JP6681256B2 - X-ray CT system - Google Patents

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus, and relates to a technique of reducing an exposure dose due to a penumbra in a collimator apparatus that dynamically controls an area irradiated with X-rays.

  An X-ray CT device is obtained by rotating an X-ray source that irradiates the subject with X-rays and an X-ray detector that detects the X-ray dose that has passed through the subject as projection data, around the subject. The tomographic image of the subject is reconstructed using projection data from a plurality of different directions, and the reconstructed tomographic image is displayed. The image displayed by the X-ray CT apparatus depicts the shape of an organ in the subject and is used for image diagnosis.

  It is desirable that all of the projection data acquired with X-ray exposure be effectively used for reconstruction of a tomographic image. However, when the X-ray irradiation width in the body axis direction of the subject in the spiral scan, so-called slice width is fixed, part of the projection data acquired at the start and end of the spiral scan is not used for reconstruction, It causes unnecessary exposure to the subject. In Patent Document 1, a combination of a position-fixed front diaphragm and a movable slit plate, or a combination of two diaphragm members that can be individually moved, unnecessary radiation dose at the start and end of a spiral scan. A dynamic collimator is disclosed that reduces the.

JP 2014-144368 JP

  However, although the unnecessary exposure dose at the start and end of the spiral scan can be reduced in Patent Document 1, since the penumbra is not taken into consideration, it is not sufficient to reduce the exposure dose. That is, since the focus of X-rays has a finite size, a region called a penumbra occurs near the outside of the region irradiated with X-rays, and unnecessary exposure occurs in this region.

  Therefore, an object of the present invention is to provide an X-ray CT apparatus capable of reducing the exposure dose at the start and end of a spiral scan and also reducing the exposure dose due to penumbra.

  In order to achieve the above-mentioned object, the present invention operates in conjunction with the movement of a dynamic collimator that controls the area irradiated with X-rays according to the position of the X-ray focal point with respect to the reconstruction range during spiral scanning. It is characterized by providing a shadow cutter.

  Specifically, the present invention is an X-ray source that generates X-rays, a collimator device that controls a region in which the X-rays are irradiated to a subject, and the X-ray source and the collimator device are arranged to face each other, and An X-ray CT apparatus including an X-ray detector that detects X-rays that have passed through a subject, the X-ray source and the collimator device, and a rotating disk that rotates the X-ray detector around the subject. The collimator device includes a dynamic collimator that controls an area irradiated with the X-rays according to a position of a focus of the X-rays with respect to a reconstruction range at the time of spiral scanning, and the X-ray detection rather than the dynamic collimator. A penumbra cutter is disposed on the container side and operates in conjunction with the movement of the dynamic collimator to reduce the penumbra generated in the dynamic collimator.

  According to the present invention, it is possible to provide an X-ray CT apparatus capable of reducing the exposure dose at the start and end of the spiral scan and also reducing the exposure dose due to the penumbra.

Overall configuration diagram of the X-ray CT apparatus according to the first embodiment Perspective view for explaining the outline of the dynamic collimator Side view for explaining the operation of the dynamic collimator Side view for explaining penumbra generated in dynamic collimator The perspective view for demonstrating the outline of the penumbra cutter of 1st embodiment. The side view for demonstrating operation | movement of the penumbra cutter of 1st embodiment. Second side view for explaining the operation of the penumbra cutter of the first embodiment Diagram for explaining the flow of processing of the first embodiment Side view for supplementary explanation of S805 and S806 in FIG. The perspective view for demonstrating the outline of the penumbra cutter of 2nd embodiment. Side view for explaining the operation of the penumbra cutter of the second embodiment Second side view for explaining the operation of the penumbra cutter of the second embodiment Diagram for explaining the flow of processing of the second embodiment Side view for supplementary explanation of S1305 in FIG. Side view for explaining the operation of the penumbra cutter of the third embodiment Side view for explaining the operation of the penumbra cutter of the fourth embodiment Second side view for explaining the operation of the penumbra cutter of the fourth embodiment

  Hereinafter, preferred embodiments of an X-ray CT apparatus according to the present invention will be described with reference to the accompanying drawings. In addition, in the following description and the accompanying drawings, components having the same functional configuration will be denoted by the same reference numerals, and redundant description will be omitted.

[First embodiment]
The outline of the X-ray CT apparatus according to the present embodiment will be described with reference to FIG. As shown in FIG. 1, the X-ray CT apparatus 1 includes a scan gantry unit 100 and an operation unit 120.

  The scan gantry unit 100 includes an X-ray tube device 101, a rotating disk 102, a collimator device 103, an X-ray detector 106, a data acquisition device 107, a bed device 105, a gantry control device 108, and a bed control device. 109, an X-ray controller 110, and a collimator controller 111.

  The X-ray tube device 101 is an X-ray source that generates X-rays. The collimator device 103 is a device that limits an area where a subject placed on the bed device 105 is irradiated with X-rays from the X-ray tube device 101. Details of the operation of the collimator device 103 will be described later.

  The rotating disk 102 is provided with an opening 104 into which the subject placed on the bed device 105 enters, the X-ray tube device 101, the collimator device 103, and the X-ray detector 106 are mounted, and the X-ray tube device 101 and The collimator device 103 and the X-ray detector 106 are rotated around the subject. The X-ray detector 106 is a device that is arranged to face the X-ray tube device 101 and the collimator device 103, and measures the spatial distribution of the transmitted X-rays by detecting the X-rays that have passed through the subject. The elements are arranged two-dimensionally in the rotation direction of the rotating disk 102 and the rotation axis direction.

  The data collection device 107 is a device that collects the X-ray dose detected by the X-ray detector 106 as digital data. The gantry control device 108 is a device that controls the rotation and tilt of the rotating disk 102. The bed control device 109 is a device for controlling the up / down, front / rear, left / right movement of the bed device 105. Note that the up, down, front, back, left, and right directions are the directions shown in FIG. 1, and are also referred to as the Y direction, Z direction, and X direction in the following description.

  The X-ray controller 110 is a device that controls the electric power input to the X-ray tube device 101. The collimator control device 111 is a device that controls the collimator device 103 according to the process of scanning. Details of the collimator control device 111 will be described later together with the operation of the collimator device 103.

  The operation unit 120 includes an input device 121, an image processing device 122, a display device 125, a storage device 123, and a system control device 124.

  The input device 121 is a device for inputting the name of a subject, examination date and time, scan conditions, and the like, and is specifically a keyboard, a pointing device, a touch panel, or the like. The image processing device 122 is a device that performs arithmetic processing on the measurement data sent from the data collection device 107 to reconstruct a CT image.

  The display device 125 is a device that displays a CT image or the like created by the image processing device 122, and is specifically a CRT (Cathode-Ray Tube), a liquid crystal display, or the like. The storage device 123 is a device that stores data collected by the data collection device 107, image data of a CT image created by the image processing device 122, and the like, and is specifically a HDD (Hard Disk Drive) or the like. The system control device 124 is a device that controls these devices and the gantry control device 108, the bed control device 109, the X-ray control device 110, and the collimator control device 111. Further, the system control device 124 may execute the processing flow described later.

  The X-ray tube device 101 is controlled by controlling the electric power input to the X-ray tube device 101 by the X-ray control device 110 based on the scan conditions input from the input device 121, particularly the X-ray tube voltage and the X-ray tube current. Irradiates the subject with X-rays according to the scanning conditions. The X-ray detector 106 detects the X-rays emitted from the X-ray tube device 101 and transmitted through the subject with a large number of X-ray detection elements, and measures the distribution of the transmitted X-rays. The rotating disk 102 is controlled by the gantry control device 108, and rotates based on the scan conditions input from the input device 121, particularly the rotation speed and the like. The couch device 105 is controlled by the couch controller 109, and operates based on the scan conditions input from the input device 121, particularly the spiral pitch and the like.

  The projection data from various angles is acquired by repeating the X-ray irradiation from the X-ray tube device 101 and the measurement of the transmitted X-ray distribution by the X-ray detector 106 as the rotating disk 102 rotates. The projection data is associated with a view that represents each angle, a channel number that is a detection element number of the X-ray detector 106, and a column number. The acquired projection data from various angles is transmitted to the image processing device 122. The image processing device 122 reconstructs a CT image by subjecting the transmitted projection data from various angles to back projection processing. The CT image obtained by the reconstruction is displayed on the display device 125.

  An example of a dynamic collimator which is a part of the collimator device 103 will be described with reference to FIGS. 2 and 3. Dynamic collimators reduce unnecessary exposure doses at the beginning and end of spiral scans. FIG. 2 is a perspective view of an example of the dynamic collimator. The dynamic collimator shown in FIG. 2 includes a movable slit plate 201 and a flat plate pair 202. Hereinafter, each unit will be described.

  The movable slit plate 201 is a metal plate having a sufficient thickness to shield the X-rays emitted from the focal point 200, and a slit for transmitting the X-rays is provided at the center of the metal plate. The size of the slit is set according to the size of the X-ray detector 106. That is, the area irradiated with the X-rays that have reached the X-ray detector 106 through the slit is orthogonal to the Z-direction width and the Z-direction of the slit so that the area is larger than the size of the X-ray detector 106. The direction length is set. The movable slit plate 201 is arranged so that the center of the slit is aligned with the focal center line 203 in the initial state, and moves in the Z direction according to the progress of the scan during the spiral scan. Here, the focus center line 203 is a line connecting the center of the focus and the center of the X-ray detector 106.

  The flat plate pair 202 is a pair of metal flat plates 202A having a thickness sufficient to shield X-rays, and each flat plate 202A moves in the Z direction symmetrically with respect to the focal center line 203. That is, when one flat plate 202A moves in the positive Z direction by a predetermined distance, the other flat plate 202A moves in the negative Z direction by the same distance. The distance between the flat plates 202A is set according to the so-called slice width in the scan conditions, and is kept constant during the spiral scan.

  FIG. 3 is a side view showing the operation of the dynamic collimator of FIG. 2, and the progress of the spiral scan is shown in FIGS. 3 (a) to 3 (c). In FIG. 3, reference numeral 300 is the reconstruction range, and reference numeral 301 is the rotation center of the rotating disk 102. That is, the X-rays irradiated to the outside of the reconstruction range 300 bring unnecessary exposure to the subject. Therefore, in the dynamic collimator, by moving the movable slit plate 201 to the position as shown in FIG. 3 (a) at the start of the spiral scan and FIG. It blocks X-rays emitted to the outside of the constituent range 300. In addition, in FIG. 3A and FIG. 3C, the shielded region is shown by hatching. 3 (a) and FIG. 3 (b), and also between FIG. 3 (b) and FIG. 3 (c), by moving the movable slit plate 201 to an appropriate position, the outside of the reconstruction range 300. Reduce the X-rays that are emitted to the.

  By the way, the actual focal point 200 has a finite size as shown in FIG. 4 instead of the point shown in FIG. Therefore, a penumbra is formed in the hatched area in FIG. 4, that is, in the vicinity of the outside of the area irradiated with X-rays, which causes unnecessary exposure to the subject. Therefore, in this embodiment, a penumbra cutter that shields penumbra is combined with a dynamic collimator to reduce the exposure dose at the start and end of the spiral scan and also reduce the exposure due to penumbra.

  The penumbra cutter 501 of this embodiment will be described with reference to FIG. The penumbra cutter 501 is a metal plate having a thickness sufficient to shield X-rays, which is arranged on the X-ray detector 106 side after the movable slit plate 201 and the flat plate pair 202 which are dynamic collimators. The metal plate is provided with a slit 501A for transmitting X-rays. The width of the slit 501A in the Z direction is the distance from the focus 200 to the surface of the penumbra cutter 501 on the X-ray detector 106 side, the width of the slit of the movable slit plate 201 in the Z direction, and the focus 200 of the movable slit plate 201. It is set according to the distance to the surface on the X-ray detector 106 side. The penumbra cutter 501 is arranged so that the center of the slit 501A is aligned with the focal center line 203 in the initial state, and moves in the Z direction according to the progress of the scan during the spiral scan.

  The penumbra cutter 501 is supported at both ends by two guide rails 503. The guide rail 503 is fixed to the rotating disk 102 so that the longitudinal direction is along the Z direction. Furthermore, since the penumbra cutter 501 is connected to the motor 502 via a rack and pinion or the like, it can be moved in the Z direction by the driving force of the motor 502. An operation instruction is transmitted from the collimator control device 111 to the motor 502.

  The operation of the penumbra cutter 501 will be described with reference to FIG. FIG. 6 shows the case where the slice width is the maximum, and the progress of the spiral scan is shown in FIGS. 6 (a) to 6 (c). The progress statuses of FIGS. 6 (a) to 6 (c) correspond to those of FIGS. 3 (a) to 3 (b). In FIG. 6 (a), which is the start time of the spiral scan, the penumbra cutter 501 is moved as shown in FIG. 6 to block the penumbra irradiated to the outside of the reconstruction range 300. Further, also between FIG. 6 (a) and FIG. 6 (c), the penumbra irradiating the outside of the reconstruction range 300 is shielded by moving the penumbra cutter 501 to an appropriate position.

  Next, the operation of the penumbra cutter 501 when the slice width is narrower than the maximum will be described with reference to FIG. The progress of the spiral scan is shown in FIGS. 7 (a) to 7 (c), which also correspond to FIGS. 3 (a) to 3 (b). In FIG. 7 (a), which is the start time of the spiral scan, the penumbra irradiating the outside of the reconstruction area 300 is shielded by moving the penumbra cutter 501 as shown in FIG. Further, also between FIGS. 7A and 7C, by moving the penumbra cutter 501 to an appropriate position, the penumbra irradiated to the outside of the reconstruction range 300 is reduced.

  An example of the flow of processing executed by the X-ray CT apparatus 1 including the above components will be described with reference to FIG.

  (S801) The system control device 124 acquires the scan condition, extracts the slice width from the scan condition, and transmits the slice width to the collimator control device 111.

  (S802) The collimator control device 111 sets the distance 2Wc between the flat plates 202A according to the transmitted slice width. Note that Wc is the distance from the focal center line 203 to the end of the flat plate 202A in the Z direction, as shown in FIG.

  (S803) When the scan is ready, the system controller 124 starts the spiral scan. At the start and immediately after the spiral scan and at the end and immediately before the spiral scan, the movable slit plate 201 moves in the Z direction as described with reference to FIG.

  (S804) The collimator control device 111 determines whether or not the movable slit plate 201 is at the initial position, and proceeds to S805 if it is not the initial position and proceeds to S806 if it is the initial position. The initial position of the movable slit plate 201 is the position where the center of the slit of the movable slit plate 201 is aligned with the focal center line 203.

  (S805) The collimator control device 111 sets the position of the penumbra cutter 501 according to the position of the movable slit plate 201. The position of the penumbra cutter 501 is calculated by the equation (1) based on the positional relationship of each part as shown in FIG.

ここで、Wbは焦点中心線203から半影カッター501のスリット501AのZ方向の端部までの距離、Lbは焦点200から半影カッター501のX線検出器106側の面までの距離、Laは焦点200から可動スリット板201のX線検出器106側の面までの距離、Waは焦点中心線203から可動スリット板201のスリットのZ方向の端部までの距離、Dは焦点中心線203から焦点200のZ方向の端部までの幅である。

Here, Wb is the distance from the focus center line 203 to the Z-direction end of the slit 501A of the penumbra cutter 501, Lb is the distance from the focus 200 to the surface of the penumbra cutter 501 on the X-ray detector 106 side, La Is the distance from the focal point 200 to the surface of the movable slit plate 201 on the X-ray detector 106 side, Wa is the distance from the focal center line 203 to the end of the slit of the movable slit plate 201 in the Z direction, and D is the focal center line 203. To the end of the focal point 200 in the Z direction.

  Since Lb, La, and D are constants during the spiral scan, the position of the penumbra cutter 501 is set according to the position of the movable slit plate 201. Since it is not preferable that the X-ray irradiating the reconstruction area 300 is shielded by the penumbra cutter 501, a margin Δ may be added to the right side of the equation (1). The margin δ is preferably a positive number and close to zero.

  (S806) The collimator control device 111 sets the position of the penumbra cutter 501 according to the position of the flat plate pair 202. The position of the penumbra cutter 501 is calculated by the equation (2) based on the positional relationship of each part as shown in FIG.

ここで、Wbは焦点中心線203から半影カッター501のスリット501AのZ方向の端部までの距離、Lbは焦点200から半影カッター501のX線検出器106側の面までの距離、Lcは焦点200から平板対202のX線検出器106側の面までの距離、Wcは焦点中心線203から平板対202のZ方向の端部までの距離、Dは焦点中心線203から焦点200のZ方向の端部までの幅である。

Here, Wb is the distance from the focus center line 203 to the Z-direction end of the slit 501A of the penumbra cutter 501, Lb is the distance from the focus 200 to the surface of the penumbra cutter 501 on the X-ray detector 106 side, Lc Is the distance from the focus 200 to the plane of the flat plate pair 202 on the X-ray detector 106 side, Wc is the distance from the focus center line 203 to the end of the flat plate pair 202 in the Z direction, and D is the focus center line 203 to the focus 200. It is the width to the end in the Z direction.

  Since Lb, La, and D are constant during the spiral scan, the position of the penumbra cutter 501 is set according to the position of the flat plate pair 202. A margin δ may be added to the right side of Expression (2), and the margin δ is preferably a positive number and is close to zero.

  (S807) The system control device 124 determines whether or not the scan is completed, and if it is not completed, the process is returned to S804, and if it is completed, the series of processes is completed.

  When the X-ray CT apparatus 1 executes the above processing flow, it is possible to reduce the exposure dose at the start and end of the spiral scan and also reduce the exposure dose due to the penumbra. Further, since the penumbra cutter 501 of the present embodiment can be controlled by one motor 502, it can be configured with a relatively simple mechanism.

  The dynamic collimator described with reference to FIGS. 2 to 9 has the movable slit plate 201, the flat plate pair 202, and the penumbra cutter 501 arranged in this order from the X-ray focus 200 side. The pair of flat plates 202, the movable slit plate 201, and the penumbra cutter 501 may be arranged in this order from the side.

  Further, the penumbra cutter 501 described with reference to FIGS. 2 to 9 has a single slit, but the X-ray CT apparatus 1 has a number of slits corresponding to the number of slice widths that can be set, and each slit May be set according to each slice width. By using the slit according to the slice width, the penumbra can be further reduced.

  Further, the width of the slit of the penumbra cutter 501 may be set based on the equation (3).

ここで、Sbは半影カッター501のスリット501AのZ方向の幅、Lbは焦点200から半影カッター501のX線検出器106側の面までの距離、Laは焦点200から可動スリット板201のX線検出器106側の面までの距離、Saは可動スリット板201のスリットのZ方向の幅である。なお、式(3)の右辺にマージンδを加えても良く、マージンδは正数であってゼロに近いことが好ましい。

Here, Sb is the width in the Z direction of the slit 501A of the penumbra cutter 501, Lb is the distance from the focus 200 to the surface of the penumbra cutter 501 on the X-ray detector 106 side, and La is the focus 200 to the movable slit plate 201. The distance to the surface on the X-ray detector 106 side, Sa, is the width of the slit of the movable slit plate 201 in the Z direction. A margin δ may be added to the right side of Expression (3), and the margin δ is preferably a positive number and is close to zero.

[Second embodiment]
Next, a second embodiment will be described. In the first embodiment, the penumbra cutter for the dynamic collimator having the movable slit plate 201 and the flat plate pair 202 has been described. In this embodiment, a penumbra cutter for a dynamic collimator having two individually movable shield plates will be described. Hereinafter, the difference between the present embodiment and the first embodiment will be described in detail, and the description of the same configuration as the first embodiment will be omitted.

  Main parts of the present embodiment will be described with reference to the perspective view shown in FIG. The dynamic collimator of this embodiment includes two individually movable shield plates 1000-1 and 1000-2. The penumbra cutter also includes two individually movable shields 1001-1 and 1001-2. Each of the shielding plates 1000-1, 1000-2, 1001-1, 1001-2 is a metal plate having a sufficient thickness to shield X-rays. Further, each shielding plate 1000-1, 1000-2, 1001-1, 1001-2 is individually connected to a drive source such as a motor for moving in the Z direction, and according to an instruction from the collimator control device 111. , Move individually in the Z direction.

  The operation of the shielding plates 1001-1 and 1001-2 of the penumbra cutter 501 will be described with reference to FIG. FIG. 11 shows the case where the slice width is the maximum, and the progress of the spiral scan is shown in FIGS. 11 (a) to 11 (c). The progress statuses of FIGS. 11 (a) to 11 (c) correspond to those of FIGS. 3 (a) to 3 (b). At the start of the spiral scan in FIG. 11 (a), by moving the shield plates 1001-1 and 1001-2 of the penumbra cutter as shown in the figure, the shield plate 1000-1 of the dynamic collimator, Block the penumbra caused by 1000-2. Further, also between FIG. 11 (a) and FIG. 11 (c), the penumbra is shielded by moving the shielding plates 1001-1 and 1001-2 of the penumbra cutter to appropriate positions.

  Next, the operation of the shielding plates 1001-1 and 1001-2 of the penumbra cutter when the slice width is narrower than the maximum will be described with reference to FIG. The progress of the spiral scan is shown in FIGS. 12 (a) to 12 (c), which also correspond to FIGS. 3 (a) to 3 (b). In FIG. 12 (a), which is the start of the spiral scan, the penumbra is shielded by moving the shielding plates 1001-1 and 1001-2 of the penumbra cutter as shown in FIG. In addition, also between FIG. 12 (a) and FIG. 12 (c), the penumbra is shielded by moving the shielding plates 1001-1 and 1001-2 of the penumbra cutter to appropriate positions.

  An example of the flow of processing executed by the X-ray CT apparatus 1 including the above components will be described with reference to FIG.

  (S801) Same as in the first embodiment.

  (S1303) When the scan is ready, the system controller 124 starts the spiral scan. During the spiral scan, the shield plates 1000-1 and 1000-2 of the dynamic collimator move in the Z direction according to the relative positional relationship between the focus 200 and the reconstruction range 300, and the exposure dose to the reconstruction range 300 is changed. Reduce.

  (S1305) The collimator control device 111 sets the positions of the shielding plates 1001-1 and 1001-2 of the penumbra cutter according to the positions of the shielding plates 1000-1 and 1000-2 of the dynamic collimator. The position of the penumbra cutter is calculated by the formula (4) based on the positional relationship of each part as shown in FIG.

ここで、Wbnは焦点中心線203から半影カッターの遮蔽板1001-1、1001-2のZ方向の端部までの距離、nは1又は2であっていずれかの遮蔽板を示す添え字、Lbは焦点200から半影カッターの遮蔽板1001-1、1001-2のX線検出器106側の面までの距離、Laは焦点200から動的コリメータの遮蔽板1000-1、1000-2のX線検出器106側の面までの距離、Wanは焦点中心線203から動的コリメータの遮蔽板1000-1、1000-2のZ方向の端部までの距離、Dは焦点中心線203から焦点200のZ方向の端部までの幅である。

Here, Wbn is the distance from the focus center line 203 to the Z direction end of the shielding plates 1001-1 and 1001-2 of the penumbra cutter, n is 1 or 2 and is a subscript indicating one of the shielding plates. , Lb is the distance from the focus 200 to the shield plates 1001-1 and 1001-2 of the penumbra cutter on the X-ray detector 106 side, and La is the focus 200 to the shield plates 1000-1 and 1000-2 of the dynamic collimator. To the surface of the X-ray detector 106 side, Wan is the distance from the focus center line 203 to the Z direction end of the shield plates 1000-1 and 1000-2 of the dynamic collimator, and D is from the focus center line 203. It is the width to the end of the focal point 200 in the Z direction.

  Since Lb, La, and D are constant during the spiral scan, the position of the penumbra cutter is set according to the positions of the shield plates 1000-1 and 1000-2 of the dynamic collimator. Since it is not preferable that the X-rays irradiated on the reconstruction area 300 be shielded by the shielding plates 1001-1 and 1001-2 of the penumbra cutter, a margin δ may be added to the right side of the formula (4). . The margin δ is preferably a positive number and close to zero, as in the first embodiment.

  (S807) The system control device 124 determines whether or not the scan is completed, and if it is not completed, the process is returned to S804, and if it is completed, the series of processes is completed.

  When the X-ray CT apparatus 1 executes the above processing flow, it is possible to reduce the exposure dose at the start and end of the spiral scan and to shield the exposure by the penumbra. Further, as compared with the first embodiment, even when the slice width is narrow, it is possible to further reduce the exposure due to the penumbra.

[Third embodiment]
Next, a third embodiment will be described. In the second embodiment, it has been described that the individually movable penumbra cutter moves in the Z direction. In this embodiment, the individually movable penumbra cutters move in parallel with the focal center line 203 orthogonal to the Z direction. Hereinafter, differences between the present embodiment and the second embodiment will be described in detail, and description of the same configuration as the second embodiment will be omitted.

  Main parts of the present embodiment will be described with reference to FIG. It should be noted that FIG. 15 shows only the shield plate 1000-2 side for simplification of the drawing. The difference from the second embodiment is the arrangement and operation direction of the shielding plate of the penumbra cutter. As shown in FIG. 15, the longitudinal direction of the shielding plate 1501-2 is arranged parallel to the focal center line 203. The operating direction of the shielding plate 1501-2 is also parallel to the focal center line 203.

  The process flow executed by the X-ray CT apparatus 1 is the same as that of FIG. 13 except for S1305, and is substantially the same as that of the second embodiment. Here, only S1305 of this embodiment will be described.

  (S1305) The collimator control device 111 sets the positions of the shielding plates 1501-1 and 1501-2 of the penumbra cutter in accordance with the positions of the shielding plates 1000-1 and 1000-2 of the dynamic collimator. The position of the penumbra cutter is calculated by the equation (5) based on the positional relationship of each part as shown in FIG.

ここで、Lbnは焦点200から半影カッターの遮蔽板1501-1、1501-2のX線検出器106側の面までの距離、nは1又は2であっていずれかの遮蔽板を示す添え字、Wbは焦点中心線203から半影カッターの遮蔽板1501-1、1501-2のZ方向の端部までの距離、Dは焦点中心線203から焦点200のZ方向の端部までの幅、Wanは焦点中心線203から動的コリメータの遮蔽板1000-1、1000-2のZ方向の端部までの距離、Laは焦点200から動的コリメータの遮蔽板1000-1、1000-2のX線検出器106側の面までの距離である。

Here, Lbn is the distance from the focus 200 to the surface of the shielding plates 1501-1 and 1501-2 of the penumbra cutter on the side of the X-ray detector 106, and n is 1 or 2 and is attached to indicate either shielding plate. W, Wb is the distance from the focus center line 203 to the Z-direction end of the shielding plates 1501-1 and 1501-2 of the penumbra cutter, and D is the width from the focus center line 203 to the Z-direction end of the focus 200. , Wan is the distance from the focus center line 203 to the ends of the dynamic collimator shields 1000-1 and 1000-2 in the Z direction, and La is the focus 200 to the dynamic collimator shields 1000-1 and 1000-2. It is the distance to the surface on the X-ray detector 106 side.

  Since Wb, D, and La are constants during the spiral scan, the position of the penumbra cutter is set according to the positions of the shield plates 1000-1 and 1000-2 of the dynamic collimator. Since it is not preferable that the X-rays irradiated on the reconstruction area 300 are shielded by the shielding plates 1501-1 and 1501-2 of the penumbra cutter, a margin δ may be added to the right side of the equation (5). . The margin δ is preferably a positive number and close to zero, as in the first embodiment.

  According to the present embodiment, it is possible to reduce the exposure dose at the start and end of the spiral scan and to shield the exposure by the penumbra. Further, as compared with the second embodiment, since the longitudinal direction of the shielding plates 1501-1, 1501-2 of the penumbra cutter are arranged in the centrifugal force direction of the rotating disc 102, the rotating disc 102 rotates at a higher speed. Moreover, the rigidity of the shielding plates 1501-1 and 1501-2 is ensured, which is an advantageous structure.

[Fourth Embodiment]
Next, a fourth embodiment will be described. In the second embodiment, it has been described that the individually movable penumbra cutter moves in the Z direction. In the present embodiment, the individually movable penumbra cutters rotate around the hinge portion provided on the surface of the shield plate of the dynamic collimator on the X-ray detector 106 side. Hereinafter, differences between the present embodiment and the second embodiment will be described in detail, and description of the same configuration as the second embodiment will be omitted.

  The main part of this embodiment will be described with reference to FIG. Note that FIG. 16 shows only the shield plate 1000-2 side for the sake of simplicity. The difference from the second embodiment is the arrangement and operation direction of the shielding plate of the penumbra cutter. As shown in FIG. 16, the shielding plate 1601-2 of the penumbra cutter is connected to the surface of the shielding plate 1000-2 of the dynamic collimator on the X-ray detector 106 side via a hinge portion 1601-2A.

  The process flow executed by the X-ray CT apparatus 1 is the same as that of FIG. 13 except for S1305, and is substantially the same as that of the second embodiment. Here, only S1305 of this embodiment will be described.

  (S1305) The remeter controller 111 sets the positions of the shielding plates 1601-1 and 1601-2 of the penumbra cutter according to the positions of the shielding plates 1000-1 and 1000-2 of the dynamic collimator. The position of the penumbra cutter is calculated by the equation (6) based on the positional relationship of each part as shown in FIG.

Wanは焦点中心線203から動的コリメータの遮蔽板1000-1、1000-2のZ方向の端部までの距離、nは1又は2であっていずれかの遮蔽板を示す添え字、Dは焦点中心線203から焦点200のZ方向の端部までの幅、Laは焦点200から動的コリメータの遮蔽板1000-1、1000-2のX線検出器106側の面までの距離、θnは動的コリメータの遮蔽板1000-1、1000-2と半影カッターの遮蔽板1600-1、1600-2とのなす角、Raはヒンジ部1601-1A、1601-2Aから動的コリメータの遮蔽板1000-1、1000-2のZ方向の端部までの距離、Rbはヒンジ部1601-1A、1601-2Aから半影カッターの遮蔽板1600-1、1600-2の端部までの距離である。

Wan is the distance from the focus center line 203 to the ends in the Z direction of the shield plates 1000-1 and 1000-2 of the dynamic collimator, n is 1 or 2 and is a subscript indicating either shield plate, and D is The width from the focus center line 203 to the end of the focus 200 in the Z direction, La is the distance from the focus 200 to the surface of the shield plates 1000-1 and 1000-2 of the dynamic collimator on the X-ray detector 106 side, and θn is The angle between the shield plates 1000-1, 1000-2 of the dynamic collimator and the shield plates 1600-1, 1600-2 of the penumbra cutter, Ra is the hinge plate 1601-1A, 1601-2A from the shield plate of the dynamic collimator. Distance to the Z direction end of 1000-1, 1000-2, Rb is the distance from the hinge 1601-1A, 1601-2A to the end of the shielding plate 1600-1, 1600-2 of the penumbra cutter .

  Since La, D, Ra, and Rb are constants, the angle θn of the penumbra cutter is set so as to satisfy equation (6) according to Wan corresponding to the positions of the shield plates 1000-1 and 1000-2 of the dynamic collimator. Is set.

  According to the present embodiment, it is possible to reduce the exposure dose at the start and end of the spiral scan and to shield the exposure by the penumbra.

  Further, as shown in FIG. 17, just below the focal point 200, it is possible to completely shield the X-rays by rotating them so that the shielding plates 1601-1 and 1601-2 of the penumbra cutter overlap each other. It will be possible. Even if the distance between the shield plate 1000-1 and the shield plate 1000-2 of the dynamic collimator is set to zero, a gap occurs because the two shield plates 1000-1 and 1000-2 are in surface contact, X-rays sometimes leaked. On the other hand, according to the present embodiment, it is possible to completely shield X-rays.

  Although the four embodiments have been described above, the X-ray CT apparatus 1 of the present invention is not limited to the above embodiments, and constituent elements can be modified and embodied without departing from the scope of the invention. Moreover, you may combine suitably the some component disclosed in the said embodiment. For example, the dynamic collimator described in the first embodiment may be combined with the penumbra cutter described in the second to fourth embodiments. Further, some constituent elements may be deleted from all the constituent elements shown in the above embodiment.

  1 X-ray CT device, 100 scan gantry unit, 101 X-ray tube device, 102 rotating disk, 103 collimator device, 104 opening, 105 bed, 106 X-ray detector, 107 data acquisition device, 108 gantry control device, 109 bed Control device, 110 X-ray control device, 111 collimator control device, 120 console, 121 input device, 122 image processing device, 123 storage device, 124 system control device, 125 display device, 200 focus, 201 movable slit plate, 202 flat plate Pair, 300 reconstruction range, 301 rotation center, 501 penumbra cutter, 501A slit part, 502 motor, 503 guide rail, 1000-1, 1000-2 shielding plate (dynamic collimator), 1001-1, 1001-2 shielding Plate (half shadow cutter), 1501-1, 1501-2 Shield plate (half shadow cutter), 1601-1, 1601-2 Shield plate (half shadow cutter), 1601-1A, 1601-2A Hinge part

Claims (6)

An X-ray source that generates X-rays, a collimator device that controls a region where the X-rays are irradiated to the subject, a X-ray source that is arranged to face the X-ray source and the collimator device, and that transmits X-rays that pass through the subject. An X-ray CT apparatus comprising an X-ray detector for detecting, the X-ray source and the collimator device, and a rotating disk for rotating the X-ray detector around the subject,
The collimator device includes a dynamic collimator that controls a region irradiated with the X-ray according to a position of a focal point of the X-ray with respect to a reconstruction range at the time of spiral scanning, and the X-ray detector rather than the dynamic collimator. A penumbra cutter disposed on the side to reduce the penumbra generated in the dynamic collimator by operating in conjunction with the movement of the dynamic collimator ,
The dynamic collimator includes a first slit plate having a slit of a predetermined width that moves in the body axis direction of the subject, and a flat plate pair that is a pair of flat plates, each of the flat plates being the center of the focal point. And symmetrically with respect to the center line of the focal point connecting the center of the X-ray detector and the body axis direction of the subject,
The penumbra cutter is a second slit plate having a slit having a predetermined width that moves in the body axis direction of the subject, and shields penumbra outside the reconstruction range,
The position of the second slit plate is the distance from the center line of the focus to the end of the slit of the second slit plate, Wb, and the surface from the focus to the X-ray detector side of the second slit plate. To Lb, the distance from the focus to the surface of the first slit plate on the X-ray detector side is La, and the distance from the focus center line to the end of the slit of the first slit plate. Wa, where D is the distance from the focus center line to the end of the focus,

An X-ray CT apparatus characterized by being set based on An X-ray source that generates X-rays, a collimator device that controls a region where the X-rays are irradiated to the subject, a X-ray source that is arranged to face the X-ray source and the collimator device, and that transmits X-rays that pass through the subject. An X-ray CT apparatus comprising an X-ray detector for detecting, the X-ray source and the collimator device, and a rotating disk for rotating the X-ray detector around the subject,
The collimator device includes a dynamic collimator that controls a region irradiated with the X-ray according to a position of a focal point of the X-ray with respect to a reconstruction range at the time of spiral scanning, and the X-ray detector rather than the dynamic collimator. A penumbra cutter disposed on the side to reduce the penumbra generated in the dynamic collimator by operating in conjunction with the movement of the dynamic collimator ,
The dynamic collimator has a first shield plate and a second shield plate that are individually movable,
The penumbra cutter has a third shield plate and a fourth shield plate that are individually movable, the third shield plate moves in accordance with the movement of the first shield plate, and the fourth shield plate moves. The shielding plate moves according to the movement of the second shielding plate,
The third shielding plate and the fourth shielding plate move in the body axis direction of the subject,
The positions of the third shield plate and the fourth shield plate are set to the third shield plate or the fourth shield plate from the focus center line connecting the center of the focus and the center of the X-ray detector. The distance to the end is Wbn, the distance from the focus to the surface of the third shield plate or the fourth shield plate on the X-ray detector side is Lb, and the distance from the focus to the first shield plate or the La is the distance from the X-ray detector side surface of the second shield plate, Wan is the distance from the focus center line to the end of the first shield plate or the second shield plate, and the focus center When the distance from the line to the end of the focal point is D, the following equation

An X-ray CT apparatus characterized by being set based on An X-ray source that generates X-rays, a collimator device that controls a region where the X-rays are irradiated to the subject, a X-ray source that is arranged to face the X-ray source and the collimator device, and that transmits X-rays that pass through the subject. An X-ray CT apparatus comprising an X-ray detector for detecting, the X-ray source and the collimator device, and a rotating disk for rotating the X-ray detector around the subject,
The collimator device includes a dynamic collimator that controls a region irradiated with the X-ray according to a position of a focal point of the X-ray with respect to a reconstruction range at the time of spiral scanning, and the X-ray detector rather than the dynamic collimator. A penumbra cutter disposed on the side to reduce the penumbra generated in the dynamic collimator by operating in conjunction with the movement of the dynamic collimator ,
The dynamic collimator has a first shield plate and a second shield plate that are individually movable,
The penumbra cutter has a third shield plate and a fourth shield plate that are individually movable, the third shield plate moves in accordance with the movement of the first shield plate, and the fourth shield plate moves. The shielding plate moves according to the movement of the second shielding plate,
The X-ray CT apparatus, wherein the third shield plate and the fourth shield plate move in parallel with a focus center line connecting the center of the focus and the center of the X-ray detector. An X-ray source that generates X-rays, a collimator device that controls a region where the X-rays are irradiated to the subject, a X-ray source that is arranged to face the X-ray source and the collimator device, and that transmits X-rays that pass through the subject. An X-ray CT apparatus comprising an X-ray detector for detecting, the X-ray source and the collimator device, and a rotating disk for rotating the X-ray detector around the subject,
The collimator device includes a dynamic collimator that controls a region irradiated with the X-ray according to a position of a focal point of the X-ray with respect to a reconstruction range at the time of spiral scanning, and the X-ray detector rather than the dynamic collimator. A penumbra cutter disposed on the side to reduce the penumbra generated in the dynamic collimator by operating in conjunction with the movement of the dynamic collimator ,
The dynamic collimator has a first shield plate and a second shield plate that are individually movable,
The penumbra cutter has a third shield plate and a fourth shield plate that are individually movable, the third shield plate moves in accordance with the movement of the first shield plate, and the fourth shield plate moves. The shielding plate moves according to the movement of the second shielding plate,
The third shield plate and the fourth shield plate are connected via a hinge portion provided on a surface of the first shield plate or the second shield plate on the X-ray detector side, respectively. An X-ray CT apparatus characterized in that the X-ray CT apparatus rotates about the hinge portion. The X-ray CT apparatus according to claim 3 ,
The positions of the third shielding plate and the fourth shielding plate are set such that the distance from the focus to the surface of the third shielding plate or the fourth shielding plate on the X-ray detector side is Lbn, and the focus is The distance from the center line to the end of the third shield plate or the fourth shield plate is Wb, the distance from the focus center line to the end of the focus is D, and the focus center line is to the first end. The distance to the end of the shield plate or the second shield plate was Wan, and the distance from the focus to the surface of the first shield plate or the second shield plate on the X-ray detector side was La. Where

An X-ray CT apparatus characterized by being set based on The X-ray CT apparatus according to claim 4 ,
The positions of the third shielding plate and the fourth shielding plate are located on the first shielding plate or the second shielding plate from the focus center line connecting the center of the focus and the center of the X-ray detector. The distance to the end is Wan, the distance from the focus center line to the end of the focus is D, and the focus is to the surface of the first shield plate or the second shield plate on the X-ray detector side. Is La, the angle formed by the first shielding plate and the third shielding plate or the angle formed by the second shielding plate and the fourth shielding plate is θn, and The distance from the provided hinge portion to the first shield plate or the distance from the hinge portion provided to the second shield plate to the second shield plate is Ra, the third shield plate, or When the length of the fourth shielding plate is Rb,

An X-ray CT apparatus characterized by being set based on

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