JP2011160947A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus formable of an image preventing generation of artifact. <P>SOLUTION: An inclining structure part 22 inclines an X-ray tube vessel 12 and an X-ray detector 14 to a body axial direction of a subject. A scan control part 40 exposes X-ray from the X-ray tube vessel 12 under a condition in which a support part 10 is inclined with a first inclining angle to the body axial direction, and it exposes X-ray from the X-ray tube vessel 12 under a condition in which the support part 10 is inclined with a second inclining angle to the body axial direction. An image forming part 50 forms the image data based on first projection data collected under a condition in which the support part 10 is inclined with the first inclining angle and second projection data collected under a condition in which the support part 10 is inclined with the second inclining angle. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an X-ray CT apparatus that exposes a subject to X-rays, collects projection data, and generates image data based on the collected projection data.

  The X-ray CT apparatus has an X-ray tube and an X-ray detector that are arranged to face each other with a subject interposed therebetween. The X-ray CT apparatus emits X-rays from the X-ray tube while rotating the X-ray tube and the X-ray detector around the subject, and X-rays transmitted through the subject are detected by the X-ray detector. To detect. Data detected by the X-ray detector is collected as projection data by a data collection device (DAS), and image data of the subject is reconstructed by the collected projection data. For example, the projection data is collected by rotating the X-ray tube and the X-ray detector by 360 ° or (180 ° + fan angle), and the projection data for 360 ° or (180 ° + fan angle) is collected. Based on this, the image data is reconstructed.

  A set of detection data detected by an X-ray detector having a plurality of detection elements at a certain angle with respect to the subject is referred to as a view. For example, when collecting projection data of one view every 1 °, the X-ray tube and the X-ray detector are rotated once to obtain projection data of 360 views, and the projection data of 360 views is used. The image will be reconstructed.

  The X-ray CT apparatus can capture a three-dimensional imaging region having a width in the body axis direction (slice direction) of the subject by performing volume scanning (for example, Patent Document 1). The X-ray CT apparatus uses a two-dimensional X-ray detector (multi-row detector) provided with a plurality of detection elements in the slice direction to image a three-dimensional imaging region having a width in the slice direction, Volume data can be generated by the shooting. For example, when imaging a part such as the heart, brain, or child's lung field, volume data that represents the part to be imaged is generated by moving the bed top plate on which the subject is placed. can do.

  With reference to FIG. 8 and FIG. 9, a region where X-rays are exposed in the volume scan will be described. FIG. 8 is a diagram schematically showing a region to which X-rays are exposed in the volume scan according to the related art. FIG. 9 is a diagram schematically showing a region to which X-rays are exposed when scanning is performed while moving the bed top. As shown in FIGS. 8A and 8B, the X-ray tube 12 and the X-ray detector 14 are arranged to face each other with a bed top 33 on which the subject P is placed. . The bed top 33 is movable in the body axis direction (slice direction) of the subject P. The X-ray detector 14 includes a plurality of detection elements in the slice direction. The X-rays exposed from the X-ray tube 12 spread in a cone shape toward the X-ray detector 14. That is, the X-rays emitted from the X-ray tube 12 travel toward the X-ray detector 14 while spreading in the slice direction. The X-ray tube 12 and the X-ray detector 14 are rotated in the rotation direction (φ direction) around the bed top plate 33.

  FIG. 8A is a diagram showing a state in which the X-ray tube 12 is at the origin in the rotation direction (position where the rotation angle φ is 0 °). FIG. 8B is a diagram showing a state where the X-ray tube 12 is at a position where the rotation angle φ is 180 °. As described above, the X-rays emitted from the X-ray tube 12 travel toward the X-ray detector 14 while spreading in a cone shape. Therefore, when the X-ray tube 12 is at a position where the rotation angle φ is 0 °, as shown in FIG. 8A, the X-rays are exposed to a region S1 where the X-rays spread in a cone shape. X-rays are not exposed to the area A1 outside S1. On the other hand, when the X-ray tube 12 is at a position where the rotation angle φ is 180 °, as shown in FIG. 8B, the X-rays are exposed to the region S2 where the X-rays spread in a cone shape. X-rays are not exposed to the area A2 outside S2.

  Also, as shown in FIG. 8B, when the X-ray tube 12 is at a position where the rotation angle φ is 180 °, X-rays are exposed to a part of the region A1. Similarly, as shown in FIG. 8A, when the X-ray tube 12 is at a position where the rotation angle φ is 0 °, X-rays are exposed to a part of the region A2. As described above, there are regions (region A1, region A2, etc.) where X-rays are exposed or not exposed depending on the rotation angle φ of the X-ray tube 12.

  Then, when the X-ray tube 12 is rotated once (360 ° rotation), X-rays are present in the region near the center of the X-ray spreading in a cone shape regardless of the rotation angle φ of the X-ray tube 12. Be exposed. That is, X-rays are exposed to regions where the X-ray tube 12 is at any rotation angle φ in regions where X-rays are exposed at each rotation angle φ. On the other hand, there is a region (region A1 or region A2) where X-rays are not exposed by the rotation angle φ of the X-ray tube 12.

  Depending on the rotation angle φ, the transmission amount of X-rays detected by the X-ray detector 14 becomes poor in regions where the X-rays are not exposed (region A1, region A2, etc.). For this reason, there is a problem that an image representing an area such as the area A1 or the area A2 is likely to cause artifacts and image quality is deteriorated.

  Therefore, in the prior art, as shown in FIG. 9, an attempt has been made to solve the above problem by continuously performing scanning while moving the couchtop 33 in the body axis direction (slice direction) of the subject. .

  In addition, attempts have been made to suppress the occurrence of artifacts and suppress the deterioration of image quality by correcting the acquired image data.

JP 2007-301228 A

  However, when scanning is performed while moving the bed top 33 in the body axis direction (slice direction) of the subject, the body position and position of the subject may change during the movement. Thus, the position of the subject may be shifted during scanning, and it is difficult to suppress the occurrence of artifacts due to this position shift.

  In addition, as the distance by which the bed top 33 is moved in the slice direction is shorter, it is possible to capture the entire region such as the region A1 and the region A2. However, if the moving distance of the couch top 33 is shortened, the merit of the multi-row X-ray detector is not utilized. That is, by using a multi-row X-ray detector, a wide area can be imaged with respect to the slice direction. When the couch top 33 is moved in the slice direction, a wider area is originally imaged. can do. However, since the moving distance of the couch top 33 is shortened, the area to be imaged becomes narrow, and the merit of the multi-row X-ray detector is not utilized. Further, when scanning is performed while the bed top 33 is moved in the slice direction, the portions exposed to X-rays overlap with each other, which may cause the subject to be exposed excessively.

  The present invention solves the above-described problems, and an object thereof is to provide an X-ray CT apparatus capable of generating an image in which the occurrence of artifacts is suppressed.

  According to the first aspect of the present invention, an X-ray generating unit and an X-ray generating unit disposed opposite to the X-ray generating unit with the subject interposed therebetween, and are exposed from the X-ray generating unit and transmitted through the subject. An X-ray CT apparatus, wherein the X-ray generation means and the X-ray detection means are configured to be rotatable around the subject, Inclining means for inclining the X-ray generation means in the body axis direction of the subject, and from the X-ray generation means in a state where the X-ray generation means is inclined by the inclination means in the body axis direction at a first inclination angle. X-rays are emitted, and the X-ray generation means emits X-rays in a state in which the X-ray generation means is inclined in the body axis direction by a second inclination angle different from the first inclination angle. Control means for exposing, and the X-ray generation means at the first tilt angle. The first projection data detected by the X-ray detection means in a tilted state and the second projection data detected by the X-ray detection means in a state where the X-ray generation means is inclined at the second tilt angle. And an image generation means for generating image data based on the projection data of the X-ray CT apparatus.

  According to the present invention, by exposing X-rays from a plurality of tilt angles, X-rays are exposed from different tilt angles to a region where the X-ray dose is small in the X-ray exposure from each tilt angle. It becomes possible. As a result, by generating image data using projection data detected at each inclination angle, image data with reduced artifacts can be obtained.

1 is a block diagram showing an X-ray CT apparatus according to an embodiment of the present invention. It is a figure which shows the state which inclined the X-ray tube. It is a figure for demonstrating the process which produces | generates image data using the projection data detected by a different inclination angle. It is a figure which shows the state which inclined the X-ray tube. It is a figure which shows the state which inclined the X-ray tube. It is an external view which shows the external appearance of a mount frame (gantry). It is sectional drawing which shows the inside of a mount frame. It is a figure which shows typically the area | region where an X-ray is exposed in the volume scan which concerns on a prior art. It is a figure which shows typically the area | region to which an X-ray is exposed when performing a scan, moving a bed top plate.

  An X-ray CT apparatus according to an embodiment of the present invention will be described with reference to FIG. An X-ray CT apparatus according to an embodiment of the present invention includes a gantry device 1, a console unit 2, and a bed device 3. The gantry device 1 exposes the subject to X-rays and collects X-rays transmitted through the subject as projection data. The projection data is output to the console unit 2 and reconstructed. The couch device 3 includes a couch 31 for placing a subject.

(Mounting device 1)
The gantry device 1 includes a support unit 10 and a support unit drive unit 20.

(Supporting part 10)
The support unit 10 stores a high voltage generation unit 11, an X-ray tube 12, a collimator 13, an X-ray detector 14, and a data collection unit 15. The support unit 10 has an opening (not shown) that penetrates in the body axis direction (slice direction) of the subject. A couch top on which the subject is placed is inserted into the opening.

  The X-ray tube 12 and the X-ray detector 14 are arranged to face each other with the opening of the support portion 10 therebetween. A collimator 13 is installed at the X-ray exposure port of the X-ray tube 12. The X-ray tube 12 emits X-rays, and the X-ray detector 14 detects X-rays transmitted through the subject. The X-ray tube 12 corresponds to an example of “X-ray generation means” of the present invention.

  The collimator 13 has a slit (opening) having a predetermined width. By changing the width of the slit, the fan angle (expansion angle in the channel direction) of the X-rays exposed from the X-ray tube 12 and the cone of the X-rays. Adjust the angle (spread angle in the slice direction). The slice direction corresponds to the body axis direction of the subject, and the channel direction corresponds to the rotation direction of the X-ray tube 12.

  As the X-ray detector 14, a two-dimensional X-ray detector in which a plurality of detection elements are arranged in two directions (slice direction and channel direction) orthogonal to each other is used. That is, as the X-ray detector 14, a two-dimensional X-ray detector having a plurality of detection elements in the body axis direction (slice direction) of the subject is used. Thus, a three-dimensional imaging region having a width in the slice direction is imaged (volume scan).

  The high voltage generator 11 supplies a tube voltage for exposing X-rays to the X-ray tube 12 under the control of the scan controller 40. Thereby, X-rays are generated from the X-ray tube 12.

  The X-ray detector 14 is provided with a data collection unit (DAS) 15. The data collection unit 15 includes data collection elements arranged in the same manner as the detection elements of the X-ray detector 14. The data collection unit 15 collects X-rays (detection signals) detected by the X-ray detector 14 in correspondence with the data collection control signal (View Trigger signal (VT signal)) output from the scan control unit 40. . This collected data is projection data. The data collection unit 15 outputs projection data to the console unit 2. The X-ray detector 14 and the data collection unit 15 constitute an example of the “X-ray detection means” of the present invention.

  X-rays emitted from the X-ray tube 12 are irradiated to the subject via the collimator 13. X-rays transmitted through the subject are detected by the X-ray detector 14, and the detected signals are collected as projection data by the data collection unit 15.

(Supporting unit driving unit 20)
The support unit drive unit 20 includes a rotation mechanism unit 21, a tilt mechanism unit 22, and a tilt angle detection unit 23.

(Rotating mechanism 21)
The rotation mechanism unit 21 rotates the support unit 10 around the subject based on the gantry control signal output from the scan control unit 40. As a result, the X-ray tube 12 and the X-ray detector 14 stored in the support unit 10 are rotated around the subject.

(Inclination mechanism part 22, inclination angle detection part 23)
The tilt mechanism unit 22 tilts the support unit 10 in the body axis direction (slice direction) of the subject based on the tilt control signal output from the scan control unit 40. As a result, the X-ray tube 12 and the X-ray detector 14 stored in the support unit 10 are inclined in the slice direction. The tilt mechanism unit 22 includes a drive unit (not shown) including a structural mechanism that tilts the support unit 10 and a motor that moves the mechanism. The tilt mechanism unit 22 is controlled by the scan control unit 40 and tilts the support unit 10 in the slice direction until a target tilt angle is detected by the tilt angle detection unit 23. The tilt angle detection unit 23 includes an encoder that detects the drive amount of the tilt mechanism unit 22 and a counter that counts the output from the encoder. The tilt angle detection unit 23 sets the position when the support unit 10 stands vertically as the tilt origin position, resets the count value at that time to 0 (zero), and counts the encoder output corresponding to the tilt movement. To do. The tilting mechanism 22 corresponds to an example of the “tilting unit” of the present invention.

  In this embodiment, the support unit 10 (X-ray tube 12 and X-ray detector 14) is inclined at a plurality of inclination angles, and X-rays are exposed from the X-ray tube 12 at each inclination angle. Projection data is collected at each tilt angle.

(Specific example of tilt movement)
With reference to FIG. 2, the inclination movement of the support part 10 (X-ray tube 12 and X-ray detector 14) is demonstrated. As an example, the support portion 10 is inclined at two inclination angles, and X-rays are exposed from the X-ray tube 12 at the respective inclination angles.

  As shown in FIGS. 2A and 2B, the X-ray tube 12 and the X-ray detector 14 are arranged to face each other with a bed top 33 on which the subject P is placed. . The bed top 33 is movable in the body axis direction (slice direction) of the subject P. The X-ray detector 14 includes a plurality of detection elements in the slice direction. The X-rays exposed from the X-ray tube 12 spread in a cone shape toward the X-ray detector 14. That is, the X-rays emitted from the X-ray tube 12 travel toward the X-ray detector 14 while spreading in the slice direction. The X-ray tube 12 and the X-ray detector 14 are rotated around the subject P in the rotation direction (φ direction). A position where the support unit 10 (the X-ray tube 12 and the X-ray detector 14) stands vertically is defined as a vertical position VL. The vertical position VL corresponds to the tilt origin position in the direction in which the support portion 10 tilts (tilt direction (θ direction)).

  For example, as shown in FIG. 2 (a), the tilt mechanism unit 22 makes the tilt angle the tilt angle θa with respect to the X-ray tube 12 and the X-ray detector 14 in the slice direction with the vertical position VL as a reference. Tilt to position. The X-ray tube 12 and the X-ray detector 14 are rotated around the subject P while the X-ray tube 12 and the X-ray detector 14 are inclined at the inclination angle θa. 12 is exposed to X-rays. The X-ray detector 14 detects X-rays that have passed through the subject. The data collection unit 15 collects X-rays detected by the X-ray detector 14 as projection data. For example, when collecting projection data for one view (view) for each rotation angle of 1 °, the X-ray tube 12 and the X-ray detector 14 are rotated once around the subject P (360 ° rotation). The data collection unit 15 collects 360 view projection data. The inclination angle θa corresponds to an example of the “first inclination angle” of the present invention.

  FIG. 2A is a diagram showing a state in which the X-ray tube 12 is at the origin in the rotational direction (position where the rotational angle φ is 0 °). X-rays emitted from the X-ray tube 12 travel toward the X-ray detector 14 while spreading in a cone shape. When the X-ray tube 12 is at a position where the rotation angle φ is 0 °, the X-rays are exposed to the region Sa where the X-rays spread in a cone shape, and the X-rays are emitted to the region A outside the region Sa. Not exposed. When the X-ray tube 12 is rotated once (360 °) in the rotation direction (φ direction), the rotation angle φ of the X-ray tube 12 is in the region near the center of the X-ray spreading in a cone shape. Even X-rays are exposed. That is, X-rays are exposed to regions where the X-ray tube 12 is at any rotation angle φ in regions where X-rays are exposed at each rotation angle φ. On the other hand, there is a region where X-rays are not exposed depending on the rotation angle φ. For example, in the region A, X-rays are not exposed when the rotation angle φ is 0 °, but X-rays are exposed to a part of the region A when the rotation angle φ is 180 °. As described above, in the region A, X-rays are exposed or not exposed depending on the rotation angle φ, so that the amount of transmitted X-rays is smaller than the region near the center of the X-rays spreading in a cone shape.

  Further, as shown in FIG. 2B, the tilt mechanism unit 22 tilts the X-ray tube 12 and the X-ray detector 14 at a tilt angle θb different from the tilt angle θa. For example, the tilt mechanism unit 22 detects the X-ray tube 12 and the X-rays at a position where the tilt angle becomes the tilt angle θb in the direction opposite to the tilt angle θa with the vertical position VL as the tilt origin position. The container 14 is tilted. While rotating the X-ray tube 12 and the X-ray detector 14 around the subject P in a state where the X-ray tube 12 and the X-ray detector 14 are inclined at the inclination angle θb, the X-ray tube 12 is exposed to X-rays. For example, when collecting projection data of one view at every rotation angle of 1 °, the X-ray tube 12 and the X-ray detector 14 are rotated around the subject P once (360 ° rotation), thereby obtaining a data collection unit. 15 collects 360 view projection data. The inclination angle θb corresponds to an example of the “second inclination angle” of the present invention.

  FIG. 2B is a diagram showing a state where the X-ray tube 12 is at the origin in the rotation direction (position where the rotation angle φ is 0 °). X-rays emitted from the X-ray tube 12 travel toward the X-ray detector 14 while spreading in a cone shape. When the X-ray tube 12 is at a position where the rotation angle φ is 0 °, the X-rays are exposed to the region Sb where the X-rays spread in a cone shape, and the X-rays are emitted to the region B outside the region Sb. Not exposed. Similarly to the region A described above, the region B is not exposed to X-rays when the rotation angle φ is 0 °, but is exposed to a part of the region B when the rotation angle φ is 180 °. Be shot. As described above, in the region B, X-rays are exposed or not exposed depending on the rotation angle φ, so that the amount of transmitted X-rays is smaller than the region near the center of the X-rays spreading in a cone shape.

  The data collection unit 15 outputs projection data (hereinafter, also referred to as “projection data Da”) collected in a state where the X-ray tube 12 is inclined at the inclination angle θa to the console unit 2. In addition, the data collection unit 15 outputs projection data (hereinafter, also referred to as “projection data Db”) collected in a state where the X-ray tube 12 is inclined at the inclination angle θb to the console unit 2. The projection data Da corresponds to an example of “first projection data” of the present invention. The projection data Db corresponds to an example of “second projection data” of the present invention.

(Console section 2)
The console unit 2 includes a scan control unit 40, a preprocessing unit 41, an image generation unit 50, an image storage unit 42, a display control unit 43, and a display unit 44.

(Scan control unit 40)
The scan control unit 40 outputs a tilt control signal to the support unit drive unit 20 in order to tilt the support unit 10 in the body axis direction (slice direction) of the subject. For example, the scan control unit 40 generates a tilt control signal including tilt angle information, and outputs the tilt control signal to the support unit driving unit 20. The tilt angle information indicates the tilt angle θ with respect to the vertical position VL. In the example illustrated in FIG. 2, the scan control unit 40 generates a tilt control signal including tilt angle information indicating the tilt angle θa and tilt angle information indicating the tilt angle θb, and sends the tilt control signal to the support unit driving unit 20. Output to. The tilt mechanism unit 22 receives the tilt control signal from the scan control unit 40 and tilts the support unit 10 in the slice direction according to the tilt control signal. The inclination angle θ may be stored in advance in a storage unit (not shown), or the operator may input an arbitrary inclination angle θ using an operation unit (not shown). The scan control unit 40 corresponds to an example of the “control unit” of the present invention.

  Further, the scan control unit 40 outputs a gantry control signal to the support unit drive unit 20 in order to rotate the support unit 10 in the rotation direction φ at a constant speed. Further, the scan control unit 40 outputs an X-ray generation control signal for controlling X-ray generation to the high voltage generation unit 11, and outputs a data collection control signal indicating the detection timing of the X-rays to the data collection unit 15.

  Further, the scan control unit 40 outputs X-ray information indicating the spread angle of X-rays and tilt angle information to the image generation unit 50. The X-ray spread angle includes a fan angle (a spread angle in the channel direction) and a cone angle (a spread angle in the slice direction).

(Pre-processing unit 41)
The preprocessing unit 41 performs processes such as sensitivity correction and X-ray intensity correction on the projection data output from the data collection unit 15. The projection data processed by the preprocessing unit 41 is output to the image generation unit 50.

(Image generation unit 50)
The image generation unit 50 includes a processing unit 51 and a reconstruction processing unit 54. The image generation unit 50 includes first projection data (projection data Da) collected in a state where the X-ray tube 12 is inclined at the first inclination angle (inclination angle θa), and a second inclination angle (inclination). Image data is generated based on the second projection data (projection data Db) collected with the X-ray tube 12 tilted at an angle θb). The image generation unit 50 corresponds to an example of the “image generation unit” of the present invention.

(Processing unit 51)
The processing unit 51 includes an imaging area calculation unit 52 and an interpolation processing unit 53. When the X-ray tube 12 is exposed to X-rays in a state where the X-ray tube 12 is inclined at a certain inclination angle, the processing unit 51 obtains projection data in a region where the X-rays are not exposed at another inclination angle. Determined using data. With reference to FIG. 3, the process by the process part 51 is demonstrated.

(Shooting area calculation unit 52)
The imaging region calculation unit 52 receives the X-ray information indicating the X-ray spread angle and the tilt angle information indicating the tilt angle θ of the support unit 10 from the scan control unit 40, and the position of the region where the X-rays are exposed. Ask for. That is, when the X-ray tube 12 is tilted at the tilt angle θ indicated by the tilt angle information and the X-ray is exposed with a spread angle indicated by the X-ray information, the imaging region calculation unit 52 The position of the area where X-rays are exposed is obtained. The imaging region calculation unit 52 obtains the position of the region where the X-rays are exposed when the X-ray tube 12 is at each rotation angle φ. That is, the imaging region calculation unit 52 obtains the position of the region where X-rays are exposed for each rotation angle φ.

  For example, as illustrated in FIG. 3, the imaging region calculation unit 52 sets the X-ray tube 12 to the tilt angle θa based on the tilt angle θa of the X-ray tube 12 and the spread angle of the X-ray spreading in a cone shape. The position of the region Sa to which X-rays are exposed in a tilted state is obtained. Similarly, the imaging region calculation unit 52 is in a state where the X-ray tube 12 is tilted to the tilt angle θb based on the tilt angle θb of the X-ray tube 12 and the spread angle of the X-ray that spreads in a cone shape. The position of the region Sb to which the X-ray is exposed is obtained. Regions Sa and Sb shown in FIG. 3 are regions to which X-rays are exposed in a state where the rotation angle φ is 0 °. The imaging area calculation unit 52 obtains an area where X-rays are exposed for each rotation angle φ. For example, the imaging region calculation unit 52 obtains a region to which X-rays are exposed every 1 ° when the rotation angle φ is 0 ° to 360 °.

(Interpolation processing unit 53)
The interpolation processing unit 53 obtains projection data in a region where X-rays are not exposed depending on the rotation angle φ. For example, the interpolation processing unit 53 synthesizes projection data collected at different inclination angles θ at each rotation angle φ of the X-ray tube 12. Specifically, the interpolation processing unit 53 obtains an area that does not overlap with the area Sa in the area Sb as an interpolation area. And the interpolation process part 53 calculates | requires the synthetic | combination projection data D by synthesize | combining the projection data Da in the area | region Sa, and the projection data Db in the said interpolation area | region. That is, the interpolation processing unit 53 obtains the projection data in the area Sa collected at the inclination angle θa and the projection data in the interpolation area that is the projection data of the area Sb collected at the inclination angle θb and does not overlap with the area Sa. Synthesize. The interpolation processing unit 53 synthesizes the projection data Da in the region Sa and the projection data Db in the interpolation region for the case where the X-ray tube 12 is at each rotation angle φ, thereby combining the projection at each rotation angle φ. Data D is obtained. For example, the interpolation processing unit 53 combines the projection data in the region Sa and the projection data Db in the interpolation region every rotation angle φ from 0 ° to 360 °, thereby combining the projection data at each rotation angle φ. Ask for.

(Reconstruction processing unit 54)
The reconstruction processing unit 54 reconstructs image data by performing a back projection process on the projection data. In this embodiment, the reconstruction processing unit 54 generates image data by performing a back projection process on the composite projection data D. Thereby, image data representing the subject is generated. The reconstruction processing unit 54 outputs the image data to the image storage unit 42. The image storage unit 42 stores image data.

  Note that the image generation unit 50 may generate image data by combining the projection data before the reconstruction process, or by combining the image data after the reconstruction process, X-rays may be generated depending on the rotation angle φ. Image data including image data of a region that is not exposed may be generated.

(Display control unit 43)
The display control unit 43 reads image data from the image storage unit 42 and causes the display unit 44 to display an image based on the image data. In this embodiment, an image generated based on the composite projection data D is displayed on the display unit 44.

(Bed apparatus 3)
The bed apparatus 3 includes a bed 31 and a bed driving unit 32. The couch 31 includes a couch top 33 for placing a subject and a couch base that supports the couch top 33. As described above, the couchtop 33 can be moved in the body axis direction (slice direction) of the subject by the couch driving unit 32. The bed base can move the bed top plate 33 in the vertical direction by the bed driving unit 32.

  Each of the scan control unit 40, the image generation unit 50, and the display control unit 43 includes a processing device (not shown) such as a CPU, GPU, or ASIC and a storage device (not shown) such as a ROM, RAM, or HDD. Also good. The storage device stores a scan control program for executing the functions of the scan control unit 40. The storage device stores an image generation program for executing the function of the image generation unit 50. The storage device stores a display control program for executing the function of the display control unit 43. The image generation program includes a processing program for executing the function of the processing unit 51 and a reconstruction processing program for executing the function of the reconstruction processing unit 54. The processing program includes an imaging region calculation program for executing the function of the imaging region calculation unit 52 and an interpolation processing program for executing the function of the interpolation processing unit 53. A processing device such as a CPU executes the functions of each unit by executing each program stored in the storage device.

  According to the X-ray CT apparatus according to this embodiment having the above-described configuration, the X-ray tube 12 is tilted to the inclination angle θa and the inclination angle θb, respectively, and X-rays are exposed to thereby expose X from the inclination angle θa. In the radiation exposure, an X-ray can be exposed from a different inclination angle θb to a region where the X-ray dose is relatively small (for example, the region A). And about the area | region which is not included in area | region Sa, the reconstruction process was performed using the projection data in area | region Sb obtained by inclination-angle (theta) b, the deficiency of X-ray dose was eliminated, and generation | occurrence | production of the artifact was suppressed. Image data can be generated. Further, X-rays can be exposed to a region with a relatively small X-ray dose without moving the bed top 33 in the slice direction. As a result, there is no position shift of the subject that may occur during the movement of the couch top 33, so that artifacts due to the position shift can be prevented.

  In the embodiment described above, shooting is performed by tilting the support portion 10 at two tilt angles θ (θa, θb), but shooting may be performed by tilting at three or more tilt angles θ. Further, one of the two or more inclination angles θ may be 0 °. In other words, the inclination angle θ may include 0 °, and the photographing may be performed in a state where the support portion 10 is standing vertically (inclination angle θ is 0 °). For example, even when photographing is performed with either one of the inclination angle θa and the inclination angle θb set to 0 °, the above-described operations and effects can be achieved.

  With reference to FIG. 4, the case where the support part 10 is inclined at three inclination angles (θa, θb, θc) will be described.

  As shown in FIG. 4A, the tilt mechanism unit 22 tilts the X-ray tube 12 and the X-ray detector 14 to a position where the tilt angle becomes the tilt angle θa. By exposing X-rays in this state, the data collection unit 15 collects the projection data Da.

  As shown in FIG. 4B, the tilt mechanism unit 22 tilts the X-ray tube 12 and the X-ray detector 14 to a position where the tilt angle becomes the tilt angle θb. By exposing X-rays in this state, the data collection unit 15 collects projection data Db.

  As shown in FIG. 4C, the tilt mechanism unit 22 tilts and moves the X-ray tube 12 and the X-ray detector 14 to a position where the tilt angle is 0 ° (tilt angle θc). By exposing X-rays in this state, the data collection unit 15 collects projection data Dc.

  Similar to the above-described embodiment, the image generation unit 50 generates image data based on projection data collected at different inclination angles. That is, the imaging region calculation unit 52 obtains a region where X-rays are exposed at each inclination angle (θa, θb, θc). The interpolation processing unit 53 obtains an interpolation area as described above, and obtains composite projection data D. The reconstruction processing unit 54 generates image data based on the composite projection data D.

  As described above, even when imaging is performed by tilting the support portion 10 at three tilt angles, X-rays from a different tilt angle are applied to an area where the X-ray dose from a certain tilt angle is relatively small. Exposure is possible. Therefore, it is possible to generate image data that eliminates the poor X-ray dose and suppresses the occurrence of artifacts. In addition, by performing imaging while tilting the support portion 10 at a larger angle of inclination, it is possible to capture a region that covers a relatively small amount of X-rays more finely.

(Modification 1)
Modification 1 will be described with reference to FIG. The X-ray CT apparatus according to the first modification changes the spread angle of X-rays emitted from the X-ray tube 12 for each inclination angle θ. That is, the X-ray CT apparatus according to the first modification changes the width of the slit of the collimator 13 for each inclination angle θ.

  The scan control unit 40 outputs slit information indicating the width of the slit with respect to each inclination angle θ to the support unit driving unit 20. The support unit driving unit 20 receives the slit information from the scan control unit 40 and changes the width of the slit of the collimator 13 according to the slit information. Information indicating the width of the slit for each inclination angle θ may be stored in advance in a storage unit (not shown), or the operator may input the width of the slit using an operation unit (not shown).

  For example, as shown in FIG. 5, in the state where the inclination angle θa is 0 ° and the width of the slit of the collimator 13 is set to the width Wa, X-rays are exposed from the X-ray tube 12 so that the region Sa has X-rays. Is exposed. In addition, when the X-ray tube 12 is inclined at the inclination angle θb and the slit width of the collimator 13 is set to the width Wb (> width Wa), X-rays are exposed from the X-ray tube 12 to the region Sb. X-rays are emitted. Since the width Wb at the inclination angle θb is wider than the width Wa at the inclination angle θa, the region Sb is wider than the region Sa.

  For example, when the region to be imaged is small, imaging is performed by narrowing the slit width of the collimator 13 in order to suppress exposure of the subject. In order to cover the region where the X-ray dose is relatively small in this imaging, the imaging is performed by changing the inclination angle θ from the inclination angle θa to the inclination angle θb and further widening the slit width. Thereby, it is possible to capture a wider area while suppressing exposure of the subject.

  As described above, even when the slit width of the collimator 13 is changed according to the inclination angle θ, the image generation unit 50 obtains the composite projection data D similarly to the above-described embodiment, and the image data is obtained based on the composite projection data D. Generate. Thereby, it becomes possible to generate image data in which the poor X-ray dose is eliminated and the occurrence of artifacts is suppressed.

(Modification 2)
Modification 2 will be described with reference to FIGS. 6 and 7. As shown in FIGS. 6A and 6B, an X-ray tube is obtained by inclining a gantry for storing the X-ray tube 12 and the X-ray detector 14 in the slicing direction, including the gantry outer cover 200. The sphere 12 can be tilted in the slice direction. However, when the X-ray tube 12 including the outer cover 200 is tilted in the slicing direction, a gap 220 is generated between the base 210 of the X-ray CT apparatus and the outer cover 200. When the gap 220 is generated in this way, there is a possibility that an engineer or a patient may be caught, and thus means for preventing it is necessary.

  In the X-ray CT apparatus according to the second modification, the support unit 10 including the X-ray tube 12 and the X-ray detector 14 is tilted in the exterior cover 200 without tilting the exterior cover 200.

  A specific example is shown in FIG. As shown in FIG. 7, a support unit 10 including an X-ray tube 12 and an X-ray detector 14 is provided inside an exterior cover 100 of a gantry (storage unit). The tilt mechanism unit 22 tilts the support unit 10 in the slice direction inside the exterior cover 100. The rotation mechanism unit 21 rotates the support unit 10 in the rotation direction (φ direction) inside the exterior cover 100. The exterior cover 100 has an opening 110 penetrating in the slicing direction, and the bed top 33 on which the subject is placed is inserted into the opening 110.

  As described above, the support unit 10 (the X-ray tube 12 and the X-ray detector 14) is inclined in the slicing direction inside the outer cover 100, so that the gap 220 shown in FIG. 6 does not occur. This makes it possible to ensure the safety of the engineer and the patient when the support portion 10 is tilted.

DESCRIPTION OF SYMBOLS 1 Stand apparatus 2 Console part 3 Sleeper apparatus 10 Support part 11 High voltage generation part 12 X-ray tube 13 Collimator 14 X-ray detector 15 Data collection part 20 Support part drive part 21 Rotation mechanism part 22 Inclination mechanism part 23 Inclination angle detection 23 Unit 40 scan control unit 41 pre-processing unit 42 image storage unit 43 display control unit 44 display unit 50 image generation unit 51 processing unit 52 imaging region calculation unit 53 interpolation processing unit 54 reconstruction processing unit

Claims (4)

X-ray generation means;
X-ray detection means that is disposed opposite to the X-ray generation means with a subject interposed therebetween, detects X-rays that are exposed from the X-ray generation means and transmitted through the subject as projection data;
An X-ray CT apparatus in which the X-ray generation means and the X-ray detection means are configured to be rotatable around the subject,
Tilting means for tilting the X-ray generating means in the body axis direction of the subject;
The X-ray generation means is exposed to X-rays from the X-ray generation means in a state where the X-ray generation means is inclined at the first inclination angle in the body axis direction by the inclination means. Control means for exposing X-rays from the X-ray generation means in a state tilted in a second tilt angle different from the first tilt angle in the axial direction;
The first projection data detected by the X-ray detection unit in a state where the X-ray generation unit is tilted to the first tilt angle, and the X-ray generation unit is tilted to the second tilt angle. Image generation means for generating image data based on the second projection data detected by the X-ray detection means in a state;
An X-ray CT apparatus comprising:   The image generation unit generates the image data by combining the first projection data with projection data in an area where X-rays are not exposed at the first tilt angle in the second projection data. The X-ray CT apparatus according to claim 1, wherein: A collimator for adjusting the spread angle of the X-rays emitted from the X-ray generation means;
3. The X-ray according to claim 1, wherein the control unit controls the collimator so as to change the divergence angle between the first inclination angle and the second inclination angle. 4. CT device. A storage unit for storing the X-ray generation means and the X-ray detection means;
The X-ray CT apparatus according to claim 1, wherein the tilting unit tilts the X-ray generation unit within the storage unit.

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