JP2022011724A - X-ray ct apparatus - Google Patents

Abstract

To reduce scattered rays.SOLUTION: An X-ray CT apparatus includes an X-ray tube, an X-ray detector and a first shield part. The X-ray tube radiates an X-ray. The X-ray detector detects the X-ray. The first shield part is disposed between the X-ray tube and the X-ray detector so as to block an X-ray radiated to a range other than an irradiation range with an X-ray that is directly incident upon the X-ray detector from the X-ray tube.SELECTED DRAWING: Figure 2A

Description

The embodiments disclosed in the specification and the like relate to an X-ray CT apparatus.

The X-rays emitted from the X-ray tube are incident on the detector as well as the surrounding members. X-rays incident on peripheral members cause scattered radiation incident from the side or rear of the detector. Since scattered rays adversely affect the image quality of CT images, high-performance X-ray CT equipment such as X-ray CT (Computed Tomography) equipment or spectral CT equipment (including photon counting CT equipment) that can collect high-definition medical images , Especially a problem.
In order to remove scattered rays, generally, a slit is provided in front of and in the vicinity of the X-ray tube to remove the incident of X-rays on the peripheral member.

However, for example, when the focal point moves in irradiation with X-rays, the positional relationship between the focal point and the detector changes, so that the irradiation range may shift. Therefore, the slit installed in the vicinity of the X-ray tube needs to be installed with a margin to secure a wide X-ray irradiation range so that the detection surface of the detector is included in the X-ray irradiation range. Therefore, even when the focus is adjusted so that the X-rays transmitted through the subject are incident on the entire surface of the detector, the X-rays are applied to a region wider than the region of the sensor surface of the detector due to the influence of the margin. Is incident, so scattered rays from peripheral parts other than the detector cannot be removed.

Japanese Unexamined Patent Publication No. 2006-38975

One of the problems to be solved by the embodiment disclosed in the specification and the like is to reduce the scattered radiation. However, the problems to be solved by the embodiments disclosed in the present specification and the drawings are not limited to the above problems. The problem corresponding to each effect by each configuration shown in the embodiment described later can be positioned as another problem.

The X-ray CT apparatus according to the present embodiment includes an X-ray tube, an X-ray detector, and a first shielding unit. The X-ray tube irradiates X-rays. The X-ray detector detects the X-ray. The first shielding unit includes the X-ray tube and the X-ray detector so as to shield the X-rays emitted from the X-ray tube to a range other than the irradiation range of the X-rays directly incident on the X-ray detector. Placed in between.

FIG. 1 is a block diagram showing an X-ray CT apparatus according to the present embodiment. FIG. 2A is a diagram showing an example of a rotating portion according to the first embodiment. FIG. 2B is a diagram showing an example of a rotating portion according to the first embodiment. FIG. 3 is a diagram showing an arrangement relationship between the shield portion and the X-ray detector according to the first embodiment. FIG. 4 is a diagram showing the arrangement relationship between the shield portion and the X-ray detector according to the second embodiment. FIG. 5A is a diagram showing an example of a rotating portion according to the third embodiment. FIG. 5B is a diagram showing an example of a rotating portion according to the third embodiment.

Hereinafter, the X-ray CT (Computed Tomography) apparatus according to the present embodiment will be described with reference to the drawings. In the following embodiments, the parts with the same reference numerals perform the same operation, and duplicate description will be omitted as appropriate. Hereinafter, one embodiment will be described with reference to the drawings.

(First Embodiment)
Hereinafter, the X-ray CT apparatus according to this embodiment will be described with reference to the block diagram of FIG. The X-ray CT device 1 shown in FIG. 1 includes a gantry device 10, a sleeper device 30, and a console device 40. In FIG. 1, for convenience of explanation, a plurality of gantry devices 10 are drawn.

In the present embodiment, the rotation axis of the rotation frame 13 in the non-tilt state or the longitudinal direction of the top plate 33 of the sleeper device 30 is orthogonal to the Z-axis direction and the Z-axis direction, and is horizontal to the floor surface. Is orthogonal to the X-axis direction and the Z-axis direction, and the axial direction perpendicular to the floor surface is defined as the Y-axis direction, respectively.

For example, the gantry device 10 and the sleeper device 30 are installed in the CT examination room, and the console device 40 is installed in the control room adjacent to the CT examination room. The console device 40 does not necessarily have to be installed in the control room. For example, the console device 40 may be installed in the same room together with the gantry device 10 and the bed device 30. In any case, the gantry device 10, the sleeper device 30, and the console device 40 are connected to each other by wire or wirelessly so as to be able to communicate with each other.

The gantry device 10 is a scanning device having a configuration for X-ray CT imaging of the subject P. The gantry device 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and a data acquisition device 18 (hereinafter referred to as a data acquisition device 18). , DAS (Data Acquisition System) 18).

The X-ray tube 11 is a vacuum tube that generates X-rays by irradiating thermoelectrons from the cathode (filament) toward the anode (target) by applying a high voltage from the X-ray high voltage device 14 and supplying a filament current. Is. Specifically, X-rays are generated by thermions colliding with the target. For example, the X-ray tube 11 has a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermions. The X-rays generated in the X-ray tube 11 are formed into a cone beam shape through, for example, a collimator 17, and are applied to the subject P.

The X-ray detector 12 detects X-rays irradiated from the X-ray tube 11 and passed through the subject P, and outputs an electric signal corresponding to the X-ray dose to the DAS 18. The X-ray detector 12 has, for example, a plurality of X-ray detection element trains in which a plurality of X-ray detection elements are arranged in a channel direction along one arc centering on the focal point of the X-ray tube 11. The X-ray detector 12 has, for example, a column structure in which a plurality of X-ray detection element sequences in which a plurality of X-ray detection elements are arranged in the channel direction are arranged in a slice direction (column direction, row direction).

Specifically, the X-ray detector 12 is an indirect conversion type detector having, for example, a grid, a scintillator array, and an optical sensor array. As the X-ray detector 12, both a general integral type detector and a photon counting detector can be assumed. The X-ray detector 12 is an example of a detection unit.

The scintillator array has a plurality of scintillators. The scintillator converts the incident X-rays into a number of photons according to the intensity of the incident X-rays.

The grid is arranged on the surface of the scintillator array on the X-ray incident side and has an X-ray shielding plate having a function of absorbing scattered X-rays. The grid may also be called a collimator.

The optical sensor array has a function of amplifying the light received from the scintillator and converting it into an electric signal, and has, for example, an optical sensor such as a photomultiplier tube (PMT).

The X-ray detector 12 may be a direct conversion type detector having a semiconductor element that converts incident X-rays into an electric signal.

The rotating frame 13 rotatably supports the X-ray generator and the X-ray detector 12 around a rotation axis. Specifically, the rotating frame 13 is an annular frame in which the X-ray tube 11 and the X-ray detector 12 are opposed to each other and the X-ray tube 11 and the X-ray detector 12 are rotated by a control device 15 described later. Is. The rotating frame 13 is rotatably supported by a fixed frame (not shown) made of a metal such as aluminum. Specifically, the rotating frame 13 is connected to the edge of the fixed frame via a bearing. The rotating frame 13 receives power from the drive mechanism of the control device 15 and rotates at a constant angular velocity around the axis of rotation Z.

The rotating frame 13 further includes and supports an X-ray high voltage device 14 and a DAS 18 in addition to the X-ray tube 11 and the X-ray detector 12. Such a rotating frame 13 is housed in a substantially cylindrical housing in which an opening (bore) 19 forming a photographing space is formed. The opening substantially coincides with the FOV. The central axis of the opening coincides with the rotation axis Z of the rotation frame 13. The detection data generated by the DAS 18 is provided in a non-rotating portion (for example, a fixed frame; not shown in FIG. 1) of the gantry device by optical communication from a transmitter having a light emitting diode (LED), for example. It is transmitted to a receiver (not shown) having a photodiode and transferred to the console device 40. The method of transmitting the detection data from the rotating frame to the non-rotating portion of the gantry device is not limited to the above-mentioned optical communication, and any method may be adopted as long as it is a non-contact type data transmission.

Hereinafter, in the present embodiment, the rotating frame 13 and the configurations arranged on the rotating frame are collectively referred to as a rotating portion, and a non-rotating portion such as a fixed frame in the gantry device 10 is also referred to as a fixed portion.

The X-ray high voltage device 14 has an electric circuit such as a transformer and a rectifier, and has a function of generating a high voltage applied to the X-ray tube 11 and a filament current supplied to the X-ray tube 11. It has a generator and an X-ray control device that controls an output voltage according to the X-rays emitted by the X-ray tube 11. The high voltage generator may be a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13 described later, or may be provided on the fixed frame (not shown) side of the gantry device 10.

The control device 15 has a processing circuit having a CPU (Central Processing Unit) and the like, and a drive mechanism such as a motor and an actuator. The processing circuit has a processor such as a CPU and an MPU (Micro Processing Unit) and a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory) as hardware resources. Further, the control device 15 includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and another complex programmable logic device (CPLD). ), It may be realized by a simple programmable logic device (SPLD). The control device 15 controls the X-ray high voltage device 14, the DAS 18, and the like in accordance with a command from the console device 40. The processor realizes the above control by reading and realizing a program stored in the memory.

Further, the control device 15 has a function of receiving an input signal from an input interface 43 described later attached to the console device 40 or the gantry device 10 and controlling the operation of the gantry device 10 and the sleeper device 30. For example, the control device 15 controls to rotate the rotating frame 13 in response to an input signal, controls to tilt the gantry device 10, and controls to operate the sleeper device 30 and the top plate 33. The control for tilting the gantry device 10 is such that the control device 15 rotates around an axis parallel to the X-axis direction based on the tilt angle (tilt angle) information input by the input interface 43 attached to the gantry device 10. It is realized by rotating 13. Further, the control device 15 may be provided in the gantry device 10 or in the console device 40. The control device 15 may be configured to directly incorporate the program into the circuit of the processor instead of storing the program in the memory. In this case, the processor realizes the control by reading and executing a program incorporated in the circuit.

The wedge 16 is a filter for adjusting the X-ray dose emitted from the X-ray tube 11. Specifically, the wedge 16 transmits and attenuates the X-rays emitted from the X-ray tube 11 so that the X-rays emitted from the X-ray tube 11 to the subject P have a predetermined distribution. It is a filter to do. For example, the wedge 16 (wedge filter, bow-tie filter) is a filter obtained by processing aluminum so as to have a predetermined target angle and a predetermined thickness.

The collimator 17 is a lead plate or the like for narrowing the irradiation range of X-rays transmitted through the wedge 16, and a slit is formed by a combination of a plurality of lead plates or the like. The collimator 17 may be called an X-ray diaphragm.

When the X-ray detector 12 is an integral type detector, the DAS 18 reads an electric signal from the X-ray detector 12, and based on the read electric signal, relates to the dose of X-rays detected by the X-ray detector 12. Generates digital data (hereinafter, also referred to as detection data). The detection data is a set of data indicating the channel number, column number, view number indicating the collected view (also referred to as projection angle), and the integrated value of the detected X-ray dose of the X-ray detection element of the generation source. be.

Further, when the X-ray detector 12 is a photon counting type detector, the DAS 18 reads an energy signal from the X-ray detector 12, and based on the read energy signal, X-rays detected by the X-ray detector 12. Detection data showing the count of is generated for each of multiple energy bands (energy bins). The detection data is a set of data of count values identified by the channel number, column number, view number indicating the collected view, and energy bin number of the detector pixel from which it was generated.

The DAS 18 is realized by, for example, an ASIC (Application Specific Integrated Circuit) equipped with a circuit element capable of generating detection data. The detection data is transferred to the console device 40.

For example, the DAS 18 includes a preamplifier, a variable amplifier, an integrator and an A / D converter for each detector pixel. The preamplifier amplifies the electrical signal from the source X-ray detector with a predetermined gain. The variable amplifier amplifies the electrical signal from the preamplifier with a variable gain. The integrator circuit integrates the electrical signal from the preamplifier over a period of one view to generate the integrator signal. The peak value of the integrated signal corresponds to the dose value of X-rays detected by the X-ray detection element of the connection source over one view period. The A / D converter converts the integrated signal from the integrating circuit into analog-digital and generates detection data.

The sleeper device 30 is a device for placing and moving the subject P to be scanned, and includes a base 31, a sleeper drive device 32, a top plate 33, and a support frame 34.

The base 31 is a housing that supports the support frame 34 so as to be movable in the vertical direction.
The sleeper drive device 32 is a motor or an actuator that moves the top plate 33 on which the subject P is placed in the long axis direction of the top plate 33. The sleeper drive device 32 moves the top plate 33 under the control of the console device 40 or the control device 15. For example, the sleeper drive device 32 moves the top plate 33 in the direction orthogonal to the subject P so that the body axis of the subject P placed on the top plate 33 coincides with the central axis of the opening of the rotating frame 13. do. Further, the sleeper drive device 32 may move the top plate 33 along the body axis direction of the subject P in accordance with the X-ray CT imaging performed by using the gantry device 10. The sleeper drive device 32 generates power by driving at a rotation speed according to the duty ratio and the like of the drive signal from the control device 15. The sleeper drive device 32 is realized by, for example, a motor such as a direct drive motor or a servo motor.

The top plate 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. In addition to the top plate 33, the sleeper drive device 32 may move the support frame 34 in the long axis direction of the top plate 33.

The console device 40 includes a memory 41, a display 42, an input interface 43, and a processing circuit 44. Data communication between the memory 41, the display 42, the input interface 43, and the processing circuit 44 is performed via the bus (BUS). Although the console device 40 will be described as a separate body from the gantry device 10, the gantry device 10 may include a part of each component of the console device 40 or the console device 40.

The memory 41 is a storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various information. The memory 41 stores, for example, projection data and reconstructed image data. In addition to HDDs and SSDs, the memory 41 is located between a portable storage medium such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a flash memory, and a semiconductor memory element such as a RAM (Random Access Memory). It may be a drive device that reads and writes various information. Further, the storage area of the memory 41 may be in the X-ray CT device 1 or in an external storage device connected by a network. For example, the memory 41 stores data of a CT image or a display image. Further, the memory 41 stores the control program according to the present embodiment.

The display 42 displays various information. For example, the display 42 outputs a medical image (CT image) generated by the processing circuit 44, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. For example, the display 42 may be, for example, a liquid crystal display (LCD), a CRT (Cathode Ray Tube) display, an organic EL display (OELD), a plasma display, or any other display. , Can be used. Further, the display 42 may be provided on the gantry device 10. Further, the display 42 may be a desktop type, or may be configured by a tablet terminal or the like capable of wireless communication with the console device 40 main body.

The input interface 43 receives various input operations from the operator, converts the received input operations into electric signals, and outputs the received input operations to the processing circuit 44. For example, the input interface 43 receives from the operator collection conditions for collecting projection data, reconstruction conditions for reconstructing a CT image, image processing conditions for generating a post-processed image from a CT image, and the like. .. As the input interface 43, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad, a touch panel display, and the like can be appropriately used. In the present embodiment, the input interface 43 is not limited to the one provided with physical operation parts such as a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad, and a touch panel display. For example, an example of the input interface 43 includes an electric signal processing circuit that receives an electric signal corresponding to an input operation from an external input device provided separately from the device and outputs the electric signal to the processing circuit 44. .. The input interface 43 may be provided on the gantry device 10. Further, the input interface 43 may be configured by a tablet terminal or the like capable of wireless communication with the console device 40 main body.

The processing circuit 44 controls the operation of the entire X-ray CT apparatus 1 according to the electric signal of the input operation output from the input interface 43. For example, the processing circuit 44 has a processor such as a CPU, MPU, and GPU (Graphics Processing Unit) and a memory such as a ROM or RAM as hardware resources. The processing circuit 44 executes the system control function 441, the preprocessing function 442, the reconstruction processing function 443, the acquisition function 444, the correction processing function 445, and the display control function 446 by the processor that executes the program expanded in the memory. It should be noted that each function (system control function 441, pre-processing function 442, reconstruction processing function 443, acquisition function 444, correction processing function 445, and display control function 446) is not limited to the case where it is realized by a single processing circuit. A processing circuit may be configured by combining a plurality of independent processors, and each processor may execute a program to realize each function.

The system control function 441 controls each function of the processing circuit 44 based on the input operation received from the operator via the input interface 43. Specifically, the system control function 441 reads out the control program stored in the memory 41, expands it on the memory in the processing circuit 44, and controls each part of the X-ray CT apparatus 1 according to the expanded control program. .. For example, the processing circuit 44 controls each function of the processing circuit 44 based on the input operation received from the operator via the input interface 43. For example, the system control function 441 acquires a two-dimensional positioning image of the subject P for determining a scan range, imaging conditions, and the like. The positioning image is also referred to as a scanno image or a scout image. The system control function 441 is an example of a system control unit.

The preprocessing function 442 generates data obtained by subjecting the detection data output from the DAS 18 to preprocessing such as logarithmic conversion processing, offset correction processing, sensitivity correction processing between channels, and beam hardening correction. The data before preprocessing (detection data) and the data after preprocessing may be collectively referred to as projection data.

The reconstruction processing function 443 performs reconstruction processing on the projection data generated by the preprocessing function 442 using a filter-corrected back projection method (FBP method: Filtered Back Projection), a successive approximation reconstruction method, or the like. To generate CT image data.

The acquisition function 444 acquires medical data. The medical data is, for example, CT image data or projection data taken by the X-ray CT apparatus 1.

The correction processing function 445 executes the scattered radiation correction processing on the medical data acquired by the acquisition function 444, and generates the medical data from which the scattered radiation component is removed.

The display control function 446 is a process of controlling the display 42 so as to display information during or as a result of the process in each function or process of the process circuit 44.

The processing circuit 44 also performs scan control processing and image processing.
The scan control process is a process for controlling various operations related to X-ray scanning, such as supplying a high voltage to the X-ray high voltage device 14 and irradiating the X-ray tube 11 with X-rays.
In the image processing, based on the input operation received from the operator via the input interface 43, the CT image data generated by the reconstruction processing function 443 is subjected to a tomographic image data or a three-dimensional image data of an arbitrary cross section by a known method. It is a process to convert to. The reconstruction processing function 443 may directly generate the three-dimensional image data.

The processing circuit 44 is not limited to the case where it is included in the console device 40, and may be included in an integrated server that collectively performs processing on data acquired by a plurality of medical diagnostic imaging devices.

Although the console device 40 has been described as executing a plurality of functions on a single console, a plurality of functions may be executed by different consoles. For example, the functions of the processing circuit 44 such as the preprocessing function 442 and the reconstruction processing function 443 may be distributed and provided.

Next, an example of the rotating portion according to the first embodiment will be described with reference to FIGS. 2A and 2B. FIG. 2A is a schematic cross-sectional view of the gantry device 10 as viewed from the X-axis direction, and shows a fixed portion 101 and a rotating portion.

As shown in FIG. 2A, the shielding portion 21 is arranged on the X-ray detector 12 side in the rotating frame 13. The material of the shielding portion 21 may be the same material as the collimator 17 arranged on the X-ray tube 11 side, such as lead and tungsten.

More specifically, the shielding unit 21 together with the X-ray tube 11 so as to shield X-rays emitted from the X-ray tube 11 other than the irradiation range 201 of the X-rays directly incident on the X-ray detector 12 as much as possible. It is arranged between the X-ray detector 12 and the X-ray detector 12. In the example of FIG. 2A, it is assumed that the shielding portion 21 is arranged along the channel direction of the X-ray detector 12.

The X-ray detector 12 is transmitted from the X-ray tube 11 so that the X-rays emitted from the X-ray tube 11 pass through the subject P and then are incident on the entire surface of the sensor surface which is the upper surface of the X-ray detector 12. It is incident on the X-ray detector 12 with an angular spread from the central axis of the irradiation to be connected.
At this time, the collimator 17 covers the irradiation range 201 shown by the broken line in FIG. 2A so that the portion other than the X-ray detector 12, for example, the peripheral member 102 arranged adjacent to the X-ray detector 12 is not irradiated with X-rays. It is desirable to squeeze. However, it is necessary to arrange the collimators 17 at a slightly wider interval in order to assume that the irradiation range such as the movement of the focal point shifts. Therefore, the portion other than the X-ray detector 12 is also irradiated, and the irradiation range 202 may be generated outside the irradiation range 201.

Therefore, the shielding unit 21 is arranged so as to shield the X-rays in the irradiation range 202, in other words, the shielding unit 21 is arranged so as to shield the X-rays from being incident on the peripheral member 102 existing in the irradiation range 202. do. As a result, the amount of X-rays incident on the peripheral member 102 is reduced, so that it is possible to reduce the amount of scattered rays generated from the peripheral member 102 incident on the X-ray detector 12.

Further, the shielding portion 21 has an X-ray tube on the side surface of the shielding portion 21 from the first surface of the shielding portion 21 on the X-ray tube 11 side to the second surface of the X-ray detector 12 side facing the first surface. It is formed in a notched state so as to be separated from the axis A connecting the 11 and the center of the X-ray detector 12.

In other words, the surface of the shielding unit 21 near the X-ray detector 12 is the first path (that is, the axis A) of X-rays incident on the center of the X-ray detector 12 from the X-ray tube 11 and the X-ray tube 11. The angle θ ₂ between the first path and the surface near the X-ray detector 12 of the shielding unit 21 is larger than the angle θ ₁ formed by the second path of X-rays incident on the end of the X-ray detector 12. Tilt so that it is larger. In FIG. 2A, for convenience of drawing, the angle formed by the virtual line parallel to the axis A and the surface of the shielding portion 21 near the X-ray detector 12 is shown as an angle θ ₂ , but the first path and the shielding portion are shown. It is the same as the angle formed by the surface of 21 near the X-ray detector 12.

The reason why the surface of the shielding portion 21 is tilted at the angle θ ₂ is that when the angle θ ₂ on the side surface of the shielding portion 21 is set to the angle θ ₁ or less, the X-rays incident on the side surface of the shielding portion 21 are reflected. However, there is a possibility that the scattered rays will be incident on the X-ray detector 12. Therefore, by making the angle θ ₂ larger than the angle θ ₁ , it is possible to shield and reduce X-rays on the first surface of the shielding portion 21, and it is possible to design so that X-rays are not incident on the side surface.

Further, when the X-ray detector 12 is viewed from the X-ray tube 11 side, a part of the first surface of the shielding portion 21 is arranged so as to overlap the columnwise end portion of the X-ray detector 12. In the example of FIG. 2A, when viewed from the X-axis direction, the shield portion 21 is arranged so as to cover a part of the shielding portion 21 above the row direction of the X-ray detector 12. As for the range to be covered, for example, a part of the first surface of the shielding portion 21 may be covered to the extent that the second path of X-rays incident on the end of the X-ray detector 12 from the X-ray tube 11 is not shielded. By doing so, the amount of X-rays incident on the peripheral member 102 existing in the irradiation range 202 can be further reduced.

Next, FIG. 2B is a schematic view of a cross section of the gantry device 10 seen from the Z-axis direction.
Also in the case shown in FIG. 2B, the shielding portion 21 is formed and arranged in the rotating portion in the same manner as in FIG. 2A. That is, the shielding unit 21 is arranged closer to the X-ray tube 11 than the X-ray detector 12, and is arranged so as to shield X-rays incident on other than the X-ray detector 12 as much as possible. Further, it is formed so as to cover a part of the shielding portion 21 above the X-ray tube 11 side at the end in the row direction of the X-ray detector 12.

That is, in FIGS. 2A and 2B, an example in which the shielding unit 21 is arranged along the channel direction and the column direction of the X-ray detector 12 is shown, but the present invention is not limited to this, and the shielding unit 21 is not limited to this and is located in either the channel direction or the column direction. It may be arranged.
Here, the angle θ ′ ₂ on the side surface of the shielding portion 21 may be set larger than θ ′ ₁ as in the case of FIG. 2A.

The lower limit of the angle θ ₂ shown in FIG. 2A is θ ₂ > θ ₁ , and the lower limit of the angle θ ′ ₂ shown in FIG. 2B is θ ′ ₂ > θ ′ ₁ , but the upper limit is appropriately designed. Just do it. For example, if the angle is made too large, the thickness of the shielding portion 21 decreases, so the shielding ability of the shielding portion 21, the positional relationship between the X-ray tube 11 and the X-ray detector 12, the thickness of the shielding portion 21 depending on the angle, etc. are taken into consideration. Then, the angle θ ₂ and the angle θ ′ ₂ may be designed so as to reduce the scattered rays generated from the peripheral member 102.

Next, the arrangement relationship between the shielding unit 21 and the X-ray detector 12 will be described with reference to FIG.
FIG. 3 is an enlarged view of FIG. 2A around the X-ray detector 12. FIG. 3 is common to both the channel direction and the column direction of the X-ray detector 12. The shielding unit 21 is X when the first distance 51, which is the shortest distance between the point on the first surface of the shielding unit 21 and the sensor surface 121 of the X-ray detector 12, does not arrange the shielding unit 21. It is arranged so as to be longer than the second distance 52, which is the shortest distance between the point on the peripheral member 102 that can generate scattered rays to the line detector 12 and the sensor surface 121 of the X-ray detector 12. ..

This is because a part of the X-rays incident on the shielding unit 21 can pass through the inside of the shielding unit 21 and be incident on the X-ray detector 12 as scattered rays. Scattered rays are generated by fluorescent X-rays and Compton scattering during photoelectric absorption. X-ray fluorescence is emitted isotropically, and Compton scattering occurs more strongly in forward scattering than in backscattering. Therefore, when the shielding unit 21 is arranged closer to the sensor surface 121 than the member existing on the arrangement surface of the X-ray detector that causes backscatter, by arranging the shielding unit 21, the scattered radiation from the member is emitted. The shielding unit 21 itself may generate more scattered radiation than it removes.

Therefore, by arranging the shielding portion 21 on the X-ray tube 11 side of the X-ray detector 12 so that the first distance 51 is longer than the second distance, the scattered rays generated from the shielding portion 21 itself are generated. The effect can be smaller than the effect of scattered rays by the member that causes backscatter.

According to the first embodiment shown above, a shielding unit 21 is provided above the X-ray detector 12 so that the first distance is longer than the second distance, and the vicinity of the X-ray detector 12 of the shielding unit 21 is provided. By inclining the angle θ ₂ formed with the surface of the X-ray detector so that it is larger than the angle θ ₁ , the X-ray detector is shielded from the incident of X-rays to the peripheral members, and the scattered rays from the peripheral members are the X-ray detector. It can be prevented from being incident on. As a result, the image quality can be improved.

(Second embodiment)
The shielding unit 21 according to the first embodiment X-rays the shielding unit 21 so as not to shield the X-rays incident on the sensor surface of the X-ray detector and not to be closer to the X-ray detector 12 than the peripheral member 102. It needs to be placed away from the line detector 12. Therefore, all the X-rays incident on the vicinity of the X-ray detector 12 cannot be removed, and scattered rays due to backscattering may occur.

Therefore, the second embodiment is different from the first embodiment in that the shielding portion 22 is further provided on the side surface of the X-ray detector in addition to the configuration of the shielding portion 21 according to the first embodiment.

The arrangement relationship between the shielding portion and the X-ray detector 12 according to the second embodiment will be described with reference to FIG.
FIG. 4 is an enlarged view of the periphery of the X-ray detector 12 as in FIG. 3, and is common to both the channel direction and the column direction. In addition to the shielding unit 21 according to the first embodiment, the shielding unit 22 is arranged on the side surface of the X-ray detector with respect to the sensor unit. The material of the shielding portion 22 may be the same material as that of the shielding portion 21.

Further, the shielding portion 22 has a shape in which X-rays passing between the shielding portion 21 and the X-ray detector 12 are not directly incident, and is arranged on the side surface of the X-ray detector 12. Specifically, the shielding portion 22 is formed on a taper that spreads along the X-ray irradiation direction from the X-ray tube 11 as the distance from the X-ray tube 11 side increases. This is because when the shielding portion 22 is formed of a rectangular parallelepiped or the like, X-rays passing between the X-ray detector 12 and the shielding portion 21 are incident on the upper surface of the shielding portion 22, so that the scattered X-rays are caused by the incident X-rays. This is because the line may be incident on the sensor surface 121 of the X-ray detector 12 at a position closer to the peripheral member 102.

Therefore, the angle and shape may be such that they are in the shadow of the X-ray detector 12 in the X-ray irradiation region. For example, the shielding portion 22 may have a surface in contact with the X-ray detector 12 and a surface in contact with the peripheral member 12, and may have a shape in which the cross section perpendicular to these two surfaces is triangular.
The shielding unit 22 may be arranged inside the X-ray detector 12 at the end of the X-ray detector 12 instead of being arranged outside the X-ray detector. Further, the shielding portion 22 is not limited to the side surface of the sensor portion, and may be arranged on the back surface of the sensor portion.

According to the second embodiment shown above, by arranging the shielding portion 22 on the side surface of the X-ray detector, it is possible to further reduce the scattered radiation from the peripheral members. As a result, the image quality can be improved.

(Third embodiment)
The third embodiment is different in that the shielding portion 21 is not arranged in the rotating frame 13, that is, in the rotating portion, but in the fixed portion 101.

The X-ray CT apparatus according to the third embodiment will be described with reference to FIGS. 5A and 5B.
5A is a schematic view of a cross section of the gantry device 10 seen from the same X-axis direction as FIG. 2A, and FIG. 5B is a schematic view of a cross section of the gantry device 10 seen from the same Z-axis direction as FIG. 2B.
When the shielding portion 21 is arranged along the channel direction of the X-ray detector 12, it is arranged over the entire inner circumference of the fixing portion 101, that is, 360 degrees so as to correspond to the rotation of the rotating portion. The shielding portion 21 arranged on the fixed portion 101 may be arranged in the same manner as the shielding portion 21 according to the first embodiment.
Although not shown, the shielding portion 22 according to the second embodiment may also be arranged.

According to the third embodiment shown above, even when the shielding portion 21 is arranged in the fixed portion, the scattered rays from the peripheral members are incident on the X-ray detector as in the first embodiment. Can be prevented. As a result, the image quality can be improved.

In addition, each function according to the embodiment can also be realized by installing a program for executing the process on a computer such as a workstation and expanding these on a memory. At this time, the program capable of causing the computer to execute the method can be stored and distributed in a storage medium such as a magnetic disk (hard disk or the like), an optical disk (CD-ROM, DVD or the like), or a semiconductor memory. ..

According to at least one embodiment described above, the scattered radiation can be reduced.

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 embodiments, and various omissions, replacements, changes, and combinations of embodiments can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope of the invention described in the claims and the equivalent scope thereof, as are included in the scope and gist of the invention.

10 Mount device 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high voltage device 15 Control device 16 Wedge 17 Collimeter 18 Data collection device 19 Opening 21, 22 Shielding unit 30 Sleep device 31 Base 32 Sleep drive device 33 Top plate 34 Support frame 40 Console device 41 Memory 42 Display 43 Input interface 44 Processing circuit 51, 52 Distance 101 Fixed part 102 Peripheral member 121 Sensor surface 201, 202 Irradiation range 441 System control function 442 Preprocessing function 443 Reconstruction processing function 444 Acquisition function 445 Correction processing function 446 Display control function

Claims (10)

An X-ray tube that irradiates X-rays and
An X-ray detector that detects the X-rays and
A first arranged between the X-ray tube and the X-ray detector so as to shield X-rays emitted from the X-ray tube outside the irradiation range of the X-rays directly incident on the X-ray detector. 1 shield and
An X-ray CT apparatus comprising. The X-ray CT apparatus according to claim 1, wherein the first shielding unit is arranged so as to shield the X-ray from being incident on a peripheral member adjacent to the X-ray detector. The X-ray CT apparatus according to claim 1 or 2, wherein the first shielding unit is arranged along at least one of a row direction and a channel direction of the X-ray detector. In the first shielding portion, the surface on the X-ray detector side is the first path of X-rays incident from the X-ray tube to the center of the X-ray detector, and the X-ray detector from the X-ray tube. Claimed to be inclined so that the second angle formed by the first path and the side surface on the X-ray detector side is larger than the first angle formed by the second path of X-rays incident on the end of the X-ray. The X-ray CT apparatus according to any one of claims 1 to 3. A part of the first shielding portion is arranged so as to overlap the end portion of the X-ray detector at a position that does not shield the second path when the X-ray detector is viewed from the X-ray tube side. , The X-ray CT apparatus according to claim 4. In the case where the first shielding portion is not arranged, the first distance, which is the shortest distance between the point on the surface on the X-ray tube side and the sensor surface of the X-ray detector, is the shortest distance. According to claim 1, the X-ray detector is arranged so as to be longer than the second distance, which is the shortest distance between a point on a peripheral member adjacent to the X-ray detector and the sensor surface. The X-ray CT apparatus according to any one of claim 5. The first shielding portion is according to any one of claims 1 to 6, wherein the first shielding portion is arranged on the X-ray detector side of a rotating portion in which the X-ray tube and the X-ray detector are arranged. X-ray CT device. When the first shielding portion is arranged along the channel direction of the X-ray detector, the first shielding portion is a fixed portion located inside the gantry device rather than the rotating portion in which the X-ray tube and the X-ray detector are arranged. The X-ray CT apparatus according to any one of claims 1 to 7, which is arranged in. It has a shape in which X-rays passing between the first shielding portion and the X-ray detector are not directly incident, and further includes a second shielding portion arranged on the side surface or the back surface of the sensor portion of the X-ray detector. The X-ray CT apparatus according to any one of claims 1 to 8. The second shielding portion has a first surface in contact with the X-ray detector and a second surface in contact with peripheral members adjacent to the X-ray detector, and is perpendicular to the first surface and the second surface. The X-ray CT apparatus according to claim 9, which has a shape having a triangular cross section.

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