X-ray CT device, x-ray adjustment device, x-ray adjustment method, and x-ray adjustment program

Abstract

To dynamically adjust a dose of an X-ray detected by an X-ray detector.SOLUTION: An X-ray CT device according to an embodiment includes an X-ray tube, a wedge, a rotor, and a rotor control part. The wedge includes an annular part that attenuates an X-ray emitted from the X-ray tube. An attenuation rate of the X-ray changes according to a circumferential position of the annular part. The rotor rotates the wedge. The rotor control part controls rotation of the rotor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray CT (Computed Tomography) apparatus, an X-ray adjustment apparatus, an X-ray adjustment method, and an X-ray adjustment program. [Background technology]

[0002] In the X-ray CT device, for example, a dose attenuator is provided that attenuates the X-ray dose so as to correspond to a predetermined X-ray conversion efficiency in the X-ray detector. The dose attenuator is configured such that, for example, a support part that supports a plurality of wedge filters slides in a certain direction by the rotation of a shaft. This allows a selected wedge filter to be placed in the X-ray irradiation area by the rotation of the shaft. However, in a configuration in which a plurality of wedge filters are slid in a certain direction by rotating a shaft, it takes a certain amount of time to change the wedge filters placed in the X-ray irradiation area. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-183857 A Summary of the Invention [Problem to be solved by the invention]

[0004] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to dynamically adjust the dose of X-rays detected by an X-ray detector. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in each embodiment described later can also be positioned as other problems. [Means for solving the problem]

[0005] The X-ray CT apparatus according to the embodiment includes an X-ray tube, a wedge, a rotor, and a rotor controller. The wedge includes an annular portion that attenuates X-rays irradiated from the X-ray tube, and the attenuation rate of the X-rays changes depending on the circumferential position. The rotor rotates the wedge. The rotor controller controls the rotation of the rotor. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an X-ray CT apparatus 1 according to the first embodiment. [Diagram 2] FIG. 2 is a top view and a cross-sectional view of the annular portion of the wedge according to the first embodiment. [Diagram 3] FIG. 3 is a top view and a cross-sectional view of the annular portion of the wedge according to the first embodiment. [Figure 4] FIG. 4 is a schematic diagram showing the relationship between the rotational position of the rotating frame and the rotational position of the annular portion of the wedge according to the first embodiment. [Diagram 5] FIG. 5 is a cross-sectional view of a circular portion of a wedge according to a second embodiment. [Figure 6] FIG. 6 is a view of the annular portion of the wedge according to the second embodiment as viewed from the filter side. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, embodiments of an X-ray CT apparatus, an X-ray adjustment apparatus, an X-ray adjustment method, and an X-ray adjustment program will be described in detail with reference to the drawings.

[0008] The X-ray CT apparatus according to the embodiment may be provided with any one of an energy-integrating detector unit, a photon-counting detector unit, and a hybrid detector unit that combines both of them. Hereinafter, a case where the X-ray CT apparatus is provided with a photon-counting detector unit U will be described, but the present invention is not limited to this case.

[0009] In addition, there are various data collection methods using the X-ray CT apparatus according to the embodiment, such as a Rotation / Rotation (RR) method in which the X-ray source and the X-ray detector rotate around the subject as a single unit, and a Stationary / Rotation (SR) method in which a large number of detection elements are arrayed in a ring shape and only the X-ray tube rotates around the subject. The present invention can be applied to any of these methods. Below, the X-ray CT apparatus according to the embodiment will be described taking as an example a case in which the currently mainstream third-generation rotation / rotation method is adopted.

[0010] [First embodiment] 1 is a schematic diagram showing the configuration of an X-ray CT apparatus 1 according to the first embodiment. The X-ray CT apparatus 1 includes a gantry device 10, a bed device 30, and a medical image processing device, that is, a console device 40. The gantry device 10 acquires X-ray detection data (also called "pure raw data") relating to a subject (e.g., a patient) P placed on the bed device 30. The console device 40 generates raw data by performing pre-processing on the detection data for multiple views, and reconstructs and displays CT image data by performing reconstruction processing on the raw data.

[0011] In FIG. 1, for convenience of explanation, a plurality of gantry devices 10 are drawn above and below on the left side, but in the actual configuration, there is only one gantry device 10.

[0012] The gantry device 10 includes an X-ray tube 11, an X-ray detector 12, a DAS 13, a rotating frame 14, an X-ray high voltage device 15, a control device 16, a wedge 17, a collimator 18, and a rotor 19.

[0013] In the embodiment, the rotation axis of the rotating frame 14 in a non-tilted state or the longitudinal direction of the tabletop 33 of the bed device 30 is defined as the z-axis direction, the axis direction perpendicular to the z-axis direction and horizontal to the floor surface is defined as the x-axis direction, and the axis direction perpendicular to the z-axis direction and perpendicular to the floor surface is defined as the y-axis direction. Also, the "column direction" described later coincides with the z-axis direction.

[0014] The X-ray tube 11 is provided on a rotating frame 14. The X-ray tube 11 is a vacuum tube that generates X-rays by irradiating thermoelectrons from a cathode (filament) to an anode (target) when a high voltage is applied from an X-ray high voltage device 15. For example, the X-ray tube 11 may be a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons.

[0015] The X-ray detector 12 and the DAS 13 configure a photon counting type detector unit U. The detector unit U is provided on a rotating frame 14. The X-ray detector 12 of the detector unit U is provided in the detector unit U so as to face the X-ray tube 11. The X-ray detector 12 has, for example, an X-ray detection element row in which a plurality of X-ray detection elements are arranged in the channel direction along one arc with the focus of the X-ray tube 11 as the center.

[0016] The DAS 13a is composed of an ASIC (Application Specific Integrated Circuit) and is a readout circuit that counts the X-ray photons detected by the X-ray detection elements. The ASIC counts the number of X-ray photons incident on the X-ray detection elements (hereinafter referred to as the count number) by discriminating the individual charges output by the X-ray detection elements. The ASIC also measures the energy of the counted X-ray photons by performing arithmetic processing based on the magnitude of each charge. The measurement result is transferred to the control device 16.

[0017] The rotating frame 14 supports the X-ray tube 11 and the X-ray detector 12 of the detector unit U so that they face each other. The rotating frame 14 is an annular frame that rotates the X-ray tube 11 and the detector unit U as a unit under the control of a control device 16, which will be described later. Note that the rotating frame 14 may also be equipped with and support an X-ray high voltage device 15 in addition to the X-ray tube 11 and the detector unit U.

[0018] In this way, the X-ray CT device 1 collects multiple views, i.e., detection data for 360° of the patient P, by rotating the rotating frame 14, which supports the X-ray tube 11 and the X-ray detector 12 of the detector unit U in opposing relation, around the patient P. Note that the reconstruction method of the CT image data is not limited to the full scan reconstruction method that uses detection data for 360°. For example, the X-ray CT device 1 may employ a half reconstruction method that reconstructs CT image data based on detection data for half a circumference (180°) plus the fan angle.

[0019] The X-ray high voltage device 15 is provided on the rotating frame 14 or a non-rotating part (for example, a fixed frame not shown) that rotatably supports the rotating frame 14. The X-ray high voltage device 15 has electric circuits such as a transformer and a rectifier. The X-ray high voltage device 15 has a high voltage generator (not shown) that generates a high voltage to be applied to the X-ray tube 11 under the control of the control device 16 described later, and an X-ray control device (not shown) that controls an output voltage according to the X-rays irradiated by the X-ray tube 11 under the control of the control device 16 described later. The high voltage generator may be of a transformer type or an inverter type. In FIG. 1, for convenience of explanation, the X-ray high voltage device 15 is disposed in a position in the positive direction of the x-axis with respect to the X-ray tube 11, but may be disposed in a position in the negative direction of the x-axis with respect to the X-ray tube 11.

[0020] The control device 16 has a processing circuit 161, a memory 162, and a drive mechanism 163 such as a motor and an actuator. The configurations of the processing circuit 161 and the memory 162 are the same as those of the processing circuit 44 and the memory 41 of the console device 40 described later, and therefore a description thereof will be omitted.

[0021] The control device 16 has a function of controlling the operation of the gantry device 10 and the bed device 30 upon receiving an input signal from an input interface 43 (described later) attached to the console device 40 or an input interface (not shown) attached to the gantry device 10. For example, the control device 16 receives an input signal and controls the rotation of the rotating frame 14, the tilt of the gantry device 10, and the operation of the bed device 30 and the tabletop 33. The control of tilting the gantry device 10 is realized by the control device 16 rotating the rotating frame 14 around an axis parallel to the X-axis direction based on inclination angle (tilt angle) information inputted by an input interface attached to the gantry device 10. The control device 16 may be provided in the gantry device 10 or in the console device 40.

[0022] In addition, the control device 16 controls the rotation angle of the X-ray tube 11 and the operation of the wedge 17 and collimator 18, which will be described later, based on imaging conditions input from an input interface 43, which will be described later and is attached to the console device 40, or an input interface (not shown) attached to the gantry device 10.

[0023] 1, the processing circuit 161 realizes a rotor control function F1 by executing a computer program stored in a non-transitory recording medium such as memory 162 or a memory within the processing circuit 161. The rotor control function F1 includes a function of controlling the rotation of the rotor 19.

[0024] The wedge 17 is provided on the rotating frame 14 so as to be disposed on the X-ray emission side of the X-ray tube 11. The wedge 17 is a filter for adjusting the amount of X-rays irradiated from the X-ray tube 11 under the control of the control device 16. Specifically, the wedge 17 includes an annular portion 171 (shown in FIG. 4 and FIG. 5) that transmits and attenuates the X-rays irradiated from the X-ray tube 11 so that the X-rays irradiated from the X-ray tube 11 to the patient P have a predetermined distribution. As shown as an example of annular portions 171a to 171d in FIG. 2 and FIG. 3, the attenuation rate of the X-rays of the wedge 17 changes depending on the position in the circumferential direction of the annular portion 171. For example, the wedge 17 (wedge filter) or bow-tie filter is a filter made by processing aluminum so as to have a predetermined target angle and a predetermined thickness. Details of FIG. 2 to FIG. 5 will be described later.

[0025] Returning to the explanation of Fig. 1, the collimator 18 is also called an X-ray aperture or a slit, and is provided on the rotating frame 14 so as to be disposed on the X-ray emission side of the X-ray tube 11. The collimator 18 is a lead plate or the like for narrowing down the irradiation range of the X-rays transmitted through the wedge 17 under the control of the control device 16, and forms an X-ray irradiation aperture by combining a plurality of lead plates or the like.

[0026] The rotor 19 rotates about a rotation axis (shaft) to rotate the wedge 17. The rotor 19 is held by a rotating frame .

[0027] The bed device 30 includes a base 31, a bed driving device 32, a top board 33, and a support frame 34. The bed device 30 is a device on which a patient P to be scanned is placed and which moves the patient P under the control of the control device 16.

[0028] The base 31 is a housing that supports the support frame 34 so as to be movable in the vertical direction (y-axis direction). The bed driving device 32 is a motor or actuator that moves the top board 33, on which the patient P is placed, in the longitudinal direction (z-axis direction) of the top board 33. The top board 33 provided on the upper surface of the support frame 34 is a plate having a shape on which the patient P can be placed.

[0029] The bed driving device 32 may move the support frame 34 in the longitudinal direction (z-axis direction) of the tabletop 33 in addition to the tabletop 33. The bed driving device 32 may also move the base 31 of the bed device 30 together.

[0030] The console device 40 includes a memory 41, a display 42, an input interface 43, and a processing circuit 44. Although the console device 40 will be described as being separate from the gantry device 10, the gantry device 10 may include the console device 40 or some of the components of the console device 40. In the following description, the console device 40 is a single console that executes all functions, but these functions may be executed by multiple consoles. The console device 40 is an example of a medical image processing device.

[0031] The memory 41 is configured, for example, by a semiconductor memory element such as a random access memory (RAM) or a flash memory, a hard disk, an optical disk, or the like. The memory 41 may be configured by a portable medium such as a universal serial bus (USB) memory or a digital video disk (DVD). The memory 41 stores various processing programs (including application programs and an operating system (OS) and the like) used in the processing circuit 44, and data required for executing the programs. The OS may also include a graphical user interface (GUI) that makes extensive use of graphics to display information to the operator on the display 42 and enables basic operations to be performed by the input interface 43.

[0032] The memory 41 stores, for example, detection data before preprocessing, raw data after preprocessing and before reconstruction, and CT image data after reconstruction based on the raw data. The preprocessing means at least one of logarithmic conversion processing, offset correction processing, sensitivity correction processing between channels, beam hardening processing, etc. for the detection data. In addition, a cloud server connectable to the X-ray CT device 1 via a communication network such as the Internet may be configured to receive a storage request from the X-ray CT device 1 and store the detection data, raw data, or CT image data.

[0033] The display 42 displays various types of information. For example, the display 42 outputs CT image data generated by the processing circuitry 44, a GUI for receiving various operations from an operator, and the like. For example, the display 42 is a liquid crystal display, a CRT (Cathode Ray Tube) display, an OLED (Organic Light Emitting Diode) display, or the like. The display 42 may be provided on the gantry device 10. The display 42 may be a desktop type, or may be configured as a tablet terminal or the like capable of wireless communication with the console device 40 main body.

[0034] The input interface 43 includes an input device that can be operated by an operator such as an engineer, and an input circuit that inputs a signal from the input device. The input device is realized by a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad that performs an input operation by touching the operation surface, a touch screen in which a display screen and a touchpad are integrated, a non-contact input circuit using an optical sensor, a voice input circuit, or the like. When the input device receives an input operation from an operator, the input circuit generates an electric signal according to the input operation and outputs it to the processing circuit 44. The input interface 43 may be provided in the gantry device 10. The input interface 43 may be configured by a tablet terminal or the like that can wirelessly communicate with the console device 40 main body. The input interface 43 is an example of an input unit.

[0035] The console device 40 may also include a network interface (not shown). The network interface is configured with a connector conforming to a parallel connection specification or a serial connection specification. When the X-ray CT device 1 is provided on a medical imaging system, the network interface transmits and receives information to and from an external device on the network. For example, under the control of the processing circuit 44, the network interface receives an examination order for a CT examination from an external device, and transmits detection data acquired by the X-ray CT device 1 and generated raw data or CT image data to the external device.

[0036] The processing circuit 44 controls the overall operation of the X-ray CT apparatus 1. The processing circuit 44 means a dedicated or general-purpose CPU (Central Processing Unit), MPU (Micro Processor Unit), or GPU (Graphics Processing Unit), as well as an ASIC, a programmable logic device, etc. Examples of the programmable logic device include a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA).

[0037] The processing circuit 44 may be formed by a single circuit, or may be formed by a combination of multiple independent processing circuit elements. In the latter case, the memory 41 may be provided for each processing circuit element, or a single memory 41 may store programs corresponding to the functions of the multiple processing circuit elements.

[0038] 2 and 3 are a top view and a cross-sectional view showing the shape of the annular portion 171 of the wedge 17 according to the first embodiment. The cross-sectional view shows a cross section perpendicular to the circumferential direction of the annular portion 171.

[0039] 2A shows an annular portion 171a which is a first example of the annular portion 171 shown in FIG. 4 and FIG. 5. As shown in FIG. 2A, a cross section perpendicular to the circumferential direction of the annular portion 171a has a concave shape, and the width of the bottom side of the concave changes continuously depending on the position in the circumferential direction. Also, a cross section perpendicular to the circumferential direction of the annular portion 171a has a concave shape, and the inclination angle of both oblique sides of the concave changes continuously depending on the position in the circumferential direction. The difference between the width of the bottom side and the inclination angle (i.e., the X-ray absorption rate) is determined in advance depending on the shape of the cross section of the patient P.

[0040] On the right side of the cross-sectional view of FIG. 2(A), the width of the base of the recess is relatively large, and the inclination angle of both oblique sides is relatively large. On the other hand, on the left side of the cross-sectional view of FIG. 2(A), the width of the base of the recess is relatively small, and the inclination angle of both oblique sides is relatively small. In the top view of FIG. 2(A), the width of the base of the recess and the inclination angle of both oblique sides are maximum at the position where the minute hand of the clock indicates 3 o'clock. As moving away from that position in either the clockwise or counterclockwise direction, the width and the inclination angle gradually become smaller. Then, at the position where the minute hand of the clock indicates 9 o'clock, the width of the base of the recess and the inclination angle of both oblique sides are minimum.

[0041] Therefore, the position of the annular portion 171a where the minute hand of the clock indicates 3 o'clock has a small attenuation rate of X-rays passing through the annular portion 171a, and is therefore suitable for the rotation position of the rotating frame 14 where X-rays pass in the left-right direction of the patient P (the direction passing through the thick parts of the patient P). On the other hand, the position of the annular portion 171a where the minute hand of the clock indicates 9 o'clock has a large attenuation rate of X-rays passing through the annular portion 171a, and is therefore suitable for the rotation position of the rotating frame 14 where X-rays pass in the front-back direction of the patient P (the direction passing through the thin parts of the patient P). For example, when X-ray irradiation from the X-ray tube 11 on the rotating frame 14 starts from the front of the patient P, the front-back direction of the patient P, the left-right direction of the patient P, the front-back direction of the patient P, and the left-right direction of the patient P appear regularly in this order during one rotation of the rotating frame 14. Therefore, the rotor control function F1 aligns the position of the annular portion 171a where the X-ray attenuation rate is large with the rotational position of the rotating frame 14 corresponding to the direction in which the X-rays pass through the thin parts of the patient P, and controls the rotor 19 so that the annular portion 171a synchronizes with the rotating frame 14 by rotating the annular portion 171a twice for every rotation of the rotating frame 14 (i.e., doubling the rotational speed).

[0042] The difference in the attenuation rate of the X-rays is determined in advance according to the shape of the cross section of the patient P.

[0043] Fig. 2(B) shows an annular portion 171b which is a second example of the annular portion 171 shown in Fig. 4 and Fig. 5. As shown in Fig. 2(B), a cross section perpendicular to the circumferential direction of the annular portion 171b has a shape in which the thickness changes continuously depending on the position in the circumferential direction. On the other hand, unlike the annular portion 171a, the annular portion 171b does not have a recess.

[0044] On the right side of the cross-sectional view in FIG. 2(B), the cross-sectional thickness is relatively small. On the other hand, on the left side of the cross-sectional view in FIG. 2(A), the cross-sectional thickness is relatively large. In the top view of FIG. 2(A), the cross-sectional thickness is smallest at the position where the minute hand of the clock indicates 3 o'clock. The thickness gradually increases as one moves away from that position in either a clockwise or counterclockwise direction. Then, the cross-sectional thickness is greatest at the position where the minute hand of the clock indicates 9 o'clock.

[0045] Therefore, the position of the annular portion 171b where the minute hand of the clock indicates 3 o'clock has a small attenuation rate of X-rays passing through the annular portion 171b, and is therefore suitable for the rotation position of the rotating frame 14 where X-rays pass in the left-right direction of the patient P (the direction passing through the thick parts of the patient P). On the other hand, the position of the annular portion 171b where the minute hand of the clock indicates 9 o'clock has a large attenuation rate of X-rays passing through the annular portion 171b, and is therefore suitable for the rotation position of the rotating frame 14 where X-rays pass in the front-back direction of the patient P (the direction passing through the thin parts of the patient P). For example, when X-ray irradiation from the X-ray tube 11 on the rotating frame 14 starts from the front of the patient P, the front-back direction of the patient P, the left-right direction of the patient P, the front-back direction of the patient P, and the left-right direction of the patient P appear regularly in this order during one rotation of the rotating frame 14. Therefore, the rotor control function F1 aligns the position of the annular portion 171b where the X-ray attenuation rate is large with the rotational position of the rotating frame 14 corresponding to the direction in which the X-ray passes through the thin part of the patient P, and controls the rotor 19 so that the annular portion 171b synchronizes with the rotating frame 14 by rotating the annular portion 171b twice for each rotation of the rotating frame 14 (i.e., doubling the rotation speed).

[0046] FIG. 3(A) shows a circular ring portion 171c which is a third example of the circular ring portion 171 shown in FIG. 4 and FIG. 5. As shown in FIG. 3(A), the cross section of the circular ring portion 171c perpendicular to the circumferential direction is a concave shape in which the width of the bottom side of the recess changes continuously depending on the position in the circumferential direction. Also, the cross section of the circular ring portion 171c perpendicular to the circumferential direction is a concave shape in which the inclination angle of both oblique sides of the recess changes continuously depending on the position in the circumferential direction. On the other hand, the circular ring portion 171c is different from the circular ring portion 171a in that the position where the width of the bottom side of the recess and the inclination angle of both oblique sides are maximum appears twice, and the position where the width of the bottom side of the recess and the inclination angle of both oblique sides are minimum appears twice in one revolution of the circular ring portion 171a.

[0047] In the cross-sectional view of Fig. 3(A), the width of the base of the recess is relatively large on both the right and left sides, and the inclination angle of both oblique sides is relatively large. In the top view of Fig. 3(A), the width of the base of the recess and the inclination angle of both oblique sides are maximum at the positions where the minute hand of the clock indicates 3 o'clock and 9 o'clock. As one moves away from that position in either the clockwise or counterclockwise direction, the width and the inclination angle gradually become smaller. Then, at the positions where the minute hand of the clock indicates 0 o'clock and 6 o'clock, the width of the base of the recess and the inclination angle of both oblique sides are minimum.

[0048] Therefore, the positions of the annular portion 171c where the minute hand of the clock indicates 3 o'clock and 9 o'clock have a small attenuation rate of X-rays passing through the annular portion 171c, and are therefore suitable for rotation positions of the rotating frame 14 where X-rays pass in the left-right direction of the patient P (the direction passing through the thick parts of the patient P). On the other hand, the positions of the annular portion 171c where the minute hand of the clock indicates 0 o'clock and 6 o'clock have a large attenuation rate of X-rays passing through the annular portion 171c, and are therefore suitable for rotation positions of the rotating frame 14 where X-rays pass in the front-back direction of the patient P (the direction passing through the thin parts of the patient P). For example, when X-ray irradiation from the X-ray tube 11 on the rotating frame 14 starts from the front of the patient P, the front-back direction of the patient P, the left-right direction of the patient P, the front-back direction of the patient P, and the left-right direction of the patient P appear regularly in this order during one rotation of the rotating frame 14. Therefore, the rotor control function F1 aligns the position of the annular portion 171c where the X-ray attenuation rate is large with the rotational position of the rotating frame 14 corresponding to the direction in which the X-rays pass through the thin parts of the patient P, and controls the rotor 19 so that the annular portion 171c synchronizes with the rotating frame 14 by rotating the annular portion 171c once with one rotation of the rotating frame 14 (i.e., making the rotation speed the same).

[0049] FIG. 3B shows a fourth example of the annular portion 171 shown in FIG. 4 and FIG. 5, a circular portion 171d. As shown in FIG. 3B, a cross section perpendicular to the circumferential direction of the circular portion 171d has a concave shape, and the width of the bottom side of the recess changes intermittently depending on the position in the circumferential direction. Also, a cross section perpendicular to the circumferential direction of the circular portion 171d has a concave shape, and the inclination angle of both oblique sides of the recess changes intermittently depending on the position in the circumferential direction. On the other hand, unlike the circular portion 171a, the width of the bottom side of the recess and the inclination angle of both oblique sides of the circular portion 171d change intermittently, not continuously, over one revolution of the circular portion 171a.

[0050] On the right side of the cross-sectional view of FIG. 3(B), the width of the base of the recess is relatively large, and the inclination angle of both oblique sides is relatively large. On the other hand, on the left side of the cross-sectional view of FIG. 3(B), the width of the base of the recess and the inclination angle of both oblique sides are relatively small. In the top view of FIG. 3(B), the width of the base of the recess and the inclination angle of both oblique sides are maximum at the position where the minute hand of the clock indicates 3 o'clock. As moving away from that position in the clockwise or counterclockwise direction, the width and the inclination angle become smaller in stages. Then, at the position where the minute hand of the clock indicates 9 o'clock, the width of the base of the recess and the inclination angle of both oblique sides become minimum. Note that the number of the widths and the inclination angles does not have to be four as shown in FIG. 3(B) and is not limited.

[0051] Therefore, the position of the annular portion 171d where the minute hand of the clock indicates 3 o'clock has a small attenuation rate of X-rays passing through the annular portion 171d, and is therefore suitable for the rotation position of the rotating frame 14 where the X-rays pass in the left-right direction of the patient P (the direction passing through the thick parts of the patient P). On the other hand, the position of the annular portion 171d where the minute hand of the clock indicates 9 o'clock has a large attenuation rate of X-rays passing through the annular portion 171d, and is therefore suitable for the rotation position of the rotating frame 14 where the X-rays pass in the front-back direction of the patient P (the direction passing through the thin parts of the patient P). For example, when X-ray irradiation from the X-ray tube 11 on the rotating frame 14 starts from the front of the patient P, the front-back direction of the patient P, the left-right direction of the patient P, the front-back direction of the patient P, and the left-right direction of the patient P appear regularly in this order during one rotation of the rotating frame 14. Therefore, the rotor control function F1 aligns the position of the annular portion 171d where the attenuation rate of the X-rays is large with the rotational position of the rotating frame 14 corresponding to the direction in which the X-rays pass through the thin parts of the patient P, and controls the rotor 19 so that the annular portion 171d synchronizes with the rotating frame 14 by rotating the annular portion 171d twice for each rotation of the rotating frame 14 (i.e., doubling the rotational speed).

[0052] In addition, with respect to the wedge 17 in FIG. 2(A), FIG. 2(B), and FIG. 3(A), the shape of the cross section perpendicular to the circumferential direction of the annular portion 171 changes continuously depending on the position in the circumferential direction. On the other hand, with respect to the wedge 17 in FIG. 3(B), the shape of the cross section perpendicular to the circumferential direction of the annular portion 171 changes intermittently depending on the position in the circumferential direction. In addition, the technical ideas described in FIG. 2(A), FIG. 2(B), FIG. 3(A), and FIG. 3(B) can be arbitrarily combined. For example, the annular portions 171b and 171c in FIG. 2(B) and FIG. 3(C) may have a shape that intermittently changes the attenuation rate of X-rays, or the annular portion 171b in FIG. 2(B) may have a configuration that rotates once per one rotation of the rotating frame.

[0053] 4 is a schematic diagram showing the relationship between the rotational position of the rotating frame 14 according to the first embodiment and the rotational position of the annular portion 171 of the wedge 17. The rotor control function F1 synchronizes the rotation (e.g., rotational position and rotational speed) of the annular portion 171 with the rotation of the rotating frame 14. The rotation axis RA of the annular portion 171 is set approximately parallel to the central path CP of the X-rays irradiated from the X-ray tube 11. The central path CP refers to a straight line passing through the apex of the cone and the center of the circle that is the base of the cone when the X-rays irradiated from the X-ray tube 11 are conical. Furthermore, approximately parallel includes not only parallel but also an error in the installation of the annular portion 171.

[0054] 4(A), when the X-ray tube 11 is at a position where the minute hand of a clock on the rotating frame 14 indicates 0 o'clock, that is, when X-rays are irradiated from the front of the patient P in a direction in which the patient's body thickness is thin, the X-rays are transmitted through a thicker part of the annular portion 171 of the wedge 17 in order to reduce the X-ray dose received by the patient P. In other words, the rotor control function F1 controls the rotation of the rotor 19 in accordance with the rotation of the rotating frame 14 so that the X-rays irradiated from the X-ray tube 11 pass through a part of the annular portion 171 where the attenuation rate of the X-rays is large, and then transmit through a thinner part of the patient P.

[0055] 4(B), when the X-ray tube 11 is at the position where the minute hand of the clock on the rotating frame 14 indicates 9 o'clock, that is, when X-rays are irradiated from the side of the patient P in the direction of the thicker body thickness, the X-rays are transmitted through the thinner part of the annular part 171 of the wedge 17 in order to increase the X-ray dose received by the patient P. In other words, the rotor control function F1 controls the rotation of the rotor 19 in accordance with the rotation of the rotating frame 14 so that the X-rays irradiated from the X-ray tube 11 pass through a part of the annular part 171 where the attenuation rate of the X-rays is small, and then transmit through the thicker part of the patient P.

[0056] The above-described control of the rotor control function F1 shown in FIG. 4 makes it possible to make the dose of X-rays hitting the X-ray detector 12 uniform regardless of the rotational position of the rotating frame 14 (i.e., the X-ray irradiation angle and the cross-sectional shape of the patient P).

[0057] 2A, 171b, and 171d in FIG. 3B are synchronized with a half rotation of the rotating frame 14. On the other hand, one rotation of the circular portion 171c in FIG. 3A is synchronized with one rotation of the rotating frame 14.

[0058] This allows high-speed rotation synchronization between the rotating frame 14 and the annular portion 171 of the wedge 17. Therefore, the dose of X-rays can be smoothly adjusted according to the direction of the patient P to which the X-rays are irradiated. The material of the annular portion 171 may change according to its circumferential position. In this case, the attenuation rate of the X-rays changes because the material of the annular portion 171 changes.

[0059] Then, the contour of the patient P may be photographed as a scano image or the like, and an appropriate wedge 17 may be selected from a plurality of wedges having different differences in attenuation rates (for example, in FIG. 2(A), a plurality of wedges having different differences in base width and inclination angle) according to the shape of the contour. Note that a scano image refers to an image obtained by a pre-scan (also called a scout scan, etc.) for determining the conditions of the main scan prior to the main scan for a diagnostic CT image. Alternatively, the external appearance of the patient P may be photographed by an optical camera, and the wedge 17 may be selected according to the external shape. Furthermore, the user may select the wedge 17 by looking at the shape of the patient P.

[0060] Also, an X-ray adjustment device may be configured that includes the wedge 17, the rotor 19, and the rotor control function F1.

[0061] [Effects of the first embodiment] The annular portion 171 of the wedge 17 can be made relatively easily since it is made by simply cutting a groove out of a disk-shaped material. The rotation axis of the annular portion 171 is set approximately parallel to the central path of the X-rays emitted from the X-ray tube 11, so it is less susceptible to the centrifugal force of the rotating frame 14 and is less likely to shake. This stabilizes the X-rays, preventing damage to the X-ray detector 12.

[0062] Since the thickness etc. of the annular portion 171 changes continuously according to the rotation angle of the rotating frame 14, it is possible to make the tube current modulation for adjusting the X-ray dose gentler or to eliminate the need for tube current modulation. Furthermore, the annular portion 171 can be used not only in a manner synchronized with the rotation of the rotating frame 14, but also in a manner that rotates and fixes it at a specific position according to conditions, like an existing wedge.

[0063] Second Embodiment Fig. 5 is a cross-sectional view of a wedge 17 according to the second embodiment. As shown in Fig. 5, the wedge 17 includes an annular portion 171 and a filter 172 attached to the bottom surface of the annular portion 171. The filter 172 further attenuates the X-rays that are irradiated from the X-ray tube 11 and pass through the annular portion 171.

[0064] 6 is a view of the annular portion 171 of the wedge 17 according to the second embodiment, viewed from the filter 172 side. In other words, FIG. 6 shows a combination of an example of the arrangement of the filter 172 attached to the bottom surface of the annular portion 171 and an example of the shape of the annular portion 171 corresponding to the arrangement. As shown in FIG. 6, the filter 172 changes the attenuation rate of X-rays depending on the circumferential area of ​​the annular portion 171 (i.e., the range of angles around the rotation axis of the annular portion 171). The filter 172 can adjust the attenuation rate of X-rays in each area of ​​the filter 172 by changing the material and thickness of the area.

[0065] FIG. 6A is a diagram showing the annular portion 171e and the filter 172a. As shown in FIG. 6A, the attenuation rate of X-rays in the filter 172a changes intermittently for each 1 / 2 circumference region. In addition, in the 1 / 2 circumference region, the width of the bottom side of the recess of the annular portion 171e changes continuously from large to small to large to small to large, that is, the attenuation rate of X-rays in the annular portion 171e changes continuously from small to large to small to large to small. In each region in which the attenuation rate of X-rays in the filter 172a does not change, the attenuation rate of X-rays in the annular portion 171e changes continuously from small to large to small to small to small. Therefore, a 1 / 2 rotation of each region of the filter 172a corresponds to one rotation of the rotating frame 14.

[0066] FIG. 6B is a diagram showing the annular portion 171f and the filter 172b. As shown in FIG. 6B, the attenuation rate of the X-rays in the filter 172b changes intermittently between a 1 / 3 region and a 2 / 3 region. Therefore, 1 / 3 rotation and 2 / 3 rotation of each region of the filter 172b correspond to one rotation of the rotating frame 14. FIG. 6C is a diagram showing the annular portion 171g and the filter 172c. As shown in FIG. 6C, the attenuation rate of the X-rays in the filter 172c changes intermittently between a 1 / 4 region, another 1 / 4 region, and a 1 / 2 region. Therefore, 1 / 4 rotation, 1 / 4 rotation, and 1 / 2 rotation of each region of the filter 172c correspond to one rotation of the rotating frame 14. This allows the attenuation rate of the X-rays passing through the filter 172 to be changed at high speed in accordance with the rotation of the rotating frame 14. Furthermore, by providing a filter 172 having multiple regions with different X-ray attenuation rates in one wedge 17, it is possible to use one wedge 17 to accommodate multiple types of patients P (e.g., adults, children, etc.) for whom it is desirable to change the X-ray attenuation rate.

[0067] Fig. 6(D) is a diagram showing the annular portion 171h and the filter 172d. As shown in Fig. 6(D), the attenuation rate of X-rays does not change over the entire area of ​​the filter 172d. Therefore, one rotation of the area of ​​the filter 172d corresponds to one rotation of the rotating frame 14. In this case, by changing the attenuation rate of X-rays for each filter 172d, for example, the wedge 17 equipped with the filter 172d for adults (with a small attenuation rate) and the wedge 17 equipped with the filter 172d for children (with a large attenuation rate) can be used separately.

[0068] According to at least one of the embodiments described above, the dose of X-rays detected by the X-ray detector can be dynamically adjusted.

[0069] The rotor control function F1 is an example of a rotor control unit.

[0070] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0071] 1...X-ray CT device 11...X-ray tube 14...Rotating frame 17…Wedge 19…Rotor 171…Ring section 172…Filter P…Patient F1…Rotor control function CP: Center Path RA…Rotation axis

Claims

1. An X-ray tube; a wedge including an annular portion for attenuating X-rays emitted from the X-ray tube, the attenuation rate of the X-rays varying depending on a position in a circumferential direction of the wedge; a rotor for rotating the wedges; A rotor control unit that controls the rotation of the rotor; Equipped with X-ray CT device.

2. The rotation axis of the annular portion is set substantially parallel to the central path of the X-ray. The X-ray CT apparatus according to claim 1 .

3. A cross section of the annular portion perpendicular to the circumferential direction has a concave shape, and the width of the bottom of the concave changes depending on the position in the circumferential direction. The X-ray CT apparatus according to claim 1 .

4. A cross section of the annular portion perpendicular to the circumferential direction has a concave shape, and the inclination angle of both oblique sides of the concave changes depending on the position in the circumferential direction. The X-ray CT apparatus according to claim 1 .

5. A cross section perpendicular to the circumferential direction of the annular portion has a shape in which the thickness changes depending on the position in the circumferential direction. The X-ray CT apparatus according to claim 1 .

6. The shape of the cross section perpendicular to the circumferential direction of the annular portion changes continuously depending on the position in the circumferential direction.

6. The X-ray CT apparatus according to claim 3.

7. The material of the annular portion changes depending on the position in the circumferential direction. The X-ray CT apparatus according to claim 1 .

8. a filter for attenuating the X-rays is attached to a bottom surface of the annular portion, the filter having an attenuation rate of the X-rays that changes depending on a circumferential area of ​​the annular portion; 8. The X-ray CT apparatus according to claim 3, 4, 5, or 7.

9. a rotating frame that holds the X-ray tube, the wedge, and the rotor; The rotor control unit includes: controlling rotation of the rotor in accordance with rotation of the rotating frame so that the X-rays pass through a portion of the annular portion where an attenuation rate of the X-rays is small and then pass through a thick portion of the subject; controlling rotation of the rotor in accordance with rotation of the rotating frame so that the X-rays pass through a portion of the annular portion where an attenuation rate of the X-rays is large and then pass through a thin portion of the subject; The X-ray CT apparatus according to claim 1 .

10. a wedge having an annular portion for attenuating X-rays emitted from an X-ray tube, the attenuation rate of the X-rays varying depending on the position in the circumferential direction; a rotor for rotating the wedges; A rotor control unit that controls the rotation of the rotor; An X-ray adjustment device comprising:

11. The rotor control unit includes: controlling rotation of the rotor in accordance with rotation of an X-ray tube, the wedge, and a rotating frame that holds the rotor so that the X-rays pass through a portion of the annular portion where an attenuation rate of the X-rays is small and then pass through a thick portion of the subject; controlling rotation of the rotor in accordance with rotation of the rotating frame so that the X-rays pass through a portion of the annular portion where an attenuation rate of the X-rays is large and then pass through a thin portion of the subject; The X-ray adjustment device according to claim 10.

12. 1. An X-ray adjustment method using a wedge that includes an annular portion for attenuating X-rays emitted from an X-ray tube, the wedge changing an attenuation rate of the X-rays depending on a position in a circumferential direction of the annular portion, the method comprising: controlling a rotation of the annular portion such that the X-rays pass through a portion of the annular portion where an attenuation rate of the X-rays is small and then pass through a thick portion of the subject; controlling a rotation of the annular portion such that the X-rays pass through a portion of the annular portion where an attenuation rate of the X-rays is large and then pass through a thin portion of the subject; X-ray adjustment method.

13. An X-ray adjustment program for adjusting the X-rays using a wedge that has a circular ring portion for attenuating the X-rays emitted from an X-ray tube and whose attenuation rate varies depending on a position in a circumferential direction, the program comprising: On the computer, controlling a rotation of the annular portion such that the X-rays pass through a portion of the annular portion where an attenuation rate of the X-rays is small and then pass through a thick portion of the subject; realizing a function of controlling the rotation of the annular portion so that the X-ray passes through a portion of the annular portion where the attenuation rate of the X-ray is large and then passes through a thin portion of the subject; X-ray adjustment program.

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