JP2019180834A - X-ray ct apparatus - Google Patents

Abstract

To make it possible to appropriately perform production scan even on a subject extending off an imaging range at scanographic imaging.SOLUTION: An X-ray CT apparatus according to the embodiment controls first scanographic imaging such that X-rays are projected while a top plate or an X-ray tube is moved along a longitudinal direction of the top plate. The X-ray CT apparatus generates a first scanographic image on the basis of an output of an X-ray detection unit. The X-ray CT apparatus sets each position along the longitudinal direction. The X-ray CT apparatus controls second scanographic imaging such that X-rays are projected as the X-ray tube is stopped at each position in order. The X-ray CT apparatus generates a plurality of second scanographic images on the basis of outputs of the X-ray detection unit in the second scanographic imaging. The X-ray CT apparatus estimates a contour on the basis of each of the first scanographic image and the second scanographic images.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an X-ray CT apparatus.

  In general, in an X-ray CT (Computed Tomography) apparatus, before CT scanning, which is the main scan, scanography that captures a two-dimensional X-ray fluoroscopic image (hereinafter referred to as a scanogram) as a positioning image is performed. Done.

  Scanography is performed by running a bed without rotating a gantry having an X-ray tube. Alternatively, scanography may be performed by irradiating the subject on the bed with X-rays from two directions such as a front direction and a side direction. For example, scanography in the front direction is performed by placing an X-ray tube at a position of 0 ° facing the subject, irradiating the subject with X-rays from the X-ray tube, and running a bed. Scanning in the lateral direction is performed by placing an X-ray tube at a position of the side surface (90 °) with respect to the subject, irradiating the subject with X-rays from the X-ray tube, and running a bed. The bi-directional scanography may be executed first in either the front direction or the side direction.

  In this way, a scano image is taken by scano imaging in one direction or two directions. After the scano shooting, the shooting conditions are set based on the scanano image, the bed is run, and the rotation of the gantry is started. Thereafter, a tomographic image is taken by the main scan.

  Such an X-ray CT apparatus includes an asymmetric detector having an asymmetric detection surface in the channel direction with respect to a center line passing through the focal point of the X-ray tube and the rotation axis of the gantry device, or symmetrical in the channel direction. A symmetrical detector with a detection surface is used as appropriate. Even if an asymmetric detector or a symmetric detector is used, when scanning an object with a physique or posture that protrudes from the imaging range during scanning, either the left or right side or both sides of the subject is missing. A scanned image is obtained.

  However, when performing a main scan based on such a scanogram, there is a possibility that the main scan cannot be performed properly. On the other hand, it is desirable that the main scan can be appropriately executed even for a subject that protrudes from the imaging range during the scano imaging.

JP 2007-111515 A JP 2010-279532 A

  The problem to be solved by the invention is to make it possible to appropriately execute the main scan even for a subject that protrudes from the imaging range during the scan imaging.

An X-ray CT apparatus according to an embodiment includes an X-ray tube, an X-ray detection unit, a first control unit, a first generation unit, a setting unit, a second control unit, a second generation unit, and an estimation Part.
The X-ray tube irradiates a subject placed on a top board with X-rays.
The X-ray detection unit detects X-rays transmitted through the subject.
The first control unit controls first scan imaging so as to irradiate the X-ray while moving the top plate or the X-ray tube along the longitudinal direction of the top plate.
The first generation unit generates a first scan image showing a part of the subject along the longitudinal direction based on an output of the X-ray detection unit by the first scan imaging.
The setting unit includes a plurality of setting units along the longitudinal direction before the second scan imaging that images a region including a part of the contour of the subject that protrudes from the first scan image in the short direction of the top board. Set the position of.
The second control unit controls the second scanography so that the X-ray tube is stopped in order at the plurality of positions and irradiated with the X-rays.
The second generation unit generates a plurality of second scan images indicating a region including a part of the contour based on the output of the X-ray detection unit by the second scan imaging.
The estimation unit estimates the contour based on each of the first scano image and the second scano image.

FIG. 1 is a block diagram showing the configuration of the X-ray CT apparatus according to the first embodiment. FIG. 2 is a schematic diagram for explaining a first scano image and a second scano image in the first embodiment. FIG. 3 is a schematic diagram for explaining setting of positions in the first embodiment. FIG. 4 is a schematic diagram for explaining the setting of the position in the first embodiment. FIG. 5 is a schematic diagram for explaining the number of positions in the first embodiment. FIG. 6 is a schematic diagram for explaining setting of a position and an angle in the first embodiment. FIG. 7 is a schematic diagram for explaining the second scano imaging in the first embodiment. FIG. 8 is a time chart for explaining the operation in the first embodiment. FIG. 9 is a flowchart for explaining the operation in the first embodiment. FIG. 10 is a schematic diagram for explaining the operation in the first embodiment. FIG. 11 is a flowchart for explaining the operation in the first embodiment. FIG. 12 is a schematic diagram for explaining the operation in the first embodiment. FIG. 13 is a schematic diagram for explaining the operation in the first embodiment. FIG. 14 is a schematic diagram for explaining the operation in the first embodiment. FIG. 15 is a schematic diagram for explaining setting of positions in a modification of the first embodiment. FIG. 16 is a schematic diagram for explaining second scan imaging in a modification of the first embodiment. FIG. 17 is a schematic diagram for explaining the first scanogram in the second embodiment. FIG. 18 is a schematic diagram for explaining setting of a position and an angle in the second embodiment. FIG. 19 is a schematic diagram for explaining the second scan photographing in the second embodiment. FIG. 20 is a time chart for explaining the operation in the second embodiment. FIG. 21 is a schematic diagram for explaining setting of positions in a modification of the second embodiment. FIG. 22 is a schematic diagram for explaining second scan photographing in a modification of the second embodiment. FIG. 23 is a schematic diagram for explaining X-ray imaging in the third embodiment. FIG. 24 is a time chart for explaining the operation in the third embodiment. FIG. 25 is a flowchart for explaining the operation in the third embodiment. FIG. 26 is a schematic diagram for explaining the operation in the third embodiment.

  Hereinafter, the X-ray CT apparatus according to each embodiment will be described with reference to the drawings. In the X-ray CT apparatus, an X-ray tube and an X-ray detector integrally rotate around the subject, Rotate / Rotate-Type (third generation CT), and a large number of X-rays arrayed in a ring shape. There are various types such as Stationary / Rotate-Type (fourth generation CT) in which the detection element is fixed and only the X-ray tube rotates around the subject, and any type can be applied to the embodiment. Each of the following embodiments will be described using the third generation CT as an example.

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of an X-ray CT apparatus according to the first embodiment, and FIG. 2 is a schematic diagram for explaining a first scanogram and a second scanogram. The X-ray CT apparatus 1 irradiates the subject P with X-rays from the X-ray tube 11 and detects the irradiated X-rays with the X-ray detector 12. The X-ray CT apparatus 1 generates a CT image related to the subject P based on the output from the X-ray detector 12.

  The X-ray CT apparatus 1 shown in FIG. 1 includes a gantry device 10, a couch device 30, and a console device 40. The gantry device 10 is a scanning device having a configuration for X-ray CT imaging of the subject P. The plurality of gantry devices 10 depicted in FIG. 1 show the front and side surfaces of one gantry device 10. The bed apparatus 30 is an apparatus for placing the subject P to be X-ray CT imaging and moving to a position where X-ray CT imaging is performed. The console device 40 is a computer that controls the gantry device 10.

  For example, the gantry device 10 and the couch device 30 are installed in a CT examination room, and the console device 40 is installed in a control room adjacent to the CT examination room. Note that the console device 40 is not necessarily 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 couch device 30. In any case, the gantry device 10, the couch device 30, and the console device 40 are connected to each other in a wired or wireless manner so that they can communicate with each other.

  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 DAS 18.

  The X-ray tube 11 irradiates the subject P placed on the top board 33 with X-rays. Specifically, the X-ray tube 11 emits X-rays by irradiating thermoelectrons from the cathode (filament) to the anode (target) by applying a high voltage from the X-ray high voltage device 14 and supplying a filament current. A vacuum tube to be generated. The irradiated thermoelectrons are converted into X-rays by energy when colliding with the focal point of the target. As a result, the X-ray tube 11 generates X-rays that irradiate the subject P from the focus of the target with which the thermal electrons collide. X-rays generated in the X-ray tube 11 are shaped through the collimator 17 and irradiated onto the subject P on the top plate 33.

  The X-ray detector 12 detects X-rays irradiated from the X-ray tube 11 and passed through the subject P, and outputs an electrical signal corresponding to the X-ray dose to the DAS 18. The X-ray detector 12 includes, for example, a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arranged in the channel direction along one arc around the focal point of the X-ray tube. For example, the X-ray detector 12 has a structure in which a plurality of X-ray detection element arrays in which a plurality of X-ray detection elements are arrayed in the channel direction are arrayed in the slice direction (column direction, row direction). The X-ray detector 12 is an indirect conversion type detector having a grid, a scintillator array, and an optical sensor array, for example. The scintillator array has a plurality of scintillators, and the scintillator has a scintillator crystal that outputs a photon amount of light corresponding to the incident X-ray dose. The grid has an X-ray shielding plate that is disposed on the surface of the scintillator array on the X-ray incident side and has a function of absorbing scattered X-rays. The grid is sometimes called a collimator (a one-dimensional collimator or a two-dimensional collimator). The optical sensor array has a function of converting into an electric signal corresponding to the amount of light from the scintillator, and includes an optical sensor such as a photomultiplier tube (photomultiplier: PMT). The X-ray detector 12 may be a direct conversion type detector (semiconductor detector) having a semiconductor element that converts incident X-rays into electrical signals. The X-ray detector 12 is an example of an X-ray detection unit.

  The rotating frame 13 supports the X-ray tube 11 and the X-ray detector 12 so as to be rotatable around the rotation axis. Specifically, the rotating frame 13 supports the X-ray tube 11 and the X-ray detector 12 so as to face each other, and the control device 15 described later rotates the X-ray tube 11 and the X-ray detector 12. It is. The rotating frame 13 is rotatably supported by a fixed frame (not shown) formed of a metal such as aluminum. Specifically, the rotating frame 13 is connected to the edge of the fixed frame via a bearing. In this embodiment, the present invention can be applied to a single-tube type X-ray CT apparatus, and a so-called multi-tube in which a plurality of pairs of an X-ray tube 11 and an X-ray detector 12 are mounted on a rotating frame 13. The present invention can also be applied to a spherical X-ray CT apparatus. In the present embodiment, the axis of rotation of the rotating frame 13 in the non-tilt state or the longitudinal direction of the top plate 33 of the bed apparatus 30 is orthogonal to the Z-axis direction and the Z-axis direction and is horizontal to the floor surface. Are defined as an Y-axis direction and an axial direction perpendicular to the X-axis direction and the Z-axis direction and perpendicular to the floor surface. The rotating frame 13 receives power from the drive mechanism of the control device 15 and rotates around the rotation axis Z at a constant angular velocity. In addition to the X-ray tube 11 and the X-ray detector 12, the rotating frame 13 further includes and supports an X-ray high voltage device 14 and a DAS 18. Such a rotating frame 13 is accommodated in a substantially cylindrical casing in which an opening (bore) forming a photographing space is formed. The central axis of the opening coincides with the rotation axis Z of the rotary frame 13. The rotation axis Z of the rotation frame 13 may be called the rotation axis Z of the X-ray tube 11. The detection data generated by the DAS 18 is a photodiode provided in a non-rotating portion (for example, a fixed frame not shown) of the gantry device by optical communication from a transmitter having a light emitting diode (LED) provided in the rotating frame. Is transmitted to the console device 40. Note that the detection data transmission method from the rotating frame to the non-rotating portion of the gantry device is not limited to the optical communication described above, and any method may be adopted as long as it is a non-contact type data transmission. The rotating frame 13 is an example of a rotating unit.

  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. A generator and an X-ray controller that controls an output voltage corresponding to the X-rays emitted by the X-ray tube 11; The high voltage generator may be a transformer system or an inverter system. The X-ray high voltage device 14 may be provided on the rotary frame 13 described later, or may be provided on the fixed frame (not shown) side of the gantry device 10. The fixed frame is a frame that rotatably supports the rotating frame 13. The X-ray high voltage device 14 is an example of an X-ray high voltage unit.

  The control device 15 includes a processing circuit having a CPU (Central Processing Unit) and the like, and a driving mechanism such as a motor and an actuator. The processing circuit includes, as hardware resources, a processor such as a CPU or MPU (Micro Processing Unit) and a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). In addition, the control device 15 includes an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and other complex programmable logic devices (CPLD). ), Or a simple programmable logic device (SPLD). The control device 15 controls the X-ray high voltage device 14, the DAS 18, and the like according to a command from the console device 40. The processor implements the control by reading and implementing a program stored in the memory. In addition, the control device 15 has a function of receiving an input signal from the console device 40 or the input interface 43 attached to the gantry device 10 and performing operation control of the gantry device 10 and the couch device 30. For example, the control device 15 performs control for receiving the input signal to rotate the rotating frame 13, control for tilting the gantry device 10, and control for operating the bed device 30 and the top plate 33. The tilt control of the gantry device 10 is controlled by the control device 15 about the axis parallel to the X-axis direction based on the tilt angle (tilt angle) information input by the input interface attached to the gantry device 10. It is realized by rotating. The control device 15 may be provided in the gantry device 10 or may be provided in the console device 40. The control device 15 is an example of a control unit. Note that 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 irradiated from the X-ray tube 11. Specifically, the wedge 16 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. 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 or 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 forms a slit by a combination of a plurality of lead plates or the like. The collimator 17 is sometimes called an X-ray stop.

  The DAS 18 (Data Acquisition System) is an amplifier that performs amplification processing on an electric signal output from each X-ray detection element of the X-ray detector 12 and A / D conversion that converts the amplified electric signal into a digital signal. And detecting data having a digital value indicated by the digital signal. The detection data is a set of digital values of X-ray intensity identified by the source X-ray detector element channel number, column number, and view number indicating the collected view. As the view number, the order (collection time) in which the views are collected may be used, or a number (for example, 1-1000) indicating the rotation angle of the X-ray tube 11 may be used. The detection data generated by the DAS 18 is transferred to the console device 40 via a non-contact data transmission circuit (not shown) accommodated in the gantry device 10. The DAS 18 may be called a data collection unit.

  The couch device 30 is a device for placing and moving the subject P to be scanned, and includes a base 31, a couch driving 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 couch driving device 32 is a motor or an actuator that moves the top plate 33 on which the subject P is placed in the longitudinal direction of the top plate 33. As a method of moving the top plate 33, for example, a method of moving only the top plate 33 or a method of moving together with the support frame 34 of the bed apparatus 30 may be used. In the case of standing CT, a method of moving a patient support mechanism corresponding to the top board 33 may be used. The couch driving device 32 moves the couchtop 33 in accordance with control by the console device 40 or control by the control device 15. For example, the couch driving device 32 moves the top plate 33 with respect to the subject P so that the body axis of the subject P placed on the top plate 33 coincides with the rotation axis (center axis of the opening) of the rotary frame 13. Move in the orthogonal direction. Further, the couch driving device 32 may move the top plate 33 on which the subject P is placed along the longitudinal direction of the top plate 33 in accordance with X-ray CT imaging performed using the gantry device 10. Good. The bed driving device 32 generates power by being driven at a rotational speed corresponding to the duty ratio of the 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, for example.

  The top plate 33 provided on the upper surface of the support frame 34 is a plate on which the subject P is placed. The couch driving device 32 may move the support frame 34 in the longitudinal direction of the top plate 33 in addition to the top plate 33. When performing a scan (helical scan, positioning scan, etc.) involving a relative change in the positional relationship of the top plate 33 of the gantry device 10, the relative change in the positional relationship is performed by driving the top plate 33. Alternatively, it may be performed by running the gantry device 10 or may be performed by combining them.

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

  The memory 41 is realized by, for example, a RAM (Random Access Memory), a semiconductor memory element such as a flash memory, a hard disk, an optical disk, or the like. The memory 41 stores, for example, projection data, reconstructed image data, a first scan image, a plurality of second scan images, data of images being processed and display images, and a control program and table according to the present embodiment. The memory 41 is an example of a storage unit.

  The first scano image is a scano image (positioning image) acquired by the same inspection as the main scan. As shown in an example in FIG. 2, the first scan image g <b> 10 according to the present embodiment is an image showing a part of the subject P along the longitudinal direction Z of the top plate 33. The first scan image g10 is a first scan image in which the X-ray tube 11 is fixed at a predetermined rotation angle and the top plate 33 or the X-ray tube 11 is moved along the longitudinal direction Z of the top plate 33 and X-rays are irradiated. It is generated from detection data acquired by photographing. The first scano image is not limited to a single imaging direction, and may be an image obtained in a plurality of imaging directions.

  Each of the second scanograms g21 and g22 is an image (positioning image) showing a region including a part of the contour of the subject P protruding from the first scanogram g10 in the short direction X of the top board 33. Each of the second scanograms g21 and g22 is an image acquired by second scanography in which the X-ray tube 11 is stopped still in order at a plurality of positions along the longitudinal direction of the top board and X-rays are irradiated. In the second scanography, since the X-ray tube 11 is irradiated with X-rays at a position where the X-ray tube 11 is stationary, the exposure area is narrower than the first scanography in which X-rays are irradiated while moving the X-ray tube 11. For this reason, when scanning an area that protrudes from the first scanogram g10, the second scano imaging with a narrow exposure area is not performed again, but the second scanography with a narrow exposure area does not perform again. Can be reduced. Note that the first scan image and the second scan image may be called a first positioning image and a second positioning image, respectively, and may be called a first scout image and a second scout image, respectively.

  The table may be, for example, information set by associating each of a plurality of positions along the longitudinal direction of the top plate 33 used for the second scan imaging and an angle around the rotation axis of the X-ray tube 11. The angle of the X-ray tube 11 in the second scanography may be a common value at a plurality of positions, or may be a separate value. In addition, as the angle of the X-ray tube 11 in the second scanography, a value obtained from an empirical rule such as 30 ° or 45 ° can be used.

  Note that the storage area of the memory 41 may be in the X-ray CT apparatus 1 or in an external storage device connected by a network.

  The display 42 displays various information. For example, the display 42 outputs a medical image generated by the processing circuit 44, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. For example, as the display 42, for example, a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic EL display (OELD), a plasma display, or any other display is appropriately used. Can be used. The display 42 is an example of a display unit. The display 42 may be provided in the gantry device 10. The display 42 may be a desktop type, or may be configured by a tablet terminal or the like that can communicate wirelessly with the console device 40 main body.

  The input interface 43 receives various input operations from the operator, converts the received input operations into electrical signals, and outputs them to the processing circuit 44. For example, the input interface 43 receives from the operator collection conditions when collecting projection data, reconstruction conditions when reconstructing a CT image, image processing conditions when generating a post-process 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 used as appropriate. The input interface 43 is an example of an input unit. In this embodiment, the input interface 43 is a physical operation component such as a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad, and a touch panel display. It is not restricted to what comprises. 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 apparatus and outputs the electric signal to the processing circuit 44. . Further, the input interface 43 may be provided in 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. For example, the processing circuit 44 includes, as hardware resources, a processor such as a CPU, MPU, or GPU (Graphics Processing Unit) and a memory such as a ROM or RAM. The processing circuit 44 executes a system control function 441, a scan control function 442, a display control function 443, an image generation function 444, an image processing function 445, and the like by a processor that executes each program expanded in the memory. Supplementally, the processing circuit 44 in a state where each program is read has each function shown in the processing circuit 44 of FIG. In FIG. 1, it has been described that each function is executed by a single processor, but a processing circuit 44 is configured by combining a plurality of independent processors, and each processor executes a program to realize the function. It does n’t matter what you do. In FIG. 1, the single memory 41 is described as storing programs corresponding to the respective functions. However, a plurality of memories are distributed and the processing circuit 44 loads the corresponding programs from individual memories. It may be configured to read. The processing circuit 44 is an example of a processing unit.

  The system control function 441 controls each function of the processing circuit 44 based on an input operation received from the operator via the input interface 43. Specifically, the system control function 441 reads out a control program stored in the memory 41 and develops it on the memory in the processing circuit 44, and controls each part of the X-ray CT apparatus 1 according to the developed control program. . The system control function 441 is an example of a control unit.

  The scan control function 442 has a first control function, a setting function, and a second control function.

  The first control function (first control unit) controls the first scan imaging so that X-rays are emitted while moving the top plate 33 or the X-ray tube 11 along the longitudinal direction of the top plate 33.

  The setting function (setting unit) is configured to scan the top 33 before the second scan imaging that captures an area including a part of the contour of the subject P protruding from the first scan image g10 in the short direction of the top 33. A plurality of positions along the longitudinal direction are set. For example, the setting function sets a plurality of positions z1 and z2 manually or automatically as shown in FIGS. Specifically, in the case of manual operation, as shown in FIGS. 3A and 4A, the coordinates (xa, z1) of the point p1 and the point p2 specified by the operator are operated by operating the input interface 43. Based on the coordinates (xb, z2), positions z1 and z2 along the longitudinal direction may be set. Or in the case of automatic, pixel value distribution of a channel direction is extracted for every position along the longitudinal direction Z in the 1st scano image g10, and the said pixel is based on the shape or statistical value (average value, dispersion | variation) of pixel value distribution. The value distribution may be classified into groups, the pixel value distribution may be selected for each group, and the position in the longitudinal direction Z corresponding to the selected pixel value distribution may be set. In the case of classification based on a shape, some patterns such as a substantially L-shape or a convex shape may be held in advance and classified by comparison with the pattern. In the case of classification based on a statistical value, a threshold value may be stored in advance for each type of statistics such as an average value and a standard deviation, and the classification may be performed by comparing the threshold value with the threshold value. For example, as shown in FIG. 3B, the setting function sets the position z1 by classifying the pixel value distribution into the first group based on a substantially L-shaped pixel value distribution or a low average value. Also good. Specifically, the position z1 may be a central position within the range of the longitudinal direction Z in the pixel value distribution in the first group, and is a position at a predetermined distance from the end of the first scan image g10 in the longitudinal direction Z. Also good. Similarly, as shown in FIG. 4B, the setting function classifies the pixel value distribution into the second group based on the convex shape or large variation (standard deviation, variance) of the pixel value distribution. z2 may be set. Specifically, the position z2 may be a central position within the range of the longitudinal direction Z in the pixel value distribution in the second group, and is a position at a predetermined distance from the end of the first scan image g10 in the longitudinal direction Z. Also good. The plurality of positions are not limited to the two positions z1 and z2, but may be three positions z1 to z3 as shown in FIG. 5, and four or more positions (within the scan range of the first scan imaging) ( (Not shown). However, the number of positions for second scan imaging is preferably two in consideration of the fact that the exposure dose increases in proportion to the number of positions and the accuracy of the estimated contour may be low. When the number of positions of the second scanography is two, it is preferable that the two positions are separated from each other by a predetermined distance or more from the viewpoint of ensuring the accuracy of the estimated contour. Further, as shown in FIG. 6, the setting function may set each of the plurality of positions z1 and x2 in association with the angles θ1 and θ2 around the rotation axis of the X-ray tube 11. For example, the setting function may set the table in the memory 41 in association with the positions z1 and z2 and the angles θ1 and θ2.

  The second control function (second control unit) controls the second scan imaging so that the X-ray tube 11 is stopped still in order and irradiated with X-rays at the set positions z1 and z2. As shown in FIGS. 6 and 7, the second control function makes the X-ray tube 11 stand still and X-rays at an angle θ1 (or θ2) associated with the position z1 (or z2) to be stopped. X-rays may be irradiated with the tube 11 disposed. By such second scano imaging, second scan images g21 and g22 are generated by an image generation function 444 described later.

  The display control function 443 controls the display 42 to display various information.

  The image generation function 444 has a first generation function and a second generation function for generating a scanogram based on the output of the X-ray detector 12. The output of the X-ray detector 12 is transferred to the console device 40 as detection data via the DAS 18 and a non-contact data transmission circuit (not shown).

  The first generation function (first generation unit) is configured to move a part of the subject P along the longitudinal direction of the top 33 based on the output of the X-ray detection unit (X-ray detector 12) by the first scan imaging. The first scanogram g10 shown is generated.

  The second generation function (second generation unit) includes a plurality of second regions indicating regions including a part of the contour of the subject P based on the output of the X-ray detection unit (X-ray detector 12) by the second scan imaging. Two scanograms g21 and g22 are generated.

  In addition, the image generation function 444 generates data obtained by performing preprocessing such as logarithmic conversion processing, offset correction processing, and channel sensitivity correction processing on the detection data output from the DAS 18. Note that pre-processing data (detection data) and pre-processing data may be collectively referred to as projection data or raw data.

The image generation function 444 generates CT image data by performing a reconstruction process using a filtered back projection method, a successive approximation reconstruction method, or the like on the generated projection data. When reconstructing a CT image, the full scan reconstruction method requires 360 degrees of projection data around the subject, and the half scan reconstruction method also requires projection data for 180 ° + fan angle. . The present embodiment can be applied to any reconstruction method of full scan or half scan. The CT image data represents a spatial distribution of CT values related to the subject P. The CT value is a value for expressing a CT image, and refers to a relative value defined as 0 for water and -1000 for air. The CT value is determined by the X-ray attenuation coefficient, and calibration (calibration) is performed so that the X-ray attenuation coefficient μ_water of water becomes 0 and the X-ray attenuation coefficient μ_air of air becomes −1000. Therefore, a tissue having a higher X-ray attenuation coefficient than water has a high CT value. When the tissue X-ray attenuation coefficient is μ, the tissue CT value [HU] is obtained from the following equation.
CT value [HU] of tissue = 1000 × (μ−μ_water) / μ_water
The image processing function 445 has an estimation function. The estimation function is based on each of the first scano image g10 and the second scano images g21 and g22 generated by the image generation function 444, and the subject protrudes from the first scano image g10 in the lateral direction X of the top 33. Estimate a partial contour of P. For example, the estimation function is a part of the contour included in the region indicated by each of the second scano images g21 and g22 in a state where the first scano image g10 and the plurality of second scano images g21 and g22 are partially overlapped. The outline may be estimated by connecting the lines with a line.

  In addition to this, the image processing function 445 uses the CT image data generated by the image generation function 444 based on an input operation received from the operator via the input interface 43 by a known method to obtain tomographic image data of an arbitrary cross section. Or convert to 3D image data. The tomographic image data and three-dimensional image data after conversion are data having CT value distribution information in a three-dimensional space. It is displayed on the display 42. As known methods, for example, three-dimensional image processing such as volume rendering, surface rendering, image value projection processing, MPR (Multi-Planer Reconstruction) processing, CPR (Curved MPR) processing, etc. can be used as appropriate. . The image processing function 445 is an example of an image processing unit.

  The system control function 441, the scan control function 442, the display control function 443, the image generation function 444, and the image processing function 445 may be implemented by the processing circuit 44 on one substrate, or the processing circuits 44 on a plurality of substrates. May be distributed and implemented. Similarly, 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. The processing circuit 44 is not limited to being included in the console device 40, and may be included in an integrated server that collectively performs processing on detection data acquired by a plurality of medical image diagnostic apparatuses (not shown).

  Next, the operation of the X-ray diagnostic apparatus configured as described above will be described with reference to FIGS. FIG. 8 is a time chart, and FIGS. 9 and 11 are flowcharts. 10 and 12 to 14 are schematic views.

  First, the X-ray CT apparatus 1 acquires subject information (patient information) regarding a subject to be examined from an examination reservation system or the like via a communication interface (not shown). The subject information includes patient ID, patient name, date of birth, age, weight, sex, and examination site. The subject information may include implant information indicating an implant of the subject.

  Subsequently, in the X-ray CT apparatus 1, a patient is set on the top plate 33 by the operator. Further, as shown in FIG. 8, the top 33 moves to the first scano imaging start position zs by the operation of the input interface 43 by the operator. A preset scan plan is selected by the operation of the input interface 43 by the operator, and detailed conditions of the scan plan are set.

  Thereafter, in step ST1 shown in FIGS. 8 and 9, the scan control function 442 of the processing circuit 44 irradiates the X-ray while moving the top 33 along the longitudinal direction Z of the top 33 according to the scan plan. In this way, the first scano imaging is controlled. Thereby, the first scan imaging of the subject P is executed. The scan control function 442 stops the top plate 33 and ends the first scan imaging when the top 33 reaches the end position ze of the first scan imaging.

  After step ST1, in step ST2, the image generation function 444 of the processing circuit 44 removes a part of the subject P from the sky based on the output of the X-ray detector 12 by the first scan imaging as shown in FIG. A first scan image g10 shown along the longitudinal direction of the plate 33 is generated. The first scanogram g10 is stored in the memory 41.

  After step ST2, in step ST3, the scan control function 442 captures an area including a part of the contour of the subject P that protrudes from the first scan image g10 in the lateral direction X of the top board 33. Before the above, a plurality of positions z1 and z2 along the longitudinal direction Z of the top plate 33 are set. At this time, the scan control function 442 associates and sets each of the plurality of positions z1 and x2 and the angles θ1 and θ2 around the rotation axis of the X-ray tube 11.

  This step ST3 may be executed, for example, as shown in steps ST3-1 to ST3-5 in FIG. For example, the scan control function 442 reads the first scanogram g10 from the memory 41 (step ST3-1), and calculates the pixel value distribution in the channel direction for each position along the longitudinal direction Z in the first scanogram g10. Extract (step ST3-2). The “pixel value distribution” indicates a distribution of detected values of the amount of X-ray transmission with respect to the subject P, and may be called a “detected value distribution”. Subsequently, the scan control function 442 classifies the pixel value distribution into groups according to the shape or statistical value (step ST3-3), and selects the pixel value distribution for each group (step ST3-4). Thereafter, the scan control function 442 sets the position in the longitudinal direction Z corresponding to the selected pixel value distribution (step ST3-5). The scan control function 442 also sets each of the plurality of positions z1 and x2 and the angles θ1 and θ2 around the rotation axis of the X-ray tube 11 in association with each other.

  After step ST3, in step ST4, the scan control function 442 controls the second scanography so that the X-ray tube 11 is stopped still and irradiated with X-rays at the set positions z1 and z2. In this embodiment, the scan control function 442 stops the X-ray tube 11 and places the X-ray tube 11 at an angle θ1 (or θ2) associated with the position z1 (or z2) to be stopped. X-rays are irradiated. The timing at which the X-ray tube 11 is arranged at the angle θ1 (or θ2) may be during the movement of the top plate 33 or the X-ray tube 11, and after the top plate 33 or the X-ray tube 11 is stopped at the position z1 (or z2). But you can. The X-ray detector 12 detects X-rays that have passed through the subject P. The output of the X-ray detector 12 is transferred to the console device 40 as detection data via the DAS 18 and a non-contact data transmission circuit (not shown). In this way, the second scano imaging is performed.

  After step ST4, in step ST5, the image generation function 444 has a plurality of second scan images indicating a region including a part of the contour of the subject P based on the output of the X-ray detector 12 by the second scan imaging. g21 and g22 are generated.

  After step ST5, in step ST6, the image processing function 445 protrudes from the first scan image g10 in the lateral direction X of the top 33 based on each of the first scan image g10 and the second scan images g21 and g22. The contour of a part of the subject P is estimated. For example, as shown in FIG. 12, the image processing function 445 specifies a point p1c indicating a part of the contour from a portion having a large change in the pixel value distribution in the channel direction of the second scan image g21. Similarly, for example, as shown in FIG. 13, the image processing function 445 has a contour that extends from the outermost part of the subject P among the parts having a large change in the pixel value distribution in the channel direction of the second scan image g22. The point p2c which shows a part is specified. Thereafter, as shown in FIG. 14, the image processing function 445 causes each of the second scanograms g21 and g22 to partially overlap the first scanogram g10 and the plurality of second scanograms g21 and g22. The contour Cp of the subject P is estimated by connecting points p1c and p2c indicating a part of the contour included in the region to be shown with a line. The line connecting the points p1c and p2c is preferably a straight line in consideration of easy processing and the accuracy of the estimated contour may be low. However, the line connecting the points p1c and p2c is not limited to a straight line, and may be a predetermined curve. Alternatively, the line connecting the points p1c and p2c may be an inverted contour line obtained by inverting the contour line of the subject in the first scanogram g10 around the spine center. That is, since the line connecting the points p1c and p2c only needs to know the field of view (FOV) of the main scan range, a line having an arbitrary shape such as a straight line or a curve can be used as appropriate. In addition, a line connecting the points p1c and p2c may be drawn by operating the input interface 43 by the operator. In any case, the contour of the subject P is estimated in step ST6.

  Further, the image processing function 445 stores a scanogram g30 including the estimated contour Cp in the memory 41 as shown in FIG.

  After step ST6, in step ST7, the display control function 443 controls the display 42 to display the scanogram g30 in the memory 41. Thereby, the display 42 displays the scano image g30 including the estimated contour Cp.

  Hereinafter, based on the displayed scanogram g30, the scan plan used by the operator for the main scan is determined. Subsequently, the X-ray CT apparatus 1 sets an imaging range using the scanogram in the memory 41 according to the operation of the input interface 43 by the operator, and moves the top board 33 to the imaging start position. Thereafter, the X-ray CT apparatus 1 executes the main scan according to the determined scan plan.

  As described above, according to the first embodiment, the first scanography is controlled so that X-rays are emitted while moving the top plate or the X-ray tube along the longitudinal direction of the top plate. Based on the output of the X-ray detection unit by the first scan imaging, a first scan image showing a part of the subject along the longitudinal direction is generated. A plurality of positions along the longitudinal direction are set before the second scan imaging for imaging a region including a part of the contour of the subject that protrudes from the first scan image in the short direction of the top board. The second scan imaging is controlled so that the X-ray tube is stopped at the plurality of positions in order and X-rays are irradiated. Based on the output of the X-ray detection unit by the second scan imaging, a plurality of second scan images indicating a region including a part of the contour are generated. A contour is estimated based on each of the first scano image and the second scano image.

  As described above, even when the first scano image in which one side of the subject is missing is obtained, the contour of the subject can be estimated using each of the second scano images. (FOV) can be selected appropriately. Therefore, the main scan can be appropriately executed even for a subject that protrudes from the imaging range during the scan imaging.

  Further, since the second scan imaging irradiates X-rays at a position where the X-ray tube is stationary, the exposure area is narrower than the first scan imaging that irradiates X-rays while moving the X-ray tube. The amount is low. Unlike the present embodiment, if the first scano imaging is performed twice on the subject that protrudes from the imaging range, the exposure dose of the scano imaging is doubled.

  Therefore, in addition to the above-described effects, the exposure amount in the scan imaging can be applied to the subject that protrudes from the imaging range by the configuration in which the second scan imaging with a narrow exposure area is performed when the region protruding from the first scan image is scanned. Can be reduced. For this reason, even if the detector width is reduced in the future and the number of examinations in which a part of the subject does not fall within the scope of scanography is increased, the contour of the subject is suppressed while suppressing the exposure dose during scanography. Can be estimated.

  In addition, according to the first embodiment, a part of the outline included in the region indicated by each of the second scanograms in a state where the first scanogram and the plurality of second scanograms are partially overlapped with a line. By tying, the contour can be estimated. In this case, the contour can be estimated by a simple process of connecting a part of the contour indicated by each of the second scanograms with a line.

  In addition, according to the first embodiment, before the second scan imaging, each of a plurality of positions in the longitudinal direction and an angle around the rotation axis of the X-ray tube are set in association with each other. At the time of the second scanography, the X-ray tube is stopped and X-rays are irradiated in a state where the X-ray tube is disposed at the angle corresponding to the position to be stopped. In this case, the X-ray tube can be arranged so that the X-ray irradiation position and the irradiation direction are appropriate during the second scanography.

<Modification>
Next, a modification of the first embodiment will be described. In this modification, in the X-ray CT apparatus 1 described above, the angle of the X-ray tube 11 is fixed at the time of the second scan imaging, and the X-ray tube 11 (including the gantry device 10) or the top plate 33 is used as the top plate. It is configured to move along the short direction X of 33.

  Accordingly, the setting function (setting unit) of the scan control function 442 includes each of a plurality of positions z1, z2 along the longitudinal direction Z of the top plate 33 and the short side of the top plate 33 as shown in FIG. The positions x1 and x2 in the direction X are set in association with each other. For example, the setting function may set the table in the memory 41 in association with the positions z1, z2 and the positions x1, x2.

  As shown in FIGS. 15 and 16, the second control function (second control unit) of the scan control function 442 stops the X-ray tube 11 or the top plate 33 in order at a plurality of the set positions z <b> 1 and z <b> 2. At the same time, X-rays are irradiated in a state where the X-ray tube 11 is opposed to the positions x1 and x2 in the short direction associated with the positions z1 and z2 to be stopped. By such second scano imaging, the second scanograms g21 and g22 are generated by the image generation function 444.

  Other configurations are the same as those of the first embodiment.

  According to the modified example having the above-described configuration, after the first scan image is generated, each of the plurality of positions along the longitudinal direction of the top board and the position in the short side direction of the top board are set in association with each other. To do. Subsequently, in the second scan radiography, the X-ray tube or the top plate is stopped in order at the set positions, and the X-ray tube is opposed to the position in the short direction associated with the position to be stopped. In this state, X-rays are irradiated. Therefore, according to the modification, the same operational effects as those of the first embodiment can be obtained except for the operational effects related to the angle of the X-ray tube 11.

<Second Embodiment>
Next, an X-ray CT apparatus according to the second embodiment will be described.

  Unlike the first embodiment, the second embodiment relates to a configuration when the right and left contours of the subject P protrude from the first scan image g11 as shown in FIG.

  In this case, the setting function (setting unit) of the scan control function 442 performs a part of the right contour of the subject P and a part of the left contour of the subject P as shown in FIGS. Each of the plurality of positions z1 and z2 and two angles (θ1a, θ1b) and (θ2a, θ2b) around the rotation axis of the X-ray tube 11 are set in association with each other so that the images are taken separately.

  Other configurations are the same as those of the first embodiment.

  Next, the operation of the X-ray CT apparatus configured as described above will be described with reference to the time chart of FIG.

  Now, it is assumed that step ST1 is executed as described above.

  After step ST1, in step ST2, the image generation function 444 of the processing circuit 44 removes a part of the subject P from the sky based on the output of the X-ray detector 12 by the first scan imaging as shown in FIG. A first scan image g11 shown along the longitudinal direction of the plate 33 is generated. In this example, the first scanogram g11 shows a body portion where both the left and right sides of the subject P protrude as a part of the subject P. Such first scanogram g11 is stored in the memory 41.

  After step ST2, in step ST3, the scan control function 442 captures a region including a part of the contour of the subject P that protrudes from the first scan image g11 in the lateral direction X of the top board 33. Before the above, a plurality of positions z1 and z2 along the longitudinal direction Z of the top plate 33 are set. Specifically, the scan control function 442 includes a plurality of positions z1 and z2 so that a part of the right contour of the subject P and a part of the left contour of the subject P are separately photographed. The two angles (θ1a, θ1b) and (θ2a, θ2b) around the rotation axis of the X-ray tube 11 are set in association with each other.

  After step ST3, in step ST4, the scan control function 442 controls the second scanography so that the X-ray tube 11 is stopped still and irradiated with X-rays at the set positions z1 and z2. In the present embodiment, the scan control function 442 stops the X-ray tube 11 at the position z2 and sets the X-ray tube 11 at an angle θ2a (or θ2b) associated with the position z2 to be stopped. Irradiate the line. The timing at which the X-ray tube 11 is arranged at the angle θ2a (or θ2b) may be during the movement of the top plate 33 or the X-ray tube 11 or after the top plate 33 or the X-ray tube 11 is stopped at the position z2. The X-ray detector 12 detects X-rays that have passed through the subject P. The output of the X-ray detector 12 is transferred to the console device 40 as detection data via the DAS 18 and a non-contact data transmission circuit (not shown). Similarly, the scan control function 442 stops the X-ray tube 11 at the position z1 and outputs X-rays in a state where the X-ray tube 11 is disposed at an angle θ1a (or θ1b) associated with the position z1 to be stopped. Irradiate. The timing at which the X-ray tube 11 is arranged at the angle θ1a (or θ1b) may be during the movement of the top plate 33 or the X-ray tube 11 or after the top plate 33 or the X-ray tube 11 is stopped at the position z1. The X-ray detector 12 detects X-rays that have passed through the subject P. The output of the X-ray detector 12 is transferred to the console device 40 as detection data via the DAS 18 and a non-contact data transmission circuit (not shown). In this way, the second scano imaging is performed.

  After step ST4, in step ST5, the image generation function 444 has a plurality of second scan images indicating a region including a part of the contour of the subject P based on the output of the X-ray detector 12 by the second scan imaging. g21a, g21b, g22a, and g22b are generated.

  After step ST5, in step ST6, the image processing function 445 uses the first scano image g10 to the short side of the top 33 based on each of the first scano image g11 and the second scano image g21a, g21b, g22a, g22b. A contour Cp of a part of the subject P protruding in the direction X is estimated. The estimation method is the same as that in the first embodiment. For example, as shown in FIG. 19, the image processing function 445 identifies points p1a and p1b indicating a part of the contour from the portion where the change is large in the pixel value distribution in the channel direction of the second scan images g21a and g21b. Similarly, for example, the image processing function 445 indicates a point p2a indicating a part of the contour from the outermost part of the subject P among the parts having a large change in the pixel value distribution in the channel direction of the second scan images g22a and g22b. , P2b. Thereafter, the image processing function 445 performs processing for each of the second scanograms g21a, g21b, g22a, and g22b in a state where the first scanogram g11 and the plurality of second scanograms g21a, g21b, g22a, and g22b are partially overlapped. The contour Cp of the subject P is estimated by connecting points p1a, p1b, p2a, and p2b indicating a part of the contour included in the region indicated by. Note that, as described above, straight lines, curved lines, and inverted contour lines can be used as appropriate for the lines connecting the respective points. In any case, the contour Cp of the subject P is estimated in step ST6.

  In addition, the image processing function 445 saves a scanogram including the estimated contour Cp in the memory 41.

  Thereafter, the processing after step ST7 is executed as described above.

  As described above, according to the second embodiment, when the left and right contours of the subject protrude from the first scan image, a part of the right contour of the subject and a part of the left contour of the subject. Are set in association with each other and two angles around the rotation axis of the X-ray tube.

  Thus, even when the left and right contours of the subject protrude from the first scan image, a part of the right contour of the subject and a part of the left contour of the subject are captured during the second scan imaging. You can shoot separately. Therefore, even when the left and right contours of the subject protrude from the first scanogram, the exposure dose for scanography can be reduced as in the first embodiment.

<Modification>
Next, a modification of the second embodiment will be described. In this modification, in the X-ray CT apparatus 1 described above, the angle of the X-ray tube 11 is fixed at the time of the second scan imaging, and the X-ray tube 11 (including the gantry device 10) or the top plate 33 is used as the top plate. It is configured to move along the short direction X of 33.

  Accordingly, as shown in FIG. 21, the setting function (setting unit) of the scan control function 442 causes the right side of the subject P when the contours on the left and right sides of the subject P protrude from the first scan image g11. Each of a plurality of positions z1 and z2 along the longitudinal direction Z of the top 33 and the short side of the top 33 so that a part of the contour and a part of the left contour of the subject P are separately photographed. Two positions (x1a, x1b) and (x2a, x2b) in the direction X are set in association with each other. For example, the setting function may set the positions z1, z2 and the positions (x1a, x1b), (x2a, x2b) in association with each other in a table in the memory 41.

  As shown in FIGS. 21 and 22, the second control function (second control unit) of the scan control function 442 causes the X-ray tube 11 or the top plate 33 to stand still at the set positions z1 and z2. At the same time, X-rays are irradiated with the X-ray tube 11 facing the positions (x1a, x1b), (x2a, x2b) in the short direction associated with the positions z1, z2 to be stopped. As a result of such second scanography, the image generation function 444 generates second scanograms g21a, g21b, g22a, and g22b.

  Other configurations are the same as those of the first embodiment.

  According to the modified example having the above-described configuration, after the first scan image is generated, when the left and right contours of the subject protrude from the first scan image, a part of the right contour of the subject and the subject are detected. Each of a plurality of positions and two positions in the short direction are set in association with each other so that a part of the left contour of the sample is separately photographed. Subsequently, in the second scan radiography, the X-ray tube or the top plate is stopped in order at the set positions, and the X-ray tube is opposed to the position in the short direction associated with the position to be stopped. In this state, X-rays are irradiated. Therefore, according to the modification, the same operational effects as those of the second embodiment can be obtained except for the operational effects related to the angle of the X-ray tube 11.

<Third Embodiment>
Next, an X-ray CT apparatus according to the third embodiment will be described.

  The third embodiment is a modification of the first or second embodiment, and relates to a configuration for estimating a tube current value for the main scan. Specifically, the reason why the main scan cannot be performed properly is not limited to the case where the field of view (FOV) is not known, but the correct dose cannot be obtained from the first scanogram that has been lost, and AEC (Auto Exposure Control: automatic) The accuracy of (exposure control) may be reduced. In the third embodiment, such a decrease in accuracy is prevented, and the main scan can be appropriately executed. In the following description, the first and second embodiments are mainly modified examples of the second embodiment (when the right and left contours of the subject P protrude from the first scan image g11). Is described.

  Specifically, the setting function of the scan control function 442 is the longitudinal direction corresponding to a part of the protruding outline when the left and right or left and right outlines of the subject P protrude from the first scan image g10 or g11. A position z2 along the direction Z is set. Note that the setting function may set a plurality of positions z1 and z2 along the longitudinal direction of the top board 33 as described above.

  The scan control function 442 has an X-ray imaging control function in addition to the functions described above. The X-ray imaging control function (X-ray imaging control unit) stops the X-ray tube 11 at the position z2 set by the setting function, and is within the X-ray irradiation range among the angles around the rotation axis of the X-ray tube 11. X-ray imaging is controlled so as to irradiate X-rays with the X-ray tube disposed at an angle (for example, 90 °) where the contours of the upper and lower sides of the subject P enter.

  The image generation function 444 has an X-ray image generation function in addition to the functions described above. The X-ray image generation function (X-ray image generation unit), as shown in FIG. 23, shows an X-ray image g showing a partial region of the subject P based on the output of the X-ray detector 12 in X-ray imaging. (90 °) is generated. Note that “X-ray imaging” and “X-ray image” may be referred to as “third scano imaging” and “third scano image”, respectively.

  The image processing function 445 has a tube current estimation function in addition to the functions described above. The tube current estimation function (tube current estimation unit) is set based on a difference value between the pixel value of the first scanogram g10 or g11 at the position set by the setting function and the pixel value of the X-ray image g (90 °). The tube current value for the main scan at the specified position is estimated.

  Here, the tube current estimation function may execute the following two processes (i) and (ii) when the left and right contours of the subject P protrude from the first scanogram g11.

  (I) A process of adding half the difference value to the pixel value of the first scanogram g11 and obtaining the pixel value of the addition result. Here, the “difference value” corresponds to a region (left and right sides) where the subject P protrudes. The “half value of the difference value” corresponds to one of the left and right sides of the subject P protruding. In the case where only the left and right sides originally protrude (first scanogram g10), “half the difference value” may be read as “difference value”.

  (Ii) A process of estimating the tube current value for the main scan based on the pixel value of the addition result and the pixel value of the reference image of the main scan.

  Other configurations are the same as those in the first or second embodiment. However, from the viewpoint of estimating the tube current value, the above-described function relating to the second scan imaging is not essential and may be omitted. Here, as functions that can be omitted, there are a second control function that controls the second scano imaging, a second generation function that generates the second scano image, and an estimation unit that estimates the contour.

  Next, the operation of the X-ray CT apparatus configured as described above will be described with reference to the time chart of FIG. 24, the flowchart of FIG. 25, and the schematic diagram of FIG. In the following description, the case where the right and left contours of the subject P protrude from the first scan image g11 will be mainly described as an example.

  In this operation, steps ST4X, ST5X, and ST6X for estimating the tube current value are executed when executing the above-described steps ST1 to ST7 for estimating the contour. Steps ST4X, ST5X, and ST6X are executed, for example, immediately before steps ST4, ST5, and ST6, respectively.

  Now, assume that steps ST1 to ST3 have been executed as described above. However, one of the positions set in step ST3 is also used in steps ST4X and ST6X.

  After step ST3, in step ST4X, the scan control function 442 stops the X-ray tube 11 at the set position z2, and within the X-ray irradiation range of the angle around the rotation axis of the X-ray tube 11, the scan control function 442 X-ray imaging is controlled so that X-rays are irradiated with the X-ray tube disposed at an angle (for example, 90 °) where the contours of the upper and lower sides of P enter.

  After step ST4X, step ST4 is executed as described above.

  After step ST4, in step ST5X, the image generation function 444 generates an X-ray image g (90 °) indicating a partial region of the subject P based on the output of the X-ray detector 12 in X-ray imaging. To do.

  After step ST5X, step ST5 is executed as described above.

  After step ST5, in step ST6X, the image processing function 445 sets based on the difference value between the pixel value of the first scanogram g11 at the set position z2 and the pixel value of the X-ray image g (90 °). The tube current value for the main scan at the position z2 is estimated. For example, the image processing function 445 adds half the difference value to the pixel value of the first scanogram g11, and obtains the pixel value of the addition result. Thereafter, the image processing function 445 estimates the tube current value for the main scan based on the pixel value of the addition result and the pixel value of the reference image of the main scan.

  For example, it is assumed that the pixel value of the addition result is a pixel value Px1 for scan imaging, and the tube current value for scan imaging is Ti1. Further, the pixel value of the reference image for the main scan is Px2, and the tube current value for the main scan is Ti2. At this time, there is the following relationship.

Px1: Ti1 = Px2: Ti2
Therefore, the tube current value Ti2 for the main scan is estimated as shown in the following equation.

Ti2 = Ti1 × Px2 / Px1
For example, as shown in FIG. 26, the estimated tube current value Ti2 for the main scan is the position of the abdomen as compared to the solid line indicating the tube current value for the main scan when the loss from the first scan image is not considered. A high value is shown in z2. The same applies to the foot position zf illustrated in FIG. However, since the foot part illustrated in FIG. 26 is missing on the left and right sides, the difference value is added instead of adding half the difference value. On the other hand, in the head position zh illustrated in FIG. 26, since there is no defect from the first scanogram, a solid line that does not consider the defect overlaps with a point that considers the defect. Although not shown, similarly, when other parts are also out of the irradiation range and missing from the first scan image g11, the tube current value for the main scan of the other parts is estimated to be higher than the solid line. The

  After step ST6X, the processing after step ST6 is executed as described above.

  As described above, according to the third embodiment, when the left and right contours of the subject protrude from the first scan image, a position along the longitudinal direction corresponding to a part of the protruding contour is set. . With the X-ray tube stationary at the set position, the X-ray tube is placed at an angle around the rotation axis of the X-ray tube so that the contours of the upper and lower sides of the subject are within the X-ray irradiation range. X-ray imaging is controlled so as to emit X-rays. Based on the output of the X-ray detector in the X-ray imaging, an X-ray image showing a partial region of the subject is generated. Based on the difference value between the pixel value of the first scanogram at the set position and the pixel value of the X-ray image, the tube current value for the main scan at the set position is estimated.

  Therefore, even if the first scanogram in which both sides of the subject are missing is obtained, the tube current value for the main scan is obtained using an X-ray image obtained by X-ray imaging at an angle where the contours of the upper and lower sides of the subject enter Since it can be estimated, a decrease in the accuracy of AEC in the main scan can be prevented. Therefore, the main scan can be appropriately executed even for a subject that protrudes from the imaging range during the scan imaging. In addition, when X-ray imaging is performed at an angle where the contours of the upper and lower sides of the subject are included, the state in which the X-ray tube is stationary is performed, so that the exposure area by X-ray imaging can be narrowed. For this reason, it is possible to reduce the exposure dose in the X-ray imaging for estimating the tube current value for the subject protruding from the imaging range.

  Further, according to the third embodiment, when the tube current value is estimated, a half value of the difference value is added to the pixel value of the first scanogram, and the pixel value of the addition result is obtained. The tube current value for the main scan is estimated based on the pixel value of the addition result and the pixel value of the reference image of the main scan. Therefore, when the left and right sides of the subject are missing at the same rate, the tube current value for the main scan can be estimated by adding half the difference value.

  In addition, according to the third embodiment, the steps ST1 to ST7 of the second embodiment can be performed, so that the effects of the second embodiment can be obtained together.

  According to at least one embodiment described above, the first scanography is controlled so as to irradiate X-rays while moving the top plate or the X-ray tube along the longitudinal direction of the top plate. Based on the output of the X-ray detection unit by the first scan imaging, a first scan image showing a part of the subject along the longitudinal direction is generated. A plurality of positions along the longitudinal direction are set before the second scan imaging for imaging a region including a part of the contour of the subject that protrudes from the first scan image in the short direction of the top board. The second scan imaging is controlled so that the X-ray tube is stopped at the plurality of positions in order and X-rays are irradiated. Based on the output of the X-ray detection unit by the second scan imaging, a plurality of second scan images indicating a region including a part of the contour are generated. A contour is estimated based on each of the first scano image and the second scano image.

  Therefore, the main scan can be appropriately executed even for a subject that protrudes from the imaging range during the scan imaging.

  The term “processor” used in the above description is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an application specific integrated circuit (ASIC)), a programmable logic device (for example, It means a circuit such as a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). The processor implements the function by reading and executing the program stored in the memory. Instead of storing the program in the memory, the program may be directly incorporated into the processor circuit. In this case, the processor realizes the function by reading and executing the program incorporated in the circuit. Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining a plurality of independent circuits to realize the function. Good. Furthermore, a plurality of components in FIG. 1 may be integrated into one processor to realize the function.

  In addition, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof in the same manner as included in the scope and gist of the invention.

DESCRIPTION OF SYMBOLS 1 X-ray CT apparatus 10 Mounting apparatus 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high voltage apparatus 15 Control apparatus 16 Wedge 17 Collimator 18 DAS
DESCRIPTION OF SYMBOLS 30 Bed apparatus 31 Base 32 Bed drive apparatus 33 Top plate 34 Support frame 40 Console apparatus
41 Memory 42 Display 43 Input interface 44 Processing circuit 441 System control function 442 Scan control function 443 Display control function 444 Image generation function 445 Image processing function P Subject g10, g11 First scan image g21, g22 Second scan image

Claims (9)

An X-ray tube for irradiating the subject placed on the top plate with X-rays;
An X-ray detector that detects X-rays transmitted through the subject;
A first control unit that controls first scanography so as to irradiate the X-ray while moving the top plate or the X-ray tube along the longitudinal direction of the top plate;
A first generation unit that generates a first scan image showing a part of the subject along the longitudinal direction based on an output of the X-ray detection unit by the first scano imaging;
A plurality of positions along the longitudinal direction are set before the second scan imaging for imaging a region including a part of the contour of the subject that protrudes from the first scan image in the lateral direction of the top plate. A setting section;
A second control unit that controls the second scan imaging so as to irradiate the X-ray with the X-ray tube stationary in order at the plurality of positions;
A second generation unit that generates a plurality of second scan images indicating a region including a part of the contour based on an output of the X-ray detection unit by the second scan imaging;
An X-ray CT apparatus comprising: an estimation unit that estimates the contour based on each of the first scanogram and the second scanogram.   The estimation unit connects a part of the contour included in the region indicated by each of the second scanograms with a line in a state where the first scanogram and the plurality of second scanograms are partially overlapped. The X-ray CT apparatus according to claim 1, wherein the contour is estimated. The setting unit associates and sets each of the plurality of positions and an angle around the rotation axis of the X-ray tube,
The said 2nd control part makes the said X-ray tube stand still, and irradiates the said X-ray in the state which has arrange | positioned the said X-ray tube at the said angle matched with the position to make it stand still. X-ray CT system.   The setting unit separates a part of the right contour of the subject and a part of the left contour of the subject separately when the contours on the left and right sides of the subject protrude from the first scan image. The X-ray CT apparatus according to claim 3, wherein each of the plurality of positions and two angles around the rotation axis of the X-ray tube are set in association with each other so as to perform imaging. The setting unit sets each of the plurality of positions and the position in the short direction in association with each other,
The second control unit makes the X-ray tube or the top plate stand still in order at the plurality of positions, and the X-ray tube faces the position in the short direction associated with the position to be stopped. The X-ray CT apparatus according to claim 1, wherein the X-ray is irradiated with the X-ray CT.   The setting unit separates a part of the right contour of the subject and a part of the left contour of the subject separately when the contours on the left and right sides of the subject protrude from the first scan image. The X-ray CT apparatus according to claim 5, wherein each of the plurality of positions and the two positions in the lateral direction are set in association with each other so as to perform imaging. An X-ray tube for irradiating the subject placed on the top plate with X-rays;
An X-ray detector that detects X-rays transmitted through the subject;
A first control unit that controls first scanography so as to irradiate the X-ray while moving the top plate or the X-ray tube along the longitudinal direction of the top plate;
A first generation unit that generates a first scan image showing a part of the subject along the longitudinal direction based on an output of the X-ray detection unit by the first scano imaging;
A setting unit that sets a position along the longitudinal direction corresponding to a part of the protruding outline when the right and left or right and left sides of the subject protrude from the first scan image;
The X-ray tube is stopped at the set position, and the X-ray tube is positioned at an angle around the rotation axis of the X-ray tube so that the upper and lower contours of the subject are within the X-ray irradiation range. An X-ray imaging control unit that controls X-ray imaging so as to irradiate the X-rays with the
An X-ray image generation unit that generates an X-ray image showing a partial region of the subject based on an output of the X-ray detection unit in the X-ray imaging;
A tube current estimation unit that estimates a tube current value for the main scan at the set position based on a difference value between a pixel value of the first scanogram at the set position and a pixel value of the X-ray image; X-ray CT apparatus provided. The tube current estimator is
A process of adding a half value of the difference value to the pixel value of the first scan image and obtaining a pixel value of the addition result when the right and left contours of the subject protrude from the first scan image. ,
The X-ray CT apparatus according to claim 7, wherein a process of estimating a tube current value for the main scan is performed based on a pixel value of the addition result and a pixel value of a reference image of the main scan. A second control unit, a second generation unit, and an estimation unit;
The setting unit sets a plurality of positions along the longitudinal direction,
The second control unit controls second scan imaging so that the X-ray tube is stopped in order at the plurality of set positions and the X-ray is irradiated.
The second generation unit generates a plurality of second scan images indicating a region including a part of the contour based on an output of the X-ray detection unit by the second scan imaging.
The X-ray CT apparatus according to claim 7 or 8, wherein the estimation unit estimates the contour based on each of the first scanogram and the second scanogram.