According to one embodiment, an X-ray computed tomography apparatus includes a gantry that performs X-ray CT imaging; a bed that movably supports a table top on which a subject lies; an optical emitter that is provided on the gantry and emits a light beam to the subject lying on the table top; and an estimator that estimates a shape index value of a cross section of the subject in an imaging range by utilizing the light beam emitted to the subject.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the Japanese Patent Application No. 2017-153427, filed Aug. 8, 2017, and the Japanese Patent Application No. 2018-143736, filed Jul. 31, 2018 the entire contents of all of which are incorporated herein by reference.

FIELD

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

BACKGROUND

SSDE (Size-Specific Dose Estimates) is known as a dose index in CT imaging. SSDE is calculated based on a cross-sectional shape of an object that was estimated by using a positioning image. Thus, to estimate a cross-sectional shape, positioning imaging is necessary.

On the other hand, at a stage prior to CT imaging, positioning of an object is performed using a light projector that emits a light beam indicating a reference line of an imaging range. In recent years, positioning imaging for positioning can be omitted by using a light projector that emits a light beam indicating an outer frame of an imaging range. However, when positioning imaging is omitted, a cross-sectional shape cannot be estimated, and accordingly, a predicted dose index, such as SSDE, cannot be calculated.

DETAILED DESCRIPTION

In general, according to one embodiment, an X-ray computed tomography apparatus includes a gantry, a bed, an optical emitter, and processing circuitry. The gantry performs X-ray CT imaging. The bed movably supports a table top on which a subject lies. The optical emitter is mounted on the gantry and emits light beams to the subject lying on the table top. The processing circuitry estimates a cross-sectional shape index value of the subject in the imaging range utilizing the light beams emitted to the subject.

An X-ray computed tomography apparatus according to the present embodiment will be described in detail with reference to the accompanying drawings.

First Embodiment

FIG. 1is a diagram showing a configuration of an X-ray computed tomography apparatus according to a first embodiment. As shown inFIG. 1, the X-ray computed tomography apparatus of the first embodiment includes a gantry10and a console100. For example, the gantry10is placed in an examination room, and the console100is placed in a control room adjacent to the examination room. The gantry10and the console100are communicably connected to each other. The gantry10includes an imaging mechanism configured to perform X-ray CT imaging of a subject P, such as a patient. The console100is a computer that controls the gantry10.

As shown inFIG. 1, the gantry10includes an almost cylindrical rotation frame11with a bore. The rotation frame11is also referred to as a rotation unit. As shown inFIG. 1, an X-ray tube13and an X-ray detector15, arranged to face each other via the bore, are mounted on the rotation frame11. The rotation frame11is a metal frame made of, for example, aluminum, in an annular shape. As will be detailed later, the gantry10includes a main frame made of metal, such as aluminum. The main frame is also referred to as a stationary unit. The rotation frame11is rotatably supported by the main frame.

The X-ray tube13generates X-rays. The X-ray tube13is a vacuum tube which holds a cathode that generates thermoelectrons, and an anode that generates X-rays by receiving the thermoelectrons that have traveled from the cathode. The X-ray tube13is connected to an X-ray high voltage device17via a high voltage cable.

The X-ray high voltage device17may adopt any type of high voltage generator such as a transformer type X-ray high voltage generator, a constant voltage type X-ray high voltage generator, a capacitor type X-ray high voltage generator, or an inverter type X-ray high voltage generator. The X-ray high voltage device17is attached, for example, to the rotation frame11. The X-ray high voltage device17adjusts a tube voltage applied to the X-ray tube13, a tube current, and the focus size of the X-rays in accordance with control by a gantry control circuitry33.

As shown inFIG. 1, the rotation frame11rotates about a center axis Z at a predetermined angular velocity upon receiving power from a rotation actuator21. For the rotation actuator21, any motor, for example, a direct drive motor or a servo motor, is used. The rotation actuator21is housed in, for example, the gantry10. The rotation actuator21generates power to rotate the rotation frame11upon receiving a drive signal from the gantry control circuitry33.

A CT imaging range (FOV: Field Of View) is set at the bore of the rotation frame11. A table top supported by the bed23is inserted into the bore of the rotation frame11. The patient P is placed on the table top. The bed23movably supports the table top. The bed23houses a bed actuator25. Upon receipt of a drive signal from the gantry control circuitry33, the bed actuator25generates power to move the table top back and forth, up and down, and left and right. The bed23moves the table top for positioning so that an imaging target area of the patient P can fit in the CT imaging range.

The X-ray detector15detects the X-rays generated by the X-ray tube13. Specifically, the X-ray detector15includes a plurality of detection elements arranged on a two-dimensional curved surface. Each of the detection elements includes a scintillator and a photoelectric conversion element. The scintillator is formed of a material that converts X-rays into photons. The scintillator converts the applied X-rays into photons of the number corresponding to the intensity of the applied X-rays. The photoelectric conversion element is a circuit element that amplifies photons received from the scintillator and converts the received photons into an electrical signal. For example, a photomultiplier tube, a photodiode, or the like is applied as the photoelectric conversion element. The detection elements may adopt an indirect conversion-type detection element, which converts X-rays into photons and then detects the photons; or a direct conversion-type detection element, which directly converts X-rays into an electrical signal.

The X-ray detector15is connected to data acquisition circuitry19. In accordance with the instruction from the gantry control circuitry33, the data acquisition circuitry19reads from the X-ray detector15an electrical signal corresponding to the intensity of X-rays detected by the X-ray detector15, and acquires raw data with a digital value corresponding to the dose of X-rays during a view period. The data acquisition circuitry19is implemented by, for example, an ASIC (Application Specific Integrated Circuit) on which a circuit element capable of generating count data is mounted.

A light projector27is mounted on the rotation frame11. In accordance with the instructions from the gantry control circuitry33, the light projector27projects visible light beams (projection laser) indicating reference lines of the CT imaging range to the table top inserted in the bore, or to the patient P placed on the table top. The visible light beams are projected for the positioning of the patient P.

An optical camera29is an optical imaging unit that generates an optical image of the patient P as a subject irradiated with the visible light beams from the light projector27. The optical camera29may be located at any position where the patient P irradiated with the visible light beams from the light projector can be imaged. The optical image is transmitted to the console100.

Input circuitry31receives various instructions from the user about positioning of the bed23or the light projector27. Specifically, the input circuitry31includes an input device and an input interface. The input device includes a switch button—or the like—of hardware or software. The input interface is connected to the gantry control circuitry33. The input interface converts an operation input from the user via the input device into an electric signal, and outputs the electric signal to the gantry control circuitry33.

The gantry control circuitry33synchronously controls the X-ray high voltage device17, the data acquisition circuitry19, the rotation actuator21, the bed actuator25, etc. to perform X-ray CT imaging in accordance with imaging conditions transmitted from the processing circuitry101of the console100. The gantry control circuitry33controls the rotation actuator21and the light projector27for positioning or the like of the patient P. The gantry control circuitry33includes a processor, such as a CPU (Central Processing Unit) and an MPU (Micro Processing Unit), and a memory, such as a ROM (Read Only Memory) and a RAM (Random Access Memory), as hardware resources. The gantry control circuitry33may be implemented by an ASIC or an FPGA (Field Programmable Gate Array), a CPLD (Complex Programmable Logic Device), or an SPLD (Simple Programmable Logic Device). The gantry control circuitry33of this embodiment achieves a light projector setting function291by executing a control program of the light projector27.

By the light projector setting function291, the gantry control circuitry33sets setting parameters that define an irradiation position of the visible light beam by the light projector27, in accordance with the instructions from the user via the input circuitry31. The setting parameter is referred to as the light projection parameter. The light projection parameters that define the irradiation position of the visible light beam include an irradiation angle of the visible light beam by the light projector27, the position of a light source of the light projector27, etc.

As shown inFIG. 1, the console100includes the processing circuitry101, a display103, input circuitry105, and a memory107.

The processing circuitry101includes a processor such as a CPU, an MPU, or a GPU (Graphics Processing Unit), etc. and a memory such as a ROM or a RAM, etc. as hardware resources. The processing circuitry101executes various programs to implement a preprocessing function111, a reconstruction function113, an image processing function115, a cross-sectional shape estimation function117-1, an SSDE calculation function119, a correction parameter determination function121, an imaging parameter determination function123, and a system control function125. The preprocessing function111, the reconstruction function113, the image processing function115, the cross-sectional shape estimation function117-1, the SSDE calculation function119, the correction parameter determination function121, the imaging parameter determination function123, and the system control function125may be implemented on one substrate of the processing circuitry101or separately implemented on a plurality of substrates of the processing circuitry101.

By the preprocessing function111, the processing circuitry101performs preprocessing such as logarithmic conversion to raw data transmitted from the gantry10. The preprocessed raw data is also referred to as projection data.

By the reconstruction function113, the processing circuitry101generates a CT image representing a space distribution of CT values relating to the patient P based on the preprocessed raw data. The known image reconstruction algorithm, such as an FBP (Filtered Back Projection) method or a successive approximation reconstruction method, may be adopted.

By the image processing function115, the processing circuitry101performs various image processing to a CT image reconstructed by the reconstruction function113. For example, the processing circuitry101performs three-dimensional image processing, such as volume rendering, surface volume rendering, pixel value projection processing, MPR (Multi-Planer Reconstruction) processing, CPR (Curved MPR) processing, etc. to the CT image to generate a display image.

By the cross-sectional shape estimation function117-1, the processing circuitry101estimates a shape index value relating to an imaged cross section of the patient P included in the CT imaging range, based on the positions of the visible light beams projected by the light projector27to the patient P. The shape index value is referred to as a cross-sectional shape index value. For example, the processing circuitry101applies the radiation position of the visible light beam to be projected on the patient P to a human body model resembling a three-dimensional shape of a human body, thereby estimating a cross-sectional shape index value relating to the imaged cross section corresponding to the radiation position of the visible light beam.

By the SSDE calculation function119, the processing circuitry101calculates an SSDE (Size-Specific Dose Estimates) value based on the cross-sectional shape index value estimated by the cross-sectional shape estimation function117-1and a CTDI (Computed Tomography Dose Index) value measured in advance.

By the imaging parameter determination function123, the processing circuitry101determines a plurality of imaging parameters constituting imaging conditions for CT imaging. The imaging parameters include a tube voltage value, a tube current value, and a modulation parameter relating to a directional modulation of the tube current.

The processing circuitry101determines the modulation parameter based on the cross-sectional shape index value estimated by the cross-sectional shape estimation function117-1.

By the system control function125, the processing circuitry101integrally controls the X-ray computed tomography apparatus according to the present embodiment. Specifically, the processing circuitry101reads a control program stored in the memory107, deploys the control program, and controls the respective units of the X-ray computed tomography apparatus in accordance with the deployed control program.

The display103displays various data, such as a CT image, etc. For the display103, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in this technical field may be used as appropriate.

The input circuitry105accepts various instructions from the user. Specifically, the input circuitry105includes an input device and an input interface. The input device receives various instructions from the user. A keyboard, a mouse, various types of switches, a touch pad, a touch panel display, etc. can be used as the input device. The input interface supplies an output signal from the input device to the processing circuitry101via a bus. The input device of the input circuitry105may be computer equipment connected to the console100by wired or wireless connection and including the input device.

The memory107is a storage device, such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device, etc. which stores various types of information. The memory107may also be a driving device, etc. which reads and writes various information to and from portable storage media, such as a CD-ROM drive, a DVD drive, and a flash memory. For example, the memory107stores a control program, etc. relating to CT imaging according to the present embodiment.

FIG. 2is a schematic view showing an appearance of the gantry10according to the first embodiment.FIG. 3is a cross-sectional view including a Z axis of the gantry10shown inFIG. 2. The central axis of the rotation frame11is defined as a Z axis; an axis vertically perpendicular to the Z axis is defined as a Y axis; and an axis horizontally perpendicular to the Z axis is defined as an X axis. As shown inFIG. 2andFIG. 3, the gantry10includes a gantry housing40with a substantially cylindrical bore41. The gantry housing40houses a main frame43which serves as a fixed unit, and the rotation frame11which serves as a rotation unit. The main frame43supports the rotation frame11so that the rotation frame11can be continuously rotated around the Z axis via a bearing. The X-ray tube13, the X-ray detector15, and the data acquisition circuitry19, which are not shown inFIG. 2andFIG. 3, are mounted on the rotation frame11. The light projector27is mounted on the rotation frame11in such a manner that a visible light beam projected from the light projector27can be directed toward the bore41. The light projector27projects visible light beams which render the reference lines of the CT imaging range directly visible. The reference lines of the CT imaging range include central lines relating to X, Y and Z directions of the CT imaging range, and frame lines constituting an outer frame of the CT imaging range. The reference lines of the CT imaging range are not limited to the above, but may be any lines which are useful for positioning of the imaging target area of the patient P in the CT imaging range.

As shown inFIG. 2andFIG. 3, a gap47is provided to allow passage of the visible light beams projected from the light projector27and the X-rays generated from the X-ray tube13(not shown) on a part of the inner wall of the gantry housing40that faces the bore41. Since the light projector27and the X-ray tube13are mounted on the rotation frame11, the gap47is provided in the entire circumference of the inner wall around the Z axis. A transmission film45is attached to cover the gap47. The visible light beams projected from the light projector27and the X-rays generated from the X-ray tube13transmit through the transmission film45. For example, the transmission film45is formed as a transparent or translucent film made of polyester.

To specifically explain the embodiment, it is assumed that visible light beams projected from the light projector27represent frame lines constituting an outer frame of the CT imaging range.

FIG. 4is a diagram showing an example of visible light beams Lz and Lx which represent frame lines constituting the outer frame of the CT imaging range. As shown inFIG. 4, the visible light beams Lz represent an outer frame of the imaging range in the Z direction. More specifically, the visible light beams Lz include a light beam Lz1on a front side (for example, the head side of the patient P) of the Z axis and a light beam Lz2on a back 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; 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 radiation position of the light beam Lz1and the radiation position of the light beam Lz2are adjustable independently of each other along the Z axis. The visible light beams Lx include a light beam Lx1on a left side of the X axis and a light beam Lx2on a right side. The radiation position of the light beam Lx1and the radiation position of the light beam Lx2are adjustable independently of each other along the X axis. For example, the user performs adjustment of the radiation positions of the visible light beams Lz1, Lz2, Lx1, and Lx2by operating the input circuitry31or105. The gantry control circuitry33sets light projection parameters to apply the visible light beams Lz1, Lz2, Lx1, and Lx2to the radiation positions in accordance with the adjustment. In other words, the gantry control circuitry33sets positions of the light source of the light projector27or irradiation angles of the light beams so that the visible light beams Lz1, Lz2, Lx1, and Lx2can be applied to the radiation positions in accordance with the adjustment. Then, the gantry control circuitry33moves the light source of the light projector27to the set positions or inclines the light source of the light projector27at the irradiation angles. As a result, the visible light beams Lz1, Lz2, Lx1, and Lx2can be applied to the radiation positions in accordance with the light projection parameters.

FIG. 2andFIG. 3show an example in which two light projectors271are mounted on the rotation frame11. However, the X-ray computed tomography apparatus of the embodiment is not limited to this. Any number of light projectors27may be mounted on the rotation frame11. Should the light projector27not need to be rotated around the rotation axis Z, it may be mounted on a component other than the rotation frame11of the gantry10, for example, to the main frame43or the gantry housing40.

FIG. 5is a flowchart illustrating a typical operation of the X-ray computed tomography apparatus, performed by execution of the system control function125of the processing circuitry101according to the first embodiment. First, as shown inFIG. 5, the processing circuitry101directs the gantry control circuitry33to perform radiation of the visible light beams (step SA1). In step SA1, the gantry control circuitry33directs the light projector27to project the visible light beams representing the reference lines of the CT imaging range to the patient P. For example, the user, such as a healthcare professional, performs operations with the input circuitry31to include the imaging target area of the patient P in the CT imaging range, thereby adjusting the height of the table top231of the bed23(hereinafter referred to as the bed height). At this time, the light projector27projects visible light beams representing an outer frame of the CT imaging range as the visible light beams representing the reference lines of the CT imaging range. The radiation positions of the visible light beams can be adjusted at desired positions by the user via the input circuitry31or105. The light projection parameters corresponding to the radiation positions of the visible light beams are transmitted from the gantry control circuitry33to the console100and stored in the memory107.

After step SA1, the processing circuitry101directs the optical camera29to perform optical imaging (step SA2). In step SA2, the optical camera29optically images the patient P irradiated with the visible light beams, and generates an optical image (step SA2). In the optical image, for example, RGB values are allocated to the respective pixels. At an optical imaging time, the center of the height in the imaging range of the patient P need not coincide with the height of the isocenter. The generated optical image is transmitted to the console100and stored in the memory107. At this time, the value of the bed height is stored in association with the optical image.

FIG. 6is a schematic view showing a placement of the optical camera29. As shown inFIG. 6, at a positioning time, the visible light beams L representing an outer frame of the CT imaging range are projected from the light projector27toward the patient P placed in the table top231of the bed23. The optical camera29is mounted on an end of the table top231, opposite to the gantry housing40via a support bar49. The optical camera29is attached to a height and at an angle so that the patient P irradiated with the visible light beams L projected from the light projector27is covered by the optical imaging range. For example, the optical camera29is not necessarily mounted on the table top231via the support bar49, but may be mounted on the gantry10, or a ceiling or side wall of the examination room.

After step SA2, the processing circuitry101executes the cross-sectional shape estimation function117-1. By the cross-sectional shape estimation function117-1, first, the processing circuitry101subjects the optical image generated by the optical camera29to image processing, and specifies an anatomical location of the part irradiated with the visible light beams (step SA3). In the embodiment, the anatomical location does not denote the coordinates of the optical image, but denotes a location in the anatomical site irradiated with the visible light beams. For example, the anatomical location is defined by a position relative to a reference point of the imaging target area. The specified anatomical location is hereinafter referred to as the image side location.

FIG. 7is a schematic view showing an example of an optical image I1generated by the optical camera29. As shown inFIG. 7, the optical image I1includes an image region R1relating to the patient P (hereinafter referred to as the patient region), and an image region R2relating to visible light beams (hereinafter referred to as the visible light beam region). The processing circuitry101subjects the optical image I1to threshold processing or the like, and specifies the visible light beam region R2. Then, by image recognition processing or the like, the processing circuitry101specifies as the image side location an anatomical location in the patient region R1where the visible light beam region R2is present. For example, in the case shown inFIG. 7, the imaging target area is a chest region. In this case, a part of the chest region is specified as the image side location R2by the image processing mentioned above. The image side location may be specified at a location designated by the user via the input circuitry105. Information on the imaging target area may be specified by the image recognition processing for the optical image I1, or may be acquired from the imaging conditions.

After executing step SA3, the processing circuitry101specifies an anatomical location in the human body model that corresponds to the image side location specified in step SA3(step SA4). The specified anatomical location is referred to as the model side location. Data on the human body model is stored in the memory107.

FIG. 8is an example of a human body model MD. The human body model MD is data on a human body model resembling a three-dimensional shape of a human body. The human body model MD reflects not only the outer shape of a human body but also internal structures such as internal organs. For example, if the partial region R2of the chest region is specified as the image side location as shown inFIG. 7, a partial region of the human body model that anatomically corresponds to the chest region R2is specified as a model side location R2′. It is assumed that the coordinate system of the human body model MD and the coordinate system of the optical image I1are associated with each other in advance.

After executing step SA4, the processing circuitry101estimates a cross-sectional shape index value relating to the cross section at the model side location specified in step SA4(step SA5). In step SA5, the processing circuitry101first sets an estimation target cross section included in the model side location. The estimation target cross section is determined at discretion from a plurality of imaged cross sections included in the model side location. The imaged cross sections are assumed to be cross sections in the CT imaging range of the patient P.

Once the estimation target cross section is set, the processing circuitry101estimates a cross-sectional shape index value in the cross section. Specifically, the cross-sectional shape index value is defined by a length in an AP (Anterior-Posterior) direction (hereinafter referred to as the AP length) of the human body model, a length in an LR (Left-Right) direction (hereinafter referred to as the LR length), the total of the AP length and the LR length, an effective diameter, a water equivalent diameter, etc.

FIG. 9is a schematic view of an example of an imaged cross section of the human body model MD. InFIG. 9, “A” represents an anterior side, “P” represents a posterior side, “L” represents a left side, and “R” represents a right side of the patient. For example, if the cross-sectional shape of the human body model is expressed by a water equivalent length (a dimension obtained by converting a length of an X-ray transmission path to a length of a water transmission path), the diameter of the cross section of the human body model is equal to the water equivalent diameter. In this case, the processing circuitry101can estimate a water equivalent diameter of the patient P by measuring the diameter of the cross section of the human body model. On the other hand, if the cross-sectional shape of the human body model is expressed by an actual path length, the AP length of the patient P can be estimated by measuring the length in the AP direction of the cross section of the human body model, and the LR length of the patient P can be estimated by measuring the length in the LR direction of the cross section of the human body model. 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.

The processing circuitry101can correct the estimated cross-sectional shape index value based on the bed height correction parameter. The correction parameter in accordance with the bed height is determined by the correction parameter determination function121of the processing circuitry101.

As shown inFIG. 10, there is a linear relationship between the bed height correction parameter and the bed height; specifically, the bed height correction parameter has a smaller value as the bed height is increased. The correction parameter at the height Iso is set to “1”. The processing circuitry101stores a table (LUT: Look Up Tale) that defines the relationship between the bed height and the bed height correction parameter shown inFIG. 10. In the following description, the table is referred to as the bed height correction table. The processing circuitry101acquires a bed height value at the optical imaging time for the patient P by the optical camera29from the gantry10, and determines a bed height correction parameter from the bed height correction table based on the acquired bed height value. By the cross-sectional shape estimation function117-1, the processing circuitry101estimates a cross-sectional shape index value by multiplying the determined bed height correction parameter by a provisionally determined cross-sectional shape index value.

After execution of step SA5, the cross-sectional shape estimation function117-1is ended.

Next, the processing circuitry101executes the SSDE calculation function119(step SA6). In step SA6, the processing circuitry101calculates an SSDE value based on the water equivalent diameter and the CTDI value measured in advance. More specifically, the processing circuitry101determines a conversion factor from the water equivalent diameter, and calculates the SSDE value by multiplying the determined conversion factor by the CTDI value. For example, the processing circuitry101stores a table (LUT: Look Up Tale) that associates the water equivalent diameter with the conversion factor. The table is referred to as the water equivalent diameter/conversion factor table. The processing circuitry101searches the water equivalent diameter/conversion factor table using the water equivalent diameter calculated in step SA5as a search key, and determines the conversion factor associated with the water equivalent diameter. The CTDI value is measured by CT imaging of a phantom for CTDI measurement in a geometry for the CTDI measurement. The CTDI value is stored in the memory107.

The SSDE value may be calculated for each of all imaged cross sections included in the model side location. In this case, the processing circuitry101calculates an average value, central value, maximum value, or minimum value of a plurality of SSDE values relating to a plurality of imaged cross sections as the SSDE value of the entire CT imaging range.

After step SA6, the processing circuitry101directs the display103to display the SSDE value calculated in the step SA6(step SA7). Specifically, the display103may display the SSDE value of each imaged cross section or the SSDE value of the entire CT imaging range. The user checks the displayed SSDE value, and if the SSDE value is determined to be unacceptable, the user reviews the imaging conditions or the like. If the SSDE value is determined to be acceptable, the user inputs imaging instructions via the input circuitry31or105.

After step SA7, once the user inputs imaging instructions via the input circuitry31or105, the processing circuitry101directs the gantry control circuitry33to start imaging (step SA8). The gantry control circuitry33, which has been instructed to start imaging, synchronously controls the X-ray high voltage device17, the data acquisition circuitry19, the rotation actuator21, the bed actuator25, etc. in accordance with imaging conditions, to perform CT imaging for the patient P.

The operation flow of the X-ray computed tomography apparatus according to the first embodiment is completed with the above explanations.

A plurality of human body models of different physical types may be stored in the memory107, and the processing circuitry101may choose one of the human body models that is similar to the body shape of the patient P. For example, the human body model may be chosen in accordance with an instruction given by the user via the input circuitry105. Alternatively, the human body model that is closest to the body shape of the patient P may be chosen based on patient information, such as the age, the sex, and anthropometric measurements. The anthropometric measurements in this embodiment include any measurements concerning the body shape of the patient, such as the body height, the weight, and the chest circumference. The processing circuitry101may correct the shape of the human body model to conform to the body shape of the patient P based on the patient information, such as the age, the sex, and anthropometric measurements. Thus, by using the human body model approximate to the body shape of the patient P, the estimation target cross section is more approximate to the actual cross section of the patient P. Accordingly, the accuracy of the estimation of the cross-sectional shape is improved, and the accuracies of the cross-sectional shape index value and the SSDE value are also improved.

The cross-sectional shape index value is applicable to various purposes, not only the calculation of the SSDE value. For example, by the imaging parameter determination function123, the processing circuitry101can determine parameters that define a directional modulation of the tube current (hereinafter referred to as the tube current modulation parameters) based on the cross-sectional shape index value estimated by the cross-sectional shape estimation function117-1. Specifically, the processing circuitry101determines a ratio of a tube current value in the AP direction to a reference value of the tube current, and a ratio of a tube current value in the LR direction to the reference value of the tube current in accordance with the ratio of the water equivalent diameter in the AP direction to the water equivalent diameter in the LR direction. The ratios are set as the tube current modulation parameters. The tube current modulation parameters may be the tube current value in the AP direction and the tube current value in the LR direction.

As described above, according to the first embodiment, the tube current modulation parameters can be determined based on the cross-sectional shape index value estimated in accordance with the radiation positions of the visible light beams projected from the light projector27, and not a cross-sectional shape index value estimated in accordance with a positioning image. Therefore, the exposure to radiation of the patient P can be reduced.

Furthermore, the processing circuitry101may determine the correction parameter of the SSDE value in accordance with a difference between the SSDE value and the dose value which has been actually measured by the correction parameter determination function121. The processing will be described in detail below. When the CT imaging is performed in step SA8, the processing circuitry101measures the actual dose value of the patient P. The memory107stores the dose value which has been actually measured and the SSDE value relating to the patient P in association with each other. The memory107stores the dose value which has been actually measured and the SSDE value in association with each other for each of a plurality of patients. By the correction parameter determination function121, the processing circuitry101calculates a difference value between the dose value which has been actually measured and the SSDE value stored in the memory107, analyzes the calculated difference value, and determines a correction parameter (hereinafter referred to as the SSDE correction parameter) to approximate the SSDE value calculated by the SSDE calculation function119to the does value which has been actually measured. The SSDE correction parameter may be a parameter common to all patients P, or may be a parameter determined for each classification of patients P, such as the body shape. When the SSDE correction parameter is determined, the processing circuitry101estimates the SSDE value based on the cross-sectional shape index value, the CTDI value, and the SSDE correction parameter in step SA6. As a result, the accuracy of estimating the SSDE value can be further improved.

In the above example, only one optical camera29is placed. However, the present embodiment is not limited to this. A plurality of optical cameras29may be placed. For example, one optical camera29to optically image the anterior side of the patient P and another optical camera29to optical image a side of the patient P may be placed. The processing circuitry101can determine the anatomical location in the CT imaging range based on optical images in a plurality of directions, thereby improving the accuracy of estimation of the anatomical location and also the accuracies of the cross-sectional shape index value and estimation of the SSDE value.

The optical camera29may be mounted on the rotation frame11. By mounting the optical camera29on the rotation frame11, an optical image of the entire circumference of the patient P can be generated by the single optical camera29. By determining the anatomical location of the CT imaging range based on the optical image of the entire circumference, the processing circuitry101can improve the estimation accuracy of the anatomical location, and accordingly the estimation accuracies of the cross-sectional shape index value and the SSDE value.

If the body shape of the patient P is very large, the patient may be too close to the light projector27. In this case, it is difficult to make the radiation positions of the visible light beams from the light projector27coincide with the CT imaging range. For example, triggered by an alert instruction input by the user via the input circuitry31or105, the processing circuitry101generates an alert indicating that a cross-sectional shape index value cannot be estimated. The generation of the alert may be an output of an alert sound by a speaker, a display of an alert message in the display103, etc. Accordingly, the user can switch the estimation to the estimation of the SSDE value based on the positioning image.

With the configuration described above, according to the first embodiment, the cross-sectional shape index value can be estimated on the basis of the human body model and the optical image of the patient P irradiated with the visible light beams projected from the light projector27at the time of positioning the patient P. In other words, when estimating the cross-sectional shape index value, the X-ray computed tomography apparatus according to the first embodiment does not require imaging for positioning. Therefore, the X-ray computed tomography apparatus according to the first embodiment can estimate the cross-sectional shape index value with less exposure to radiation of the patient P as compared to the case in which imaging for positioning is performed.

Second Embodiment

The X-ray computed tomography apparatus of the first embodiment described above is equipped with the optical camera29. However, the present embodiment is not limited to this. In the second embodiment, the estimation of the cross-sectional shape index value and the calculation of the SSDE value are performed without using the optical camera29. Details of the second embodiment will be described below. In the description below, structural elements with substantially the same functions as those of the first embodiment will be denoted by the same reference symbols, and a repetitive description will be given only where necessary.

FIG. 11is a diagram showing a configuration of the X-ray computed tomography apparatus according to the second embodiment. As shown inFIG. 11, the X-ray computed tomography apparatus of the second embodiment does not include an optical camera. By a cross-sectional shape estimation function117-2, processing circuitry101of the second embodiment specifies radiation positions of visible light beams projected to a patient P from a light projector27based on projection parameters, and estimates a cross-sectional shape index value of a cross section corresponding to the specified radiation positions using a human body model.

FIG. 12is a flowchart illustrating a typical operation of the X-ray computed tomography apparatus, performed by execution of a system control function125of the processing circuitry101according to the second embodiment.

As shown inFIG. 12, first, the processing circuitry101directs gantry control circuitry33to perform radiation of visible light beams (step SB1). In step SB1, in the same manner as in step SA1of the first embodiment, the gantry control circuitry33directs the light projector27to project the visible light beams to the patient P (step SB1). In the former step of the radiation of the visible light beams, projection parameters relating to the radiation positions of the visible light beams are set in the same manner as in step SA1. The light projection parameters are transmitted to a console100and stored in a memory107.

After step SB1, the processing circuitry101executes the cross-sectional shape estimation function117-2. By the cross-sectional shape estimation function117-2, first, the processing circuitry101specifies an anatomical location of the part irradiated with the visible light beams based on the light projection parameters acquires in step SB1(step SB2). Specifically, the processing circuitry101specifies anatomical locations irradiated with the visible light beams based on an imaging target area and the light projection parameters (the position of a light source and an irradiation angle of the light projector27) included in imaging conditions. In addition to the imaging target area and the light projection parameters, an anatomical location may be specified utilizing a Z-axis coordinate and a Y-axis coordinate of a table top231.

After executing step SB2, the processing circuitry101specifies an anatomical location in the human body model that corresponds to the actual location specified in step SB2(step SB3). Specifically, the processing circuitry101specifies the anatomical location in the human body model in the same manner as in step SA4of the first embodiment.

After executing step SB3, the processing circuitry101estimates a water equivalent diameter in the cross section at a model side location specified in step SB3(step SB4). Specifically, the processing circuitry101estimates the water equivalent diameter in the same manner as in step SA5of the first embodiment.

After step SB4, the processing circuitry101calculates an SSDE value based on the water equivalent diameter estimated in step SB4and the CTDI value measured in advance (Step SB5). Specifically, the processing circuitry101calculates the SSDE value in the same manner as in step SA6of the first embodiment.

After step SB5, the processing circuitry101directs the display103to display the SSDE value calculated in the step SB5(step SB6). Specifically, the display103displays the SSDE value in the same manner as in step SA7of the first embodiment. The user checks the displayed SSDE value, and if the SSDE value is determined to be unacceptable, reviews the imaging conditions or the like. If the SSDE value is determined to be acceptable, the user inputs imaging instructions via the input circuitry31or105.

After step SB6, once the user inputs imaging instructions via the input circuitry31or105, the processing circuitry101directs the gantry control circuitry33to start imaging (step SB7). The gantry control circuitry33, which has been instructed to start imaging, synchronously controls the X-ray high voltage device17, the data acquisition circuitry19, the rotation actuator21, the bed actuator25, etc. in accordance with imaging conditions, to perform CT imaging for the patient P.

The operation flow of the X-ray computed tomography apparatus according to the second embodiment is completed with the above explanations.

With the configuration described above, according to the second embodiment, the cross-sectional shape index value can be estimated on the basis of the human body model and the projection light parameters of the light projector27at the time of positioning the patient P. In other words, when estimating the cross-sectional shape index value, the X-ray computed tomography apparatus according to the second embodiment does not require imaging for positioning. Therefore, the X-ray computed tomography apparatus according to the second embodiment can estimate the cross-sectional shape index value with less exposure to radiation of the patient P as compared to the case in which imaging for positioning is performed. Since the second embodiment does not use an optical camera, it can estimate the cross-sectional shape index value via a simpler apparatus design as compared to the first embodiment. In other words, since the first embodiment uses the optical camera, it can estimate a cross section and further a cross-sectional shape index value more accurately as compared to the second embodiment.

Third Embodiment

In the X-ray computed tomography apparatuses according to the first and second embodiments, the estimation of the cross-sectional shape index value and the calculation of the SSDE value are performed using the human body model. However, the present embodiment is not limited to this. The third embodiment performs estimation of a cross-sectional shape index value and calculation of an SSDE value without using a human body model. Details of the third embodiment will be described below. In the description below, structural elements with substantially the same functions as those of the first and second embodiments will be denoted by the same reference symbols, and a repetitive description will be given only where necessary.

FIG. 13is a diagram showing a configuration of an X-ray computed tomography apparatus according to the third embodiment. As shown inFIG. 13, the processing circuitry101of the third embodiment executes a cross-sectional shape estimation function117-3. By the cross-sectional shape estimation function117-3, the processing circuitry101estimates across-sectional shape index value based on light projection parameters of a light projector27in two or more directions.

FIG. 14is a flowchart illustrating a typical operation of the X-ray computed tomography apparatus, performed by execution of the system control function125of the processing circuitry101according to the third embodiment. As shown inFIG. 14, first, the processing circuitry101executes the cross-sectional shape estimation function117-3in steps SC1through SC4.

FIG. 15is a schematic diagram illustrating a cross-sectional shape estimation function117-3executed by the processing circuitry101in steps SC1through SC4.

As shown inFIG. 14andFIG. 15, the processing circuitry101directs the gantry control circuitry33to rotate a rotation frame11. The gantry control circuitry33, first, controls a rotation actuator21to arrange the light projector27at a rotation angle of 0° or 180° (step SC1).

After step SC1, the processing circuitry101measures an LR length of a patient P based on the light projection parameters of the light projector27(step SC2). First, the user inputs a light projection start instruction via input circuitry31. Upon receipt of the light projection start instruction, the gantry control circuitry33directs the light projector27to project visible light beams Lz1, Lz2, Lx1, and Lx2to the patient P. Next, in accordance with the instruction by the user via the input circuitry31, the gantry control circuitry33adjusts the distance between the visible light beams Lx1and Lx2in the LR direction to coincide with the CT imaging range in the LR direction of the patient P. When the adjustment is completed, the user inputs an adjustment completion instruction via the input circuitry31.

The processing circuitry101estimates the LR length based on the light projection parameters at the time of the adjustment completion instruction and a geometry between the light projector27and the patient P or a table top231. Specifically, the processing circuitry101measures an angle between the visible light beam Lx1and the visible light beam Lx2(hereinafter referred to as an interbeam angle) based on the irradiation angle of the visible light beam Lx1and the irradiation angle of the visible light beam Lx2at a rotation angle of 0°, and estimates a distance between the visible light beam Lx1and the visible light beam Lx2based on the interbeam angle and a bed height. The distance is set as the LR length. Alternatively, the processing circuitry101may measure a distance between the visible light beam Lx1and the visible light beam Lx2(hereinafter referred to as an interbeam distance) based on the light source position of the light projector27corresponding to the irradiation position of the visible light beam Lx1and the light source position of the light projector27corresponding to the irradiation position of the visible light beam Lx2at a rotation angle of 0°, and may estimate an LR length based on the interbeam distance and a bed height. The processing circuitry101may estimate the LR length based on a predicted value of the LR length of the patient P in addition to the interbeam angle or the interbeam distance and the bed height. Furthermore, the processing circuitry101may estimate the LR length using a distance between the light projector27and the patient P or the table top231. Upon receipt of the adjustment completion instruction, the gantry control circuitry33transmits the LR length to a console100, and a memory107stores the LR length.

After step SC2, the gantry control circuitry33controls a rotation actuator21to arrange the light projector27at a rotation angle of 90° or 270° (step SC3).

After step SC3, the processing circuitry101measures an AP length of the patient P based on the light projection parameters of the light projector27(step SC4). First, the user inputs a light projection start instruction via the input circuitry31. Upon receipt of the light projection start instruction, the gantry control circuitry33directs the light projector27to project visible light beams Lz1, Lz2, Lx1, and Lx2to the patient P. Next, in accordance with the instruction by the user via the input circuitry31, the gantry control circuitry33adjusts the distance between the visible light beams Lx1and Lx2in the AP direction to coincide with the CT imaging range in the AP direction of the patient P. When the adjustment is completed, the user inputs an adjustment completion instruction via the input circuitry31.

The processing circuitry101estimates the AP length based on the light projection parameters at the time of the adjustment completion instruction and a geometry between the light projector27and the patient P or the table top231. Specifically, the processing circuitry101measures the interbeam angle based on the irradiation angle of the visible light beam Lx1and the irradiation angle of the visible light beam Lx2at a rotation angle of 90°, and estimates the distance between the visible light beam Lx1and the visible light beam Lx2based on the interbeam angle and the distance between the light projector27and the patient P or the table top231. The distance is set as the AP length. Alternatively, the processing circuitry101may measure the interbeam distance based on the light source position of the light projector27corresponding to the irradiation position of the visible light beam Lx1and the light source position of the light projector27corresponding to the irradiation position of the visible light beam Lx2at a rotation angle of 90°, and may estimate the AP length based on the interbeam distance between the light projector27and the patient P or the table top231. Furthermore, the processing circuitry101may estimate the AP length based on a predicted value of the AP length of the patient P in addition to the interbeam angle or the interbeam distance and the bed height. Upon receipt of the adjustment completion instruction, the gantry control circuitry33transmits the AP length to the console100, and the memory107stores the AP length.

After steps SC1through SC4, the processing circuitry101ends the cross-sectional shape estimation function117-3. It is to be noted that steps SC1and SC2and steps SC3and SC4may be carried out in reverse order. In other words, the AP length may be estimated first and the LR length may be estimated later.

After step SC4, the processing circuitry101calculates the SSDE value based on the LR length estimated in step SC2, the AP length estimated in step SC4, and the CTDI value calculated in advance (step SC5). In step SC5, the processing circuitry101determines a conversion factor from the combination of the LR length and the AP length, and calculates the SSDE value by multiplying the determined conversion factor by the CTDI value. The conversion factor is determined for each combination of an LR length and an AP length. The conversion factor is not necessarily determined directly from the combination of an LR length and an AP length. For example, the processing circuitry101may include a table (LUT) in which the combination of an LR length and an AP length is associated with a water equivalent diameter, determine the water equivalent diameter from the combination of the LR length and the AP length utilizing the LUT, and determine the conversion factor utilizing the water equivalent diameter/conversion factor table.

After step SC5, the processing circuitry101directs the display103to display the SSDE value calculated in the step SC5(step SC6). The user checks the displayed SSDE value, and if the SSDE value is determined to be unacceptable, reviews the imaging conditions or the like. If the SSDE value is determined to be acceptable, the user inputs imaging instructions via the input circuitry31or105.

After step SC6, once the user inputs imaging instructions via the input circuitry31or105, the processing circuitry101directs the gantry control circuitry33to start imaging (step SC7). The gantry control circuitry33, which has been instructed to start imaging, synchronously controls the X-ray high voltage device17, the data acquisition circuitry19, the rotation actuator21, the bed actuator25, etc. in accordance with imaging conditions, to perform CT imaging for the patient P.

The operation flow of the X-ray computed tomography apparatus according to the third embodiment is completed with the above explanations.

In the above example, both the AP length and the LR length are measured. However, the present embodiment is not limited to this. For example, if the conversion factor is obtained from only one of the AP length and the LR length, measurement of the other one of the AP length and the LR length may be omitted. In the example described above, the distance between the visible light beam Lx1and the visible light beam Lx2at an angle of 0° or 180° is defined as the LR length; however, the embodiment is not limited to this. For example, the distance between the visible light beam Lx1and the visible light beam Lx2at another angle may be defined as the LR length in accordance with the position of the patient P on the table top231. Similarly, in the example described above, the distance between the visible light beam Lx1and the visible light beam Lx2at an angle of 90° or 270° is defined as the AP length; however, the embodiment is not limited to this. For example, the distance between the visible light beam Lx1and the visible light beam Lx2at another angle may be defined as the AP length in accordance with the position of the patient P on the table top231.

With the configuration described above, according to the third embodiment, the cross-sectional shape index value can be estimated on the basis of the projection light parameters of the light projector27at a plurality of rotation angles. In other words, when estimating the cross-sectional shape index value, the X-ray computed tomography apparatus according to the third embodiment does not require imaging for positioning. Therefore, the X-ray computed tomography apparatus according to the third embodiment can estimate the cross-sectional shape index value with less exposure to radiation of the patient P as compared to the case in which imaging for positioning is performed. Since the third embodiment does not use an optical camera, it can estimate the cross-sectional shape index value via a simpler apparatus design as compared to the first embodiment. Furthermore, unlike the first and second embodiments, the third embodiment directly estimates (measures) the AP length and the LR length by the adjustment of the radiation positions of the visible light beams by the user. Therefore, the estimation accuracy of the cross-sectional shape index value, such as the AP length and the LR length, is improved.

Fourth Embodiment

According to the first, second, and third embodiments, the X-ray computed tomography apparatus estimates the cross-sectional shape index value and calculates the SSDE value using the visible light beams projected from the light projector. However, the present embodiment is not limited to this. The fourth embodiment estimates the cross-sectional shape index value and calculates the SSDE value using infrared. Details of the fourth embodiment will be described below. In the description below, structural elements with substantially the same functions as those of the first, second, and third embodiments will be denoted by the same reference symbols, and a repetitive description will be given only where necessary.

FIG. 16is a diagram showing a configuration of the X-ray computed tomography apparatus according to the fourth embodiment. As shown inFIG. 16, a gantry10according to the fourth embodiment includes an infrared emitter35and an optical receptor37. The infrared emitter35irradiates a patient P lying on the table top with infrared. The infrared of the embodiment includes near infrared, infrared in a narrow sense, and far infrared. The infrared emitter35is realized, for example, by an LED (Light-Emitting Diode). The optical receptor37receives the infrared projected on and reflected from the patient P, and outputs an electric signal corresponding to the received infrared. The optical receptor37is realized, for example, by an infrared camera, in which optical sensors such as CMOS (Complementary Metal-Oxide Semiconductor) are two-dimensionally arrayed.

The gantry control circuitry33of the fourth embodiment realizes an infrared information measurement function293. By the infrared information measurement function293, the gantry control circuitry33measures information on the infrared received by the optical receptor37. The information on the infrared is, for example, time of flight. The time of flight is defined by an elapsed time, from a time when the infrared emitter35emits infrared to a time when the optical receptor37receives the infrared reflected from the patient P. Other information on the infrared that is utilized in this embodiment may include, for example, an intensity of the received infrared.

Processing circuitry101of the fourth embodiment executes a cross-sectional shape estimation function117-4. By the cross-sectional shape estimation function117-4, the processing circuitry101estimates a cross-sectional shape index value relating to a cross section of the patient P in an imaging range based on the information on the infrared.

FIG. 17is a flowchart illustrating a typical operation of the X-ray computed tomography apparatus, performed by execution of a system control function125of the processing circuitry101according to the fourth embodiment.FIG. 18is a schematic diagram illustrating an overview of estimation of a cross-sectional shape index value utilizing infrared.

As shown inFIG. 17andFIG. 18, the processing circuitry101first directs the gantry control circuitry33to image the patient P with infrared IR. When imaging the patient P with the infrared IR, the infrared emitter35irradiates the patient P lying on a table top231, and the optical receptor37receives the infrared reflected from the patient (step SD1). As shown inFIG. 18, the infrared emitter35and the optical receptor37are provided on a ceiling200of an examination room. The set of the infrared emitter35and the optical receptor37is preferably housed in a discretionary housing39. The patient P is placed on the table top231. Imaging of the patient P using the infrared emitter35and the optical receptor37is typically performed before the table top231is inserted into a bore41to prevent the infrared IR from being interrupted by a gantry housing40. The infrared IR is preferably projected on the entire width of the patient P including the imaging range to measure a body thickness (AP length) and a width (LR length) of the patient P with the infrared IR.

After step SD1, the gantry control circuitry33executes the infrared information measurement function293and measures the time of flight of the infrared received by the optical receptor37(step SD2). In step SD2, the gantry control circuitry33calculates as a time of flight an elapsed time, from a time when the infrared emitter35emits infrared to a time when the optical receptor37receives the infrared reflected from the patient P.

After step SD2, the processing circuitry101executes the cross-sectional shape estimation function117-4and estimates the cross-sectional shape index value based on the time of flight of the infrared and the height of the table top231(Step SD3). In step SD3, the processing circuitry101estimates the AP length (thickness) and the LR length (width) of the patient P as the cross-sectional shape index values.

The AP length is estimated, for example, as follows. As shown inFIG. 18, the AP length of the patient P can be estimated from the propagation velocity of the infrared IR, the time of flight of the infrared IR reflected from the patient P, and time of flight of the infrared IR reflected from the table top231in the absence of the patient P. The time of flight of the infrared IR reflected from the table top231is measured or predicted in advance. For example, the gantry control circuitry33sets the table top231at a plurality of heights, directs the infrared emitter35to project the infrared IR on the surface of the table top at each height, and directs the optical receptor37to receive the infrared reflected from the surface of the table top231. The gantry control circuitry33calculates a difference between the projection time when the infrared is projected and the reception time when the infrared is received, and sets the difference as the time of flight for each of the heights of the table top. The gantry control circuitry33produces a table in which each height of the table top is associated with the time of flight (hereinafter referred to as the time-of-flight table), and stores the table in its own memory. If the time of flight in the presence of the patient P is measured, the time of flight associated with the corresponding height of the table top is read from the time-of-flight table based on the height of the table top used in the infrared imaging. The difference between the read time of flight and the time of flight in the pretense of the patient P is calculated, and the AP length is calculated from the difference and the propagation velocity of the infrared.

The LR length is estimated, for example, as follows. The gantry control circuitry33causes the infrared IR to be projected and received at intervals of a specific angle to pass through the patient P lying on the table top231, and records the reception time or the time of flight for each infrared radiation. The reception time or the time of flight changes abruptly at a boundary between the place where the patient is present and the place where the patient is not present. A position where the reception time or the time of flight abruptly changes on the right of the patient P and such a position on the left of the patient P are specified, and the distance between the specified positions on the right and left of the patient P is calculated as the LR length. The LR length may be estimated by using the optical camera29as used in the first and second embodiment, or by using the light projector27as used in the third embodiment.

After step SD3, the processing circuitry101calculates an SSDE value based on the LR length and the AP length estimated in step SD3and the CTDI value measured in advance (step SD4). Step SD4is similar to, for example, step SC5of the third embodiment.

After step SD4, the processing circuitry101directs the display103to display the SSDE value calculated in the step SD4(step SD5). Step SD5is similar to, for example, step SC6of the third embodiment.

After step SD5, once the user inputs imaging instructions via the input circuitry31or105, the processing circuitry101directs the gantry control circuitry33to start imaging (step SD6). The gantry control circuitry33, which has been instructed to start imaging, synchronously controls the X-ray high voltage device17, the data acquisition circuitry19, the rotation actuator21, the bed actuator25, etc. in accordance with imaging conditions, to perform CT imaging for the patient P.

The operation flow of the X-ray computed tomography apparatus according to the fourth embodiment is completed with the above explanations.

The fourth embodiment can be modified in various ways. For example, in the above explanations, whether or not the table top231is moved in CT imaging is not particularly specified. In the case of helical scan for performing a scan while moving the table top231, and in the case of intermediate movement scan for intermittently performing a scan and moving the table top231, the CT imaging range expands over a wide range. However, since the infrared imaging range that can be covered by one infrared imaging varies depending on the specification of the infrared emitter35and the optical receptor37, the CT imaging range may not be covered by one infrared imaging. In this case, the imaging range in a wide range can be imaged by the infrared by moving the table top231in its long-axis direction. For example, the CT imaging range is divided into a plurality of small ranges in accordance with the imaging range of the infrared, and infrared imaging and estimation of the cross-sectional shape index value are performed in each small range. As a result, even when the CT imaging range is wide, the cross-sectional shape index value can be estimated.

Furthermore, according to the above explanation, for example, the set of the infrared emitter35and the optical receptor37is provided on the ceiling200of the examination room. However, the set may be provided on any other place, such as the gantry housing40, so long as the infrared imaging of the patient P is possible. Furthermore, it is assumed that the set of the infrared emitter35and the optical receptor37is fixed to the ceiling200. However, the set may be provided so as to be slidable along the Z axis or the X axis in the examination room, or slidable on a two-dimensional plane defined by the Z axis and the X axis. With this configuration, the infrared IR can be projected on the patient P or the table top231substantially at right angles. Alternatively, a plurality of sets of the infrared emitter35and the optical receptor37may be provided so as to be slidable along the Z axis or the X axis, or slidable on a two-dimensional plane defined by the Z axis and the X axis. Also with this configuration, the infrared IR can be projected on the patient P or the table top231substantially at right angles.

With the configuration described above, according to the fourth embodiment, the cross-sectional shape index value can be estimated by utilizing the infrared. In other words, when estimating the cross-sectional shape index value, the X-ray computed tomography apparatus according to the fourth embodiment does not require imaging for positioning. Therefore, the X-ray computed tomography apparatus according to the fourth embodiment can estimate the cross-sectional shape index value with less exposure to radiation of the patient P as compared to the case in which imaging for positioning is performed.

As described above, the X-ray computed tomography apparatus according to the embodiments includes the gantry10, the bed23, the light projector27, and the processing circuitry101. The gantry10performs x-ray CT imaging. The bed23movably supports the table top231on which the patient P lies. The optical emitter27or35irradiates the patient P lying on the table top231with light beams. The processing circuitry101estimates the cross-sectional shape index value of the patient P in the imaging range by utilizing light beams projected on the patient P.

With the configuration described above, the X-ray computed tomography apparatus of the embodiments estimate the cross-sectional shape index value by using the optical emitter27or35without performing imaging for positioning. Therefore, the exposure to radiation of the patient P for estimation of a cross-sectional shape can be reduced.