know what happened. For example, the rectangle reflected in the X-ray image P3 moves in the direction toward the position on the X-ray image P73 starting from the position on the X-ray image P2. The moving distance is 1/72 of the distance between the position on the X-ray image P2 and the position on the X-ray image P73. The reason why the moving distance of the rectangle is 1/72 is that the X-ray image is captured 72 times between the X-ray image P2 and the X-ray image P73.

  1/72 of the distance between the position on the X-ray image P2 and the position on the X-ray image P73 is referred to as one unit of movement. For example, based on the position of the subject image reflected in the X-ray image P2, the subject image reflected in the X-ray image P1 appears on the lower side by one unit from the position on the X-ray image P2.

  That is, with respect to the X-ray images P1, P3, P4,..., P74, if the subject image on the reference cut surface to be reflected is moved in which direction and in which direction, the subject image on the X-ray image P2 is overlapped. Can be calculated. For example, if the subject image reflected in the X-ray image P1 is moved upward by one unit, it overlaps the subject image on the X-ray image P2. In this way, it is possible to calculate a correction value for moving the subject image reflected in the X-ray images P1, P3, P4,... P74 to a position on the reference X-ray image P2. The correction value calculation unit 13 actually performs such an operation. Therefore, the correction value is calculated for each of the X-ray images P1, P3, P4,. FIG. 11 shows the operation so far.

  In the above description, the correction value is determined so that the subject image reflected in the X-ray images P1, P3, P4,... P74 is moved with reference to the X-ray image P2. It is not limited to the configuration. On the tomographic image D, the position at which the subject images reflected in the X-ray images P1, P2, P3,. Therefore, generally, the X-ray image P2 is also subject to correction, and the correction value calculation unit 13 prepares a correction value corresponding to the X-ray image P2.

  FIG. 12 shows the result of applying the above correction values to the X-ray images P1, P3, P4,. The subject image shown in the X-ray images P1, P3, P4,... P74 is moved in the y direction by correction. Of the subject images that appear on the corrected X-ray images P1, P3, P4,... P74, all of the subject images on the reference cross section are moved to positions on the X-ray image P2, as shown in FIG. Yes. Therefore, the image blur as described with reference to FIG. 8 does not occur in the tomographic image D on the reference cross section generated based on the corrected X-ray images P1, P2, P3,. The corrector 14 actually performs such an operation.

  When obtaining such a correction value, it is not necessary to consider how much the FPD 4 is inclined with respect to the moving direction of the FPD 4. FIG. 13 illustrates this situation. Under the condition that the X-ray tube 3 and the FPD 4 move in parallel, the flat object Obj on the reference section is always projected at the same position on the FPD 4 regardless of the synchronous movement of the X-ray tube 3 and the FPD 4. In FIG. 13, the object Obj is illustrated as being projected on the center of the FPD 4. Therefore, in each of the X-ray images P1, P2, P3,... P74 photographed under this condition, the shadow of the object Obj is reflected in the center of the image as shown in FIG.

  Such a situation does not change even if the FPD 4 is inclined with respect to the moving direction of the FPD 4 as shown in FIG. In this case, the shadow of the object Obj is tilted over the X-ray images P1, P2, P3,... P74 due to the tilt of the FPD 4. However, the effect of the tilt of the FPD 4 is limited to the object Obj being tilted and reflected. Thus, the tomographic image D does not blur due to the inclination of the FPD 4 on the reference cut section.

  However, the inclination of the FPD 4 does not cause blurring of the tomographic image D only for the reference cut surface MA. When the tomographic image D is generated for another cut surface parallel to the reference cut surface MA, the inclination of the FPD 4 causes the blur of the tomographic image D.

<Cause of blurring of tomographic image: FPD tilt>
The second cause of the image shift on the tomographic image is the inclination of the FPD 4 with respect to the moving direction of the FPD 4. As described above, to generate the tomographic image D, as shown in FIG. 5, the FPD 4 is not inclined with respect to the moving direction of the FPD 4 (that is, the lateral direction of the FPD 4 coincides with the moving direction of the FPD 4. Is necessary). This is because the tomographic image generation unit 12 operates assuming such movement. Ideally, the X-ray detection is completed while moving in the x direction while maintaining the state in which the FPD 4 is not inclined with respect to the moving direction of the FPD 4 as shown in FIG.

  However, in the general-purpose device according to the present invention, it is difficult to make the vertical and horizontal directions of the rectangular FPD 4 exactly coincide with the x and y directions. This is because the FPD 4 is detachable from the top plate 2 and is not fixed. Therefore, in actual continuous shooting, as shown in FIG. 16, the FPD 4 is inclined with respect to the moving direction (x direction) of the FPD 4. This inclination causes a shift of the image on the tomographic image at the cut surface other than the reference cut surface.

  Then, how does the inclination of the FPD 4 with respect to the moving direction of the FPD 4 affect the X-ray image P? The answer to the question is that the cut surface other than the reference cut surface MA shown in FIG. 2, particularly the cut surface located on the FPD 4 side from the reference cut surface MA (referred to as a cut surface below the reference cut surface MA). It can be understood by generating a tomographic image of the subject M above. FIG. 17 shows X-ray images P1, P2, P3,... P74 and a tomographic image D obtained in a state deviating from the assumption that the FPD 4 is not inclined. At this time, it is considered how an image in the cut surface below the reference cut surface MA of the subject M is reflected in the tomographic image D. Such an image is actually a cross section of the bone of the subject M or other soft tissue, but in FIG. 17, for convenience of explanation, a cross section below the reference cross section MA is used. It is represented as an object having a rectangular cross section.

  In the following description including FIG. 17, it is assumed that the FPD 4 moves in parallel with the X-ray tube 3. Therefore, the shift in the moving direction, which is a problem in FIG. 8, need not be considered for the time being.

  The rectangles in the cut surface below the reference cut surface MA are reflected in the X-ray images P1, P2, P3,. That is, the rectangle is reflected in the X-ray images P1, P2, P3,. However, the position where the rectangle is reflected over the X-ray images P1, P2, P3,... P74 is displaced in the x direction. Note that the X-ray images P1, P2, P3,... P74 also overlap the subject images other than the cut surface below the reference cut surface MA, so that the X-ray images P1, P2, P3,. Even when viewing P74, it is difficult to visually recognize the rectangular shape of the cut surface below the reference cut surface MA.

  A tomographic image D generated by the tomographic image generation unit 12 based on the X-ray images P1, P2, P3,... P74 in FIG. . This is because the tomographic image generation unit 12 performs a shift process for moving the image in the x direction on the X-ray images P1, P2, P3,.

  FIG. 18 shows the movement of the image on the X-ray images P1, P2, P3,. An object having a cut surface below the reference cut surface MA is reflected while moving in the x direction between the X-ray images P1, P2, P3,. The tomographic image generation unit 12 knows in advance how the image moves, and performs a shift process so that the movement of the image is cancelled.

  FIG. 19 shows X-ray images P1, P2, P3,... P74 and a tomographic image D obtained when the FPD 4 is inclined with respect to the x direction. At this time, it is considered how a rectangular image in the cut surface below the reference cut surface MA of the subject M is reflected in the tomographic image D. The rectangles in the cut surface below the reference cut surface MA are reflected in the X-ray images P1, P2, P3,. That is, the rectangle is reflected in the X-ray images P1, P2, P3,. However, it is recognized that the rectangle is displaced in both the x direction and the y direction between the X-ray images P1, P2, P3,. Moreover, this displacement cannot be removed even if the existing shift processing described with reference to FIG. 17 is performed.

  The reason why the rectangles on the respective X-ray images P1, P2, P3,... P74 are still displaced in the x direction and the y direction even if the existing shift processing is performed will be described. The rectangular image in the cut surface below the reference cut surface MA is not located at the same position among the X-ray images P1, P2, P3,. The direction of movement coincides with the direction of movement of the FPD 4. In FIG. 19, it is assumed that the moving direction of the X-ray tube 3 coincides with the moving direction of the FPD 4.

  If the FPD 4 itself is inclined with respect to the moving direction of the FPD 4, the moving direction of the rectangular image with respect to the FPD 4 is also inclined. That is, the rectangle appears in a series of X-ray images P1, P2, P3,... P74 while moving obliquely with respect to the FPD 4, as indicated by the dotted line attached to the FPD 4 in FIG.

  The series of X-ray images P1, P2, P3,... P74 thus photographed are subjected to shift processing by the tomographic image generation unit 12. For simplification of explanation, it is assumed that the X-ray images P1, P2, P3,... P74 are shifted on the basis of the X-ray image P37. By this shift processing, the rectangular images reflected at different positions in each X-ray image P1, P2, P3,... P74 are shifted to the position of the rectangular image in the X-ray image P37.

  The left side of FIG. 20 represents the displacement of the rectangle p1 reflected in the X-ray image P1 and the rectangle p37 reflected in the X-ray image P37 on the image. The direction in which each rectangle is displaced is an oblique direction due to the influence of the FPD 4 being inclined. In order for the tomographic image generator 12 to form a rectangle, as shown in the center of FIG. 20, a shift process is performed to move the X-ray image P1 in the x and y directions so that the rectangle p1 is superimposed on the rectangle p37. It is considered necessary.

  However, the tomographic image generation unit 12 performs the shift process on the assumption that the moving direction of the rectangle matches the horizontal direction of the image. This is because the rectangle moves only in the horizontal direction under the assumption of the tomographic image generation unit 12. Therefore, the X-ray image P1 is not subjected to shift processing in the y direction. Although the tomographic image generation unit 12 barely shifts the X-ray image P1 in the x direction, the movement amount is too larger than the desired movement amount as shown on the right side of FIG. Although the tomographic image generation unit 12 originally needs to shift the X-ray image P1 by a certain amount of movement in an oblique direction, it actually shifts the X-ray image P1 by the same amount of movement. It is. Similarly, the X-ray images P2, P3, P4,... P74 have not undergone an appropriate shift process.

  Accordingly, the tomographic image D generated by the tomographic image generation unit 12 based on the X-ray images P1, P2, P3,... P74 in FIG. It will end up. In the tomographic image D, the rectangle is blurred and appears as if it was extended in an oblique direction.

  In order for the tomographic image generation unit 12 to perform appropriate shift processing on the X-ray images P1, P2, P3,... P74, the mode of shift processing performed on the X-ray images P1, P2, P3,. There is a need to. If even the shift processing is appropriately changed, the blurring seen in the tomographic image D should be eliminated as shown in FIG. In order to appropriately change the shift process, it is necessary to know the direction and size of image blurring in the tomographic image D.

  The blur direction and size of the image seen in the tomographic image D in FIG. 19 are the position of the rectangle that appears in the X-ray image P1 taken at the beginning of the continuous shooting and the X-ray image taken at the end of the continuous shooting. If it is compared with the position of the rectangle reflected in P74, it is likely to be actually measured. In practice, however, such a comparison is almost impossible. Since each X-ray image P1, P74 also overlaps with the subject image on the cut surface other than the cut surface below the reference cut surface MA, the reference cut surface MA is also viewed from the X-ray images P1, P74. This is because it is difficult to visually recognize the rectangle of the cut surface below.

  Therefore, according to the present invention, the X-ray images P1s, P2s, P3s,... Subjected to the existing shift processing, and the existing shift processing (shift processing as assumed by the tomographic image generation unit 12, see the right side in FIG. 20). The X-ray images P74s, P73s, P72s,... Subjected to the above are individually superimposed to generate two tomographic images, thereby comparing the rectangular positions. FIG. 22 shows three consecutive X-ray images P1, P2 including the first X-ray image P1 captured after 74 X-ray images P1, P2, P3,. , P3, the X-ray images P1s, P2s, and P3s that have been subjected to the existing shift process are superimposed to generate the tomographic image D2a. In this manner, since the tomographic image D2a has only three images superimposed, the rectangle of the cut surface below the reference cut surface MA is not so clearly reflected, but the purpose of knowing the position of the rectangle is achieved. Have sufficient image quality.

  However, in practice, it is insufficient to extract a rectangle simply by superimposing three consecutive X-ray images P1s, P2s, and P3s. Therefore, as an actual operation for acquiring the tomographic image D2a, it is better to generate the tomographic image D by superimposing the 30 X-ray images P1s, P2s, P3s,. Such circumstances also apply to a later tomographic image D73a described later. The reason why the number of images to be superimposed is three is for the sake of concise explanation.

  Similarly, FIG. 23 shows three consecutive X-ray images including the last imaged X-ray image P74 after 74 X-ray images P1, P2, P3,. The figure shows that the X-ray images P72s, P73s, and P74s obtained by performing the existing shift processing on P72, P73, and P74 are superimposed to generate a post-tomographic image D73a. In this way, since the rear tomographic image D73a has only three images superimposed, the rectangle on the reference cross section is not so clearly reflected, but the image quality sufficient to achieve the purpose of knowing the position of the rectangle is sufficient. It shall have.

  Since the tomographic image D in FIG. 19 is generated by superimposing all the 74 X-ray images P1s, P2s, P3s,... P74s, the rectangle on the tomographic image D is greatly blurred. Compared to this, the tomographic image D2a generated by superimposing the X-ray images P1s, P2s, and P3s after the shift processing in which the positions where the rectangles are reflected are similar to each other, the rectangles are reflected relatively without blurring. . Such a situation is the same for the rear tomographic image D73a. The tomographic image generation unit 12 generates such tomographic images D2 and D73.

  In order to suppress the blur of the subject image caused by the inclination of the FPD 4 with respect to the moving direction of the FPD 4, the existing shift processing shown on the right side of FIG. It is important to apply. If a tomographic image is generated without performing an existing shift process, the tomographic image becomes an image in the reference cut surface MA. As described above, the tomographic image at the reference cut surface MA is not blurred due to the FPD 4 being inclined with respect to the moving direction of the FPD 4 (see FIGS. 13, 14, and 15). Therefore, even if the three X-ray images P1, P2, and P3 are compared with each other and the three X-ray images P72, P73, and P74 are simply overlapped and compared, the image shift is caused by the movement direction of the FPD 4 being the X-ray tube. 3 is caused by a shift with respect to the movement direction of the FPD 4, and an image shift caused by the inclination of the FPD 4 with respect to the movement direction of the FPD 4 cannot be calculated.

  By the way, which rectangle of the three tomographic images D2a represents the position of the rectangle among the three X-ray images P1s, P2s, and P3s. Given that the number of X-ray images taken before the X-ray image P2s and the number of X-ray images taken after that are the same, the tomographic image D2a is subjected to the shift process. It is better to see that it represents the position of the rectangle reflected in the X-ray image P2s. The positions of the rectangles that appear in the X-ray image P2s after the shift process indicate the average of the positions of the rectangles that appear in the three X-ray images P1s, P2s, and P3s after the shift process, and appear in the tomographic image D2a. This is because it is considered to correspond to the position of the rectangle to be inserted. Such a situation is the same for the rear tomographic image D73a. It is better to see that the rear tomographic image D73a represents a rectangular position that appears in the X-ray image P73s after the shift processing.

  As long as the front tomographic image D2a and the rear tomographic image D73a can be acquired, it is possible to know how the subject image is reflected over the series of X-ray images P1s, P2s, P3s,. it can. That is, by comparing the positions where the rectangles appear between the front tomographic image D2a and the rear tomographic image D73a, it is possible to know how much the rectangle has moved from the X-ray image P2s to the X-ray image P73s. it can.

  The correction value calculation unit 13 actually performs such an operation. The correction value calculation unit 13 searches for the subject image reflected in the tomographic image D2a from the rear tomographic image D73a by pattern matching processing, and how much the subject image is between the tomographic image D2a and the rear tomographic image D73a. Find in which direction you moved. That is, the correction value calculation unit 13 determines the object image caused by the inclination of the FPD 4 based on the front tomographic image D2a and the rear tomographic image D73a generated by superimposing a series of X-ray images while shifting each other. Calculate blur.

  Further, as long as the moving direction and the moving amount are known, how long the rectangles reflected in the X-ray images P1s, P3s, P4s,... P72s, P74s after other shift processing are from the position reflected in the X-ray image P37s. You can know which direction you moved. For example, the rectangle shown in the X-ray image P3s moves from the position on the X-ray image P2s to the direction toward the position on the X-ray image P73s after the shift process. The movement distance is 34/72 of the distance between the position on the X-ray image P2s and the position on the X-ray image P73s. The reason why the moving distance of the rectangle is 34/72 is that the X-ray image is captured 72 times between the X-ray image P2 and the X-ray image P73.

  1/72 of the distance between the position on the X-ray image P2s and the position on the X-ray image P73s will be referred to as one unit of movement. For example, based on the position of the subject image reflected in the X-ray image P2s after the shift process, the subject image reflected in the X-ray image P1s after the shift process is only one unit from the position on the X-ray image P2s. Appears diagonally to the left.

  By using such a principle, if the X-ray images P1s, P3s, P4s,... It can be calculated whether the subject image on the image P37s overlaps. For example, if the subject image that appears in the X-ray image P1s that has undergone the shift process is moved diagonally upward to the right by 36 units, the subject image on the X-ray image P37s that has undergone the shift process will overlap. In this way, it is possible to calculate a correction value for moving the subject image reflected in the shifted X-ray images P1s, P2s, P3s,... P74s to a position on the reference X-ray image P37. Therefore, the correction value is calculated for each X-ray image P1s, P2s, P3s,. The correction value calculation unit 13 actually performs such an operation. FIG. 24 shows the operation so far.

  In the above description, the correction value is determined so that the subject image reflected in the X-ray images P1, P3, P4,... P74 is moved with reference to the X-ray image P37. It is not limited to the configuration. On the tomographic image D, the position at which the subject images reflected in the X-ray images P1, P2, P3,. Therefore, generally, the X-ray image P37 is also subject to correction, and the correction value calculation unit 13 prepares a correction value corresponding to the X-ray image P73.

  As can be seen from the above description, in order to calculate the blur of the tomographic image due to the inclination of the FPD 4, it is better to set the cut surface for generating the front tomographic image D2a and the rear tomographic image D73a as close to the FPD 4 as possible. . This is because blurring of the image on the tomographic image becomes large and measurement of blurring becomes easy.

  FIG. 25 shows the result of applying the above correction value to the X-ray images P1s, P2s, P3s,... P74s after the shift processing. The subject image shown in the X-ray images P1s, P2s, P3s,... P74s after the shift processing is moved in the x and y directions by correction. Of the subject images that appear in the corrected X-ray image P, those on the cutting plane lower than the reference cutting plane MA are all up to the position on the X-ray image P37s after the shift processing, as shown in FIG. Has been moved. Accordingly, the image blur as described in FIG. 19 does not occur in the tomographic image D on the reference cut surface generated based on the X-ray image P after the correction processing. The corrector 14 actually performs such an operation.

<Operation of X-ray imaging apparatus>
Next, the operation of the X-ray imaging apparatus will be described with reference to FIG. In order to generate a tomographic image of the subject M with the X-ray imaging apparatus according to the present invention, the subject M is first placed on the top 2 (subject placement step S1). When the operator gives an instruction to continuously shoot the X-ray image P through the console 26, the X-ray images P1, P2, P3,... P74 are taken while the X-ray tube 3 and the FPD 4 are moved in opposite directions. (X-ray image continuous shooting step S2).

  Subsequent operations are continuous image processing. The X-ray images P1, P2, P3,... P74 are sent to the tomographic image generation unit 12. The tomographic image generator 12 superimposes the X-ray images P1, P2, and P3 without shifting to generate the tip tomographic image D2 at the reference cut surface MA, and overlays the X-ray images P72, P73, and P74 without shifting. Then, a rear tomographic image D73 in the reference cut surface MA is generated and sent to the correction value calculation unit 13. The correction value calculation unit 13 examines the subject image resulting from the shift in the moving direction of the X-ray tube 3 and the FPD 4 for each of the X-ray images P1, P2, P3,. A correction value for correcting the displacement is calculated and sent to the correction unit 14. The correction unit 14 performs correction for displacing the image on each of the X-ray images P1, P2, P3,... P74 based on the correction value (moving direction deviation correction step S3).

  X-ray images P1, P2, P3,... P74 that have been corrected for the shift in the moving direction are sent to the tomographic image generation unit 12. The tomographic image generation unit 12 performs an existing shift process on the X-ray images P1, P2, and P3 that have been corrected for the displacement in the moving direction, and generates a tomographic image D2a at a cutting plane below the reference cutting plane MA. Then, based on the X-ray images P72, P73, and P74 that have been corrected for the displacement in the moving direction, a rear tomographic image D73a in the same cut surface is generated, and these are sent to the correction value calculation unit 13.

  The correction value calculation unit 13 changes the inclination of the FPD 4 with respect to the moving direction of the FPD 4 for each of the X-ray images P1, P2, P3,... P74 corrected for the moving direction deviation from the previous tomographic image D2a and the rear tomographic image D73a. A correction value for correcting the resulting displacement of the subject image is calculated and sent to the correction unit 14 (FPD tilt correction value calculation step S4). At this time, the correction value calculation unit 13 is based on a series of X-ray images P1, P2, P3,... P74 that have been corrected to cancel out blurring of the subject image caused by the moving direction of the FPD 4 shown in FIG. Based on the tomographic image D2a and the rear tomographic image D73a, the blur of the subject image due to the inclination of the FPD 4 is calculated.

  In this way, two types of correction values are calculated for the X-ray images P1, P2, P3,. Specifically, there are a correction value for correcting the displacement of the subject image due to the shift in the moving direction of the X-ray tube 3 and the FPD 4 and a correction value for correcting the displacement of the subject image due to the inclination of the FPD 4. . The former correction value is for moving the subject image in the image in the y direction, and the latter correction value is for moving the subject image in the image in an oblique direction (x direction and y direction). . In calculating the latter correction value, an X-ray image corrected based on the former correction value is used.

<Diagnostic Tomographic Image Generation Step S5>
When the surgeon gives an instruction to generate a tomographic image at an arbitrary cut surface through the console 26, the tomographic image generation unit 12 performs X-ray images P1, P2, P3,. Is subjected to the existing shift processing. This shift process is based on the premise that the FPD 4 is not inclined with respect to the moving direction of the FPD 4. Therefore, if the tomographic image D is generated by superimposing the X-ray images P1, P2, P3,... P74 in this state, the image of the tomographic image D is blurred. Therefore, the X-ray imaging apparatus of the present invention performs correction according to the position of the cut surface on the X-ray images P1, P2, P3,.

  If the surgeon gives an instruction to generate a tomographic image at the reference cut surface MA, the correction unit 14 generates the tomographic image as it is by using the X-ray images P1, P2, P3,. Send to unit 12. In this case, since the tomographic image generation unit 12 does not perform the shift process, the X-ray images P1, P2, P3,...

  Further, if the surgeon gives an instruction to generate a tomographic image at the cut surface related to the front tomographic image D2a and the rear tomographic image D73a, the correction unit 14 performs X-ray images P1 and P2 that have been corrected for displacement in the moving direction. , P3,... P74 are corrected by using a correction value for correcting the displacement of the subject image due to the inclination of the FPD 4 after the tomographic image generator 12 has performed the existing shift process. That is, the X-ray images P1, P2, P3,... P74 that have been corrected for the displacement in the moving direction are subjected to shift processing by the tomographic image generation unit 12, and further corrected for the inclination of the FPD 4 by the correction unit 14. The X-ray images P1, P2, P3,... P74 are superimposed on the tomographic image D after such a triple position adjustment.

  Assume that the surgeon issues an instruction to generate a cut surface that is neither the reference cut surface MA nor the front tomographic image D2a and the rear tomographic image D73a. Even in this case, the correction unit 14 is the same as the X-ray images P1, P2, P3,... A correction value for correcting the displacement of the specimen image is applied. However, at this time, the correction unit 14 changes the action of the correction value according to the position of the cut surface.

  For example, if the cut surface designated by the operator is a cut surface that is intermediate between the reference cut surface MA and the cut surface related to the front tomographic image D2a and the rear tomographic image D73a, the correction unit 14 sets the correction value to 0.5. The image is corrected by multiplying by the coefficient of. In this way, the correction unit 14 multiplies the correction value by a smaller coefficient as the cut surface specified by the operator is closer to the reference cut surface MA, and executes image correction based on the obtained value. The correction value is multiplied by a larger coefficient as the specified cut surface moves away from the reference cut surface MA, and the image is corrected based on the obtained value. That is, the X-ray images P1, P2, P3,... P74 that have been corrected for the displacement in the moving direction are subjected to shift processing by the tomographic image generation unit 12, and further corrected for the inclination of the FPD 4 by the correction unit 14. The X-ray images P1, P2, P3,... P74 are superimposed on the tomographic image D after such a triple position adjustment.

  The generated tomographic image D is an image suitable for diagnosis without blurring in the reflected image. The tomographic image D is displayed on the display unit 27, and the operation of the X-ray imaging apparatus according to the present invention ends.

  As described above, according to the X-ray imaging apparatus of the present invention, a clear tomographic image without blurring can be generated without imaging a marker. In the conventional configuration, by grasping the marker reflected in the X-ray image P, it is possible to know how far the image of the subject image in the series of X-ray images P is deviated from the ideal, and to correct this deviation. This prevents blurring of tomographic images. On the other hand, according to the configuration of the present invention, the blur direction and intensity of the subject image are grasped based on the actual subject image. That is, in the configuration of the present invention, the subject image itself is used to calculate the correction value that cancels the blur of the subject image.

  Unlike the marker, the subject image does not appear clearly on the X-ray image. This is because the subject M is thick and the internal structure of the subject M is reflected in the X-ray image. Therefore, in the configuration of the present invention, tomographic images D2, D2a, D73, and D73a are provisionally generated for the purpose of knowing the blurring pattern of the subject image, and the correction value calculation unit 13 uses the tomographic images D2, D2a, and D73. , D73a is used to calculate the blur direction and intensity of the subject image. The tomographic images D2, D2a, D73, and D73a include information related to blurring of the subject image.

  Therefore, according to the present invention, it is possible to provide an X-ray imaging apparatus capable of generating a blur-free tomographic image D without providing a marker. As a cause of blurring of the subject image, the actual movement direction of the FPD 4 is different from the assumption of the tomographic image generation unit 12, and the actual inclination of the FPD 4 with respect to the movement direction of the FPD 4 is different from the assumption of the tomographic image generation unit 12. There is.

  Among the series of X-ray images, the tomographic images D2 and D2a obtained by reconstructing the X-ray images belonging to the group captured earlier are the first in the process in which the subject image is blurred on the tomographic image. This shows the progress of. On the other hand, the post-tomographic images D73 and D73a obtained by reconstructing an X-ray image belonging to a group captured later in a series of X-ray images are the processes in which the subject image is blurred on the tomographic image. The last halfway is shown. Therefore, the blur of the subject image can be calculated by examining the displacement of the position of the subject image reflected in each of the front tomographic images D2 and D2a and the rear tomographic images D73 and D73a.

  As described above, when the correction value calculation unit 13 generates the front tomographic image D2 and the rear tomographic image D73 by directly superimposing a series of X-ray images without shifting each other, the subject on both the images D2 and D73 is generated. The image is not displaced by the inclination of the FPD 4. Therefore, the subject caused by the shift in the moving direction of the FPD 4 based on the front tomographic image D2 and the rear tomographic image D73 generated by the correction value calculation unit 13 superimposing a series of X-ray images without shifting each other. Image blur can be accurately calculated.

  Then, as described above, when the correction value calculation unit 13 generates the front tomographic image D2a and the rear tomographic image D73a by directly superimposing a series of X-ray images without shifting each other, the subject images on both images are There is no displacement due to the inclination of the FPD 4. Therefore, in order to calculate the blur of the subject image due to the inclination of the FPD 4, it is necessary to generate a front tomographic image D2a and a rear tomographic image D73a by superimposing a series of X-ray images while shifting each other.

  When a series of X-ray images are superimposed while being shifted from each other to generate a front tomographic image D2a and a rear tomographic image D73a, and a correction value is calculated based on these, the correction value is related to a shift in the moving direction. The correction and the correction related to the inclination of the FPD 4 overlap with each other and cannot be separated from each other. Then, it can operate only on the cut surface for which the correction value is obtained. Therefore, in the present invention, the influence of the shift in the moving direction is removed from the series of X-ray images before generating the front tomographic image D2a and the rear tomographic image D73a by superimposing the series of X-ray images while shifting each other. Keep it. With this configuration, it is possible to reliably acquire a correction value indicating only the correction related to the FPD 4.

  In a general-purpose X-ray imaging apparatus in which the X-ray tube 3 is suspended and supported in the examination room, the displacement of the FPD 4 in the moving direction and the inclination of the FPD 4 with respect to the moving direction of the FPD 4 are likely to occur. Therefore, the present invention is particularly effective when applied to such an apparatus.

  The present invention is not limited to the above-described configuration, and can be modified as follows.

  (1) In the above-described embodiment, the calculation is performed by performing the calculation of the correction value for the shift in the moving direction and the calculation of the correction value for the FPD tilt once, but the present invention is not limited to this configuration. The calculation of the correction value for the shift in the moving direction and the calculation of the correction value for the FPD tilt may be repeated many times. In some cases, the cut surface related to the front tomographic image D2 and the rear tomographic image D73 in the calculation of the shift in the moving direction is slightly shifted from the reference cut surface MA. In such a case, the blurring of the image generated in the tomographic image D cannot be accurately separated into the cause of displacement in the moving direction and the factor of FPD tilt. By repeating the calculation of the correction value for the displacement in the moving direction and the calculation of the correction value for the FPD tilt, each correction value is updated each time, and can be settled to a certain value. With such a configuration, a more accurate correction value can be calculated.

  (2) In the above-described configuration, as described with reference to FIG. 24, by generating two front tomographic images D2a and rear tomographic images D73a having different combinations of the original X-ray images, the blurring direction of the image is changed. Although acquired, this invention is not limited to this structure. It is also possible to obtain a blur direction by performing image analysis on the tomographic image D in which the 74 X-ray images P described in FIG. An example of image processing that can know the direction of blur is a two-dimensional Fourier transform. When the two-dimensional Fourier transform is applied to the tomographic image D in which the image is blurred, streaks extending in a direction orthogonal to the blurring direction of the image appear. By grasping the direction in which this line extends, the direction of blurring of the image can be known. Such an image analysis is executed by the correction value calculation unit 13.

  (3) In the above-described configuration, the cut surface in the case where the front tomographic image D2a and the rear tomographic image D73a are generated by superimposing a series of X-ray images while shifting each other is assumed to be the surface on which the subject is present. However, as described with reference to FIG. 24, the blur direction of the image is acquired by generating two front tomographic images D2a and rear tomographic images D73a having different combinations of the original X-ray images. The present invention is not limited to this configuration. By predicting several blur directions, correcting the X-ray image based on this prediction, comparing the obtained tomographic images D and selecting the one with the least blur, You may know the direction. In this case, it is desirable that the cut surface for generating the tomographic image is a position where the screen used for protecting the patient from the movement of the FPD 4 on the cover standing imaging stand of the FPD 4 or the top plate 2 is reflected. Such a cover screen and the top plate 2 are dense, and a granular structure is concentrated in the cross section. Such a structure should appear in the tomographic image. Therefore, it is possible to determine the blurring of the tomographic image with high sensitivity. The comparison is actually performed by performing frequency analysis on each tomographic image D and determining that the one having the highest frequency component is the tomographic image D with the least blur. When a tomographic image is blurred, the granular structure on the image is stretched in a certain direction to be crushed. Therefore, as the blur of the tomographic image increases, the high-frequency component included in the image decreases. Such an image analysis is executed by the correction value calculation unit 13.

  (4) In the above-described configuration, the correction value is calculated using the actual subject M. However, instead of this, the phantom may be imaged to obtain the correction value in advance.

  (5) In the above configuration, the filtered back projection method in which a series of X-ray images are superimposed is used as a tomographic image reconstruction method, but a well-known shift addition method or successive approximation method may be used.

3 X-ray tube (radiation source)
4 FPD (detection means)
7a X-ray tube moving mechanism (radiation source moving means)
7b FPD moving mechanism (detector moving means)
11 Image generation unit (image generation means)
12 Tomographic image generating unit (tomographic image generating means)
13 Correction value calculation unit (calculation means)
14 Correction unit (position correction means)

Claims (8)

A radiation source for irradiating the subject with radiation;
Detecting means for detecting radiation transmitted through the subject;
Radiation source moving means for moving the radiation source relative to the subject;
Detector moving means for moving the detection means relative to the subject;
Image generation means for generating a radiation image based on the output of the detection means;
A tomographic image generating means for generating a tomographic image based on a series of radiographic images continuously shot while the radiation source and the detecting means are moved in opposite directions;
A tomogram generated when the actual moving direction of the detecting means is different from the assumption of the tomographic image generating means, and the actual inclination of the detecting means with respect to the moving direction of the detecting means is different from the assumption of the tomographic image generating means. Calculating means for calculating a blur direction and intensity of the subject image in the image based on the tomographic image of the subject reflected in the tomographic image;
A position correction unit that corrects the position of the subject image reflected in a series of radiation images so as to cancel the blur of the subject image seen on the tomographic image based on the calculation result of the calculation unit;
The radiographic apparatus according to claim 1, wherein the tomographic image generation unit generates a diagnostic tomographic image in which the subject image without blur is reflected based on a series of corrected radiographic images. The radiographic apparatus according to claim 1,
The calculation means includes a tomographic image obtained by reconstructing a radiographic image belonging to a group captured earlier in a series of radiographic images, and a radiographic image belonging to a group captured later in the series of radiographic images. Calculating blur of the subject image based on the displacement of the position of the subject image that is obtained by reconstruction and is reflected in each of the subsequent tomographic images having the same cut surface as the previous tomographic image. A characteristic radiographic apparatus. The radiation imaging apparatus according to claim 2,
Based on the front tomographic image and the rear tomographic image generated by the calculation unit superimposing a series of radiographic images as they are without shifting each other, the blurring of the subject image due to the shift in the moving direction of the detection unit is performed. The radiation imaging apparatus characterized by calculating. In the radiography apparatus in any one of Claim 2 or Claim 3,
Calculating the blur of the subject image due to the inclination of the detection means based on the front tomographic image and the rear tomographic image generated by superimposing the series of radiation images while shifting the series of radiographic images. A characteristic radiographic apparatus. The radiation imaging apparatus according to claim 4,
Based on a tomographic image based on a series of radiographic images corrected so that the calculation means cancels out the blur of the subject image due to the moving direction of the detection means, the blur of the subject image due to the inclination of the detection means. The radiation imaging apparatus characterized by calculating. The radiographic apparatus according to any one of claims 1 to 5,
A radiation imaging apparatus, wherein the radiation source is supported by being suspended in an examination room. A radiation source for irradiating the subject with radiation; detection means for detecting radiation transmitted through the subject; radiation source moving means for moving the radiation source relative to the subject; and the detection means for the subject Radiography including: a detector moving means for moving; and a tomographic image generating means for generating a tomographic image based on a series of radiographic images continuously taken while the radiation source and the detecting means are moved in opposite directions. A blur calculation method for calculating a blur direction and intensity of the subject image in a tomographic image generated by an apparatus,
Based on the series of radiographic images, the actual moving direction of the detecting means is different from the assumption of the tomographic image generating means, and the actual inclination of the detecting means with respect to the moving direction of the detecting means is the tomographic image generation. A blur calculation method comprising: calculating a direction and intensity of blurring of the subject image in a tomographic image generated by being different from the assumption of the means based on the tomographic image of the subject reflected in the tomographic image. The blur calculation method according to claim 7, wherein
The blur calculation method includes a tomographic image obtained by reconstructing a radiographic image belonging to a group captured earlier in a series of radiographic images, and a radiographic image belonging to a group captured later in the series of radiographic images. And the blur of the subject image is calculated based on the displacement of the position of the subject image that is reflected in each of the subsequent tomographic images having the same cut surface as the previous tomographic image. A blur calculation method characterized by the above.

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