JP7158941B2 - X-ray computed tomography device - Google Patents

Description

An embodiment of the present invention relates to an X-ray computed tomography apparatus.

SSDE (Size-Specific Dose Estimates) is presented as a dose index for CT imaging. SSDE is calculated based on the cross-sectional shape of the object estimated using the localization images. That is, positioning imaging is necessary to estimate the cross-sectional shape.

On the other hand, in the pre-stage of CT imaging, a subject is positioned using a projector that emits a light beam that indicates the reference line of the imaging range. In recent years, it has become possible to omit positioning photographing for positioning by using a projector that emits light rays indicating the outer frame of the photographing range. However, if positioning radiography is omitted, it is impossible to estimate the cross-sectional shape and, in turn, to calculate a predicted dose index such as SSDE.

Japanese Patent Publication No. 2014-528284 JP 2006-116137 A JP-A-2006-26417

“Size-Specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations”, AAPM Report No.204, American Association of Physicists in Medicine, 2011 “Use of Water Equivalent Diameter for Calculating Patient Size and Size-Specific Dose Estimates (SSDE) in CT”, AAPM Report No.220, American Association of Physicists in Medicine, September 2014

A problem to be solved by the present invention is to accurately estimate the cross-sectional shape of a subject.

An X-ray computed tomography apparatus according to an embodiment includes a pedestal for performing X-ray CT imaging, a bed for movably supporting a table on which a subject is placed, and the A light irradiator that irradiates a subject with a light beam, and an estimating unit that estimates a shape index value of a cross section of the subject in an imaging range using the light beam irradiated on the subject.

FIG. 1 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the first embodiment. FIG. 2 is a diagram showing the appearance of the pedestal in the first embodiment. FIG. 3 is a diagram showing a cross section of the pedestal of FIG. 2 including the Z axis. FIG. 4 is a diagram showing an example of a visible ray indicating a frame line forming an outer frame of a CT imaging range, which is irradiated by the projector of FIG. FIG. 5 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function of the arithmetic circuit according to the first embodiment. 6 is a diagram showing the arrangement of the optical cameras in FIG. 1. FIG. 7 is a diagram showing an example of an optical image generated by the optical camera of FIG. 6. FIG. 8 is a diagram showing an example of a human body model stored in the storage circuit of FIG. 1. FIG. FIG. 9 is a diagram showing an example of an imaging cross-section of the human body model of FIG. FIG. 10 is a diagram for explaining bed height correction parameters determined by the correction parameter determination function of the arithmetic circuit in FIG. FIG. 11 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the second embodiment. FIG. 12 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function of the arithmetic circuit according to the second embodiment. FIG. 13 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the third embodiment. FIG. 14 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function of the arithmetic circuit according to the third embodiment. FIG. 15 is a diagram schematically showing the outline of the cross-sectional shape estimation function performed by the arithmetic circuit in steps SC1-SC4 of FIG. FIG. 16 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the fourth embodiment. FIG. 17 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function of the arithmetic circuit according to the fourth embodiment. FIG. 18 is a diagram schematically showing an outline of estimation of cross-sectional shape index values using infrared rays according to the fourth embodiment.

An X-ray computed tomography apparatus according to this embodiment will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the first embodiment. As shown in FIG. 1, the X-ray computed tomography apparatus according to the first embodiment has a pedestal 10 and a console 100. As shown in FIG. For example, the gantry 10 is installed in an examination room, and the console 100 is installed in a control room adjacent to the examination room. The gantry 10 and the console 100 are connected so as to be able to communicate with each other. The gantry 10 is equipped with an imaging mechanism for performing CT imaging of an object P such as a patient with X-rays. A console 100 is a computer that controls the gantry 10 .

As shown in FIG. 1, the gantry 10 has a substantially cylindrical rotating frame 11 with an opening. The rotating frame 11 is also called a rotating section. As shown in FIG. 1, an X-ray tube 13 and an X-ray detector 15 are attached to the rotating frame 11 so as to face each other across an opening. The rotating frame 11 is an annular metal frame made of metal such as aluminum. As will be described later, the mount 10 has a main frame made of metal such as aluminum. The mainframe is also called a fixed part. The rotating frame 11 is rotatably supported by the main frame.

The X-ray tube 13 generates X-rays. The X-ray tube 13 is a vacuum tube that holds a cathode that generates thermoelectrons and an anode that receives thermoelectrons flying from the cathode and generates X-rays. The X-ray tube 13 is connected to an X-ray high voltage device 17 via a high voltage cable.

The X-ray high-voltage device 17 can be applied to any type of X-ray high-voltage device, such as a transformer type X-ray high-voltage device, a constant voltage type X-ray high-voltage device, a capacitor type X-ray high-voltage device, an inverter type X-ray high-voltage device, or the like. . The X-ray high voltage device 17 is attached to the rotating frame 11, for example. The X-ray high voltage device 17 adjusts the tube voltage and tube current applied to the X-ray tube 13 and the focal size of the X-ray under the control of the gantry control circuit 33 .

As shown in FIG. 1, the rotating frame 11 receives power from the rotary drive device 21 and rotates around the central axis Z at a constant angular velocity. Any motor such as a direct drive motor or a servomotor is used as the rotary drive device 21 . The rotary drive device 21 is housed in the pedestal 10, for example. The rotation drive device 21 receives a drive signal from the gantry control circuit 33 and generates power for rotating the rotation frame 11 .

A CT imaging range (FOV: Field Of View) is set in the opening of the rotating frame 11 . A top supported by the bed 23 is inserted into the opening of the rotating frame 11 . A subject P is placed on the top plate. The bed 23 movably supports the top board. A bed driving device 25 is accommodated in the bed 23 . The bed drive device 25 receives a drive signal from the gantry control circuit 33 and generates power for moving the table top forward/backward, up/down, and left/right. The bed 23 positions the tabletop so that the imaging region of the subject P is included in the CT imaging range.

X-ray detector 15 detects X-rays generated from X-ray tube 13 . Specifically, the X-ray detector 15 has a plurality of detection elements arranged on a two-dimensional curved surface. Each detection element has a scintillator and a photoelectric conversion element. A scintillator is formed by a material that converts X-rays into photons. The scintillator converts incident X-rays into photons of a number corresponding to the intensity of the incident X-rays. A photoelectric conversion element is a circuit element that amplifies photons received from a scintillator and converts them into electrical signals. For example, a photomultiplier tube, a photodiode, or the like is used as the photoelectric conversion element. The detection element may be of an indirect conversion type that detects X-rays after converting them into photons as described above, or may be of a direct conversion type that directly converts X-rays into electrical signals.

A data acquisition circuit 19 is connected to the X-ray detector 15 . In accordance with instructions from the gantry control circuit 33, the data acquisition circuit 19 reads an electrical signal corresponding to the intensity of the X-rays detected by the X-ray detector 15 from the X-ray detector 15, and stores the read electrical signal in the view period. Raw data is collected having digital values corresponding to the dose of x-rays over a period of time. The data collection circuit 19 is implemented by, for example, an ASIC (Application Specific Integrated Circuit) equipped with circuit elements capable of generating raw data.

The light projector 27 is provided on the rotating frame 11 . In accordance with instructions from the gantry control circuit 33, the projector 27 emits visible light (projection laser) indicating the reference line of the CT imaging range to the top plate inserted into the opening or the subject P placed on the top plate. to emit light. Visible light is projected for alignment of the subject P. FIG.

The optical camera 29 is an optical imaging unit that generates an optical image of the subject P irradiated with visible light from the light projector 27 as a subject. The optical camera 29 may be installed at any position as long as it can photograph the subject P irradiated with the visible light from the light projector 27 . The optical image is transmitted to console 100 .

The input circuit 31 inputs various commands from the user regarding positioning of the bed 23 and the light projector 27 . Specifically, the input circuit 31 has an input device and an input interface. Input devices include hardware or software switch buttons and the like. The input interface is connected to the gantry control circuit 33 . The input interface converts a user's input operation through the input device into an electric signal and outputs the electric signal to the gantry control circuit 33 .

The gantry control circuit 33 controls the X-ray high-voltage device 17, the data acquisition circuit 19, the rotation drive device 21, and the bed drive device 25 in order to perform X-ray CT imaging according to the imaging conditions transmitted from the arithmetic circuit 101 of the console 100. etc. are controlled synchronously. Further, the gantry control circuit 33 controls the rotary drive device 21 and the projector 27 for positioning the subject P and the like. As hardware resources, the gantry control circuit 33 includes a processing unit (processor) such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) and a storage device (such as a ROM (Read Only Memory) or a RAM (Random Access Memory)). memory). In addition, the gantry control circuit 33 is an ASIC, a field programmable gate array (FPGA), another complex programmable logic device (CPLD), a simple programmable logic device (Simple Programmable Logic Device). : SPLD). The gantry control circuit 33 according to this embodiment implements a projector setting function 291 by executing a control program for the projector 27 .

In the projector setting function 291 , the gantry control circuit 33 sets a setting parameter that defines the irradiation position of the visible light from the projector 27 according to the user's instruction via the input circuit 31 . The setting parameters are called projection parameters. The projection parameters that define the irradiation position of the visible light include the irradiation angle of the visible light by the light projector 27, the position of the light source of the light projector 27, and the like.

As shown in FIG. 1, the console 100 has an arithmetic circuit 101 , a display 103 , an input circuit 105 and a memory circuit 107 .

The arithmetic circuit 101 has, as hardware resources, a processor such as a CPU, an MPU, or a GPU (Graphics Processing Unit), and a memory such as a ROM or a RAM. By executing various programs, the arithmetic circuit 101 performs a preprocessing function 111, a reconstruction function 113, an image processing function 115, a cross-sectional shape estimation function 117-1, an SSDE calculation function 119, a correction parameter determination function 121, an imaging parameter determination function 123, and a It implements the system control function 125 . The preprocessing function 111, the reconstruction function 113, the image processing function 115, the cross-sectional shape estimation function 117-1, the SSDE calculation function 119, the correction parameter determination function 121, the imaging parameter determination function 123, and the system control function 125 are implemented by arithmetic circuits. 101 may be mounted on one substrate, or may be distributed and mounted on a plurality of substrates of the arithmetic circuit 101 .

In the preprocessing function 111 , the arithmetic circuit 101 performs preprocessing such as logarithmic transformation on the raw data transmitted from the gantry 10 . Raw data after preprocessing is also called projection data.

In the reconstruction function 113, the arithmetic circuit 101 generates a CT image expressing the spatial distribution of CT values regarding the subject P based on the preprocessed raw data. An existing image reconstruction algorithm such as the FBP (filtered back projection) method or the iterative reconstruction method may be used as the image reconstruction algorithm.

The arithmetic circuit 101 in the image processing function 115 performs various image processing on the CT image reconstructed by the reconstruction function 113 . For example, the arithmetic circuit 101 performs three-dimensional image processing such as volume rendering, surface volume rendering, pixel value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing on the CT image to display the image. to generate

In the cross-sectional shape estimating function 117-1, the arithmetic circuit 101 estimates the shape index value for the imaging cross section of the subject P included in the CT imaging range based on the position of the visible light beam irradiated onto the subject P by the light projector 27. . The shape index value is called a cross-sectional shape index value. For example, the arithmetic circuit 101 applies the irradiation position of the visible light to the subject P to a human body model that imitates the three-dimensional shape of the human body, thereby obtaining a cross-section related to the imaging cross-section corresponding to the irradiation position of the visible light. Estimate shape index values.

In the SSDE calculation function 119, the arithmetic circuit 101 calculates SSDE (Size-Specific Dose Estimates) based on the cross-sectional shape index value estimated by the cross-sectional shape estimation function 117-1 and CTDI (Computed Tomography Dose index) values measured in advance. ) value.

In the correction parameter determination function 121, the arithmetic circuit 101 determines correction parameters for correcting the shape of the imaging cross section of the subject P, the cross-sectional shape index value of the cross section, and the SSDE value. The correction parameters according to the first embodiment include a correction parameter corresponding to the height of the tabletop (hereinafter referred to as a bed height correction parameter), an SSDE value calculated by the SSDE calculation function 119, and an actually measured dose value. There is a correction parameter (referred to as a deviation correction parameter) corresponding to the deviation of .

In the imaging parameter determination function 123, the arithmetic circuit 101 determines a plurality of imaging parameters forming imaging conditions for CT imaging. In addition to the tube voltage value and the tube current value, the imaging parameters include modulation parameters related to directional modulation of the tube current. Arithmetic circuit 101 determines a modulation parameter based on the cross-sectional shape index value estimated by cross-sectional shape estimation function 117-1.

In the system control function 125, the arithmetic circuit 101 comprehensively controls the X-ray computed tomography apparatus according to this embodiment. Specifically, the arithmetic circuit 101 reads out the control program stored in the storage circuit 107, expands it on the memory, and controls each part of the X-ray computed tomography apparatus according to the expanded control program.

A display 103 displays various data such as CT images. As display 103, for example, a CRT display, liquid crystal display, organic EL display, LED display, plasma display, or any other display known in the art can be used as appropriate.

The input circuit 105 inputs various commands from the user. Specifically, the input circuit 105 has an input device and an input interface. The input device receives various commands from the user. A keyboard, a mouse, various switches, a touch pad, a touch panel display, and the like can be used as input devices. The input interface supplies an output signal from the input device to the arithmetic circuit 101 via the bus. The input device of the input circuit 105 may be a computer device connected to the console 100 via a wire or wirelessly and having the above-described input device.

The storage circuit 107 is a storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various information. Also, the storage circuit 107 may be a drive device or the like that reads and writes various information from/to a portable storage medium such as a CD-ROM drive, a DVD drive, and a flash memory. For example, the storage circuit 107 stores control programs and the like related to CT imaging according to this embodiment.

FIG. 2 is a diagram showing the appearance of the gantry 10 according to the first embodiment. FIG. 3 is a diagram showing a cross section including the Z-axis of the pedestal 10 of FIG. The center axis of the rotating frame 11 is the Z axis, the axis perpendicular to the Z axis is the Y axis, and the axis horizontally perpendicular to the Z axis is the X axis. As shown in FIGS. 2 and 3, the gantry 10 has a gantry housing 40 in which an opening 41 having a substantially cylindrical shape is formed. The gantry housing 40 accommodates a main frame 43 functioning as a fixed part and a rotating frame 11 functioning as a rotating part. The main frame 43 supports the rotating frame 11 so as to be continuously rotatable around the Z-axis via bearings. An X-ray tube 13, an X-ray detector 15, and a data acquisition circuit 19, which are not shown in FIGS. 2 and 3, are attached to the rotating frame 11. FIG. Further, the light projector 27 is attached to the rotating frame 11 so that the visible light emitted by the light projector 27 is directed toward the opening 41 . The projector 27 emits visible light for directly viewing the reference line of the CT imaging range. The reference line of the CT imaging range includes the centerline of the CT imaging range in the X, Y and Z axial directions and the frame line forming the outer frame of the CT imaging range. Note that the reference line of the CT imaging range is not limited to the above, and may be any line useful for positioning the imaging region of the subject P in the CT imaging range.

As shown in FIGS. 2 and 3, visible rays emitted from the projector 27 and X-rays emitted from the X-ray tube 13 (not shown) are emitted from the inner wall facing the opening 41 of the frame housing 40 . A gap 47 is provided for passage. Since the projector 27 and the X-ray tube 13 are attached to the rotating frame 11, the gap 47 is formed along the entire circumference of the Z-axis of the inner wall. A permeable membrane 45 is attached so as to cover the gap 47 . Visible light emitted from the projector 27 and X-rays generated from the X-ray tube 13 pass through the transmission film 45 . For example, the permeable film 45 is formed of a transparent or translucent film made of polyester.

In the following, in order to specifically describe the present embodiment, it is assumed that the visible light emitted by the light projector 27 indicates a frame line forming the outer frame of the CT imaging range.

FIG. 4 is a diagram showing an example of visible light rays Lz and Lx indicating a frame line forming an outer frame of a CT imaging range. As shown in FIG. 4, visible light Lz indicates the outer frame of the imaging range in the Z direction. More specifically, the visible light Lz includes a light ray Lz1 on the front side of the Z axis (for example, the head side of the patient P) and a light ray Lz2 on the rear side (for example, the foot side of the patient P). The relationship between the direction of the patient P and the direction of the Z axis is not limited to this, and the front side of the Z axis may be the foot side of the patient P, and the back side of the Z axis may be the head side of the patient P. The irradiation position of the light beam Lz1 and the irradiation position of the light beam Lz2 can be adjusted independently of each other along the Z-axis. The visible ray Lx includes a ray Lx1 on the left side of the X-axis and a ray Lx2 on the right side. The irradiation position of the light beam Lx1 and the irradiation position of the light beam Lx2 can be adjusted independently of each other along the X-axis. For example, the user operates the input circuit 31 or 105 to adjust the irradiation positions of the visible rays Lz1, Lz2, Lx1 and Lx2. The gantry control circuit 33 sets light projection parameters for irradiating the visible light rays Lz1, Lz2, Lx1 and Lx2 to the irradiation positions according to the adjustment operation. That is, the positions of the light sources of the light projectors 27 capable of irradiating the visible rays Lz1, Lz2, Lx1 and Lx2 to the irradiation positions corresponding to the adjustment operation or the irradiation angles of the visible rays are set. Next, the gantry control circuit 33 moves the light source of the light projector 27 to the set position or tilts the light source of the light projector 27 to the irradiation angle. As a result, visible light rays Lz1, Lz2, Lx1, and Lx2 are irradiated to irradiation positions according to the projection parameters.

Although FIGS. 2 and 3 exemplify a mode in which two light projectors 271 are attached to the rotating frame 11, the X-ray computed tomography apparatus according to the first embodiment is not limited to this. That is, any number of light projectors 27 may be attached to the rotating frame 11 . Further, if the light projector 27 does not need to rotate around the rotation axis Z, it may be attached to components other than the rotating frame 11, for example, the main frame 43 and the gantry housing 40, among the components of the gantry 10. Also good.

FIG. 5 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function 125 of the arithmetic circuit 101 according to the first embodiment. As shown in FIG. 5, the arithmetic circuit 101 first causes the gantry control circuit 33 to irradiate visible light (step SA1). In step SA1, the gantry control circuit 33 causes the projector 27 to irradiate the patient P with visible light that indicates the reference line of the CT imaging range. For example, the height of the top plate 231 of the bed 23 (hereinafter referred to as the bed height) is adjusted by an operation via the input circuit 31 by a user such as a medical worker so that the imaging region of the patient P is included in the CT imaging range. and horizontal position are adjusted. At this time, the light projector 27 irradiates a visible ray indicating the outer frame of the CT imaging range as a visible ray indicating the reference line of the CT imaging range. The irradiation position of the visible light is arbitrarily adjusted by the user via the input circuit 31 or 105 . The projection parameters corresponding to the irradiation position of the visible light are transmitted from the gantry control circuit 33 to the console 100 and stored in the storage circuit 107 .

When step SA1 is performed, the arithmetic circuit 101 causes the optical camera 29 to perform optical photography (step SA2). In step SA2, the optical camera 29 optically photographs the patient P irradiated with visible light to generate an optical image (step SA2). An optical image, for example, has an RGB value assigned to each pixel. At the time of optical imaging, the height center in the imaging range of the patient P does not need to match the isocenter height. The generated optical image is transmitted to console 100 and stored in storage circuit 107 . At this time, the optical image is stored in association with the height value of the couch.

FIG. 6 is a diagram showing the arrangement of the optical camera 29. As shown in FIG. As shown in FIG. 6, at the time of positioning, visible light L indicating the outer frame of the CT imaging range is emitted from the projector 27 toward the patient P placed on the top plate 231 of the bed 23 . The optical camera 29 is attached via a support rod 49 to the end of the top plate 231 opposite to the gantry housing 40 . The optical camera 29 is mounted at such a height and tilt angle that the patient P irradiated with the visible light L from the light projector 27 is included in the optical photographing range. For example, the optical camera 29 is not limited to being attached to the top plate 231 via the support rods 49, and may be attached to the ceiling, side wall, floor, or pedestal 10 of the examination room.

When step SA2 is performed, the arithmetic circuit 101 executes the cross-sectional shape estimation function 117-1. In the cross-sectional shape estimation function 117-1, the arithmetic circuit 101 first processes the optical image generated by the optical camera 29 to identify the anatomical position irradiated with visible light (step SA3). In this embodiment, the anatomical position means a position within the anatomical region irradiated with visible light, not the coordinates of the optical image itself. For example, the anatomical position is defined by the relative position of the imaging site from the reference point. Hereinafter, the identified anatomical position will be referred to as an image-side position.

FIG. 7 is a diagram showing an example of the optical image I1 generated by the optical camera 29. As shown in FIG. As shown in FIG. 7, the optical image I1 includes an image region R1 for the patient P (hereinafter referred to as patient region) and an image region R2 for visible light (hereinafter referred to as visible light region). The arithmetic circuit 101 performs threshold processing or the like on the optical image I1 to specify the visible light region R2. Then, the arithmetic circuit 101 identifies an anatomical position on the patient region R1 where the visible light region R2 exists as an image side position by image recognition processing or the like. For example, in the case of FIG. 7, the imaging region is the chest. In this case, a partial region of the chest region is specified as the image-side position R2 by the above image processing. The image side position may be specified as a position specified by the user via the input circuit 105 . The information of the imaging region may be specified by image recognition processing of the optical image I1, or may be acquired from the imaging conditions.

When step SA3 is performed, arithmetic circuit 101 identifies an anatomical position in the human body model corresponding to the image-side position identified in step SA3 (step SA4). The specified anatomical position will be called the model side position. Data of the human body model are stored in the storage circuit 107 .

FIG. 8 is a diagram showing an example of the human body model MD. The human body model MD is data of a model imitating the three-dimensional shape of the human body. The human body model MD reflects not only the outer shape of the human body but also internal structures such as organs. For example, when a partial region R2 of the chest region is specified as the image-side position as shown in FIG. 7, a partial region anatomically corresponding to the chest region R2 is specified as the model-side position R2'. It is assumed that the coordinate system of the human body model MD and the coordinate system of the optical image I1 are associated in advance.

When step SA4 is performed, the arithmetic circuit 101 estimates the cross-sectional shape index value for the cross-section at the model-side position specified in step SA4 (step SA5). At step SA5, the arithmetic circuit 101 first sets an estimation target section included in the model side position. The estimation target cross section is arbitrarily determined from, for example, a plurality of imaging cross sections included in the model side position. The imaging cross section is presumed to be a cross section of the patient P's CT imaging range.

When the estimation target cross section is set, the arithmetic circuit 101 estimates the cross-sectional shape index value of the cross section. Specifically, the cross-sectional shape index value is the length of the human body model in the AP (Anterior-Posterior) direction (hereinafter referred to as AP length) and the length in the LR (Left-Right) direction (hereinafter referred to as LR length). ), the total length of the AP length and the LR length, the effective diameter, the water equivalent diameter, and the like.

FIG. 9 is a diagram showing an example of an imaging section of the human body model MD. In FIG. 9, "A" indicates the patient's front side, "P" indicates the back side, "L" indicates the patient's left side, and "R" indicates the patient's right side. For example, when the cross-sectional shape of the human body model is represented by a dimension obtained by converting the X-ray transmission path length to the water transmission path length, that is, the water equivalent length, the diameter of the cross section of the human body model is equal to the water equivalent diameter. . In this case, the arithmetic circuit 101 can estimate the water equivalent diameter of the patient P by measuring the cross-sectional diameter of the human body model. On the other hand, when the cross-sectional shape of the human body model is represented by the actual path length, the AP length of the patient P can be obtained by measuring the length in the AP direction in the cross section of the human body model, and by measuring the length in the LR direction, It is possible to estimate the patient P's LR length. Also, the total length of the patient P can be estimated by adding the AP length and the LR length, and the effective diameter of the patient P can be estimated from the square root of the product of the AP length and the LR length.

Note that the arithmetic circuit 101 can correct the cross-sectional shape index value estimated as described above based on the bed height correction parameter. A correction parameter corresponding to the height of the bed is determined by the correction parameter determination function 121 of the arithmetic circuit 101 .

FIG. 10 is a diagram for explaining the bed height correction parameters determined by the correction parameter determination function 121 of the arithmetic circuit 101. FIG. As shown in FIG. 10, the vertical axis of the graph in FIG. 10 is defined by the bed height correction parameter, and the horizontal axis is defined by the bed height. The bed height Iso is defined as the height of the top plate 231 when the center of the patient P placed on the top plate 231 in the Y-axis direction is positioned at the isocenter. The bed height HL is lower than the height Iso, and the bed height HH is higher than the height Iso. As shown in FIG. 10, the higher the height of the bed, the closer the patient P is to the projector 27, so the size D of the patient P relative to the CT imaging range (FOV), that is, the geometrical magnification increases. For example, the magnification DHL/FOV of the patient P size DHL to the FOV, the geometric magnification of the couch height HL, is the magnification DHH of the patient P size DHH to the FOV, the geometric magnification of the couch height HH. /FOV. In other words, the spread angle θHL of the region projected onto the subject P at the bed height HL is smaller than the spread angle θHH of the region projected onto the subject P at the bed height HH. Therefore, as the geometric magnification of the patient P increases, the cross-sectional shape index value is overestimated compared to the cross-sectional shape index value at the isocenter. Conversely, as the geometric magnification of the patient P decreases, the cross-sectional shape index value is underestimated compared to the cross-sectional shape index value at the isocenter. Therefore, it is necessary to correct the cross-sectional shape index value at an arbitrary bed height to the cross-sectional shape index value at the isocenter.

As shown in FIG. 10, the bed height correction parameter has linearity with the bed height, and is set so that the value decreases as the bed height increases. The correction parameter for height Iso is set to "1". The arithmetic circuit 101 stores a table (LUT: Look Up Table) that defines the relationship between the bed height and the bed height correction parameter shown in FIG. Hereinafter, this table will be referred to as a bed height correction table. The arithmetic circuit 101 acquires from the gantry 10 the height value of the bed when the patient P is optically imaged by the optical camera 29, and determines the bed height correction parameter from the bed height correction table based on the acquired bed height value. . In the cross-sectional shape estimation function 117-1, the arithmetic circuit 101 multiplies the provisionally determined cross-sectional shape index value by the determined bed height correction parameter to estimate the cross-sectional shape index value.

When step SA5 ends, the cross-sectional shape estimation function 117-1 ends.

Next, arithmetic circuit 101 executes SSDE calculation function 119 (step SA6). At step SA6, the arithmetic circuit 101 calculates the SSDE value based on the water equivalent diameter and the pre-measured CTDI value. More specifically, arithmetic circuit 101 calculates the SSDE value by determining a conversion factor from the water equivalent diameter and multiplying the CTDI value by the determined conversion factor. For example, the arithmetic circuit 101 stores a table (LUT: Look Up Table) that associates water equivalent diameters with conversion coefficients. This table will be called a water equivalent diameter/conversion factor table. Arithmetic circuit 101 searches the water equivalent diameter/conversion factor table using the water equivalent diameter calculated in step SA5 as a search key, and determines the conversion factor associated with the water equivalent diameter. The CTDI value is measured by CT imaging a CTDI measurement phantom in the CTDI measurement geometry. The CTDI value is stored in storage circuit 107 .

Note that the SSDE value may be calculated for each imaging section included in the model-side position. In this case, the arithmetic circuit 101 calculates the average value, the median value, the maximum value, and the minimum value of the plurality of SSDE values regarding the plurality of imaging slices as the SSDE value of the entire CT imaging range.

When step SA6 is performed, arithmetic circuit 101 displays the SSDE value calculated in step SA6 on display 103 (step SA7). Specifically, the display 103 may display the SSDE value for each imaging section, or may display the SSDE value for the entire CT imaging range. The user checks the displayed SSDE value, and if the SSDE value is determined to be unacceptable, reviews the shooting conditions and the like. If it is determined that the SSDE value is acceptable, the user inputs a photographing instruction via the input circuit 31, 105, or the like.

When step SA7 is performed and the user inputs an imaging instruction via the input circuit 31 or 105, the arithmetic circuit 101 instructs the gantry control circuit 33 to start imaging (step SA8). The gantry control circuit 33 instructed to start imaging synchronously controls the X-ray high-voltage device 17, the data acquisition circuit 19, the rotation driving device 21, the bed driving device 25, etc. according to the imaging conditions, and performs CT imaging on the patient P. Run.

This concludes the description of the operation flow of the X-ray computed tomography apparatus according to the first embodiment.

Note that human body models of a plurality of body types may be stored in the storage circuit 107, and the arithmetic circuit 101 may select a human body model that approximates the physique of the patient P from among the plurality of human body models. For example, a human body model may be selected in accordance with a user's instruction via the input circuit 105, or a human body model that is most similar to the body shape of the patient P may be selected based on patient information such as the patient's P age, sex, and physical measurements. It may be automatically selected. It should be noted that the physical measurement values according to this embodiment include any measurement values of the patient's physique, such as height, weight, and chest circumference. Further, the arithmetic circuit 101 may correct the shape of the human body model so as to match the physique of the patient P based on patient information such as the patient's P age, sex, body measurements, and the like. In this way, by using a human body model that approximates the physique of the patient P, the cross section to be estimated approximates the actual cross section of the patient P more, so the accuracy of estimating the cross-sectional shape is improved, and the cross-sectional shape index value and the SSDE Increases accuracy of values.

In addition, the cross-sectional shape index value can be used for various purposes other than calculating the SSDE value. For example, in the imaging parameter determination function 123, the arithmetic circuit 101 sets a parameter that defines the directional modulation of the tube current (hereinafter referred to as a tube current modulation parameter) to the cross-sectional shape index value estimated in the cross-sectional shape estimation function 117-1. can be determined based on Specifically, the arithmetic circuit 101 calculates the ratio of the tube current value in the AP direction and the tube current in the LR direction to the reference value of the tube current according to the ratio of the water equivalent diameter in the AP direction and the water equivalent diameter in the LR direction. Determine the ratio of values. The ratio is set as the tube current modulation parameter. The tube current modulation parameter may be the tube current value in the AP direction or the tube current value in the LR direction itself.

As described above, according to the first embodiment, the tube current modulation parameter is determined based on the cross-sectional shape index value estimated based on the irradiation position of the visible light by the light projector 27 instead of the cross-sectional shape index value estimated based on the positioning image. Since it can be determined, the exposure of the patient P can be reduced.

Further, in the correction parameter determination function 121, the arithmetic circuit 101 may determine the correction parameter for the SSDE value according to the difference between the SSDE value and the actually measured dose value. This process will be specifically described below. When CT imaging is performed in step SA8, the arithmetic circuit 101 measures the actually measured dose value of the patient P. FIG. The storage circuit 107 stores the actually measured dose value and the SSDE value for the patient P in association with each other. The storage circuit 107 associates and stores actually measured dose values and SSDE values for a plurality of patients. In the correction parameter determination function 121, the arithmetic circuit 101 calculates the difference value between the measured dose value and the SSDE value stored in the storage circuit 107, analyzes the calculated difference value, and the SSDE calculation function 119 calculates A correction parameter (hereinafter referred to as SSDE correction parameter) for bringing the SSDE value closer to the actually measured dose value is determined. The SSDE correction parameter may be a parameter common to all patients P, or may be a parameter determined for each category such as the physique of the patient P. When the SSDE correction parameter is determined, the arithmetic circuit 101 estimates the SSDE value based on the cross-sectional shape index value, the CTDI value, and the SSDE correction parameter at step SA6, for example. This makes it possible to further improve the estimation accuracy of the SSDE value.

In the above example, only one optical camera 29 is installed. However, this embodiment is not limited to this. That is, a plurality of optical cameras 29 may be installed. For example, an optical camera 29 for optically photographing the front of the patient P and an optical camera 29 for optically photographing the side of the patient P may be provided. The arithmetic circuit 101 determines the anatomical position of the CT imaging range based on the optical images in multiple directions, thereby improving the estimation accuracy of the anatomical position, and thus the estimation accuracy of the cross-sectional shape index value and the SSDE value. can.

Also, the optical camera 29 may be attached to the rotating frame 11 . By attaching it to the rotating frame 11, it becomes possible to generate an optical image of the entire periphery of the patient P with a single optical camera 29. FIG. The arithmetic circuit 101 determines the anatomical position of the CT imaging range based on the optical image of the entire circumference, thereby improving the estimation accuracy of the anatomical position, and thus the estimation accuracy of the cross-sectional shape index value and the SSDE value. can.

In addition, in the case of a patient P having a very large physique, the patient P may approach the light projector 27 too much. In this case, it is difficult to match the irradiation position of the visible light from the light projector 27 with the CT imaging range. For example, when the user inputs a warning instruction via the input circuit 31 or 105, the arithmetic circuit 101 issues a warning to the effect that the cross-sectional shape index value cannot be estimated. For example, the mode of warning generation includes outputting a warning sound through a speaker, displaying a warning message on the display 103, and the like. This allows the user to switch to estimating the SSDE value based on the positioning image.

With the above configuration, according to the first embodiment, the cross-sectional shape index value can be estimated based on the human body model and the optical image of the patient P irradiated with visible light from the light projector 27 when the patient P is positioned. can. That is, the X-ray computed tomography apparatus according to the first embodiment does not require positioning imaging when estimating the cross-sectional shape index value. Therefore, the X-ray computed tomography apparatus according to the first embodiment can estimate the cross-sectional shape index value without exposing the patient P to radiation as compared with the case of positioning imaging.

(Second embodiment)
The X-ray computed tomography apparatus according to the first embodiment is equipped with an optical camera 29 . However, this embodiment is not limited to this. The second embodiment estimates the cross-sectional shape index value and calculates the SSDE value without using the optical camera 29 . The second embodiment will be described in detail below. In the following description, components having substantially the same functions as those of the first embodiment are denoted by the same reference numerals, and duplicate description will be given only when necessary.

FIG. 11 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the second embodiment. As shown in FIG. 11, the X-ray computed tomography apparatus according to the second embodiment does not have an optical camera. In the cross-sectional shape estimation function 117-2, the arithmetic circuit 101 according to the second embodiment specifies the irradiation position of the visible light from the light projector 27 to the patient P based on the projection parameters, and the cross-section corresponding to the specified irradiation position The cross-sectional shape index value of is estimated using a human body model.

FIG. 12 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function 125 of the arithmetic circuit 101 according to the second embodiment.

As shown in FIG. 12, the arithmetic circuit 101 first causes the gantry control circuit 33 to irradiate visible light (step SB1). In step SB1, the gantry control circuit 33 irradiates the patient P with visible light from the light projector 27, as in step SA1 of the first embodiment (step SB1). Before visible light irradiation, the light projection parameters related to the visible light irradiation position are set as in step SA1. The projection parameters are transmitted to console 100 and stored in storage circuit 107 .

When step SB1 is performed, the arithmetic circuit 101 executes the cross-sectional shape estimation function 117-2. In the cross-sectional shape estimating function 117-2, the arithmetic circuit 101 first identifies the anatomical position irradiated with visible light based on the projection parameters acquired in step SB1 (step SB2). Specifically, the arithmetic circuit 101 identifies the anatomical position irradiated with visible light based on the imaging region and the projection parameters (position and irradiation angle of the light source of the projector 27) included in the imaging conditions. do. Note that the anatomical position may be specified using the Z-axis coordinate and the Y-axis coordinate of the tabletop 231 in addition to the imaging region and the projection parameters.

When step SB2 is performed, arithmetic circuit 101 identifies an anatomical position in the human body model corresponding to the actual position identified in step SB2 (step SB3). Specifically, the arithmetic circuit 101 identifies anatomical positions in the human body model by the same method as in step SA4 of the first embodiment.

When step SB3 is performed, arithmetic circuit 101 estimates, from the human body model, the equivalent water diameter in the cross section at the position on the model side specified in step SB3 (step SB4). Specifically, the arithmetic circuit 101 estimates the equivalent water diameter by the same method as in step SA5 of the first embodiment.

When step SB4 is performed, arithmetic circuit 101 calculates the SSDE value based on the water equivalent diameter estimated in step SB4 and the pre-measured CTDI value (step SB5). Specifically, the arithmetic circuit 101 calculates the SSDE value by the same method as in step SA6 of the first embodiment.

When step SB5 is performed, arithmetic circuit 101 displays the SSDE value calculated in step SB5 on display 103 (step SB6). Specifically, the display 103 displays the SSDE value by the same method as in step SA7 of the first embodiment. The user checks the displayed SSDE value, and if the SSDE value is determined to be unacceptable, reviews the shooting conditions and the like. If it is determined that the SSDE value is acceptable, the user inputs a photographing instruction via the input circuit 31, 105, or the like.

When step SB6 is performed and the user inputs a photographing instruction via the input circuit 31 or 105, the arithmetic circuit 101 instructs the gantry control circuit 33 to start photographing (step SB7). The gantry control circuit 33 instructed to start imaging synchronously controls the X-ray high-voltage device 17, the data acquisition circuit 19, the rotation driving device 21, the bed driving device 25, etc. according to the imaging conditions, and performs CT imaging on the patient P. Run.

This concludes the description of the operation flow of the X-ray computed tomography apparatus according to the second embodiment.

With the above configuration, according to the second embodiment, when positioning the patient P, the cross-sectional shape index value can be estimated based on the light projection parameters of the light projector 27 and the human body model. That is, the X-ray computed tomography apparatus according to the second embodiment does not require positioning imaging when estimating the cross-sectional shape index value. Therefore, the X-ray computed tomography apparatus according to the second embodiment can estimate the cross-sectional shape index value without exposing the patient P to radiation as compared with the case of positioning imaging. Further, since the optical camera is not used as compared with the first embodiment, the second embodiment can estimate the cross-sectional shape index value with a simpler device design than the first embodiment. In other words, since the first embodiment uses an optical camera, it is possible to estimate the cross-sectional position and thus the cross-sectional shape index value more accurately than in the second embodiment.

(Third Embodiment)
The X-ray computed tomography apparatuses according to the first and second embodiments use a human body model to estimate cross-sectional shape index values and calculate SSDE values. However, this embodiment is not limited to this. The third embodiment estimates cross-sectional shape index values and calculates SSDE values without using a human body model. The third embodiment will be described in detail below. In the following description, components having substantially the same functions as those of the first and second embodiments are denoted by the same reference numerals, and duplicate description will be given only when necessary.

FIG. 13 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the third embodiment. As shown in the figure, the arithmetic circuit 101 according to the third embodiment executes a cross-sectional shape estimation function 117-3. In the cross-sectional shape estimation function 117-3, the arithmetic circuit 101 estimates cross-sectional shape index values based on the light projection parameters of the light projectors 27 in two or more directions.

FIG. 14 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function 125 of the arithmetic circuit 101 according to the third embodiment. As shown in FIG. 14, the arithmetic circuit 101 first executes the cross-sectional shape estimation function 117-3 in steps SC1-SC4.

FIG. 15 is a diagram schematically showing the outline of the cross-sectional shape estimation function 117-3 performed by the arithmetic circuit 101 in steps SC1-SC4.

As shown in FIGS. 14 and 15 , the arithmetic circuit 101 instructs the gantry control circuit 33 to rotate the rotating frame 11 . The gantry control circuit 33 first controls the rotation drive device 21 to arrange the light projector 27 at a rotation angle of 0° or 180° (step SC1).

When step SC1 is performed, the arithmetic circuit 101 measures the LR length of the patient P based on the light projection parameters of the light projector 27 (step SC2). First, the user inputs a projection start instruction through the input circuit 31 . Upon receiving the light projection start instruction, the gantry control circuit 33 irradiates the patient P with the visible light rays Lz1, Lz2, Lx1 and Lx2 from the light projectors 27 . Next, the gantry control circuit 33 adjusts the distance between the visible light beam Lx1 and the visible light beam Lx2 in the LR direction so that it matches the CT imaging range in the LR direction of the patient P in accordance with the user's instruction via the input circuit 31. do. When the adjustment ends, the user inputs an adjustment end instruction through the input circuit 31 .

The arithmetic circuit 101 estimates the LR length based on the projection parameter at the time of the adjustment end instruction and the geometry between the projector 27 and the patient P or the top plate 231 . Specifically, based on the irradiation angle of the visible light Lx1 and the irradiation angle of the visible light Lx2 at the rotation angle of 0°, the arithmetic circuit 101 calculates the angle between the visible light Lx1 and the visible light Lx2 (hereinafter referred to as the inter-light angle) is measured, and the distance between visible light Lx1 and visible light Lx2 is estimated based on the inter-ray angle and the couch height. The distance is set as the LR length. Further, the arithmetic circuit 101 calculates the visible light beam Lx1 and The distance to the visible light Lx2 (hereinafter referred to as the distance between rays) may be measured, and the LR length may be estimated based on the distance between rays and the height of the bed. Note that the arithmetic circuit 101 may estimate the LR length based on the predicted value of the LR length of a predetermined patient P in addition to the inter-beam angle or inter-beam distance and the height of the bed. Also, the arithmetic circuit 101 may estimate the LR length using the distance between the light projector 27 and the patient P or the table top 231 instead of the height of the bed. Upon receiving the adjustment end instruction, the gantry control circuit 33 transmits the LR length to the console 100, and the storage circuit 107 stores the LR length.

When step SC2 is performed, the gantry control circuit 33 controls the rotary drive device 21 to arrange the light projector 27 at a rotation angle of 90° or 270° (step SC3).

When step SC3 is performed, the arithmetic circuit 101 measures the AP length of the patient P based on the light projection parameters of the light projector 27 (step SC4). First, the user inputs a projection start instruction through the input circuit 31 . Upon receiving the light projection start instruction, the gantry control circuit 33 irradiates the patient P with the visible light rays Lz1, Lz2, Lx1 and Lx2 from the light projectors 27 . Next, the gantry control circuit 33 adjusts the distance between the visible light beam Lx1 and the visible light beam Lx2 in the AP direction so that it matches the CT imaging range in the AP direction of the patient P, according to the user's instruction via the input circuit 31. do. When the adjustment ends, the user inputs an adjustment end instruction through the input circuit 31 .

The arithmetic circuit 101 estimates the AP length based on the projection parameters at the time of the adjustment end instruction and the geometry between the projector 27 and the patient P or the top plate 231 . Specifically, the arithmetic circuit 101 measures the inter-beam angle based on the irradiation angle of the visible light beam Lx1 and the irradiation angle of the visible light beam Lx2 at the rotation angle of 90°, the inter-beam angle, the projector 27 and the patient P Alternatively, the distance between the visible light Lx1 and the visible light Lx2 is estimated based on the distance to the top plate 231 . The distance is set as the AP length. Further, the arithmetic circuit 101 calculates the inter-light distance based on the light source position of the light projector 27 corresponding to the irradiation position of the visible light Lx1 at the rotation angle of 90° and the light source position of the light projector 27 corresponding to the irradiation position of the visible light Lx2. The AP length may be estimated based on the inter-beam distance and the distance between the projector 27 and the patient P or the table top 231. Note that the arithmetic circuit 101 may estimate the AP length based on the predicted value of the AP length of a predetermined patient P in addition to the inter-beam angle or inter-beam distance and the height of the bed. Upon receiving the adjustment end instruction, the gantry control circuit 33 transmits the AP length to the console 100, and the storage circuit 107 stores the AP length.

When steps SC1 to SC4 are performed, the cross-sectional shape estimation function 117-3 performed by the arithmetic circuit 101 ends. The order of steps SC1 and SC2 and steps SC3 and SC4 may be reversed. That is, the AP length may be estimated first, and the LR length may be estimated later.

When step SC4 is performed, the arithmetic circuit 101 calculates the SSDE value based on the LR length estimated at step SC2, the AP length estimated at step SC4, and the pre-measured CTDI value (step SC5). At step SC5, the arithmetic circuit 101 determines the transform coefficient from the combination of the LR length and the AP length, and multiplies the CTDI value by the determined transform coefficient to calculate the SSDE value. A conversion coefficient is determined for each combination of LR length and AP length. Note that it is not necessary to directly determine the transform coefficients from the combination of the LR length and the AP length. For example, the arithmetic circuit 101 has a table (LUT) that associates the combination of the LR length and the AP length with the water equivalent diameter, and uses the LUT to calculate the water equivalent diameter from the combination of the LR length and the AP length. , and a water equivalent diameter/conversion factor table may be used to determine the conversion factor.

When step SC5 is performed, arithmetic circuit 101 displays the SSDE value calculated in step SC5 on display 103 (step SC6). The user checks the displayed SSDE value, and if the SSDE value is determined to be unacceptable, reviews the shooting conditions and the like. If it is determined that the SSDE value is acceptable, the user inputs a photographing instruction via the input circuit 31, 105, or the like.

When step SC6 is performed and the user inputs a photographing instruction via the input circuit 31 or 105, the arithmetic circuit 101 instructs the gantry control circuit 33 to start photographing (step SC7). The gantry control circuit 33 instructed to start imaging synchronously controls the X-ray high-voltage device 17, the data acquisition circuit 19, the rotation driving device 21, the bed driving device 25, etc. according to the imaging conditions, and performs CT imaging on the patient P. Run.

This concludes the description of the operation flow of the X-ray computed tomography apparatus according to the third embodiment.

Note that both the AP length and the LR length are measured in the above example. However, this embodiment is not limited to this. For example, if transform coefficients are obtained from only one of the AP length and the LR length, the measurement of either the AP length or the LR length may be omitted. Also, although the distance between the visible light beam Lx1 and the visible light beam Lx2 at 0° or 180° is defined as the LR length, this embodiment is not limited to this. For example, the LR length may be defined as the distance between the visible light rays Lx1 and Lx2 at other rotation angles according to the posture of the patient P on the table top 231 . Similarly, the distance between visible light Lx1 and visible light Lx2 at 90° or 270° is defined as AP length, but this embodiment is not limited to this. For example, the AP length may be defined as the distance between the visible light beams Lx1 and Lx2 at other rotation angles according to the posture of the patient P on the table top 231 .

With the above configuration, according to the third embodiment, the cross-sectional shape index value can be estimated based on the light projection parameters of the light projector 27 at a plurality of rotation angles. That is, the X-ray computed tomography apparatus according to the third embodiment does not require positioning imaging when estimating the cross-sectional shape index value. Therefore, the X-ray computed tomography apparatus according to the third embodiment can estimate the cross-sectional shape index value without exposing the patient P to radiation as compared with the case of positioning imaging. Further, since the optical camera is not used as compared with the first embodiment, the third embodiment can estimate the cross-sectional shape index value with a simpler device design than the first embodiment. Further, unlike the first and second embodiments, the AP length and the LR length are directly estimated (measured) by adjusting the irradiation position of the visible light by the user. Improves estimation accuracy.

(Fourth embodiment)
The X-ray computed tomography apparatuses according to the first, second, and third embodiments use visible light emitted from the projector to estimate the cross-sectional shape index value and calculate the SSDE value. However, this embodiment is not limited to this. The fourth embodiment uses infrared rays to estimate the cross-sectional shape index value and calculate the SSDE value. The fourth embodiment will be described in detail below. In the following description, components having substantially the same functions as those of the first, second, and third embodiments are denoted by the same reference numerals, and duplicate description will be given only when necessary.

FIG. 16 is a diagram showing the configuration of an X-ray computed tomography apparatus according to the fourth embodiment. As shown in FIG. 16 , the gantry 10 according to the fourth embodiment has an infrared ray irradiator 35 and a light receiver 37 . The infrared irradiator 35 irradiates a patient P such as a subject placed on a tabletop with infrared rays. The infrared rays according to this embodiment include near-infrared rays, narrowly-defined infrared rays, and far-infrared rays. The infrared irradiator 35 is implemented by, for example, an LED (Light-Emitting Diode). The light receiver 37 receives the infrared rays irradiated and reflected by the patient P, and outputs an electric signal of the received infrared rays. The light receiver 37 is implemented by an infrared camera in which optical sensors such as CMOS (Complementary Metal-Oxide Semiconductor) are arranged two-dimensionally.

The gantry control circuit 33 according to the fourth embodiment implements an infrared information measurement function 293 . In the infrared information measuring function 293 , the gantry control circuit 33 measures information related to infrared light received by the light receiver 37 . Information related to infrared rays is, for example, flight time. The time of flight is defined by the elapsed time from the time the infrared ray is emitted from the infrared irradiator 35 to the time the infrared ray is reflected by the patient P and received by the light receiver 37 . As information related to other infrared rays, for example, the intensity of the received infrared rays may be used.

The arithmetic circuit 101 according to the fourth embodiment executes a cross-sectional shape estimation function 117-4. In the cross-sectional shape estimating function 117-4, the arithmetic circuit 101 estimates a cross-sectional shape index value regarding the cross section of the patient P in the imaging range based on the infrared information.

FIG. 17 is a diagram showing a typical operation flow of the X-ray computed tomography apparatus performed by executing the system control function 125 of the arithmetic circuit 101 according to the fourth embodiment. FIG. 18 is a diagram schematically showing an outline of estimation of a cross-sectional shape index value using infrared rays.

As shown in FIGS. 17 and 18, the arithmetic circuit 101 first instructs the gantry control circuit 33 to image the subject P using infrared rays IR. In photographing the patient P with the infrared rays IR, the infrared irradiator 35 irradiates the patient placed on the top plate 231 with the infrared rays IR, and the reflected infrared rays are received by the light receiver 37 (step SD1). As shown in FIG. 18, an infrared irradiator 35 and a light receiver 37 are provided on the ceiling 200 of the examination room. A combination of the infrared irradiator 35 and the light receiver 37 is preferably provided in an arbitrary housing 39 . A subject P is placed on a top plate 231 . Imaging of the subject P using the infrared irradiator 35 and the light receiver 37 is typically performed before the table top 231 is inserted into the opening 41 in order to prevent the infrared rays IR from being blocked by the gantry housing 40 . done in stages. In order to measure the body thickness (AP length) and lateral width (LR length) of the patient P by the infrared rays IR, the infrared rays IR are preferably applied to the entire width direction of the patient P including the imaging range.

When step SD1 is performed, the gantry control circuit 33 executes the infrared information measurement function 293 to measure the flight time of the infrared light received by the light receiver 37 (step SD2). In step SD2, the gantry control circuit 33 measures the elapsed time from the time when the infrared ray is emitted from the infrared ray irradiator 35 to the time when the infrared ray is received by the light receiver 37 after being reflected by the subject P as the time of flight.

When step SD2 is performed, arithmetic circuit 101 executes cross-sectional shape estimation function 117-4 to estimate a cross-sectional shape index value based on the flight time of infrared rays and the height of top plate 231 (step SD3). In step SD3, the arithmetic circuit 101 estimates the AP length (thickness) and LR length (horizontal width) of the patient P as cross-sectional shape index values.

The AP length is estimated, for example, as follows. As shown in FIG. 18, based on the propagation speed of the infrared rays IR, the flight time of the reflected infrared rays IR from the subject P, and the flight time of the reflected infrared rays IR from the tabletop 231 in the absence of the subject P, the patient The AP length of P can be estimated. The flight time of the reflected infrared rays IR from the top plate 231 is measured or predicted in advance. For example, the gantry control circuit 33 sets the top plate 231 to a plurality of heights, irradiates the surface of the top plate 231 with infrared rays IR from the infrared irradiator 35 at each height, and reflects off the surface of the top plate 231. Infrared rays are received by the light receiver 37 . The gantry control circuit 33 calculates the difference between the infrared irradiation time and the light reception time for each tabletop height, and sets the calculated difference as the flight time. The gantry control circuit 33 creates a table (hereinafter referred to as a flight time table) in which the flight time is associated with each table height, and stores it in its own memory or the like. When the flight time in the presence of the patient P is measured, the flight time associated with the table height is read from the flight time table based on the table height at the time of infrared imaging. A difference between the read flight time and the flight time in the presence of the patient P is calculated, and the AP length is calculated based on the calculated difference and the propagation speed of the infrared rays.

The LR length is estimated, for example, as follows. The gantry control circuit 33 irradiates and receives infrared rays IR at regular angular intervals so as to traverse the patient P placed on the tabletop 231, and records the reception time or flight time for each infrared ray irradiation. The time of light reception or flight time changes abruptly at the boundary between the portion where the patient exists and the portion where the patient does not exist. Positions where the light receiving time or the flight time abruptly changes are specified for each of the right side and the left side of the patient P, and the distance interval between each position is calculated as the LR length. Note that the LR length may be estimated using the optical camera 29 as in the first and second embodiments, or may be estimated using the light projector 27 as in the third embodiment.

When step SD3 is performed, the arithmetic circuit 101 calculates the SSDE value based on the LR length and AP length estimated in step SD3 and the pre-measured CTDI value (step SD4). Step SD4 is similar to step SC5 according to the third embodiment, for example.

When step SD4 is performed, arithmetic circuit 101 displays the SSDE value calculated in step SD4 on display 103 (step SD5). Step SD5 is similar to step SC6 according to the third embodiment, for example.

When step SD5 is performed and the user inputs an imaging instruction via the input circuit 31 or 105, the arithmetic circuit 101 instructs the gantry control circuit 33 to start imaging (step SD6). The gantry control circuit 33 instructed to start imaging synchronously controls the X-ray high-voltage device 17, the data acquisition circuit 19, the rotation driving device 21, the bed driving device 25, etc. according to the imaging conditions, and performs CT imaging on the patient P. Run.

This completes the description of the operation flow of the X-ray computed tomography apparatus according to the fourth embodiment.

Various modifications are possible for the fourth embodiment. For example, in the above description, whether or not the top board 231 is moved during CT imaging is not particularly limited. In the case of helical scanning in which scanning is performed while the table 231 is moved, and intermittent movement scanning in which the table 231 is moved and scanned intermittently, the CT imaging range is wide. On the other hand, the infrared imaging range that can be covered by one infrared imaging differs according to the specifications of the infrared irradiator 35 and the light receiver 37 . Therefore, the CT imaging range may not be covered by one infrared imaging. In this case, it is preferable to infrared photograph a wide range by moving the top plate 231 in the longitudinal direction. For example, the CT imaging range is divided into a plurality of small ranges according to the infrared imaging range, and infrared imaging and cross-sectional shape index value estimation are performed for each small range. Thereby, the cross-sectional shape index value can be estimated even when the CT imaging range is wide.

Further, for example, in the above description, the combination of the infrared irradiator 35 and the light receiver 37 is provided on the ceiling 200 of the examination room. may be provided. Also, the combination of the infrared ray irradiator 35 and the light receiver 37 is assumed to be fixed to the ceiling 200. It may be provided so as to be slidable on a two-dimensional plane. With this configuration, it is possible to irradiate the patient P and the top board 231 with the infrared rays IR substantially perpendicularly. Alternatively, multiple combinations of infrared emitters 35 and receivers 37 may be arranged along the Z-axis or the X-axis, or in a two-dimensional plane defined by the Z-axis and the X-axis. With this configuration as well, the patient P and the top board 231 can be irradiated with the infrared rays IR substantially perpendicularly.

With the above configuration, according to the fourth embodiment, infrared rays can be used to estimate the cross-sectional shape index value. That is, the X-ray computed tomography apparatus according to the fourth embodiment does not require positioning imaging when estimating the cross-sectional shape index value. Therefore, the X-ray computed tomography apparatus according to the fourth embodiment can estimate the cross-sectional shape index value without exposing the patient P to radiation, as compared with the case of positioning imaging.

As described above, according to several embodiments described above, the X-ray computed tomography apparatus according to this embodiment has the gantry 10 , the bed 23 , the projector 27 and the arithmetic circuit 101 . The gantry 10 performs CT imaging using X-rays. The bed 23 movably supports a top plate 231 on which the subject P is placed. The light irradiator 27 or 35 irradiates the subject P placed on the top plate 231 with light. The arithmetic circuit 101 estimates the shape index value of the cross section of the subject P in the imaging range by using the light beam irradiated to the subject P. FIG.

According to the above configuration, the X-ray computed tomography apparatus according to this embodiment can accurately estimate the cross-sectional shape of the subject using the light irradiator 27 or 35 without positioning imaging. Therefore, the exposure of the subject P required for estimating the cross-sectional shape can be reduced.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 10... Mounting frame, 11... Rotating frame, 13... X-ray tube, 15... X-ray detector, 17... X-ray high-voltage apparatus, 19... Data acquisition circuit, 21... Rotary drive apparatus, 23... Bed, 25... Bed drive Apparatus, 27... Projector, 29... Optical camera, 31... Input circuit, 33... Mount control circuit, 40... Mount housing, 41... Opening, 43... Main frame, 45... Transmissive film, 47... Gap, 49... Support rod , 100... Console, 101... Arithmetic circuit, 103... Display, 105... Input circuit, 107... Storage circuit, 111... Preprocessing function, 113... Reconstruction function, 115... Image processing function, 117-1... Cross-sectional shape estimation function , 117-2... cross-sectional shape estimation function, 117-3... cross-sectional shape estimation function, 119... SSDE calculation function, 121... correction parameter determination function, 123... imaging parameter determination function, 125... system control function, 231... top plate, 271... Projector, 291... Projector setting function.

Claims (7)

a pedestal for performing CT imaging using X-rays;
a bed that movably supports a top plate on which the subject is placed;
a light irradiator that irradiates the subject placed on the top plate with a light beam indicating a reference line of an imaging range of CT imaging ;
an optical imaging unit that generates an optical image of the subject irradiated with the light beam as a subject;
an estimating unit that estimates a shape index value of the cross section of the subject in the imaging range based on the optical image ;
The estimating unit specifies a first anatomical position of a light ray image area for the ray in a subject area for the subject included in the optical image, and a human body corresponding to the first anatomical position. a second anatomical position in a human body model that imitates the three-dimensional shape of the subject, and a shape index value of the cross section of the human body model at the second anatomical position, estimated as a shape index value,
X-ray computed tomography equipment. 2. The X-ray computed tomography apparatus according to claim 1 , wherein said light irradiator irradiates said light ray indicating an outer frame of said imaging range as said light ray indicating said reference line. 2. The X-ray computed tomography apparatus according to claim 1, wherein said estimation unit corrects the shape of said cross section of said subject or said shape index value based on a correction parameter corresponding to the height of said tabletop. 2. The X-ray computed tomography apparatus according to claim 1, further comprising a calculator that calculates an SSDE value based on said shape index value and a pre-measured CTDI value. 5. The X-ray computed tomography apparatus according to claim 4 , further comprising a correction parameter determination unit that determines a correction parameter for said SSDE value based on a difference between said SSDE value and an actually measured dose value. 6. The X-ray computed tomography apparatus according to claim 5 , wherein said calculation unit calculates said SSDE value based on said shape index value, said CTDI value and said correction parameter. 2. The X-ray computed tomography apparatus according to claim 1, further comprising a modulation parameter determination unit that determines a modulation parameter of tube current based on said shape index value.

Images