X-ray computed tomography apparatus

Abstract

To reduce radiation exposure while ensuring measurement information of specific areas in PCCT scans.SOLUTION: X-ray computed tomography apparatus comprises a gantry, an acquisition unit, a setting unit, a determination unit, and a scan control unit. The gantry includes a data collection circuit for collecting count data of X-rays detected by an X-ray detector for every energy bin. The acquisition unit acquires a first image collected by a first scan on a test object and depicting a region of interest on the test object. The setting unit sets a specific region including the region of interest for the first image. The determination unit determines scan conditions for a photon counting CT scan, the second scan, on the basis of the specific region. The scan conditions include x-ray dose and / or energy bins that meet image quality criteria for the region of interest. The scan control unit controls the gantry in accordance with the scan conditions to perform the second scan on the test object.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray computed tomography apparatus.

Background Art

[0002] For example, in cancer treatment, follow-up imaging is performed to confirm the treatment effect by comparing the post-treatment CT image with the pre-treatment CT image. In the CT scan performed after treatment, even when observing the treatment effect of cancer at a specific location, the X-ray dose is determined using AEC (Auto Exposure Control), taking into account the image quality not only of the region where cancer is present but also of the regions outside the region where cancer is present.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to reduce the exposure dose while ensuring the measurement information of a specific region in a PCCT scan. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. The problems corresponding to the respective effects of each configuration shown in the embodiments described later can also be regarded as other problems.

Means for Solving the Problems

[0005] The X-ray computed tomography apparatus according to the embodiment includes a gantry, an acquisition unit, a setting unit, a determination unit, and a scan control unit. The gantry includes an X-ray tube that generates X-rays, a high-voltage device that applies a high voltage to the X-ray tube, an X-ray detector that detects the X-rays generated from the X-ray tube, and a data acquisition circuit that collects the count data of the X-rays detected by the X-ray detector for each energy bin. The acquisition unit acquires a first image in which a target site existing in the subject is depicted, the first image being collected by a first scan of the subject. The setting unit sets a specific region including the target site with respect to the first image. The determination unit determines scan conditions for a photon counting CT scan that is a second scan based on the specific region, and the scan conditions include an X-ray dose and / or an energy bin that conforms to the image quality standard of the target site. The scan control unit controls the gantry according to the scan conditions and performs a second scan on the subject.

Brief Description of the Drawings

[0006]

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DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, the X-ray computed tomography apparatus according to the present embodiment will be described in detail with reference to the drawings.

[0008] The X-ray computed tomography apparatus according to the present embodiment includes various types such as third-generation CT and fourth-generation CT, and any type can be applied to the present embodiment. Here, the third-generation CT is a Rotate / Rotate-Type in which an X-ray tube and an X-ray detector rotate around a subject integrally. The fourth-generation CT is a Stationary / Rotate-Type in which a large number of X-ray detection elements arranged in a ring shape are fixed, and only the X-ray tube rotates around the subject. Further, the X-ray computed tomography apparatus according to the present embodiment can be applied to a single-tube type in which one pair of an X-ray tube and an X-ray detector is mounted on a rotating ring, and a multi-tube type in which a plurality of pairs of an X-ray tube and an X-ray detector are mounted on a rotating ring. In the following description, it is assumed to be a single-tube type.

[0009] The X-ray computed tomography apparatus according to the present embodiment is assumed to be a photon counting CT apparatus that executes photon counting CT (PCCT: Photon Counting Computed Tomography).

[0010] FIG. 1 is a diagram showing the configuration of an X-ray computed tomography apparatus 1 according to the present embodiment. As shown in FIG. 1, the X-ray computed tomography apparatus 1 includes a gantry 10, a couch 30, and a console 40. Note that, for convenience of explanation, the gantry 10 is illustrated at a plurality of positions in FIG. 1, but the X-ray computed tomography apparatus 1 may be equipped with one or a plurality of gantries 10. The gantry 10 is a scanning device having a configuration for performing PCCT scanning on a subject P. The couch 30 is a transport device for placing the subject P to be subjected to X-ray CT imaging and positioning the subject P. The console 40 is a computer for controlling the gantry 10. For example, the gantry 10 and the couch 30 are installed in a CT examination room, and the console 40 is installed in a control room adjacent to the CT examination room. The gantry 10, the couch 30, and the console 40 are connected to each other in a wired or wireless manner so as to be able to communicate with each other. Note that the console 40 does not necessarily have to be installed in the control room. For example, the console 40 may be installed in the same room as the gantry 10 and the couch 30. Further, the console 40 may be incorporated into the gantry 10.

[0011] As shown in FIG. 1, the gantry 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and a data acquisition circuit (DAS: Data Acquisition System) 18.

[0012] The X-ray tube 11 generates X-rays. Specifically, the X-ray tube 11 includes a cathode that generates thermoelectrons, an anode that receives the thermoelectrons flying from the cathode and generates X-rays, and a vacuum tube that holds the cathode and the anode. The X-ray tube 11 is connected to the X-ray high voltage device 14 via a high voltage cable. A tube voltage is applied between the cathode and the anode by the X-ray high voltage device 14. Due to the application of the tube voltage, thermoelectrons fly from the cathode toward the anode. When thermoelectrons fly from the cathode toward the anode, a tube current flows. By applying a high voltage from the X-ray high voltage device 14 and supplying a filament current, thermoelectrons fly from the cathode (filament) toward the anode (target), and when the thermoelectrons collide with the anode, X-rays are generated. For example, the X-ray tube 11 includes a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons.

[0013] The X-ray detector 12 detects the X-rays generated from the X-ray tube 11 and passing through the subject P, and outputs an electrical signal corresponding to the energy of the detected X-rays to the data acquisition circuit 18. The X-ray detector 12 has a structure in which a plurality of X-ray detector element arrays in which a plurality of X-ray detector elements are arranged in the channel direction are arranged in a plurality in the slice direction (column direction). The X-ray detector 12 is, for example, an indirect conversion type detector having a grid, a scintillator array, and an optical sensor array. The scintillator array has a plurality of scintillators. Each scintillator generates a plurality of fluorescent photons corresponding to the energy of the incident X-ray photons. The grid is disposed on the X-ray incident surface side of the scintillator array and has an X-ray shielding plate that absorbs scattered X-rays. Note that the grid may sometimes be called a collimator (one-dimensional collimator or two-dimensional collimator). The optical sensor array converts a plurality of fluorescent photons from the scintillator into an electrical signal having a pulse height value corresponding to the energy of the incident X-ray photons. As the optical sensor, for example, a photodiode is used.

[0014] The X-ray detector 12 may be a direct conversion type detector. As a direct detection type X-ray detector 12, for example, a type including a semiconductor diode having electrodes attached to both ends of a semiconductor is applicable. X-ray photons incident on the semiconductor are converted into electron-hole pairs. The number of electron-hole pairs generated by the incidence of one X-ray photon depends on the energy of the incident X-ray photon. The electrons and holes are attracted to each other by a pair of electrodes formed at both ends of the semiconductor. The pair of electrodes generates an electrical signal having a pulse height value corresponding to the charge of the electron-hole pair. One electrical signal has a pulse height value corresponding to the energy of the incident X-ray photon.

[0015] The rotating frame 13 is an annular frame that rotatably supports the X-ray tube 11 and the X-ray detector 12 around the rotation axis (Z-axis). Specifically, the rotating frame 13 oppositely supports the X-ray tube 11 and the X-ray detector 12. The rotating frame 13 is rotatably supported around the rotation axis by a fixed frame (not shown). By rotating the rotating frame 13 around the rotation axis by the control device 15, the X-ray tube 11 and the X-ray detector 12 are rotated around the rotation axis. The rotating frame 13 rotates around the rotation axis at a constant angular velocity receiving power from the drive mechanism of the control device 15. An image field of view (FOV) is set in the opening 19 of the rotating frame 13.

[0016] In this embodiment, the rotation axis of the rotating frame 13 or the longitudinal direction of the top plate 33 of the bed 30 in the non-tilted state is defined as the Z-axis direction, the axial direction orthogonal to the Z-axis direction and horizontal with respect to the floor surface is defined as the X-axis direction, and the axial direction orthogonal to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction.

[0017] The X-ray high voltage device 14 includes a high voltage generator and an X-ray control device. The high voltage generator has electric circuits such as a transformer and a rectifier, and generates a high voltage applied to the X-ray tube 11 and a filament current supplied to the X-ray tube 11. The X-ray control device controls the output voltage according to the X-rays irradiated by the X-ray tube 11. The high voltage generator may be of a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13 within the gantry 10, or may be provided on a fixed frame (not shown) within the gantry 10.

[0018] The wedge 16 adjusts the dose of X-rays irradiated onto the subject P. Specifically, the wedge 16 attenuates the X-rays so that the dose of X-rays irradiated from the X-ray tube 11 onto the subject P has a predetermined distribution. For example, as the wedge 16, a metal plate such as aluminum like a wedge filter or a bow-tie filter is used.

[0019] The collimator 17 limits the irradiation range of the X-rays that have passed through the wedge 16. The collimator 17 slidably supports a plurality of lead plates that shield the X-rays, and adjusts the form of the slit formed by the plurality of lead plates. Note that the collimator 17 may also be called an X-ray aperture.

[0020] The data acquisition circuit 18 collects the count data of the X-rays detected by the X-ray detector 12 for each energy bin. As an example, the data acquisition circuit 18 includes a preamplifier, a waveform shaping circuit, a pulse height discrimination circuit, and a counting circuit. The preamplifier amplifies an electrical signal having a pulse height value corresponding to the energy of the X-ray photons detected by the X-ray detector 12 at a predetermined magnification. The waveform shaping circuit shapes the waveform of the electrical signal output by the preamplifier. The pulse height discrimination circuit applies an energy threshold corresponding to each of a plurality of energy bins to the electrical signal output by the waveform shaping circuit, and outputs an electrical pulse signal corresponding to the energy bin to which the electrical signal belongs. The counting circuit generates count data representing the number of counts of X-ray photons for each energy bin by counting the electrical pulse signals output from the pulse height discrimination circuit for each energy bin in units of a view period. The data acquisition circuit 18 is realized by, for example, an application specific integrated circuit (ASIC). The count data is transmitted to the console 40 via a non-contact data transmission device or the like.

[0021] The control device 15 controls the X-ray high-voltage device 14 and the data acquisition circuit 18 to execute a PCCT scan in accordance with the control by the processing circuit 45 of the console 40. The control device 15 includes a processing circuit having a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), etc., and a drive mechanism such as a motor and an actuator. The processing circuit has, as hardware resources, a processor such as a CPU and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). Further, the control device 15 may be realized by an ASIC or a field programmable gate array (FPGA). Further, the control device 15 may be realized by another complex programmable logic device (CPLD) or a simple programmable logic device (SPLD). The control device 15 has a function of being attached to the console 40 or the gantry 10, receiving an input signal from an input interface 43 described later, and controlling the operations of the gantry 10 and the bed 30. For example, the control device 15 performs control to rotate the rotating frame 13 upon receiving an input signal, control to tilt the gantry 10, and control to operate the bed 30 and the top plate 33. Note that the control to tilt the gantry 10 is realized by the control device 15 rotating the rotating frame 13 about an axis parallel to the X-axis direction based on the tilt angle (tilt angle) information input by an input interface attached to the gantry 10. Note that the control device 15 may be provided on the gantry 10 or may be provided on the console 40.

[0022] The bed 30 includes a base 31, a support frame 32, a top plate 33, and a bed driving device 34. The base 31 is installed on the floor surface. The base 31 is a housing that supports the support frame 32 so as to be movable in a direction perpendicular to the floor surface (Y-axis direction). The support frame 32 is a frame provided on the upper part of the base 31. The support frame 32 supports the top plate 33 so as to be slidable along the rotation axis (Z-axis). The top plate 33 is a flexible plate on which the subject P is placed.

[0023] The bed driving device 34 is housed in the housing of the bed 30. The bed driving device 34 is a motor or an actuator that generates power for moving the support frame 32 and the top plate 33 on which the subject P is placed. The bed driving device 34 operates according to the control by the console 40 or the like.

[0024] The console 40 has a memory 41, a display 42, an input interface 43, a communication interface 44, and a processing circuit 45. Data communication among the memory 41, the display 42, the input interface 43, the communication interface 44, and the processing circuit 45 is performed via a bus (BUS). Although the console 40 is described as a separate body from the gantry 10, the gantry 10 may include the console 40 or a part of each component of the console 40.

[0025] The memory 41 is a storage device such as a HDD (Hard Disk Drive), SSD (Solid State Drive), or integrated circuit memory device that stores various information. The memory 41 stores, for example, count data and reconstructed image data. In addition to HDDs, SSDs, etc., the memory 41 may be a portable storage medium such as a CD (Compact Disc), DVD (Digital Versatile Disc), or flash memory. The memory 41 may also be a drive device that reads and writes various information to and from semiconductor memory elements such as flash memory and RAM (Random Access Memory). Further, the storage area of the memory 41 may be within the X-ray computed tomography apparatus 1 or within an external storage device connected via a network. The memory 41 stores a database described later.

[0026] The display 42 displays various information. For example, the display 42 outputs a CT image generated by the processing circuit 45, a GUI (Graphical User Interface) for receiving various operations from the operator, etc. Various arbitrary displays can be used as the display 42 as appropriate. For example, as the display 42, a liquid crystal display (LCD), a CRT (Cathode Ray Tube) display, an organic EL display (OELD), or a plasma display can be used. Further, the display 42 may be provided on the gantry 10. Also, the display 42 may be a desktop type or may be configured as a tablet terminal or the like capable of wireless communication with the console 40 main body.

[0027] The input interface 43 receives various input operations from the operator, converts the received input operations into electrical signals, and outputs them to the processing circuit 45. For example, the input interface 43 receives from the operator collection conditions when collecting count data, reconstruction conditions when reconstructing a PCCT image, image processing conditions when generating a post-processing image from the PCCT image, and the like. As the input interface 43, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad, a touch panel display, etc. can be appropriately used. In addition, in the present embodiment, the input interface 43 is not limited to those including physical operation components such as a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touch pad, and a touch panel display. For example, a processing circuit for receiving an electrical signal corresponding to an input operation from an external input device provided separately from the apparatus and outputting this electrical signal to the processing circuit 45 is also included in the example of the input interface 43. Further, the input interface 43 may be provided on the gantry 10. Also, the input interface 43 may be configured by a tablet terminal or the like capable of wireless communication with the console 40 main body.

[0028] The communication interface 44 includes a network interface card (NIC) or the like for communicating various data via a network with external devices such as a workstation, a PACS (Picture Archiving and Communication Systems), a RIS (Radiology Information System), and a HIS (Hospital Information System).

[0029] The processing circuit 45 controls the operation of the entire X-ray computed tomography apparatus 1 in response to the electrical signal of the input operation output from the input interface 43. As hardware resources, the processing circuit 45 includes a processor such as a CPU and memories such as a ROM and a RAM. The processing circuit 45 realizes various functions by a processor that executes a program developed in the memory. The various functions are not limited to being realized by a single processing circuit. It is also possible to configure a processing circuit by combining a plurality of independent processors, and each processor executes a program to realize various functions.

[0030] FIG. 2 is a diagram showing a functional configuration example of the processing circuit 45. As shown in FIG. 2, the processing circuit 45 realizes a scan control function 51, an image acquisition function 52, a region setting function 53, a condition determination function 54, a measurement value calculation function 55, and a display control function 56.

[0031] In the scan control function 51, the processing circuit 45 controls the gantry 10 to perform a PCCT scan on the subject P. When the PCCT scan is executed, the data acquisition circuit 18 collects count data for each of a plurality of energy bins. As an example, the processing circuit 45 controls the gantry 10 according to the scan conditions determined by the condition determination function 54, and executes a PCCT scan, which is a second scan, on the subject P.

[0032] In the image acquisition function 52, the processing circuit 45 acquires a first image in which a target site existing in the subject P, which is depicted by a first scan on the subject P, is drawn. The first scan means a scan performed before a treatment of interest (hereinafter referred to as the target treatment) among the treatments for the subject P. The first scan is not limited to a PCCT scan that can be performed by the X-ray computed tomography apparatus 1, and may be a PCCT scan and / or an integrated type CT scan that can be performed by other X-ray computed tomography apparatuses, a volume CT scan that can be performed by an X-ray diagnostic apparatus, magnetic resonance imaging that can be performed by a magnetic resonance imaging apparatus, an ultrasonic scan that can be performed by an ultrasonic diagnostic apparatus, a PET (Positron Emission Tomography) imaging or an SPECT (Single Photo Emission CT) imaging that can be performed by a nuclear medicine diagnostic apparatus. The first image means a medical image generated based on the raw data collected by the first scan.

[0033] In the region setting function 53, the processing circuit 45 sets a specific region including the target site for the first image acquired by the image acquisition function 52. The target site means a lesion site or tissue region to be followed up. The specific region means an image region that coincides with the target site or an image region with a margin added to the target site. The specific region can be set manually or automatically.

[0034] In the condition determination function 54, the processing circuit 45 determines the scan conditions of a PCCT scan, which is a second scan, based on the specific region set by the region setting function 53. The second scan is a PCCT scan performed by the X-ray computed tomography apparatus 1. The scan conditions include an X-ray dose and / or an energy bin that conform to the image quality criteria of the target site. The processing circuit 45 may further determine, as the scan conditions, a tube voltage, an X-ray irradiation range related to the rotation axis direction of the gantry 10 and / or an X-ray irradiation range related to the fan angle direction of the X-ray.

[0035] In the measurement value calculation function 55, the processing circuit 45 calculates the measurement value of the target site and / or the temporal change of the measurement value based on the count data collected by the data collection circuit 18 in the second scan. The processing circuit 45 calculates, as the measurement value, a characteristic value for evaluating the X-ray energy characteristics of the target site, the three-dimensional region of the target site, and / or the dimensions of the three-dimensional region.

[0036] In the display control function 56, the processing circuit 45 displays various information on the display 42. As an example, the processing circuit 45 displays the first image acquired by the image acquisition function 52, the specific region obtained by the region setting function 53, the scan conditions obtained by the condition determination function 54, the measurement values obtained by the measurement value calculation function 55, and the like.

[0037] As shown in FIG. 2, specifically, the measurement value calculation function 55 includes a PCCT image generation function 57, a region calculation function 58, a temporal change recording function 59, and a visualization image generation function 60.

[0038] In the PCCT image generation function 57, the processing circuit 45 generates a PCCT image representing the spatial distribution of characteristic values for evaluating the X-ray energy characteristics of each pixel based on the count data output from the data collection circuit 18. Examples of PCCT images include a count image representing the spatial distribution of CT values reconstructed based on the count data of a specific energy bin, a basis material image representing the spatial distribution of the density values of the basis material, a virtual monochromatic image representing the spatial distribution of CT values based on the X-ray attenuation coefficient at a single X-ray energy, a material map representing the spatial distribution of the CT values of the basis material, a K-edge image that is a count image based on the energy bin to which the K-edge of the target material belongs, an effective atomic number image representing the spatial distribution of the effective atomic number, an electron density image representing the spatial distribution of the electron density, and the like. The pixel values of the PCCT images such as CT values, density values, effective atomic numbers, and electron densities are examples of measurement values. For example, the processing circuit 45 generates a second image, which is a PCCT image representing the spatial distribution of characteristic values for the target site, based on the count data collected by the data collection circuit 18 in the second scan.

[0039] Here, the first image and / or the second image is applicable to both a two-dimensional image of one slice or slab and a three-dimensional image of one volume. Note that the two-dimensional image means image data composed of a plurality of pixels arranged in a two-dimensional space, and the three-dimensional image means image data composed of a plurality of voxels arranged in a three-dimensional space. Hereinafter, it is assumed that the first image and the second image are three-dimensional images.

[0040] In the region calculation function 58, the processing circuit 45 calculates the three-dimensional region of the target site and / or the dimensions of the three-dimensional region based on the count data collected by the data collection circuit 18 in the second scan. For example, the processing circuit 45 calculates the three-dimensional region of the target site based on the second image. Further, the processing circuit 45 may calculate the dimensions of the three-dimensional region. As the dimensions, the diameter, volume, etc. of the three-dimensional region may be used. The three-dimensional region and the dimensions of the three-dimensional region are an example of the measured values of the target site.

[0041] In the time change recording function 59, the processing circuit 45 records the time change of the measured value. For example, the processing circuit 45 records, as the time change, the change from the measured value related to the first scan to the measured value related to the second scan.

[0042] In the visualization image generation function 60, the processing circuit 45 generates a visualization image based on the first image acquired by the image acquisition function 52, the second image generated by the PCCT image generation function 57, the three-dimensional region calculated by the region calculation function 58 and / or the dimensions of the three-dimensional region, the time change recorded by the time change recording function 59, etc.

[0043] The visualization image according to this embodiment means the image data displayed on the display 42. The processing circuit 45 generates a visualization image for display by performing arbitrary visualization processing on the original images such as the first image and the second image. As the visualization processing, conversion processing from a three-dimensional image to a two-dimensional image such as a pixel value projection method, multi-planar reconstruction (MPR), volume rendering, and surface rendering can be used. Further, the processing circuit 45 can also perform a composite processing of a plurality of three-dimensional images or two-dimensional images. For example, the processing circuit 45 generates a composite image of the first image and the second image. More specifically, the processing circuit 45 generates a composite image in which a second image region corresponding to the first image region of the second image is fitted or superimposed on the first image region regarding the target site of the first image. In this embodiment, in order to avoid complication of the description, unless particularly necessary, the images before and after the visualization processing are not particularly distinguished and named.

[0044] Hereinafter, a processing example of a CT examination by the X-ray computed tomography apparatus 1 will be described. In the following description, a follow-up imaging of a tumor will be described as a clinical example. That is, it is assumed that the target site is a tumor such as cancer which is a lesion, and the target treatment is radiation therapy or chemotherapy for the tumor. Further, it is assumed that the first scan is a PCCT scan performed by the X-ray computed tomography apparatus 1, and the first image is a PCCT image based on the count data collected by the PCCT scan. In the first scan, it is assumed that the subject is scanned under injection of a contrast agent for imaging the tumor.

[0045] FIG. 3 is a diagram showing a processing procedure for follow-up imaging by the X-ray computed tomography apparatus 1. The processing shown in FIG. 3 starts at the start of the follow-up imaging examination during the implementation of the target treatment or after a certain period has elapsed after the implementation. It is assumed that a first image of the subject P has been obtained before the target treatment and is stored in the memory 41. In the first scan, the processing circuit 45 performs a PCCT scan as the first scan by realizing the scan control function 51. By the first scan, the examination site including the tumor present in the subject P is PCCT scanned. By the first scan, count data regarding a plurality of energy bins is collected. The scan conditions for the first scan are not particularly limited. Then, the processing circuit 45 reconstructs a PCCT image, which is the first image, based on the count data regarding the plurality of energy bins. The type of the first image is not particularly limited. As an example, it is assumed that the first image is an integrated image reconstructed by applying a reconstruction algorithm such as FBP (Filtered Back Projection) to the integrated data of the count data of all the energy bins among the plurality of energy bins.

[0046] As shown in FIG. 3, the processing circuit 45 acquires the first image by realizing the image acquisition function 52 (step S1). In step S1, the processing circuit 45 may acquire the first image from the memory 41 that stores the first image in advance. Note that the processing circuit 45 may acquire the first image from a PACS or another X-ray computed tomography apparatus via the communication interface 44 or the like.

[0047] When step S1 is performed, the processing circuit 45 sets a specific region in the first image acquired in step S1 by realizing the region setting function 53 (step S2). In step S2, for setting the specific region, the processing circuit 45 displays the first image on the display 42 by realizing the display control function 56. The user designates the position of the specific region with respect to the first image displayed on the display 42 via the input interface 43. The processing circuit 45 sets the specific region at the designated position.

[0048] FIG. 4 is a diagram showing an example of the first image I1 displayed in step S2. The first image I1 shown in FIG. 4 is assumed to be an axial cross-sectional image based on an integrated image related to the chest as an example. As shown in FIG. 4, the first image I1 includes a tumor region I12 which is the region of interest. The tumor region I12 is emphasized in contrast by a contrast agent. The user observes the first image I1 to confirm the position, size, type, etc. of the tumor region I12. Then the user designates the position of the specific region I11 via the input interface 43. The specific region I11 means the region where the user desires follow-up imaging. Typically, the position of the specific region I11 is designated so as to surround the tumor region I12 to be treated. When the position is designated, the processing circuit 45 sets the specific region I11 for the designated position. The position of the specific region I11 is stored in the memory 41.

[0049] When step S2 is performed, the processing circuit 45 determines the scan conditions for the second scan by realizing the condition determination function 54 (step S3). The second scan means a PCCT scan for follow-up imaging. In step S3, the processing circuit 45 determines the minimum X-ray dose and the energy bin as the scan conditions. In addition, scan conditions used in a normal PCCT scan, such as tube voltage, detector resolution, gantry rotation speed, etc., may be further determined. Further, the processing circuit 45 may determine an image generation purpose including information such as the type of the PCCT image to be generated in the second scan as the scan conditions. The type of the PCCT image to be generated in the second scan is not particularly limited, but is assumed to be a k-edge image. These scan conditions may be determined by any method. The determined scan conditions are stored in the memory 41.

[0050] Here, the determination of the minimum X-ray dose will be described. The minimum X-ray dose means the lowest dose among the X-ray doses that meet the image quality criteria for the tumor region, which is the site of interest. In other words, the minimum X-ray dose means the minimum X-ray dose that can determine the temporal changes in the tumor region. The temporal changes mean the changes in the shape, characteristics, etc. of the tumor region from the time of the first scan to the time of the second scan. The tube current value in the second scan is determined according to the minimum X-ray dose.

[0051] FIG. 5 is a diagram showing an example of the determination process of the minimum X-ray dose Dmin. The vertical axis of the graph shown in FIG. 5 represents the image quality evaluation value, and the horizontal axis represents the X-ray dose. The graph shown in FIG. 5 represents the relationship between the image quality evaluation value and the X-ray dose. As the image quality evaluation value, an index value for evaluating other image qualities such as the signal-to-noise ratio (SNR) or the contrast-to-noise ratio (CNR) may be used. The X-ray dose means the dose of the X-rays irradiated from the X-ray tube 11 in the second scan. As shown in FIG. 5, the image quality evaluation value has variations when the X-ray dose is low, but tends to stabilize at a substantially constant value when the X-ray dose is above a certain level.

[0052] The image quality standard means reaching the reference value Vth of the image quality evaluation value expected to recognize the temporal change of the tumor region. Specifically, the reference value Vth is set to the image quality evaluation value capable of recognizing the temporal change of the tumor region. The reference value Vth may be determined empirically, may be determined by predictive calculation, or may be determined as an arbitrary value by the user. Typically, the reference value Vth is set to the plateau value of the image quality evaluation value, but it may be set to any value. As an example, the processing circuit 45 uses predictive calculation of the second scan based on the probability distribution of the generation probability of X-ray photons to determine the minimum X-ray dose that satisfies the image quality standard. Specifically, since the generation probability of X-ray photons follows a Poisson distribution, the transition of the image quality evaluation value such as the SNR is predicted and calculated when the X-ray dose is increased according to the Poisson distribution. The processing circuit 45 determines the X-ray dose when the image quality evaluation value reaches the reference value Vth as the minimum X-ray dose Dmin. Here, as the image quality evaluation value, it is preferable that the image quality evaluation value limited to a specific region or the site of interest is calculated. Also, the image quality evaluation value may depend on other scan conditions other than the X-ray dose, for example, energy bins, tube voltage, scan range, etc. It is assumed that these scan conditions are set to values that can be used in the second scan.

[0053] Here, the determination of the minimum X-ray dose Dmin when observing the tumor region in the image will be described. It is assumed that as the image, a k-edge image based on the count data of the energy bin adjacent to the energy bin to which the k-edge of the contrast agent belongs and the count data of all energy bins is used. In this case, the processing circuit 45 will determine the minimum X-ray dose necessary to detect the k-edge of the contrast agent accumulated in the tumor. Specifically, the processing circuit 45 predicts and calculates the transition of the image quality evaluation value of a specific region in the k-edge image when the X-ray dose is increased according to the Poisson distribution. Then, the processing circuit 45 may determine the X-ray dose when the image quality evaluation value reaches the reference value Vth as the minimum X-ray dose Dmin.

[0054] In the above process, the k-edge image is taken as an example of the image, but it is not limited thereto. For example, a count image based on the count data of the energy bin to which the k-edge of the contrast agent accumulated in the tumor region belongs may be used. Further, the object for calculating the image quality evaluation value is not limited to a specific region, and may be a tumor region.

[0055] The method for determining the minimum X-ray dose is not limited to the above method only. As an example, the processing circuit 45 may determine the minimum X-ray dose based on the image quality evaluation value of a specific region in the first image using the AEC method. Specifically, the processing circuit 45 determines the minimum X-ray dose based on the body thickness of the subject P and the image quality evaluation value. It is assumed that the relationship between the combination of the body thickness and the image quality evaluation value and the minimum X-ray dose is recorded in a LUT (Look Up Table) in advance. The body thickness may be calculated by image processing based on a scan image or an optical image taken by an optical camera.

[0056] Next, the determination of the energy bin will be described. The processing circuit 45 determines an energy bin for detecting the k-edge of the contrast agent accumulated in the tumor. More specifically, as the energy bin, the number of energy bins and the energy range of each energy bin are determined.

[0057] FIG. 6 is a diagram showing an example of the energy bin determination process. The vertical axis on the left side of the graph shown in FIG. 6 represents the X-ray attenuation coefficient, the vertical axis on the right side represents the count number of X-ray photons, and the horizontal axis represents the X-ray energy. The unit of the X-ray energy with respect to the X-ray attenuation coefficient is keV, and the unit of the X-ray energy with respect to the count number is kV. The broken line shown in FIG. 6 represents the typical energy spectrum of the X-rays irradiated from the X-ray tube 11, and the solid line represents the X-ray attenuation coefficient of the contrast agent used in the second scan. As shown by the solid line in FIG. 6, the contrast agent used in the second scan has a k-edge near 80 keV.

[0058] The number of energy bins set and the energy range of each energy bin can be arbitrarily set. As an example, assume that the number of energy bins set is 4. The first energy bin (bin 1) is set to 0 to 20 keV corresponding to the noise range. The third energy bin (bin 3) is set to 81 to 83 keV corresponding to a narrow energy range including the k-edge. The second energy bin (bin 2) is set between the first energy bin and the third energy bin, and the fourth energy bin (bin 4) is set between the third energy bin and the energy value (120 keV) corresponding to the tube voltage value.

[0059] When step S3 is performed, the processing circuit 45 performs a second scan according to the scan conditions determined in step S3 by realizing the scan control function 51 (step S4). The second scan is executed at the timing when the contrast agent accumulates in the tumor present in the subject P. The start timing of the second scan may be determined by the monitoring scan or may be arbitrarily determined in consideration of an empirical rule based on the elapsed time from the start of injection of the contrast agent. Note that, before performing the second scan, the processing circuit 45 sets the number of energy thresholds and / or the values of the energy thresholds of the data collection circuit 18 according to the number of energy bins and / or the energy range determined in step S3. During the PCCT scan, the processing circuit 45 performs feedback control on the X-ray high voltage device 14 based on the tube voltage value determined in step S3 and the tube current value corresponding to the minimum X-ray dose. In the PCCT scan, the data collection circuit 18 collects count data regarding a plurality of energy bins. The collected count data is transmitted to the console 40.

[0060] When step S4 is performed, the processing circuit 45 generates a second image by realizing the PCCT image generation function 57 (step S5). In step S5, the processing circuit 45 reconstructs a PCCT image as the second image based on the count data collected in step S4. The type of the PCCT image is not particularly limited, but as described above, it is assumed that a k-edge image is generated.

[0061] When step S5 is performed, the processing circuit 45 records the change over time of the measurement value of the tumor region, which is the site of interest, by implementing the time change recording function 59 (step S5). The measurement value may be the characteristic value described in the above embodiment or the spatial distribution of the characteristic value, or may be the tumor region which is a three-dimensional region, or may be the dimension of the tumor region. In step S5, as an example, the processing circuit 45 records, as the change over time, the change from the measurement value at the first scan to the measurement value at the second scan. Specifically, as the measurement value at the first scan, the measurement value of the tumor region included in the first image may be used. Specifically, as the measurement value at the second scan, the measurement value of the tumor region included in the second image may be used.

[0062] When step S5 is performed, the processing circuit 45 generates a visualization image of the change over time calculated in step S5 by implementing the visualization image generation function 60 (step S6). When step S6 is performed, the processing circuit 45 displays the visualization image generated in step S6 on the display 42 by implementing the display control function 56 (step S7). Here, steps S5, S6, and S7 will be specifically described. In the following description, it is assumed that the measurement value is the dimension of the three-dimensional region of the tumor region, which is the site of interest.

[0063] In step S5, the processing circuit 45 first calculates the dimension of the tumor region, which is the site of interest, by implementing the region calculation function 58. Specifically, the processing circuit 45 extracts the tumor region from the second image and calculates the dimension of the extracted tumor region. As the dimension, the diameter, area, or volume of the tumor region may be calculated. Next, the processing circuit 45 records, by implementing the time change recording function 59, the change over time from the dimension of the tumor region at the first scan to the dimension of the tumor region at the second scan. It is assumed that the dimension of the tumor region at the first scan has been calculated in advance by the processing circuit 45. Then, the processing circuit 45 generates a visualization image representing the calculated change over time and displays the generated visualization image on the display 42.

[0064] FIG. 7 is a diagram showing an example of a visualization image I41 representing a change over time. As shown in FIG. 7, the visualization image I41 has a first image I42, a second image I43, and a display column I44. The processing circuit 45 may display the first image I42 and the second image I43 side by side. By displaying the first image I42 and the second image I43 side by side, the user can confirm the morphological change over time of the tumor region. Note that the first image I42 and the second image I43 may be provided with annotations representing symbols for identifying each tumor region, such as "#1", "#2", and "#3". The same symbol is assigned to the same tumor region.

[0065] In the display column I44, the change over time from the size of the tumor region at the first scan to the size of the tumor region at the second scan, recorded by the time change recording function 59, is displayed. As the change over time, the change in size and the difference value for each tumor region are displayed, such as "Tumor #1: 15 mm → 10 mm (-5 mm), Tumor #2: 12 mm → 8 mm (-4 mm)". Note that when a tumor disappears at the second scan, that is, when tumor #3 does not exist in the second image I43, it may be displayed that there is no tumor region at the second scan, such as "Tumor #3: 5 mm → ×".

[0066] Since the first scan for the first image I42 is performed with an X-ray dose considering the image quality of the entire image, the overall image quality of the first image I42 is good, but it is not specialized for the tumor region. Since the second scan is performed with the minimum X-ray dose capable of detecting the k-edge of the contrast agent that accumulates in the tumor, it is assumed that the image quality of the tumor region in the second image I43 is appropriate despite the low dose. Therefore, it is expected that the change over time in the size of the tumor region is also obtained with appropriate accuracy. Since the change over time of the measured values, which is useful information for observing the progress of the tumor region, is displayed, the progress can be observed easily and accurately.

[0067] Thus, the process related to the follow-up imaging shown in FIG. 3 ends.

[0068] In the above embodiment, the time change of dimensions was described as a specific example of the time change. However, the present embodiment is not limited to this. For example, as the time change, an image representing the spatial distribution of the difference value between the characteristic value of the X-ray energy at the first scan and the characteristic value of the X-ray energy at the second scan may be recorded and displayed. As the characteristic value in this case, the effective atomic number, electron density, etc. are useful. The difference value of the effective atomic number or electron density represents the alteration of the tissue present in the pixel to which the difference value is assigned. By observing the spatial distribution of the difference value, the user can confirm the anatomical site where the tissue alteration has occurred.

[0069] The alteration of the tissue can also be observed as a change in the energy spectrum (frequency distribution of the count values over a plurality of energy bins) measurable by PCCT. The processing circuit 45 may determine the alteration of the tissue based on the difference between the count data at the first scan and the count data at the second scan, and display the determination result as the time change of the measured value.

[0070] Note that, without departing from the gist of the invention, various additions, deletions, and / or changes of elements are possible in the present embodiment.

[0071] (Modification 1) The processing circuit 45 according to the above embodiment was configured to record the time change of the measured value of the target site. The processing circuit 45 according to Modification 1 is configured to calculate, as the measured value, a PCCT image that is the spatial distribution of the characteristic value of the X-ray energy characteristics as the measured value of the target site. Hereinafter, the processing related to the follow-up imaging according to Modification 1 will be described with reference to FIG. 3. Note that steps S1 to S5 are the same as those in the above embodiment, so the description thereof will be omitted.

[0072] When step S5 is performed, the processing circuit 45 generates a composite image of the first image acquired in step S1 and the second image generated in step S5 by realizing the visualization image generation function 60 (step S6). Here, steps S5 and S6 according to Modification 1 will be specifically described.

[0073] FIG. 8 is a diagram schematically showing the processing procedures of steps S5 and S6 according to Modification 1. As shown in FIG. 8, a first image I21 is acquired in step S1. Assume that the first image I21 contains three tumor regions I211. Since the first scan for the first image I21 is performed with an X-ray dose considering the image quality of the entire image, the image quality of the entire first image I21 is good, but it is not the image quality specialized for the tumor region I211.

[0074] As shown in FIG. 8, the processing circuit 45 generates a k-edge image I24 which is an example of a second image. The method for generating the k-edge image I24 is as follows. Note that the number of energy bins and the energy range are assumed to be set as shown in FIG. 6. First, the processing circuit 45 separately reconstructs a first count image I22 based on the count data of the second and fourth energy bins collected in the second scan, and a second count image I23 based on the count data of the second, third, and fourth energy bins collected in the same second scan. As described above, the third energy bin is the energy bin to which the k-edge of the contrast agent injected into the subject P belongs. Therefore, it is assumed that no tumor region is drawn in the first count image I22, and a tumor region I231 is drawn in the second count image I23. Assume that the tumor has disappeared or shrunk due to the target treatment performed before the second scan, and the second count image I23 contains two tumor regions I231. As described above, since the second scan is performed with the minimum X-ray dose capable of detecting the k-edge of the tumor, it is assumed that the image quality of the first count image I22 and the second count image I23 is worse than that of the first image I21.

[0075] Next, as shown in FIG. 8, the processing circuit 45 generates a k-edge image I24 by subtracting the first count image I22 from the second count image I23. A tumor region I241 with enhanced contrast by the contrast agent is drawn in the k-edge image I24. It is assumed that the regions other than the tumor region I241 disappear or are drawn with low contrast.

[0076] As shown in FIG. 8, the processing circuit 45 generates a composite image I25 based on the first image I21 and the k-edge image I24 such that the image region other than the specific region I213 in the first image I21 (hereinafter, the peripheral region) I212 and the tumor region I241 of the k-edge image I24 are included. The method for generating the composite image I25 is not particularly limited.

[0077] As an example, the processing circuit 45 generates the composite image I25 by fitting the image region (hereinafter, the corresponding region) I242 corresponding to the specific region I213 in the k-edge image I24 into the specific region I213 in the first image I21. Specifically, first, the processing circuit 45 reads the position of the specific region I213 in the k-edge image I24 from the memory 41 and specifies the image region corresponding to the read position as the corresponding region I242. Note that the position of the specific region I213 is specified in step S2 in advance and stored in the memory 41. Next, the processing circuit 45 cuts out the corresponding region I242 and replaces the specific region I213 in the first image I21 with the cut-out corresponding region I242. Thereby, a composite image I25 composed of the peripheral region I212 and the corresponding region I242 is generated. Alternatively, the processing circuit 45 may generate the composite image I25 by superimposing the cut-out corresponding region I242 on the specific region I213.

[0078] The method for generating the composite image I25 is not limited to the above method only. For example, in the above embodiment, the processing circuit 45 cuts out the specific region to be fitted or superimposed from the k-edge image. However, the processing circuit 45 may cut out the specific region from a PCCT image including the specific region such as the second count image I23 shown in FIG. 8. Alternatively, the processing circuit 45 may reconstruct only the specific region data based on the count data for a plurality of energy bins.

[0079] When step S6 according to Modification 1 is performed, the processing circuit 45 displays the composite image generated in step S6 by realizing the display control function 56 (step S7). In step S7, the processing circuit 45 displays the composite image on the display 42. The user observes the progress of the tumor region and the like included in the composite image displayed on the display 42. As described above, since the peripheral region I212 in the composite image I25 shown in FIG. 8 is derived from the first image I21, it has a relatively high image quality, and the corresponding region I242 is derived from the count images I22 and I23 obtained with the minimum X-ray dose capable of detecting the k-edge of the contrast agent, so it is expected to have a low dose and appropriate image quality. By observing the tumor region I241 using such a composite image I25, it becomes possible to perform follow-up with a low dose and appropriate image quality.

[0080] (Modification 2) The processing circuit 45 according to Modification 1 was configured to calculate a PCCT image, which is a spatial distribution of characteristic values of X-ray energy characteristics, as a measurement value of the target site. The processing circuit 45 according to Modification 2 is configured to calculate a three-dimensional region of the tumor region as a measurement value of the target site. Hereinafter, the processing related to the follow-up imaging according to Modification 2 will be described with reference to FIG. 3. Since steps S1 to S5 are the same as those in the above embodiment, the description thereof will be omitted.

[0081] When step S5 is performed, the processing circuit 45 calculates a three-dimensional region of the tumor region, which is the target site, by realizing the region calculation function 58 (step S6). When step S6 is performed, the processing circuit 45 generates a composite image of the first image acquired in step S1 and the three-dimensional region generated in step S6 by realizing the visualization image generation function 60 (step S7). Here, steps S6 and S7 according to Modification 2 will be specifically described.

[0082] FIG. 9 is a diagram schematically showing the processing procedures of steps S6 and S7 according to Modification 2. As shown in FIG. 9, a first image I21 is acquired in step S1. Further, the processing circuit 45 reconstructs a count image I23 based on the count data of the second, third, and fourth energy bins collected in the second scan. As described above, the third energy bin is the energy bin to which the k-edge of the contrast agent injected into the subject P belongs. A tumor region I231 is drawn in the count image I23.

[0083] Next, the processing circuit 45 aligns the first image I21 and the count image I23. Next, the processing circuit 45 extracts the tumor region I231 from the count image I23. The tumor region I231 is an example of a three-dimensional region. As the extraction method, any method such as threshold processing, region growing method, machine learning, extraction of a user-specified region, etc. may be used. Then, as shown in FIG. 9, the processing circuit 45 aligns and superimposes the extracted tumor region I231 on the first image I21. As a result, the tumor region I231 derived from the count image I23 after the target treatment is superimposed on the tumor region I211 derived from the first image I21 before the target treatment. The first image I21 on which the tumor region I231 is superimposed is the composite image I31. Note that the processing circuit 45 may perform a visualization process on the tumor region I231 and then superimpose it on the first image I21 in order to make the tumor region I211 visible. As an example, a visualization process may be performed such that the tumor region I231 is visually emphasized compared to the tumor region I211. Specifically, setting of transparency, setting of color values, shaping of the region shape, etc. may be performed as the visualization process.

[0084] Thereafter, the processing circuit 45 displays the composite image on the display 42 (step S8). The user observes the progress of the tumor region and the like included in the composite image displayed on the display 42.

[0085] According to Modification 2, since the tumor region at the time of the second scan is superimposed on the first image, it is possible to compare the tumor region at the time of the first scan and the tumor region at the time of the second scan on a single image. Further, by performing visualization processing on the tumor region at the time of the second scan, it is also possible to enhance the visibility of the tumor region.

[0086] (Modification 3) The processing circuit 45 according to the above embodiment determines the minimum X-ray dose, energy bin, etc. as scan conditions. The processing circuit 45 according to Modification 3 may further determine the X-ray irradiation range in the direction of the rotation axis of the gantry 10 and / or the X-ray irradiation range in the fan angle direction of the X-rays.

[0087] FIG. 10 is a diagram showing the X-ray irradiation range according to Modification 3. As shown in FIG. 10, the X-ray irradiation range in the direction of the rotation axis Z means the cone angle direction of the X-rays irradiated from the X-ray tube 11, or the X-ray irradiation range in the body axis direction of the subject P. The X-ray irradiation range in the fan angle direction of the X-rays irradiated from the X-ray tube 11 means the rotation direction of the X-ray tube 11, the X-ray detector 12, the rotating frame 13, etc. around the rotation axis Z. By restricting the X-ray irradiation range in the direction of the rotation axis Z and / or the fan angle direction to a specific region, the radiation dose of the subject P can be reduced.

[0088] (Summary) According to the above description, the X-ray computed tomography apparatus 1 according to the present embodiment includes a gantry 10 and a processing circuit 45. The gantry 10 includes an X-ray tube 11 that generates X-rays, an X-ray high voltage device 14 that applies a high voltage to the X-ray tube 11, an X-ray detector 12 that detects the X-rays generated from the X-ray tube 11, and a data collection circuit 18 that collects the count data of the X-rays detected by the X-ray detector 12 for each energy bin. The processing circuit 45 acquires a first image in which a target site existing in the subject P is depicted, the first image being collected by a first scan of the subject P. The processing circuit 45 sets a specific region including the target site in the first image. The processing circuit 45 determines scan conditions for a photon counting CT scan, which is a second scan, based on the specific region, and the scan conditions include an X-ray dose and / or energy bins that meet the image quality criteria of the target site. The processing circuit 45 controls the gantry 10 according to the scan conditions and performs a second scan on the subject P.

[0089] According to the above configuration, it is possible to perform follow-up imaging by PCCT scan with an X-ray dose and / or energy bins that meet the image quality criteria of the target site. By setting the image quality criteria specialized for the target site in this way and performing the PCCT scan with an X-ray dose and / or energy bins that meet the criteria, it is possible to ensure the image quality of the image using the energy bins and reduce the radiation dose of the subject P compared to a scan considering the image quality of the entire image.

[0090] According to at least one of the embodiments described above, it is possible to reduce the radiation dose while ensuring the measurement information of the specific region in the PCCT scan.

[0091] As used in the above description, the term "processor" means, for example, a CPU, a GPU, or a circuit such as an Application Specific Integrated Circuit (ASIC), a Programmable Logic Device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). The processor realizes its function by reading and executing a program stored in a storage circuit. Note that, instead of storing a program in the storage circuit, the program may be directly incorporated into the circuit of the processor. In this case, the processor realizes its function by reading and executing the program incorporated into the circuit. On the other hand, when the processor is, for example, an ASIC, instead of storing the program in the storage circuit, the function is directly incorporated as a logic circuit into the circuit of the processor. Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, and a plurality of independent circuits may be combined to form one processor to realize its function. Further, a plurality of components in FIGS. 1 and 2 may be integrated into one processor to realize its function.

[0092] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations of embodiments can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0093] 1 X-ray computed tomography device 10 Stand 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high voltage device 15 Control device 16 Wedge 17 Collimator 18 Data acquisition circuit 19 Opening 30 Bed 31 Base 32 Support frame 33 Ceiling 34 Bed drive device 40 Console 41 Memory 42 Display 43 Input interface 44 Communication interface 45 Processing circuit 51 Scan control function 52 Image acquisition function 53 Region setting function 54 Condition determination function 55 Measurement value calculation function 56 Display control function 57 PCCT image generation function 58 Region calculation function 59 Time change recording function 60 Visualization image generation function

Claims

1. An apparatus including a gantry including an X-ray tube that generates X-rays, a high-voltage device that applies a high voltage to the X-ray tube, an X-ray detector that detects the X-rays generated from the X-ray tube, and a data collection circuit that collects the count data of the X-rays detected by the X-ray detector for each energy bin; An acquisition unit that acquires a first image in which a target site existing in the subject is depicted, the first image being collected by a first scan of the subject; A setting unit that sets a specific region including the target site with respect to the first image; A determination unit that determines scan conditions for a photon counting CT scan that is a second scan based on the specific region, the scan conditions including an X-ray dose and / or an energy bin that conform to an image quality standard of the target site; A scan control unit that controls the gantry according to the scan conditions and performs a second scan on the subject; An X-ray computed tomography apparatus comprising the above components.

2. A calculation unit that calculates a measured value of the target site and / or a temporal change of the measured value based on the count data collected by the data collection circuit in the second scan; A display control unit that displays the measured value and / or the temporal change on a display device; The X-ray computed tomography apparatus according to claim 1, further comprising the above components.

3. The calculation unit calculates, as the measured value, a characteristic value for evaluating X-ray energy characteristics regarding the target site, and a three-dimensional region of the target site and / or dimensions of the three-dimensional region. The X-ray computed tomography apparatus according to claim 2.

4. The calculation unit generates a second image, which is a photon counting CT image representing a spatial distribution of the characteristic value regarding the target site, based on the count data collected by the data collection circuit in the second scan; The display control unit displays the second image; The X-ray computed tomography apparatus according to claim 3.

5. The display control unit displays a composite image in which an image region corresponding to the specific region of the second image is fitted or superimposed on the specific region of the first image. The X-ray computed tomography apparatus according to claim 4.

6. The measured value is the three-dimensional region; The display control unit displays a composite image in which the three-dimensional region is superimposed on an image region regarding the target site of the first image; The X-ray computed tomography apparatus according to claim 3.

7. The X-ray computed tomography apparatus according to claim 2, wherein the calculation unit records, as the temporal change, a change from the measurement value related to the first scan to the measurement value related to the second scan.

8. The image quality criterion is that the image quality evaluation value exceeds a reference value, The determination unit determines the X-ray dose using predictive calculation of the second scan based on a probability distribution of the generation probability of X-ray photons. The X-ray computed tomography apparatus according to claim 1.

9. The region of interest is a tumor, The determination unit determines the minimum necessary X-ray dose for detecting a k-edge of a contrast agent accumulated in the tumor. The X-ray computed tomography apparatus according to claim 1.

10. The image quality criterion is that the image quality evaluation value exceeds a reference value, The determination unit determines the X-ray dose based on the image quality evaluation value of the specific region in the first image. The X-ray computed tomography apparatus according to claim 1.

11. The region of interest is a tumor, The determination unit further determines, as the scan condition, an energy bin for detecting a k-edge of a contrast agent accumulated in the tumor. The X-ray computed tomography apparatus according to claim 10.

12. The determination unit further determines, as the scan condition, an X-ray irradiation range related to the rotation axis direction of the gantry and / or an X-ray irradiation range related to the fan angle direction of the X-rays. The X-ray computed tomography apparatus according to claim 1.

13. The first image is an integrated image collected by a PCCT scan. The X-ray computed tomography apparatus according to claim 1.

Images