JP5562021B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus, and more particularly to an X-ray CT apparatus that modulates an X-ray output.

  In recent years, X-ray CT apparatuses equipped with an automatic exposure mechanism (CT-AEC) are becoming common. The automatic exposure mechanism analyzes the scout data (scout data) obtained by scout scan and the scout image generated thereby, and the amount of X-ray absorption (X-ray transmission length) at each scan position of the subject. ) And modulation control is performed so that the X-ray output during the main scan, mainly the tube current of the X-ray tube, changes according to the amount of X-ray absorption at each scan position (for example, Patent Document 1, (See FIG. 16). Before the automatic exposure mechanism was put to practical use, the X-ray output at the time of scanning was constant, and the setting was made depending on the experience and intuition of the operator. For this reason, variations in image quality in the generated image have occurred due to differences in the amount of X-ray absorption at each subject size and slice position. However, with this automatic exposure mechanism, it is possible to optimize the X-ray output to the subject, reduce the image quality variation as described above, and reduce unnecessary exposure to the subject. .

  On the other hand, in X-ray CT imaging, in order to reduce exposure to highly sensitive organs existing near the body surface of the subject, scanning is performed with a shield member having a large X-ray absorption amount placed on the body surface. Techniques are beginning to be used. Incidentally, examples of highly sensitive organs include mammary gland, thyroid gland, and lens. Further, as the shield member, for example, one containing lead, bismuth or a compound thereof and the like formed into a sheet shape with a size and shape corresponding to the type of organ to be shielded can be considered. Such shield members are already sold by a plurality of manufacturers.

JP 2007-325853 A

  By the way, when photographing with a combination of organ protection by a shield member and an automatic exposure mechanism, it is necessary to pay attention to the following points.

  When a scout scan is performed with a shield member attached to the subject, the projection data obtained by the scout scan and the shield area in the image data appear as areas with a high X-ray absorption amount. When the automatic exposure mechanism is used based on such projection data and image data, the X-ray output for the shield area is set to be abnormally high, and the original purpose of shielding a highly sensitive organ is achieved. become unable.

  Therefore, usually, after performing a scout scan without attaching the shield member to the subject, the main member performs the main scan by the automatic exposure mechanism after attaching the shield member to the subject.

  However, in the above imaging method, the operator first prepares for the scout scan in a state where the X-ray CT apparatus is installed without attaching the shield member to the subject. Move to another operation room and operate the operation console to perform a scout scan. Next, returning to the examination room again, the shield member is attached to the subject to prepare for the main scan, and then, the main scan is performed again by moving to the operation room. That is, the operator needs to repeatedly move between the examination room and the operation room to prepare for the scout scan and the preparation for the main scan, respectively, and is complicated.

  In addition, when protecting the mammary gland as a highly sensitive organ, in order to prevent the shield member attached to the chest from falling off, it is fixed so that the subject and the shield member are covered with a fixing band provided on the imaging table (table). There are many cases. In this case, the posture of the subject and the shape of the imaging region change between the scout scan and the main scan, and the accuracy of optimization of the X-ray output by the automatic exposure mechanism is deteriorated.

  Under such circumstances, the automatic exposure mechanism functions properly even when a scout scan is performed with an X-ray absorbing member such as a shield member mounted on the subject, and the X-ray output in the shield region can be controlled appropriately. An X-ray CT apparatus is desired.

  The invention of the first aspect includes an X-ray tube, an X-ray detector, and the X-ray tube and the X-ray detector so as to perform a scout scan of a subject having an X-ray absorbing member provided on or inside the body. Control means for controlling, specifying means for specifying a region corresponding to the X-ray absorbing member in projection data collected by the scout scan or image data obtained by the projection data, and the projection data or image data, Based on the corrected projection data or the image data, correction means for correcting the data corresponding to the specified area so as to approach the data obtained when the X-ray absorbing member is not provided, and the X-ray tube Determination means for determining an X-ray output modulation pattern (pattern) according to the position with respect to the specimen, and modulating the X-ray output according to the determined X-ray output modulation pattern And an X-ray CT apparatus including the modulation means.

  According to a second aspect of the present invention, the correction means uses the X-ray absorbing member for data corresponding to the specified region in the projection data or image data based on the X-ray absorption characteristics of the X-ray absorbing member. An X-ray CT apparatus according to the first aspect of the present invention that obtains an X-ray absorption and corrects by subtracting the X-ray absorption from the projection data or image data is provided.

  In the invention of the third aspect, the type of the X-ray absorbing member and its X-ray absorption characteristic are stored in association with each type, and stored in association with the type specified by the operator. The X-ray CT apparatus according to the second aspect is further provided with an acquisition unit that acquires X-ray absorption characteristics, and the correction unit corrects based on the acquired X-ray absorption characteristics.

  The invention according to a fourth aspect is the X-ray according to the first aspect, wherein the correction means corrects data corresponding to the specified area in the projection data or image data using data in the vicinity of the data. A CT apparatus is provided.

  The invention of the fifth aspect includes an X-ray tube, an X-ray detector, and the X-ray tube and the X-ray detector so as to perform a scout scan of a subject provided with an X-ray absorption member on or inside the body. Determination of determining an X-ray output modulation pattern corresponding to the position of the X-ray tube relative to the subject based on control means for controlling and projection data collected by the scout scan or image data obtained from the projection data Means, specifying means for specifying an area corresponding to the X-ray absorbing member in the projection data or image data, and the determined X-ray output modulation pattern, wherein the pattern corresponding to the specified area is the X-ray Correction means for correcting the pattern to be obtained when there is no absorbing member, and modulation means for modulating the X-ray output in accordance with the corrected X-ray output modulation pattern To provide an X-ray CT apparatus comprising a.

  The invention according to a sixth aspect is the invention according to the fourth aspect, wherein the correction means corrects a pattern corresponding to the specified region in the X-ray output modulation pattern using an X-ray output near the pattern. An X-ray CT apparatus is provided.

  The invention according to a seventh aspect is based on the first aspect, wherein the specifying unit specifies an area corresponding to the X-ray absorbing member based on an area designated by an operator on the projection data or image data. An X-ray CT apparatus according to any one of the sixth aspects is provided.

  According to an eighth aspect of the invention, from the first aspect to the sixth aspect, the specifying unit specifies an area corresponding to the X-ray absorbing member based on a magnitude of a data value in the projection data or image data. An X-ray CT apparatus according to any one of the above aspects is provided.

  The ninth aspect of the invention is the X-ray CT apparatus according to any one of the first to eighth aspects, wherein the X-ray absorbing member is a shield member provided on a body surface of the subject. I will provide a.

  The tenth aspect of the invention is the X-ray CT apparatus according to any one of the first to eighth aspects, wherein the X-ray absorbing member is a medical member provided inside the subject. I will provide a.

  In the invention of the above aspect, the scout scan is a scan performed with an X-ray output lower than the main scan prior to the main scan, and projection data obtained by the scan or image data generated based on the projection data Is used for, for example, a scanning plan including positioning and an automatic exposure mechanism.

  In addition, the X-ray output modulation pattern is not only modulated according to the position of the X-ray tube and the X-ray detector in the body axis direction of the subject but also rotated in consideration of the slice cross-sectional shape of the subject. The pattern may be modulated according to the position of the X-ray tube and the X-ray detector in the direction. The X-ray output modulation pattern is mainly an X-ray tube current modulation pattern by fixing the X-ray tube voltage, but may be an X-ray tube voltage modulation pattern by fixing the X-ray tube current. However, a pattern in which both the X-ray tube voltage and the X-ray tube current are modulated may be used.

  Moreover, as a shielding member, what contains lead, bismuth, its compound, etc. can be considered, for example. In addition, as the shield member, it is possible to consider an application for reducing exposure to highly sensitive organs.

  In addition, as the medical member, for example, an artificial bone, an artificial organ, a wire, a bolt, a nut, and the like can be considered.

  According to the X-ray CT apparatus of the first aspect of the invention, the projection data obtained by the scout scan or the region corresponding to the X-ray absorbing member in the image data obtained from the projection data is specified, and the projection data or Since the image data is corrected so that the data corresponding to the specified region approaches the data obtained when there is no X-ray absorbing member, and the X-ray output modulation pattern is determined based on the corrected data, the shield member Even if the scout scan is performed with the X-ray absorbing member mounted on the subject, the automatic exposure mechanism functions properly, and the X-ray output in the region corresponding to the X-ray absorbing member can be appropriately controlled.

  According to the X-ray CT apparatus of the fifth aspect of the invention, an X-ray output modulation pattern is determined based on projection data obtained by a scout scan or image data obtained from the projection data, and the projection data Alternatively, the region corresponding to the X-ray absorbing member in the image data is specified, and the X-ray output modulation pattern is corrected so as to approach the pattern obtained when the pattern corresponding to the specified region does not have the X-ray absorbing member. Even if a scout scan is performed with an X-ray absorbing member such as a shield member mounted on the subject, the automatic exposure mechanism functions properly, and the X-ray output in the region corresponding to the X-ray absorbing member can be controlled appropriately. it can.

1 is a diagram schematically showing an X-ray CT apparatus according to a first embodiment. It is a functional block (block) figure showing functionally the composition of the X-ray CT apparatus of a first embodiment. It is a figure which shows an example of the subject with which the shield member was mounted | worn. It is a figure which shows an example of a scout scan typically. It is a figure which shows an example of scout data. It is a figure which shows an example of the scout image by which the shield area | region was specified. It is a figure which shows an example of the kind of shield member which an X-ray absorption characteristic memory | storage part memorize | stores, and an X-ray absorption characteristic. It is a figure which shows notionally correction | amendment of AP scout data using the X-ray absorption characteristic of a shield member. It is a figure which shows an example of AP scout data correct | amended using the X-ray absorption characteristic of a shield member. It is a figure which shows notionally correction of the lateral scout data (lateral scout data) using the X-ray absorption characteristic of the shield member. It is a figure which shows an example of the lateral scout data correct | amended using the X-ray absorption characteristic information of a shield member. It is a figure which shows notionally correction | amendment of AP scout data using the data of the vicinity of the data corresponding to a shield area | region. It is a figure which shows an example of AP scout data correct | amended using the data of the vicinity of the data corresponding to a shield area | region. It is a figure which shows notionally the correction of the lateral scout data by the data of the vicinity of the data corresponding to a shield area | region. It is a figure which shows an example of the lateral scout data correct | amended using the data of the vicinity of the data corresponding to a shield area | region. It is a figure which shows an example of the integration data obtained by integrating and projecting scout data in the direction perpendicular to the z direction. It is a flowchart (flowchart) which shows the flow of imaging | photography by the X-ray CT apparatus of 1st embodiment. It is a functional block diagram functionally showing the structure of the X-ray CT apparatus of 2nd embodiment. It is a figure which shows notionally correction | amendment of the tube current modulation curve by the tube current value of the vicinity of a shield area | region. It is a flowchart which shows the flow of imaging | photography by the X-ray CT apparatus of 2nd embodiment.

  Embodiments of the invention will be described below.

(First embodiment)
FIG. 1 is a diagram schematically showing the X-ray CT apparatus of the first embodiment. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 includes an input device 2 that receives an input from the operator, a central processing unit 3 that controls each unit for scanning the subject 40 and performs various data processing, and data acquired by the scanning gantry 20. A data collection buffer (buffer) 5 for collecting data, a monitor 6 for displaying images, and a storage device 7 for storing programs and data are provided.

  The imaging table 10 includes a cradle 12 on which the subject 40 is placed and put into and out of the opening B of the scanning gantry 20. The cradle 12 is moved up and down and horizontally moved by a motor built in the imaging table 10. Here, the body axis direction of the subject 40, that is, the horizontal linear movement direction of the cradle 12 is the z direction, the vertical direction is the y direction, and the horizontal direction perpendicular to the z direction and the y direction is the x direction.

  The scanning gantry 20 includes a rotating unit 15 and a support unit 16 that rotatably supports the rotating unit 15. The rotating unit 15 includes an X-ray tube 21, an X-ray controller (controller) 22 that controls the X-ray tube 21, and a collimator that collimates and shapes the X-ray 81 generated from the X-ray tube 21. ) 23, an X-ray detector 24 that detects X-rays 81 irradiated from the X-ray tube 21 and transmitted through the subject 40, and a data collection device that converts and collects the output of the X-ray detector 24 into projection data (DAS; Data Acquisition System) 25 and an X-ray controller 22, a collimator 23, and a rotating unit controller 26 that controls the DAS 25 are mounted. The X-ray detector 24 is a multi-detector in which a plurality of detector arrays are arranged. The support unit 16 includes a control controller 29 that communicates control signals and the like with the operation console 1 and the imaging table 10. The rotating part 15 and the support part 16 are electrically connected via a slip ring 30.

  FIG. 2 is a functional block diagram functionally representing the configuration of the X-ray CT apparatus of the first embodiment. In this figure, the main part of the operation console is functionally represented.

  As shown in FIG. 2, the operation console 1 in the X-ray CT apparatus 100 of the first embodiment includes a scan condition setting unit 60, a scan control unit (control unit) 61, a shield region specifying unit (specifying unit) 62, and a shield member. Type acquisition unit 63, X-ray absorption characteristic storage unit (storage unit) 64, X-ray absorption characteristic acquisition unit (acquisition unit) 65, data correction unit (correction unit) 66, tube current modulation curve determination unit (determination unit) 67, An image generation unit 68 and a display control unit 69 are provided.

  The scan condition setting unit 60 sets a scan condition for a scout scan and a scan condition for a main scan according to an operation from the operator. Examples of scan conditions during the scout scan include tube voltage and tube current, z-direction scan range, projection angle (0 °, 90 °, etc.), and the like. Also, the scan conditions during the main scan include, for example, tube voltage, z-direction scan range, slice thickness or number of slices, gantry rotation speed, helical pitch, and noise level of the generated image. It is.

  The scan control unit 61 sets the imaging table 10 and the scan gantry 20 so as to perform the scout scan SS and the main scan SH with respect to the subject 40 in which the shield member is attached to the body surface of the region including the highly sensitive organ. Control.

  FIG. 3 is a diagram illustrating an example of a subject to which a shield member is attached. FIG. 3A is a view of the subject 40 in the AP direction, that is, the y direction, and FIG. It is the figure which looked at 40 in the Lateral direction, ie, x direction. In the example of FIG. 3, the subject 40 is placed on the cradle 12, and a shield member 42 is mounted on the body surface of the chest to shield the mammary gland of the subject 40.

  The scout scan SS is a scan performed at a low X-ray output prior to the main scan SH in order to acquire information related to the structure of the subject 40 used for a scan plan including positioning and an automatic exposure mechanism. By performing this scout scan SS, scout data PS that is the projection data is collected, and a scout image GS that is image data is generated from the scout data PS. The scout scan SS is considered to be a scan performed by fixing the X-ray tube 21 and the X-ray detector 24 in the rotational direction and a helical scout scan performed while rotating the X-ray tube 21 and the X-ray detector 24 in the rotational direction. However, in this example, the former scan is assumed. In this case, the AP scout scan SSAP performed with the X-ray tube 21 and the X-ray detector 24 fixed in the AP direction (0 °), and the X-ray tube 21 and the X-ray detector 24 fixed in the lateral direction (90 °). Lateral scout scan SSLateral is considered.

  FIG. 4 is a diagram schematically illustrating an example of a scout scan. In the example of FIG. 4, AP scout scan SSAP is shown. The X-ray tube 21 and the X-ray detector 24 are fixed in the AP direction, and the cradle 12 is linearly moved in the z direction to emit X-rays. doing. In this example, the positions of the X-ray tube 21 and the X-ray detector 24 in the z direction with respect to the subject 40 are relatively moved from the coordinates Za to Zb, and the scout data PS in this range is collected.

  FIG. 5 is a diagram illustrating an example of scout data. 5A shows the AP scout data PSAP obtained by the AP scout scan SSAP, and FIG. 5B shows the lateral scout data PSLateral obtained by the lateral scout scan SSLateral. In this figure, the smaller the data value is, the whiter it is expressed.

As this scan SH, helical scan (helical scan), helical shuttle scan (helical shuttle)
Various scans such as scan) and axial scan are conceivable. In this example, a helical scan is assumed.

  Further, the scan control unit 61 can control the X-ray output (dose) from the X-ray tube 21 by changing at least one of the tube voltage V and the tube current A. In this example, the scan voltage V is fixed. Then, the tube current A is controlled. That is, during the main scan SH, the tube voltage V is fixed, and the tube current A is modulated according to the tube current modulation curve AM determined by the tube current modulation curve determination unit 67, thereby realizing the X-ray output modulation.

  The image generation unit 68 generates a scout image GS of the subject 40 based on the scout data PS obtained by the scout scan SS. The image generation unit 68 reconstructs and generates a tomographic image corresponding to a predetermined slice of the subject 40 based on the projection data PH obtained by the main scan SH by a three-dimensional image reconstruction process or the like.

  The display control unit 69 displays the image generated by the image generation unit 68 on the screen of the monitor 6.

  The shield region specifying unit 62 specifies a region RS (hereinafter referred to as a shield region) RS corresponding to the shield member 42 in the scout data PS or the scout image GS. The shield area specifying unit 62 can specify the shield area RS either manually or automatically. In the case of manual operation, for example, the image generation unit 68 generates a scout image GS based on the scout data PS, and the display control unit 69 displays the scout image GS on the monitor 6. The operator surrounds the area corresponding to the shield member 42 using the pointer Pt on the screen of the monitor 6 on which the scout image GS is displayed, or inputs the range of such an area as a coordinate value. To specify the area. The shield area specifying unit 62 specifies the area specified by the operator as the shield area RS. In the case of automatic, the shield region RS is specified based on the magnitude of the data value in the scout data PS or the scout image GS. For example, in the case of the scout data PS, the data value becomes smaller as the X-ray intensity reaching the detection element of the X-ray detector 24 becomes weaker. Therefore, for example, a region where the data value in the scout data PS is below a predetermined threshold is obtained, and this region is specified as the shield region RS. Note that the predetermined threshold value may be changed according to the scan condition during the scout scan SS.

  FIG. 6 is a diagram illustrating an example of a scout image in which a shield region is specified. FIG. 6A shows an AP scout image GSAP in which the shield area RSAP is specified, and FIG. 6B shows a lateral scout image GSLateral in which the shield area RSLateral is specified. In the example of FIG. 6, an area designated by the operator using the pointer Pt on the scout image is specified as the shield area RS. In general, since the shape of the shield member is often close to a rectangle, in this example, the shield region RS is approximately specified as a rectangular region. However, the present invention is not limited to this.

  The shield member type acquisition unit 63 acquires the type of the shield member 42 attached to the subject 40. For example, the type of the shield member directly input by the operator is acquired as the type of the shield member 42 attached to the subject 40. Further, for example, the type of the shield member selected by the operator from the types of the shield members stored in the X-ray absorption characteristic storage unit 64 is acquired as the type of the shield member 42 attached to the subject 40. This selection may be selected from the displayed list of types, or may be selected by searching for a keyword (keyword) such as manufacturer or application (shielded organ). .

  The X-ray absorption characteristic storage unit 64 stores the type of the shield member and the X-ray absorption characteristic in association with each type.

  FIG. 7 is a diagram illustrating an example of the types of shield members and X-ray absorption characteristics stored in the X-ray absorption characteristics storage unit. In the example of FIG. 7, the model number and name of the shield member are stored as the type of the shield member, and the manufacturer, application, and the like are additionally stored. Moreover, the lead equivalent [mmPb] is memorize | stored as an X-ray absorption characteristic, and this lead equivalent is memorize | stored about each of AP direction and Lateral direction.

  The X-ray absorption characteristic acquisition unit 65 acquires the lead equivalent as the X-ray absorption characteristic of the shield member 42 attached to the subject 40. In this example, the X-ray absorption characteristic acquisition unit 65 reads the lead equivalent stored in association with the shield member type acquired by the shield member type acquisition unit 63 from the X-ray absorption characteristic storage unit 64, Is obtained as the lead equivalent of the shield member 42, or the lead equivalent directly input by the operator is obtained as the lead equivalent of the shield member 42.

  The data correction unit 66 corrects the scout data PS so that the data corresponding to the shield region RS in the scout data PS approaches the data obtained when there is no shield member 42.

  When the X-ray absorption characteristics of the shield member 42 can be specified, the data correction unit 66 corresponds to the shield area in the scout data PS based on the scan conditions during the scout scan SS and the X-ray absorption characteristics of the shield member 42. The X-ray absorption amount of the data to be shielded by the shield member 42 is obtained, and correction is performed by subtracting the obtained X-ray absorption amount from the scout data PS (addition in calculation).

  For example, when the operator directly inputs the X-ray absorption characteristic and the X-ray absorption characteristic acquisition unit 65 acquires the input X-ray absorption characteristic as the X-ray absorption characteristic of the shield member 42, the data correction unit 66 uses the acquired X-ray absorption characteristics for the correction.

  Further, for example, when the operator inputs the type of the shield member, and the shield member type acquisition unit 63 acquires the input type of the shield member as the type of the shield member 42 attached to the subject 40, The X-ray absorption characteristic acquisition unit 65 reads out and acquires the X-ray absorption characteristic stored in association with the acquired type of the shield member from the X-ray absorption characteristic storage unit 64, and the data correction unit 66 The acquired X-ray absorption characteristics are used for the correction.

  When the type and X-ray absorption characteristics of the shield member 42 cannot be specified, or when automation is performed without an input by the operator, the data correction unit 66 uses the data corresponding to the shield region RS in the scout data PS. Correction is performed using data in the vicinity of the data.

  Here, the correction of the scout data PS by the data correction unit 66 will be described in more detail, divided into correction using the X-ray absorption characteristics of the shield member and correction using data near the data corresponding to the shield region. To do.

  First, correction using the X-ray absorption characteristics of the shield member will be described.

  FIG. 8 is a diagram conceptually illustrating correction of AP scout data using the X-ray absorption characteristics of the shield member.

  As shown in FIG. 8, the range in the z direction of the shield region RSAP in the AP scout data PSAP is set as coordinates Z1 to Z2, and the range in the x direction is set as coordinates X1 to X2. In the shield area RSAP in the AP scout data PSAP, that is, in the range of the coordinates X1 to X2 and the coordinates Z1 to Z2, the data value is relatively small by the amount of X-ray absorption by the shield member 42.

  For example, when looking at the change of the data value PSAP (Xi, Z) in the z direction at a predetermined coordinate Xi between the coordinates X1 and X2, it becomes like a graph GP1AP in FIG. .

  Incidentally, the X-ray absorption pd per detection element cell in the scout data can be obtained by the following equation, for example.

  In Equation 1, p0 is a detection element 1 cell when a shield member having an X-ray absorption rate corresponding to a lead equivalent 1 [mmPb], that is, a thickness 1 [mm], is scout scanned under a predetermined scanning condition C0. EPb is the lead equivalent [mmPb] of the shield member 42, and k (C1) is the X based on the scan condition C1 in the actual scout scan with respect to the X-ray output (dose) according to the predetermined scan condition C0. It is the ratio of line output. The data value decrease p0 and the X-ray output ratio k (Cj) for each scanning condition Cj are obtained in advance or theoretically in advance.

  For example, when looking at the change in the data value PD (Xi, Z) of the X-ray absorption in the z direction at the coordinate Xi, PD (Xi, Z) = 0 when Z <Z1, Z2 <Z, When Z1 ≦ Z ≦ Z2, PD (Xi, Z) = pd is obtained, as shown in the graph GP2AP in FIG.

  Therefore, the corrected AP scout data PS ′ is obtained by adding the data value pd corresponding to the X-ray absorption to the data value corresponding to the shield region RSAP among all the data values PSAP (X, Z) in the AP scout data PSAP. Find AP (X, Z).

  This can be seen, for example, by the change in the corrected data value PSAP (Xi, Z) in the z direction at the coordinate Xi as shown by the graph GP3AP in FIG.

  FIG. 9 is a diagram illustrating an example of AP scout data corrected using the X-ray absorption characteristics of the shield member.

  In the case of lateral scout data, correction can be performed in substantially the same manner as in the case of AP scout data.

  FIG. 10 is a diagram conceptually illustrating the correction of the lateral scout data using the X-ray absorption characteristics of the shield member.

  As shown in FIG. 10, the range in the z direction of the shield region RSLateral in the lateral scout data PSLateral is the coordinates Z1 to Z2, and the range in the y direction is the coordinates Y1 to Y2. In the shield region RSLateral, that is, in the range of the coordinates Y1 to Y2 and the coordinates Z1 to Z2, the data value is relatively small by the amount of X-ray absorption by the shield member 42.

  For example, when looking at the change of the data value PSLateral (Yi, Z) in the z direction at a predetermined coordinate Yi between the coordinates Y1 and Y2, the graph GP1Lateral in FIG. 10 is obtained.

  As described above, the X-ray absorption pd per detection element cell in the scout data can be obtained by the above Equation 1.

  For example, when looking at the change in the data value PD (Yi, Z) for the X-ray absorption in the z direction at the coordinate Yi, PD (Yi, Z) = 0 when Z <Z1, Z2 <Z, When Z1 ≦ Z ≦ Z2, PD (Yi, Z) = pd is obtained, as shown in the graph GP2Lateral of FIG.

  Therefore, the corrected lateral is obtained by adding the data value pd for the X-ray absorption by the shield member 42 to the data value corresponding to the shield region RSLateral among all the data values PSLateral (Y, Z) in the lateral scout data PSLateral. Obtain scout data PS'Lateral.

  This can be seen, for example, by the change in the corrected data value PS′Lateral (Yi, Z) in the z direction at the coordinate Yi, as shown in the graph GP3Lateral in FIG.

  FIG. 11 is a diagram illustrating an example of lateral scout data corrected using the X-ray absorption characteristic information of the shield member.

  Next, correction using data near the data corresponding to the shield area will be described.

  FIG. 12 is a diagram conceptually illustrating correction of AP scout data using data in the vicinity of data corresponding to the shield area.

  As shown in FIG. 12, the range in the z direction of the shield region RSAP in the AP scout data PSAP is set as coordinates Z1 to Z2, and the range in the x direction is set as coordinates X1 to X2. In the shield region RSAP, that is, in the range of the coordinates X1 to X2 and the coordinates Z1 to Z2, the data value is relatively small by the amount of X-ray absorption by the shield member 42.

  For example, when the change of the data value PSAP (Xi, Z) in the z direction at a predetermined coordinate Xi between the coordinates X1 and X2 is viewed, a graph GP4AP in FIG. 12 is obtained.

  By the way, considering the anatomical structure of the subject 40, the data value in the scout data often changes spatially continuously and smoothly, and the X-ray absorption amount is very large like a shield member. There are few organizations. Further, since the shield region RSAP is originally a region that corresponds to the portion shielded by the shield member, high accuracy is not required for the tube current modulation control by the automatic exposure mechanism. That is, there is an idea that it is sufficient if the portion shielded by the shield member 42 is not scanned with an extremely large X-ray output.

  Therefore, the data value corresponding to the shield region RSAP can be corrected by changing it to a value close to the data value in the vicinity thereof.

  For example, the data value corresponding to the shield area RSAP among all the data values PSAP (X, Z) in the AP scout data PSAP is changed to a value obtained by weighted addition of data values adjacent to the data in the shield area RSAP. The corrected data value PS′AP (X, Z), that is, the corrected AP scout data PS′AP is obtained.

  As a specific example, consider a straight line with an X coordinate = Xi on the AP scout data PSAP (X, Z). Of the data value PSAP (Xi, Z) on the straight line, the data value in the shield area RSAP is changed, for example, according to the following equation. That is, these data values are changed to values obtained by weighted addition of the data values PSAP (Xi, Z1-1) and PSAP (Xi, Z2 + 1) at both ends adjacent to the data in the shield area RSAP on the straight line. Thus, the corrected data value PS′AP (Xi, Z) is obtained.

  Incidentally, the change of the corrected data value PS′AP (Xi, Z) in the z direction at the coordinate Xi is as shown by a graph GP5AP in FIG.

  Such processing is performed for each coordinate Xi of the coordinates X1 to X2, and a corrected data value PS'AP (X, Z), that is, corrected AP scout data PS'AP is obtained.

  FIG. 13 is a diagram illustrating an example of AP scout data corrected using data in the vicinity of data corresponding to the shield area.

  In the case of lateral scout data, correction can be performed in substantially the same manner as in the case of AP scout data.

  FIG. 14 is a diagram conceptually illustrating the correction of the lateral scout data by the data in the vicinity of the data corresponding to the shield region.

  As shown in FIG. 14, the range in the z direction of the shield region RSLateral in the lateral scout data PSLateral is set as coordinates Z1 to Z2, and the range in the y direction is set as coordinates Y1 to Y2. In the shield region RSLateral, that is, in the range of the coordinates Y1 to Y2 and the coordinates Z1 to Z2, the data value is relatively small by the amount of X-ray absorption by the shield member 42.

  For example, when the change of the data value PSLateral (Yi, Z) in the z direction at a predetermined coordinate Yi between the coordinates Y1 and Y2 is viewed, a graph GP4Lateral in FIG. 14 is obtained.

  Here, among all the data values PSLateral (Y, Z) in the lateral scout data PSLateral, the data value corresponding to the shield area RSLateral is changed to a value obtained by weighted addition of data values adjacent to the shield area RSLateral, and corrected. A completed data value PS'Lateral (Y, Z) is obtained.

  As a specific example, consider a straight line with Y coordinate = Yi on the lateral scout data PSLateral. Then, the data value in the shield region RSLateral among the data values PSLateral (Yi, Z) on the straight line is changed, for example, according to the following equation. Thereby, the corrected data value PS′Lateral (Yi, Z) is obtained.

  Incidentally, the change of the corrected data value PS′Lateral (Yi, Z) in the z direction at the coordinate Yi is as shown in the graph GP5 Lateral in FIG.

  Such a process is performed for each coordinate Yi of the coordinates Y1 to Y2, and the corrected data value PS'Lateral (Y, Z), that is, the corrected lateral scout data PS'Lateral is obtained.

  FIG. 15 is a diagram illustrating an example of lateral scout data corrected using data in the vicinity of data corresponding to the shield region.

  The correction method described above is merely an example, and various correction methods by the data correction unit 66 can be considered. For example, the data value corresponding to the shield area in the scout data may be changed to an average value of data values adjacent to the data in the shield area, or may be changed to a predetermined value determined in advance. Also good.

  The tube current modulation curve determination unit 67, based on the corrected scout data, the tube current modulation curve (X-ray) corresponding to the coordinate Z of the position of the X-ray tube 21 and the X-ray detector 24 with respect to the subject 40 in the z direction. Output modulation pattern) AM is determined. The tube current modulation curve AM is determined as follows, for example.

  FIG. 16 is a diagram illustrating an example of accumulated data obtained by integrating and projecting scout data in a direction perpendicular to the z direction. For example, the data value PS′AP (X, Z) of the corrected AP scout data PS′AP is integrated and projected in the x direction, or the data value PS′Lateral (Y, Z) of the corrected lateral scout data PS′Lateral ) Is integrated and projected in the y direction to obtain an integrated data value PS (Z) as shown in the graph GP6 of FIG. Then, the integrated data value PS (Z) is multiplied by a coefficient corresponding to the set noise level sd of the generated image, and a tube similar to the integrated data value PS (Z) as shown in the graph GP7 of FIG. A current modulation curve AM is obtained.

  Hereafter, the flow of imaging by the X-ray CT apparatus 100 of the first embodiment will be described.

  FIG. 17 is a flowchart showing a flow of imaging by the X-ray CT apparatus of the first embodiment.

  In step S <b> 1, the subject 40 is placed on the cradle 12 of the imaging table 10.

  In step S <b> 2, the shield member 42 is attached to the subject 40.

  In step S3, the scan control unit 61 performs a scout scan SS of the subject 40. The scanning gantry 20 transmits the scout data PS collected by the scout scan SS to the image generation unit 68.

  In step S4, the shield region RS is specified. For example, the image generation unit 68 generates a scout image GS based on the scout data PS, and the display control unit 69 displays the scout image GS on the monitor 6. The operator designates an area corresponding to the shield member on the screen of the monitor 6 on which the scout image GS is displayed. The shield area specifying unit 62 specifies the area specified by the operator as the shield area RS.

  In step S5, the scout data PS correction method is determined based on the presence / absence of information on the shield member 42, the presence / absence of automatic mode setting, and the like. If the type of the shield member 42 can be specified, the process proceeds to step S6. If the X-ray absorption characteristic (lead equivalent) of the shield member 42 can be specified, the process proceeds to step S8, and these information cannot be specified or the automatic mode is set. When is set, the process proceeds to step 11.

  In step S6, the operator inputs the type of shield member. The shield member type acquisition unit 63 acquires the input type of the shield member as the type of the shield member 42 attached to the subject 40.

  In step S7, the X-ray absorption characteristic acquisition unit 65 reads the X-ray absorption characteristic stored in association with the type of shield member acquired in step S6, that is, the lead equivalent, from the X-ray absorption characteristic storage unit 64. Get. Then, the process proceeds to step S9.

  On the other hand, in step S8, the operator inputs lead equivalent as the X-ray absorption characteristic. The X-ray absorption characteristic acquisition unit 65 acquires the input lead equivalent as the lead equivalent of the shield member 42. Then, the process proceeds to step S9.

  In step S9, the data correction unit 66 determines the X by the shield member 42 in the scout data PS based on the scan condition during the scout scan SS and the lead equivalent amount of the shield member 42 acquired in step 7 or step S8. Estimate the line absorption.

  In step S10, the data correction unit 66 corrects the scout data PS by subtracting the X-ray absorption by the shield member 42 estimated in step S9 from the scout data PS. Then, the process proceeds to step S12.

  On the other hand, in step S11, the data correction unit 66 corrects the data corresponding to the shield region RS in the scout data PS using the data in the vicinity thereof. Then, the process proceeds to step S12.

  In step S12, the tube current modulation curve AM is determined from the corrected scout data PS '.

  In step S13, the scan condition setting unit 60 sets a scan condition other than the tube current in the main scan SH in accordance with the operation of the operator.

  In step S14, the scan control unit 61 performs the main scan SH according to the tube current modulation curve AM determined in step S12 and the scan conditions set in step S13.

  In step S15, the image generation unit 68 generates an image GH based on the projection data PH obtained by the main scan SH, and the display control unit 69 displays the generated image GH on the monitor 6.

  According to such a first embodiment, the shield region RS in the scout data PS or the scout image GS obtained from the scout scan SS is specified, and there is no data corresponding to the shield region RS in the scout data PS. Since the tube current modulation curve AM is determined on the basis of the corrected scout data PS ′, correction is made so as to approach the data obtained in this case, so even if the scout scan SS is performed while the shield member 42 is mounted on the subject 40 The exposure mechanism functions properly, and the tube current A in the shield region RS can be controlled appropriately.

(Second embodiment)
FIG. 18 is a functional block diagram functionally representing the configuration of the X-ray CT apparatus of the second embodiment.

  The operation console 1a in the X-ray CT apparatus 101 of the second embodiment includes a scan condition setting unit 60, a scan control unit 61, a shield region specifying unit 62, a tube current modulation curve determining unit 67, an image generating unit 68, and a display control unit 69. , And a tube current modulation curve correction unit (correction means) 70.

  The tube current modulation curve determination unit 67 in the present embodiment determines the tube current modulation curve AM based on the scout data PS.

  As in the first embodiment, the shield region specifying unit 62 in the present embodiment specifies the shield region RS in the scout data PS or the scout image GS. Here, if at least the region in the z direction of the shield region RS can be specified. Good.

  The tube current modulation curve correction unit 70 corrects the tube current modulation curve AM so that a curve corresponding to the shield region RS in the tube current modulation curve AM approaches a curve obtained when the shield member 42 is not provided. In this example, the tube current modulation curve correction unit 70 corrects the curve corresponding to the shield region RS in the tube current modulation curve AM using the tube current value in the curve near the curve.

  Here, the correction of the tube current modulation curve AM by the tube current modulation curve correction unit 70 will be described in more detail.

  FIG. 19 is a diagram conceptually showing the correction of the tube current modulation curve by the tube current value in the vicinity of the shield region. FIG. 19 shows an example in which the tube current modulation curve AM is determined based on the lateral scout data PSLateral.

  As shown in FIG. 19, the range of the shield region RS in the z direction on the lateral scout data PSLateral is set as coordinates Z1 to Z2. In the data PS (Z) obtained by integrating and projecting the lateral scout data PSLateral in the y direction, as shown in the graph GP8 of FIG. Only a relatively small data value is obtained. Therefore, for example, when the tube current modulation curve is determined based on the integrated projection data PS (Z) of such scout data, as shown in the graph GP9 in FIG. 19, in the shield region RS, that is, in the range of the coordinates Z1 to Z2, A relatively large tube current value is set.

  However, considering the anatomical structure of the subject 40, it is considered that the tube current value in the tube current modulation curve often changes spatially continuously and smoothly. Further, since the shield region RS is originally a region corresponding to a portion shielded by the shield member, high accuracy is not required for tube current modulation control by the automatic exposure mechanism. That is, there is an idea that it is sufficient if the portion shielded by the shield member 42 is not scanned with an extremely large X-ray output.

  Therefore, the tube current value of the curve corresponding to the shield region RS in the tube current modulation curve AM can be corrected by changing to a value close to the tube current value in the curve near the curve.

  For example, of the tube current values AM (Z) at each Z coordinate in the tube current modulation curve AM, the tube current value for the shield region RS is obtained by weighted addition of the tube current values adjacent to the curve of the shield region RS. To obtain a corrected tube current value AM ′ (Z), that is, a corrected tube current modulation curve AM ′.

  As a specific example, the tube current value in the shield region RS in the tube current value AM (Z) is changed, for example, according to the following equation. That is, these tube current values are changed to values obtained by weighted addition of the tube current values AM (Z1-1) and AM (Z2 + 1) at the positions of both ends adjacent to the curve of the shield region RS. Thus, a corrected tube current value AM ′ (Z), that is, a corrected tube current modulation curve AM ′ is obtained.

  Incidentally, the corrected tube current modulation curve AM ′ is as shown by a graph GP10 in FIG.

  From this, the flow of imaging by the X-ray CT apparatus 101 of the second embodiment will be described.

  FIG. 20 is a flowchart showing a flow of imaging by the X-ray CT apparatus of the second embodiment.

  In steps T1 to T4, as in steps S1 to S4, the subject 40 is placed on the cradle 12 of the imaging table 10, and the shield member 42 is attached to the subject 40. Then, the scan control unit 61 performs a scout scan SS. The operator specifies an area corresponding to the shield member 42 on the scout image GS obtained by the scout scan SS, and the shield area specifying unit 62 specifies the area specified by the operator as the shield area RS.

  In step T5, the tube current modulation curve determination unit 67 determines the tube current modulation curve AM based on the scout data PS.

  In Step T6, the tube current modulation curve correction unit 70 changes the tube current value of the curve corresponding to the shield region RS in the tube current modulation curve AM using the tube current value in the curve in the vicinity of the curve, and changes the tube current value. The current modulation curve AM is corrected.

  In step T7, as in step S13, the scan condition setting unit 60 sets a scan condition other than the tube current in the main scan SH according to the operation of the operator.

  In Step T8, the scan control unit 61 performs the main scan SH according to the tube current modulation curve AM ′ corrected in Step T6 and the scan condition set in Step T7.

  In step T9, as in step S15, the image generation unit 68 generates an image GH based on the projection data PH obtained by the main scan SH, and the display control unit 69 monitors the generated image GH on the monitor 6. To display.

  According to the second embodiment, the tube current modulation curve AM is determined based on the scout data PS or the scout image GS obtained from the scout scan SS, and the shield region RS in the scout data PS or the scout image GS is specified. Then, the tube current modulation curve AM is corrected so that the tube current value curve corresponding to the shield region RS approaches the tube current value curve obtained when the shield member 42 is not provided. Even if the scout scan SS is performed with the device mounted, the automatic exposure mechanism functions properly, and the tube current A in the shield region RS can be controlled appropriately.

  As mentioned above, although embodiment of invention was described, embodiment of invention is not limited to said embodiment, In the range which does not deviate from the meaning of invention, various combinations and deformation | transformation are possible.

  For example, in the first embodiment, the scout data PS that is the projection data obtained by the scout scan SS is corrected, and the tube current modulation curve AM is determined based on the corrected scout data PS ′. A scout image GS may be generated based on the scout data PS obtained by the SS, the scout image GS may be corrected, and the tube current modulation curve AM may be determined based on the corrected scout image. Further, the scout data obtained by the scout scan SS may be corrected, a scout image GS may be generated based on the corrected scout data PS ′, and the tube current modulation curve AM may be determined based on the scout image GS. .

  In each of the above-described embodiments, the shield member 42 provided on the body surface of the subject 40 in order to reduce exposure to highly sensitive organs is assumed as an X-ray absorbing member that affects the automatic exposure mechanism. However, a medical member provided inside the subject 40, such as an artificial bone, an artificial organ, a wire, a bolt, or a nut, can be assumed as such an X-ray absorbing member. Even in such a case, like the above-described embodiments, the automatic exposure mechanism functions properly, and the tube current A in the medical member region can be appropriately controlled.

  Further, in each of the above embodiments, the tube current modulation curve AM is for modulating according to the position coordinate Z of the X-ray tube 21 with respect to the subject 40 in the z direction. However, the modulation may be performed according to the rotational angle position θ of the X-ray tube 21 in consideration of the slice cross-sectional shape of the subject 40. Alternatively, it may be for performing both of these modulations.

  In each of the above embodiments, a tube current modulation curve (tube voltage fixed) is used as an example of the X-ray output modulation pattern in the invention. However, a tube voltage modulation curve (tube current fixed), tube voltage and tube current are used. You may use the pattern which modulates both.

  Further, in each of the above embodiments, lead equivalent is used as the X-ray absorption characteristic, but other index values may be used.

1, 1a Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Monitor 7 Storage device 10 Imaging table 12 Cradle 15 Rotating unit 16 Supporting unit 20 Scanning gantry 21 X-ray tube 22 X-ray tube controller 23 Collimator 24 X-ray detection 25 Data collection device (DAS)
DESCRIPTION OF SYMBOLS 26 Rotation part controller 29 Control controller 30 Slip ring 40 Subject 60 Scan condition setting part 61 Scan control part 62 Shield area specific | specification part 63 Shield member classification acquisition part 64 X-ray absorption characteristic memory | storage part 65 X-ray absorption characteristic acquisition part 66 Data correction Unit 67 Tube current modulation curve determination 68 Image generation unit 69 Display control unit 70 Tube current modulation curve correction unit 81 X-ray 100, 101 X-ray CT apparatus

Claims (10)

An X-ray tube;
An X-ray detector;
Control means for controlling the X-ray tube and the X-ray detector so as to perform a scout scan of a subject provided with an X-ray absorbing member on the body surface or inside;

A specifying means for specifying a region corresponding to the X-ray absorbing member in the projection data collected by the scout scan or image data obtained by the projection data;

Data correction means for correcting the projection data or the image data so that the data corresponding to the specified area approaches data obtained when the X-ray absorbing member is not provided, the X-ray of the X-ray absorbing member Based on the absorption characteristics, an X-ray absorption amount by the X-ray absorption member of data corresponding to the specified region in the projection data or image data is obtained, and the X-ray absorption amount is subtracted from the projection data or image data. Data correction means for correcting by ,

Determining means for determining an X-ray output modulation pattern according to a position of the X-ray tube relative to the subject based on the corrected projection data or image data;

An X-ray CT apparatus comprising modulation means for modulating the X-ray output according to the determined X-ray output modulation pattern. A storage unit for storing the type of the X-ray absorbing member and the X-ray absorption characteristic in association with each type;
An acquisition means for acquiring an X-ray absorption characteristic stored in association with the type designated by the operator;
The X-ray CT apparatus according to claim 1 , wherein the data correction unit performs correction based on the acquired X-ray absorption characteristics.
An X-ray tube;
An X-ray detector;
Control means for controlling the X-ray tube and the X-ray detector so as to perform a scout scan of a subject provided with an X-ray absorbing member on the body surface or inside;

An area corresponding to the X-ray absorbing member in the projection data collected by the scout scan or image data obtained by the projection data is an area designated by the operator on the projection data or image data, or the projection data Or a specifying means for specifying based on the magnitude of the data value in the image data ;

Data correction means for correcting the projection data or the image data so that the data corresponding to the specified region approaches data obtained when the X-ray absorbing member is not provided;

Determining means for determining an X-ray output modulation pattern according to a position of the X-ray tube relative to the subject based on the corrected projection data or image data;

An X-ray CT apparatus comprising modulation means for modulating the X-ray output according to the determined X-ray output modulation pattern. The X-ray CT apparatus according to claim 3 , wherein the data correction unit corrects data corresponding to the specified region in the projection data or image data using data in the vicinity of the data.
An X-ray tube;
An X-ray detector;
Control means for controlling the X-ray tube and the X-ray detector so as to perform a scout scan of a subject provided with a shield member on the body surface;

A specifying means for specifying a region corresponding to the shield member in the projection data collected by the scout scan or image data obtained from the projection data;

Data correction means for correcting the projection data or the image data so that the data corresponding to the specified region approaches data obtained when the shield member is not provided;

Determining means for determining an X-ray output modulation pattern according to a position of the X-ray tube relative to the subject based on the corrected projection data or image data;

Modulation means for modulating the X-ray output according to the determined X-ray output modulation pattern;
An X-ray CT apparatus comprising: The X-ray CT apparatus according to claim 5, wherein the data correction unit corrects data corresponding to the specified region in the projection data or image data using data in the vicinity of the data .
An X-ray tube;
An X-ray detector;
Control means for controlling the X-ray tube and the X-ray detector so as to perform a scout scan of a subject provided with an X-ray absorbing member on the body surface or inside;

Determining means for determining an X-ray output modulation pattern according to a position of the X-ray tube relative to the subject based on projection data collected by the scout scan or image data obtained from the projection data;

An area corresponding to the X-ray absorbing member in the projection data or image data is specified based on an area designated by an operator on the projection data or image data, or a magnitude of a data value in the projection data or image data Specific means to

A modulation pattern correction unit that corrects the determined X-ray output modulation pattern so that a pattern corresponding to the specified region approaches a pattern obtained when there is no X-ray absorbing member;

An X-ray CT apparatus comprising: modulation means for modulating the X-ray output according to the corrected X-ray output modulation pattern. The X-ray CT apparatus according to claim 7 , wherein the modulation pattern correction unit corrects a pattern corresponding to the specified region in the X-ray output modulation pattern using an X-ray output near the pattern.
An X-ray tube;
An X-ray detector;
Control means for controlling the X-ray tube and the X-ray detector so as to perform a scout scan of a subject provided with a shield member on the body surface;

Determining means for determining an X-ray output modulation pattern according to a position of the X-ray tube relative to the subject based on projection data collected by the scout scan or image data obtained from the projection data;

A specifying means for specifying a region corresponding to the shield member in the projection data or image data;
A modulation pattern correction unit that corrects the determined X-ray output modulation pattern so that a pattern corresponding to the specified region approaches a pattern obtained when there is no shield member ;

An X-ray CT apparatus comprising: modulation means for modulating the X-ray output according to the corrected X-ray output modulation pattern. The X-ray CT apparatus according to claim 9, wherein the modulation pattern correction unit corrects a pattern corresponding to the specified region in the X-ray output modulation pattern using an X-ray output near the pattern .

Images