X-ray CT device

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

[Technical Field]

[0001] The embodiments disclosed in the specification relate to an X-ray CT apparatus. [Background technology]

[0002] X-rays emitted from the X-ray tube impinge on the detector as well as on surrounding components. X-rays that impinge on surrounding components cause scattered rays that enter the detector from the side or rear. Scattered rays have a negative effect on the image quality of CT images, and are a particular problem in high-performance X-ray CT (Computed Tomography) systems, such as X-ray CT systems or spectral CT systems (including photon-counting CT systems), which can collect high-resolution medical images. To remove scattered radiation, a slit is generally placed in front of and near the X-ray tube to prevent X-rays from reaching surrounding components.

[0003] However, for example, if the focal point moves during X-ray irradiation, the relative positions of the focal point and the detector change, which can result in a shift in the irradiation range. Therefore, the slit installed near the X-ray tube must be installed with a margin to ensure a wide X-ray irradiation range so that the detection surface of the detector is included in the X-ray irradiation range. Therefore, even if the focal point is adjusted so that the X-rays that have passed through the subject are incident on the entire surface of the detector, the margin causes the X-rays to be incident on an area wider than the area of the detector's sensor surface, making it impossible to remove scattered radiation from surrounding components other than the detector. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-38975 Summary of the Invention [Problem to be solved by the invention]

[0005] One of the problems that the embodiments disclosed in the specification and drawings aim to solve is to reduce scattered radiation. However, the problems that the embodiments disclosed in the specification and drawings aim to solve are not limited to the above problem. Problems corresponding to the effects of the configurations shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0006] The X-ray CT apparatus according to this 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-rays. The first shielding unit is disposed between the X-ray tube and the X-ray detector so as to block X-rays irradiated outside the irradiation range of X-rays directly incident on the X-ray detector from the X-ray tube. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing an X-ray CT apparatus according to this embodiment. [Figure 2A] FIG. 2A is a diagram illustrating an example of a rotating unit according to the first embodiment. [Figure 2B] FIG. 2B is a diagram illustrating an example of a rotating unit according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the positional relationship between the shielding portion and the X-ray detector according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the positional relationship between the shielding portion and the X-ray detector according to the second embodiment. [Figure 5A] FIG. 5A is a diagram illustrating an example of a rotating unit according to a third embodiment. [Figure 5B] FIG. 5B is a diagram illustrating an example of a rotating unit according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An X-ray CT (Computed Tomography) device according to this embodiment will be described below with reference to the drawings. In the following embodiments, parts with the same reference numerals perform similar operations, and redundant description will be omitted as appropriate. One embodiment will be described below with reference to the drawings.

[0009] (First embodiment) An X-ray CT apparatus according to this embodiment will be described below with reference to the block diagram of Fig. 1. The X-ray CT apparatus 1 shown in Fig. 1 includes a gantry device 10, a bed device 30, and a console device 40. For convenience of explanation, a plurality of gantry devices 10 are depicted in Fig. 1.

[0010] In this embodiment, the rotation axis of the rotating frame 13 in the 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 perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction, and the axis perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction.

[0011] For example, the gantry 10 and the bed 30 are installed in a CT examination room, and the console 40 is installed in a control room adjacent to the CT examination room. The console 40 does not necessarily have to be installed in the control room. For example, the console 40 may be installed in the same room as the gantry 10 and the bed 30. In any case, the gantry 10, the bed 30, and the console 40 are connected to each other by wire or wirelessly so that they can communicate with each other.

[0012] The gantry device 10 is a scanning device configured to perform X-ray CT imaging of a 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 also referred to as a DAS (Data Acquisition System) 18).

[0013] The X-ray tube 11 is a vacuum tube that generates X-rays by irradiating thermoelectrons from a cathode (filament) toward an anode (target) when a high voltage is applied from the X-ray high voltage device 14 and a filament current is supplied. Specifically, X-rays are generated when the thermoelectrons collide with the target. 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. The X-rays generated by the X-ray tube 11 are shaped into a cone beam, for example, via a collimator 17, and are irradiated onto the subject P.

[0014] The X-ray detector 12 detects X-rays emitted from the X-ray tube 11 and passing through the subject P, and outputs an electrical 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 rows in which a plurality of X-ray detection elements are arranged in the channel direction along an arc centered on the focal point of the X-ray tube 11. The X-ray detector 12 has, for example, a row structure in which a plurality of X-ray detection element rows in which a plurality of X-ray detection elements are arranged in the channel direction are arranged in the slice direction (row direction).

[0015] Specifically, the X-ray detector 12 is an indirect conversion type detector having, for example, a grid, a scintillator array, and a photosensor array. The X-ray detector 12 can be either a general integral type detector or a photon counting detector. The X-ray detector 12 is an example of a detection unit.

[0016] The scintillator array includes a plurality of scintillators, which convert incident X-rays into photons, the number of which corresponds to the intensity of the incident X-rays.

[0017] The grid is placed on the X-ray incident side of the scintillator array and has an X-ray shielding plate that has the function of absorbing scattered X-rays. The grid is also sometimes called a collimator.

[0018] The photosensor array has a function of amplifying the light received from the scintillator and converting it into an electrical signal, and includes photosensors such as photomultiplier tubes (PMTs).

[0019] The X-ray detector 12 may be a direct conversion type detector having a semiconductor element that converts incident X-rays into an electrical signal.

[0020] The rotating frame 13 supports the X-ray generation unit and the X-ray detector 12 rotatably around a rotation axis. Specifically, the rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 facing each other and rotates the X-ray tube 11 and the X-ray detector 12 using a control device 15, which will be described later. The rotating frame 13 is rotatably supported on a fixed frame (not shown) made of metal such as aluminum. More specifically, the rotating frame 13 is connected to the edge of the fixed frame via bearings. The rotating frame 13 receives power from a drive mechanism of the control device 15 and rotates at a constant angular velocity around the rotation axis Z.

[0021] In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 also includes and supports an X-ray high-voltage generator 14 and a DAS 18. The rotating frame 13 is housed in a substantially cylindrical housing with an opening (bore) 19 that defines the imaging space. The opening substantially coincides with the FOV. The central axis of the opening coincides with the rotation axis Z of the rotating frame 13. The detection data generated by the DAS 18 is transmitted by optical communication from a transmitter having, for example, a light-emitting diode (LED) to a receiver (not shown) having a photodiode provided in a non-rotating part of the gantry (e.g., a fixed frame; not shown in FIG. 1 ), and then transferred to the console device 40. The method of transmitting the detection data from the rotating frame to the non-rotating part of the gantry is not limited to the optical communication described above, and any method of non-contact data transmission may be used.

[0022] Hereinafter, in this embodiment, the rotating frame 13 and the components arranged on the rotating frame are collectively referred to as a rotating section, and the non-rotating portion of the gantry 10, such as the fixed frame, is also referred to as a fixed section.

[0023] The X-ray high voltage device 14 includes a high voltage generator having electrical circuits such as a transformer and a rectifier, and having the function of generating a high voltage to be applied to the X-ray tube 11 and a filament current to be supplied to the X-ray tube 11, and an X-ray control device that controls the output voltage according to the X-rays irradiated by the X-ray tube 11. The high voltage generator may be of a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13, which will be described later, or on the fixed frame (not shown) side of the gantry device 10.

[0024] The control device 15 includes a processing circuit having a central processing unit (CPU) and other components, and a drive mechanism for motors, actuators, and other components. The processing circuit includes hardware resources such as a processor, such as a CPU or a microprocessing unit (MPU), and memories, such as read-only memory (ROM) or random-access memory (RAM). The control device 15 may also be implemented using an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), other complex programmable logic devices (CPLDs), or simple programmable logic devices (SPLDs). The control device 15 controls the X-ray high-voltage generator 14, the DAS 18, and other components in accordance with commands from the console device 40. The processor reads and executes programs stored in the memory to achieve the above control.

[0025] The control device 15 also has a function of controlling the operation of the gantry 10 and the bed 30 upon receiving input signals from an input interface 43 (described later) attached to the console device 40 or the gantry 10. For example, the control device 15 receives input signals and controls the rotation of the rotating frame 13, the tilt of the gantry 10, and the operation of the bed 30 and the tabletop 33. The control of tilting the gantry 10 is realized by the control device 15 rotating the rotating frame 13 around an axis parallel to the X-axis direction based on inclination angle (tilt angle) information input through the input interface 43 attached to the gantry 10. The control device 15 may be provided in the gantry 10 or the console device 40. The control device 15 may be configured to directly incorporate a program into the circuitry of the processor instead of storing the program in the memory. In this case, the processor realizes the above control by reading and executing the program incorporated in the circuitry.

[0026] The wedge 16 is a filter for adjusting the amount of X-rays irradiated from the X-ray tube 11. Specifically, the wedge 16 is a filter 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 subject P have a predetermined distribution. For example, the wedge 16 (wedge filter, bow-tie filter) is a filter made by processing aluminum to have a predetermined target angle and a predetermined thickness.

[0027] The collimator 17 is a lead plate or the like for narrowing down the irradiation range of the X-rays transmitted through the wedge 16, and a slit is formed by combining a plurality of lead plates or the like. The collimator 17 is also sometimes called an X-ray aperture.

[0028] When the X-ray detector 12 is an integral detector, the DAS 18 reads out electrical signals from the X-ray detector 12 and generates, based on the read out electrical signals, digital data (hereinafter also referred to as detection data) relating to the dose of X-rays detected by the X-ray detector 12. The detection data is a set of data indicating the channel number and column number of the X-ray detection element that generated the data, the view number indicating the collected view (also referred to as the projection angle), and the integral value of the detected dose of X-rays.

[0029] Furthermore, if the X-ray detector 12 is a photon-counting detector, the DAS 18 reads out energy signals from the X-ray detector 12 and generates, for each of a plurality of energy bands (energy bins), detection data indicating the count of X-rays detected by the X-ray detector 12 based on the read-out energy signals. The detection data is a set of count value data identified by the channel number, column number, view number indicating the collected view, and energy bin number of the detector pixel from which the detection data was generated.

[0030] The DAS 18 is realized by, for example, an ASIC (Application Specific Integrated Circuit) equipped with circuit elements capable of generating detection data. The detection data is transferred to the console device 40.

[0031] For example, the DAS 18 includes a preamplifier, a variable amplifier, an integration circuit, and an A / D converter for each detector pixel. The preamplifier amplifies the electrical signal from the connected X-ray detection element at a predetermined gain. The variable amplifier amplifies the electrical signal from the preamplifier at a variable gain. The integration circuit integrates the electrical signal from the preamplifier over one view period to generate an integrated signal. The peak value of the integrated signal corresponds to the X-ray dose value detected by the connected X-ray detection element over one view period. The A / D converter performs analog-to-digital conversion of the integrated signal from the integration circuit to generate detection data.

[0032] The bed device 30 is a device on which the subject P to be scanned is placed and moved, and includes a base 31, a bed driving device 32, a top board 33, and a support frame .

[0033] The base 31 is a housing that supports the support frame 34 so that the support frame 34 can move in the vertical direction. The bed driving device 32 is a motor or actuator that moves the tabletop 33, on which the subject P is placed, in the longitudinal direction of the tabletop 33. The bed driving device 32 moves the tabletop 33 under the control of the console device 40 or the control device 15. For example, the bed driving device 32 moves the tabletop 33 in a direction perpendicular to the subject P so that the body axis of the subject P placed on the tabletop 33 coincides with the central axis of the opening of the rotating frame 13. The bed driving device 32 may also move the tabletop 33 along the body axis of the subject P in accordance with X-ray CT imaging performed using the gantry device 10. The bed driving device 32 generates power by driving at a rotation speed that corresponds to the duty ratio, etc., of a drive signal from the control device 15. The bed driving device 32 is realized by a motor such as a direct drive motor or a servo motor.

[0034] The tabletop 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. The bed driving device 32 may move the support frame 34 in the longitudinal direction of the tabletop 33 in addition to the tabletop 33.

[0035] The console device 40 has 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 a bus (BUS). Note that 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.

[0036] 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 types of information. The memory 41 stores, for example, projection data and reconstructed image data. In addition to an HDD or an SSD, the memory 41 may be a portable storage medium such as a CD (Compact Disc), a DVD (Digital Versatile Disc), or a flash memory, or a drive that reads and writes various types of information from and to a semiconductor memory element such as a RAM (Random Access Memory). The storage area of the memory 41 may be located within the X-ray CT apparatus 1 or in an external storage device connected via a network. For example, the memory 41 stores data of CT images and display images. The memory 41 also stores a control program according to this embodiment.

[0037] The display 42 displays various types of information. For example, the display 42 outputs medical images (CT images) generated by the processing circuitry 44, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. For example, the display 42 may be a liquid crystal display (LCD), a cathode ray tube (CRT), an organic electroluminescence display (OLED), a plasma display, or any other display, as appropriate. The display 42 may also be provided on the gantry device 10. The display 42 may also be a desktop type, or may be configured as a tablet terminal capable of wireless communication with the console device 40 main body.

[0038] The input interface 43 accepts various input operations from the operator, converts the accepted input operations into electrical signals, and outputs the electrical signals to the processing circuitry 44. For example, the input interface 43 accepts from the operator acquisition conditions for acquiring projection data, reconstruction conditions for reconstructing CT images, and image processing conditions for generating post-processed images from CT images. Examples of the input interface 43 that can be used include a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display, as appropriate. Note that in this embodiment, the input interface 43 is not limited to a device equipped with physical operation components such as a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs the electrical signal to the processing circuitry 44 is also included as an example of the input interface 43. The input interface 43 may be provided in the gantry device 10. Alternatively, the input interface 43 may be configured as a tablet terminal or the like capable of wireless communication with the console device 40.

[0039] The processing circuitry 44 controls the overall operation of the X-ray CT apparatus 1 in response to electrical signals of input operations output from the input interface 43. For example, the processing circuitry 44 has, as hardware resources, a processor such as a CPU, MPU, or GPU (Graphics Processing Unit), and memories such as ROM and RAM. The processing circuitry 44 executes a system control function 441, a preprocessing function 442, a reconstruction processing function 443, an acquisition function 444, a correction processing function 445, and a display control function 446 using a processor that executes a program loaded in the memory. Note that each function (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) is not limited to being realized by a single processing circuit. A processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to realize each function.

[0040] The system control function 441 controls each function of the processing circuitry 44 based on an input operation received from an operator via the input interface 43. Specifically, the system control function 441 reads out a control program stored in the memory 41, expands it on the memory in the processing circuitry 44, and controls each unit of the X-ray CT apparatus 1 in accordance with the expanded control program. For example, the processing circuitry 44 controls each function of the processing circuitry 44 based on an 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 the scan range, imaging conditions, etc. The positioning image is also called a scanogram image or a scout image. The system control function 441 is an example of a system control unit.

[0041] The pre-processing function 442 generates data by performing pre-processing such as logarithmic conversion processing, offset correction processing, inter-channel sensitivity correction processing, beam hardening correction, etc. on the detection data output from the DAS 18. Note that the data before pre-processing (detection data) and the data after pre-processing may be collectively referred to as projection data.

[0042] The reconstruction processing function 443 performs reconstruction processing using a filtered back projection method (FBP method), an iterative reconstruction method, or the like on the projection data generated by the preprocessing function 442 to generate CT image data.

[0043] The acquisition function 444 acquires medical data, which may be, for example, CT image data or projection data captured by the X-ray CT device 1.

[0044] The correction processing function 445 executes scattered radiation correction processing on the medical data acquired by the acquisition function 444, and generates medical data from which scattered radiation components have been removed.

[0045] The display control function 446 is a process for controlling the display 42 so as to display information on the processing progress or results of each function or process of the processing circuit 44.

[0046] 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 causing the X-ray tube 11 to irradiate X-rays. The image processing is a process of converting the CT image data generated by the reconstruction processing function 443 into tomographic image data of an arbitrary cross section or three-dimensional image data by a known method based on an input operation received from the operator via the input interface 43. Note that the generation of three-dimensional image data may be performed directly by the reconstruction processing function 443.

[0047] The processing circuitry 44 is not limited to being included in the console device 40, but may also be included in an integrated server that collectively processes data acquired by a plurality of medical image diagnostic devices.

[0048] Although the console device 40 has been described as a single console that executes multiple functions, multiple functions may be executed by separate 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.

[0049] Next, an example of a rotating unit according to the first embodiment will be described with reference to Figures 2A and 2B. Figure 2A is a schematic cross-sectional view of the gantry device 10 as viewed from the X-axis direction, showing the fixed unit 101 and the rotating unit.

[0050] 2A, a shielding portion 21 is disposed on the X-ray detector 12 side within the rotating frame 13. The shielding portion 21 may be formed from the same material as the collimator 17 disposed on the X-ray tube 11 side, such as lead or tungsten.

[0051] More specifically, the shielding portion 21 is arranged between the X-ray tube 11 and the X-ray detector 12 so as to block as much as possible the X-rays irradiated to areas other than the irradiation range 201 of the X-rays that are directly incident on the X-ray detector 12 from the X-ray tube 11. 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.

[0052] The X-rays emitted from the X-ray tube 11 are incident on the X-ray detector 12 with an angular spread from the central axis of irradiation connecting the X-ray tube 11 to the X-ray detector 12 so that after passing through the subject P, they are incident on the entire sensor surface, which is the upper surface of the X-ray detector 12. At this time, it is desirable to narrow the irradiation range to 201 shown by the dashed line in Fig. 2A by the collimator 17 so that X-rays are not irradiated onto parts other than the X-ray detector 12, for example, onto peripheral members 102 arranged adjacent to the X-ray detector 12. However, in order to anticipate that the irradiation range may shift due to focal point movement, etc., the collimators 17 must be arranged with a slightly wider spacing. As a result, parts other than the X-ray detector 12 may also be irradiated, and an irradiation range 202 may occur outside the irradiation range 201.

[0053] Therefore, the shielding portion 21 is arranged so as to block the X-rays in the irradiation range 202, in other words, the shielding portion 21 is arranged so as to block the X-rays from entering the peripheral members 102 present in the irradiation range 202. This reduces the X-rays that enter the peripheral members 102, and therefore it is possible to reduce the incidence of scattered rays generated from the peripheral members 102 into the X-ray detector 12.

[0054] In addition, the shielding portion 21 is formed so that the side of the shielding portion 21 is cut away from the axis A connecting the centers of the X-ray tube 11 and the X-ray detector 12, from the first surface of the shielding portion 21 on the X-ray tube 11 side to the second surface on the X-ray detector 12 side opposite the first surface.

[0055] In other words, the surface of the shielding part 21 near the X-ray detector 12 is inclined so that the angle θ2 formed between a first path (i.e., axis A) of X-rays incident from the X-ray tube 11 to the center of the X-ray detector 12 and a second path of X-rays incident from the X-ray tube 11 to an end of the X-ray detector 12 is larger than the angle θ1 formed between the first path and the surface of the shielding part 21 near the X-ray detector 12. Note that, for convenience of illustration, the angle θ2 in FIG. 2A is shown as the angle formed between a virtual line parallel to the axis A and the surface of the shielding part 21 near the X-ray detector 12, but it is the same as the angle formed between the first path and the surface of the shielding part 21 near the X-ray detector 12.

[0056] The reason for inclining the surface of shielding portion 21 at angle θ2 in this manner is that if angle θ2 of the side surface of shielding portion 21 is set to angle θ1 or less, X-rays incident on the side surface of shielding portion 21 may be reflected and enter X-ray detector 12 as scattered rays. Therefore, by making angle θ2 larger than angle θ1, it is possible to design the first surface of shielding portion 21 to block and reduce X-rays and to prevent X-rays from entering the side surface.

[0057] Furthermore, when the X-ray detector 12 is viewed from the X-ray tube 11 side, the shielding portion 21 is disposed so that a portion of the first surface thereof overlaps the end of the X-ray detector 12 in the column direction. In the example of FIG. 2A , when viewed from the X-axis direction, the shielding portion 21 is disposed so that a portion of the shielding portion 21 covers the upper portion of the X-ray detector 12 in the column direction. The range of the overlap may be, for example, such that a portion of the first surface of the shielding portion 21 covers the upper portion 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 blocked. This can further reduce X-rays incident on the peripheral members 102 present in the irradiation range 202.

[0058] Next, FIG. 2B is a schematic cross-sectional view of the gantry device 10 as viewed from the Z-axis direction. 2A, in the case shown in Fig. 2B, a shielding portion 21 is formed and arranged on the rotating portion. That is, the shielding portion 21 is arranged closer to the X-ray tube 11 than the X-ray detector 12, and is arranged so as to block as much as possible X-rays incident on areas other than the X-ray detector 12. Furthermore, the shielding portion 21 is formed so as to cover a part of the end portion of the X-ray detector 12 in the column direction above the X-ray tube 11 side.

[0059] That is, although Figures 2A and 2B show an example in which the shielding portion 21 is arranged along the channel direction and column direction of the X-ray detector 12, this is not limiting and the shielding portion 21 may be arranged in either the channel direction or the column direction. Here, the angle θ'2 of the side surface of the shielding portion 21 may be set to be larger than θ'1, as in the case of FIG. 2A.

[0060] 2A has a lower limit of θ2>θ1, and the lower limit of θ'2 shown in Fig. 2B has a lower limit of θ'2>θ'1, but the upper limits can be designed appropriately. For example, if the angle is made too large, the thickness of shielding portion 21 will decrease, so angles θ2 and θ'2 can be designed so as to reduce scattered rays generated from peripheral member 102, taking into consideration the shielding ability of shielding portion 21, the positional relationship between X-ray tube 11 and X-ray detector 12, the thickness of shielding portion 21 at each angle, etc.

[0061] Next, the positional relationship between the shielding portion 21 and the X-ray detector 12 will be described with reference to FIG. 3 is an enlarged view of the periphery of the X-ray detector 12 in FIG. 2A. FIG. 3 is common to both the channel direction and the column direction of the X-ray detector 12. The shielding portion 21 is arranged so that a first distance 51, which is the shortest distance between a point on the first surface of the shielding portion 21 and the sensor surface 121 of the X-ray detector 12, is longer than a second distance 52, which is the shortest distance between a point on the peripheral member 102 that may cause scattered rays to the X-ray detector 12 if the shielding portion 21 is not arranged and the sensor surface 121 of the X-ray detector 12.

[0062] This is because some of the X-rays that enter the shielding portion 21 may pass through the inside of the shielding portion 21 and enter the X-ray detector 12 as scattered rays. Scattered rays are generated by fluorescent X-rays and Compton scattering during photoelectric absorption. Fluorescent X-rays are emitted isotropically, and Compton scattering occurs more strongly in forward scattering than in backscattering. Therefore, if the shielding portion 21 is placed closer to the sensor surface 121 than a component on the placement surface of the X-ray detector that generates backscattering, there is a possibility that the shielding portion 21 itself will generate more scattered rays than will be removed by placing the shielding portion 21.

[0063] Therefore, by arranging the shielding portion 21 closer to the X-ray tube 11 than the X-ray detector 12 so that the first distance 51 is longer than the second distance, the influence of scattered rays generated from the shielding portion 21 itself can be made smaller than the influence of scattered rays generated by components that cause backscattering.

[0064] According to the first embodiment described above, the shielding portion 21 is provided above the X-ray detector 12 so that the first distance is longer than the second distance, and is tilted so that the angle θ2 formed by the shielding portion 21 with the surface near the X-ray detector 12 is larger than the angle θ1, thereby blocking X-rays from entering components around the X-ray detector and preventing scattered rays from the components from entering the X-ray detector. As a result, image quality can be improved.

[0065] (Second embodiment) The shielding portion 21 according to the first embodiment does not shield X-rays incident on the sensor surface of the X-ray detector, and needs to be disposed away from the X-ray detector 12 so as not to be closer to the X-ray detector 12 than the peripheral member 102. Therefore, it is not possible to remove all X-rays incident near the X-ray detector 12, and scattered rays due to backscattering may occur.

[0066] Therefore, the second embodiment differs from the first embodiment in that, in addition to the configuration of the shielding portion 21 according to the first embodiment, a shielding portion 22 is further provided on the side surface of the X-ray detector.

[0067] The positional relationship between the shielding portion and the X-ray detector 12 according to the second embodiment will be described with reference to FIG. 4, like FIG. 3, is an enlarged view of the periphery of the X-ray detector 12, and is common to both the channel direction and the column direction. In addition to the shielding portion 21 according to the first embodiment, a shielding portion 22 is arranged on the side of the X-ray detector facing the sensor portion. The shielding portion 22 may be made of the same material as the shielding portion 21.

[0068] Furthermore, the shielding part 22 has a shape that prevents X-rays that pass between the shielding part 21 and the X-ray detector 12 from directly entering the shielding part 22, and is disposed on the side of the X-ray detector 12. Specifically, the shielding part 22 is formed in a tapered shape that widens as it moves away from the X-ray tube 11 side, along the direction of X-ray irradiation from the X-ray tube 11. This is because, if the shielding part 22 is formed as a rectangular parallelepiped or the like, X-rays that pass between the X-ray detector 12 and the shielding part 21 will be incident on the upper surface of the shielding part 22, and scattered rays caused by the incident X-rays may be incident on the sensor surface 121 of the X-ray detector 12 at a position closer than the peripheral member 102.

[0069] Therefore, it is sufficient that the shielding portion 22 has an angle and shape that allows it to be in the shadow of the X-ray detector 12 in the X-ray irradiation area. For example, the shielding portion 22 has a surface that contacts the X-ray detector 12 and a surface that contacts the peripheral member 12, and the cross section perpendicular to these two surfaces is triangular. The shielding portion 22 may be disposed inside the X-ray detector 12 at an end of the X-ray detector 12, rather than being disposed outside the X-ray detector 12. The shielding portion 22 is not limited to being disposed on the side of the sensor portion, but may also be disposed on the back of the sensor portion.

[0070] According to the second embodiment described above, by disposing the shielding portion 22 on the side of the X-ray detector, it is possible to further reduce scattered rays from peripheral members, thereby improving image quality.

[0071] (Third embodiment) The third embodiment differs in that the shielding unit 21 is arranged in the fixed unit 101 rather than being arranged in the rotating frame 13, that is, in the rotating unit.

[0072] An X-ray CT apparatus according to the third embodiment will be described with reference to FIGS. 5A and 5B. 5A is a schematic cross-sectional view of the gantry 10 as seen from the X-axis direction, the same as FIG. 2A, and FIG. 5B is a schematic cross-sectional view of the gantry 10 as seen from the Z-axis direction, the same 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 fixed portion 101, i.e., 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 section 22 according to the second embodiment may also be disposed.

[0073] According to the third embodiment described above, even when the shielding portion 21 is disposed on the fixed portion, scattered rays from peripheral members can be prevented from entering the X-ray detector, as in the first embodiment, and as a result, image quality can be improved.

[0074] In addition, each function according to the embodiment can be realized by installing a program that executes the above-described processes in a computer such as a workstation and expanding the program in memory. In this case, the program that causes the computer to execute the above-described methods can be stored and distributed on a storage medium such as a magnetic disk (e.g., a hard disk), an optical disk (e.g., a CD-ROM or a DVD), or a semiconductor memory.

[0075] According to at least one of the embodiments described above, scattered radiation can be reduced.

[0076] Although several 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 within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0077] 10 Mounting device 11 X-ray tube 12 X-ray detector 13 Rotating Frame 14 X-ray high voltage device 15 Control device 16 Wedge 17 Collimator 18 Data Collection Equipment 19 Aperture 21,22 Shielding part 30 Bed Device 31 Foundation 32 Bed drive unit 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 parts 121 Sensor surface 201,202 Irradiation range 441 System Control Functions 442 Pre-processing function 443 Reconstruction Processing Function 444 Retrieval Function 445 Correction processing function 446 Display Control Function

Claims

1. An X-ray tube that irradiates an object with X-rays; an X-ray detector that detects the X-rays that have passed through the subject; a first shielding unit disposed between the subject and the X-ray detector so as to shield X-rays irradiated from the X-ray tube to areas other than an irradiation range of X-rays directly incident on the X-ray detector; Equipped with an opening is formed in the first shielding portion so as not to cover an irradiation range of X-rays that are directly incident on the X-ray detector from the X-ray tube; the opening is formed in a tapered shape widening from the X-ray tube side toward the X-ray detector side at a second angle larger than a first angle formed by a first path of X-rays incident on the center of the X-ray detector from the X-ray tube and a second path of X-rays incident on an end portion of the X-ray detector from the X-ray tube. X-ray CT device.

2. the first shielding unit is disposed on a rotating unit where the X-ray tube and the X-ray detector are disposed opposite each other across the subject, and is disposed so as to block the X-rays from entering peripheral members adjacent to the X-ray detector. The X-ray CT apparatus according to claim 1.

3. the first shielding portion is arranged along at least one of a column direction and a channel direction of the X-ray detector.

3. The X-ray CT apparatus according to claim 1.

4. a part of the first shielding portion is disposed so as to overlap an end 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 any one of claims 1 to 3.

5. the first shielding portion is disposed so that a first distance, which is the shortest distance between a point on the surface on the X-ray tube side and a sensor surface of the X-ray detector, is longer than a second distance, which is the shortest distance between a point on a peripheral member adjacent to the X-ray detector that may generate scattered rays if the first shielding portion is not disposed and the sensor surface. The X-ray CT apparatus according to any one of claims 1 to 4.

6. when the first shielding unit is arranged along a channel direction of the X-ray detector, the first shielding unit is arranged on a fixed unit that is located more inside the gantry than a rotating unit where the X-ray tube and the X-ray detector are arranged opposite each other with the subject interposed therebetween. The X-ray CT apparatus according to any one of claims 1 to 5.

7. the X-ray tube and the X-ray detector are disposed in a rotating section that faces each other across the subject, and the second shielding section has a shape that prevents direct incidence of X-rays that have passed between the first shielding section and the X-ray detector, and is further provided on a side or rear surface of a sensor section of the X-ray detector so as to shield scattered rays from peripheral members adjacent to the X-ray detector. The X-ray CT apparatus according to any one of claims 1 to 6.

8. When the second shielding portion is disposed on a side surface of a sensor unit of the X-ray detector, the second shielding portion has a first surface in contact with the X-ray detector and a second surface in contact with a peripheral member adjacent to the X-ray detector, and has a shape in which a cross section perpendicular to the first surface and the second surface is triangular. The X-ray CT apparatus according to claim 7.

9. Further comprising a second shielding portion arranged around the X-ray detector so as to shield scattered radiation from peripheral members adjacent to the X-ray detector; the second shielding portion is formed in a tapered shape that widens from the X-ray tube side toward the X-ray detector side at an angle smaller than the first angle. The X-ray CT apparatus according to any one of claims 1 to 8.

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