Patent ID: 12213821

DETAILED DESCRIPTION OF THE INVENTION

An X-ray CT apparatus, a determination method, and a storage medium according to an embodiment will be described below with reference to the drawings.

The X-ray CT apparatus of the embodiment includes a processing circuitry. The processing circuitry detects X-rays radiated from an X-ray tube in units of photons. The processing circuitry stores first energy spectrum information acquired by detecting X-rays at a first timing. The processing circuitry acquires second energy spectrum information by detecting X-rays at a second timing after the first timing. The processing circuitry determines a state of the X-ray tube on the basis of the first energy spectrum information and the second energy spectrum information.

In the following embodiments, parts denoted by the same reference numerals are assumed to perform the same operations and redundant descriptions will be omitted as appropriate. For specific description, an X-ray computed tomography apparatus according to an embodiment is described as a photon counting type X-ray computed tomography apparatus capable of performing photon counting CT (hereinafter referred to as an X-ray computed tomography (CT) apparatus). The X-ray CT apparatus is an apparatus capable of reconstructing X-ray CT image data with a high SN ratio by counting X-rays that have passed through a subject using a photon counting type X-ray detector (hereinafter referred to as a photon counting X-ray detector). The X-ray computed tomography apparatus according to the embodiment may have an integration type (current mode measurement type) X-ray detector instead of the photon counting X-ray detector.

FIG.1is a configuration diagram of an X-ray CT apparatus1according to an embodiment. The X-ray CT apparatus1includes a gantry device10, a bed device30, and a console device40, for example. AlthoughFIG.1shows both a diagram of the gantry device10viewed in the Z-axis direction and a diagram of the gantry device10viewed in the X-axis direction for convenience of description, there is a single gantry device10. In the present embodiment, a rotation axis of a rotating frame17in a non-tilt state or the longitudinal direction of a top plate33of the bed device30is defined as the Z-axis direction, an axis orthogonal to the Z-axis direction and parallel to a floor surface is defined as the X-axis direction, and a direction orthogonal to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction.

The gantry device10includes, for example, an X-ray tube11, a wedge12, a collimator13, an X-ray high voltage device14, an X-ray detector15, a data acquisition system (DAS)16, the rotating frame17, and a control device18.

The X-ray tube11generates X-rays by radiating thermal electrons from a cathode (filament) to an anode (target) according to a high voltage applied from the X-ray high voltage device14. The X-ray tube11includes a vacuum tube. For example, the X-ray tube11includes a rotating anode type X-ray tube that generates X-rays by radiating thermal electrons to a rotating anode. The X-ray tube11has a unique energy spectrum depending on the material/thickness of an X-ray filter, the material/thickness of a target, and a target angle. In the X-ray CT apparatus1, it is important to provide an energy spectrum assumed by the system. The energy spectrum changes the contrast of a scanned image, and particularly in a PCCT apparatus, a change in the energy spectrum greatly affects the material discrimination performance.

The wedge12is a filter for adjusting an X-ray dose radiated from the X-ray tube11to a subject P. The wedge12is a filter that transmits and attenuates X-rays radiated from the X-ray tube11such that a distribution of an X-ray dose radiated from the X-ray tube11to the subject P becomes a predetermined distribution. For example, the wedge12is also called a wedge filter or a bow-tie filter. The wedge12is, for example, made by processing aluminum to have a predetermined target angle and a predetermined thickness.

The collimator13is a mechanism for narrowing down a radiation range of X-rays that have passed through the wedge12. The collimator13narrows down a radiation range of X-rays by combining a plurality of lead plates to form a slit, for example. The collimator13may also be called an X-ray diaphragm.

The X-ray high voltage device14includes, for example, a high voltage generator and an X-ray controller. The high voltage generator has electrical circuits that include a transformer, a rectifier, and the like. The high voltage generator generates a high voltage to be applied to the X-ray tube11. The X-ray controller controls the output voltage of the high voltage generator depending on an X-ray dose to be generated by the X-ray tube11. The high voltage generator may boost the voltage using the transformer described above or boost the voltage using an inverter. The X-ray high voltage device14may be provided in the rotating frame17or may be provided on the side of a fixed frame (not shown) of the gantry device10. The fixed frame is a support frame that allows the rotating frame17to be rotatable. The X-ray controller controls the output voltage of the high voltage generator depending on the X-ray dose to be generated by the X-ray tube11.

The X-ray detector15is, for example, a photon counting X-ray detector (PCD). The X-ray detector15counts photons of X-rays generated by the X-ray tube11. For example, the X-ray detector15detects X-rays that have been radiated from the X-ray tube11and passed through the subject P in units of photons and outputs an electrical signal corresponding to the X-ray dose to the DAS16. Specifically, the X-ray detector15is configured to record the energy of each incident X-ray photon. After amplifying the detected output signal, the X-ray detector15counts the number of incident X-ray photons for each window divided according to a signal level, and thus the energy range of X-rays is recorded by a counter and arranged in a bin. The X-ray detector15has, for example, a plurality of detector element arrays in which a plurality of detector elements are arranged in a channel direction along one circular arc having the focal point of the X-ray tube11as the center. The X-ray detector15has, for example, a structure in which a plurality of detector element arrays are arranged in a slice direction (column direction or row direction).

Specifically, the X-ray detector15is, 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. The scintillators have scintillator crystals that output light with an amount of photons corresponding to an incident X-ray dose. The grid has an X-ray shielding plate that is arranged on the surface of the X-ray incidence side of the scintillator array and has a function of absorbing scattered X-rays. The grid may also be called a collimator (one-dimensional collimator or two-dimensional collimator). The optical sensor array has a plurality of optical sensor groups. An optical sensor group has a plurality of optical sensors. The optical sensor has a function of amplifying light received from a scintillator and converting the amplified light into an electrical signal. The optical sensor is, for example, a photo multiplier (PMT), an avalanche photo-diode (APD), or a silicon photo multiplier (SiPM). The optical sensor receives light from a scintillator and outputs an electrical signal (pulses) corresponding to incident X-ray photons. An electrical signal output by each detection element is also called a detection signal. The pulse height value (voltage) of this electrical signal (pulses) has a correlation with the energy value of X-ray photons. The X-ray detector15may be a direct conversion type detector having a semiconductor element that converts incident X-rays into an electrical signal. Further, the X-ray detector15is an example of an X-ray detection unit.

The DAS16includes, for example, an amplifier, an integrator, and an A/D converter. The amplifier amplifies an electrical signal output from each X-ray detection element of the X-ray detector15. The integrator integrates the amplified electrical signal over a view period (which will be described later). The A/D converter converts an electrical signal representing the integration result into a digital signal. The DAS16outputs detection data based on the digital signal to the console device40. The detection data is a digital value of X-ray intensity identified by a channel number and a row number of the X-ray detection element which is a generation source, and a view number indicating a collected view. A view number is a number that changes according to rotation of the rotating frame17and is a number that increments according to rotation of the rotating frame17, for example. Therefore, the view number is information indicating the rotation angle of the X-ray tube11. A view period is a period that falls between a rotation angle corresponding to a certain view number and a rotation angle corresponding to the next view number. The DAS16may detect switching of a view by a timing signal input from the control device18, by an internal timer, or by a signal obtained from a sensor that is not shown. When X-rays are continuously emitted from the X-ray tube11during full scanning, the DAS16collects detection data groups for the entire circumference (for 360 degrees). When X-rays are continuously emitted from the X-ray tube11during half scanning, the DAS16collects detection data for a half circumference (for 180 degrees). Further, the DAS16is an example of a data collection unit.

The rotating frame17is an annular member that supports the X-ray tube11, the wedge12, the collimator13, and the X-ray detector15while facing them. The rotating frame17is rotatably supported by the fixed frame around the subject P introduced therein. The rotating frame17further supports the X-ray high voltage device14and the DAS16. The rotating frame17is rotatably supported by a non-rotating part (for example, the fixed frame which is not shown inFIG.1) of the gantry device10. A rotating mechanism includes, for example, a motor that generates a rotational driving force and a bearing that transmits the rotational driving force to the rotating frame17to rotate the rotating frame17. The motor is provided, for example, in the non-rotating part, the bearing is physically connected to the rotating frame17and the motor, and the rotating frame rotates according to the rotational force of the motor.

The rotating frame17and the non-rotating part are provided with a non-contact type or contact-type communication circuit, whereby communication between a unit supported by the rotating frame17and the non-rotating part or an external device of the gantry device10is performed. For example, when optical communication is adopted as a non-contact communication method, detection data generated by the DAS16is transmitted from a transmitter having a light emitting diode (LED) provided in the rotating frame17to a receiver having a photodiode provided in the non-rotating part of the gantry device10through optical communication and further forwarded by the transmitter from the non-rotating part to the console device40. In addition to non-contact type data transmission such as a capacitive coupling type and a radio wave type as a communication method, a contact type data transmission method using a slip ring and an electrode brush may be adopted. The rotating frame17is not limited to an annular member and may be a member such as an arm as long as it can support and rotate the X-ray tube11and the like.

Although the X-ray CT apparatus1is, for example, a rotate/rotate-type X-ray CT apparatus (third generation CT) in which both the X-ray tube11and the X-ray detector15are supported by the rotating frame17and rotate around the subject P, it is not limited thereto and may be a stationary/rotate-type X-ray CT apparatus (fourth generation CT) in which a plurality of X-ray detection elements arranged in an annular form are fixed to a fixed frame and the X-ray tube11rotates around the subject P.

The control device18includes, for example, a processing circuitry having a processor such as a central processing unit (CPU), and a driving mechanism including a motor, an actuator, and the like. The control device18receives an input signal from an input interface43attached to the console device40or the gantry device10and controls the operations of the gantry device10and the bed device30.

The control device18rotates the rotating frame17, tilts the gantry device10, and moves the top plate33of the bed device30, for example. When tilting the gantry device10, the control device18rotates the rotating frame17about an axis parallel to the Z-axis direction on the basis of an inclination angle (tilt angle e) input to the input interface43. The control device18ascertains the rotation angle of the rotating frame17from the output of a sensor which is not shown, or the like. Further, the control device18provides the rotation angle of the rotating frame17to a processing circuitry50at any time. The control device18may be provided in the gantry device10or may be provided in the console device40. Further, the control device18is an example of a control unit.

The bed device30is a device on which the subject P that is a scanning target is placed and which is moved and introduced into the rotating frame17of the gantry device10. The bed device30includes, for example, a base31, a bed driving device32, the top plate33, and a support frame34. The base31includes a housing that supports the support frame34such that the support frame34is movable in the vertical direction (Y-axis direction). The bed driving device32includes a motor and an actuator. The bed driving device32moves the top plate33on which the subject P is placed in the longitudinal direction (Z-axis direction) of the top plate33along the support frame34. The top plate33is a plate-like member on which the subject P is placed.

The bed driving device32may move not only the top plate33but also the support frame34in the longitudinal direction of the top plate33. Contrary to the above, the gantry device10may be movable in the Z-axis direction, and the rotating frame17may be controlled to come around the subject P according to movement of the gantry device10. Moreover, both the gantry device10and the top plate33may be configured to be movable. Further, the X-ray CT apparatus1may be an apparatus in which the subject P is scanned in a standing or sitting position. In this case, the X-ray CT apparatus1includes a subject supporting mechanism instead of the bed device30, and the gantry device10rotates the rotating frame17about the axial direction perpendicular to the floor surface. The X-ray CT apparatus1may not have the bed device30. For example, when the opening of the X-ray CT apparatus1has a substantially cylindrical shape extending in the vertical direction, the subject is imaged in a standing position, and thus the bed device30is not necessary.

The console device40includes, for example, a memory41, a display42, an input interface43, a network connection circuitry44, and the processing circuitry50. Although the console device40is described as being separate from the gantry device10in the embodiment, the gantry device10may include some or all of the components of the console device40.

The memory41is realized by, for example, a random access memory (RAM), a semiconductor memory device such as a flash memory, a hard disk, an optical disk, or the like. The memory41stores, for example, projection data, reconstructed image (CT image) data, and the like. Such data may be stored in an external memory with which the X-ray CT apparatus1can communicate, instead of the memory41(or in addition to the memory41). The external memory is controlled by the cloud server, for example, when the cloud server that manages the external memory receives a read/write request. The external memory is realized, for example, by a system called picture archiving and communication systems (PACS). The PACS is a system that systematically stores images and the like captured by various image diagnostic apparatuses. The memory41is an example of a storage unit.

FIG.2is a diagram showing an example of data stored in the memory41. As shown inFIG.2, the memory41stores information such as imaging conditions41-1in which various conditions (scanning conditions and the like) at the time of imaging the subject P are set, projection data41-2generated by the processing circuitry50, reconstructed image data41-3, sample data41-4used to determine a difference in X-ray tube settings and a degree of deterioration, determination results41-5, notification information41-6, for example. The sample data41-4is first energy spectrum (radiation spectrum) information obtained by detecting X-rays from a genuine X-ray tube (genuine tube) which is a design recommended at a first timing. The first timing is, for example, the timing when the X-ray CT apparatus1is shipped. The timing of shipment may be a timing of shipment from a manufacturer to a sales destination, a timing at which initial setting (initial adjustment) is performed after installation at the sales destination, or the like. The notification information41-6is information in which notification content is associated with each state of the X-ray tube determined by a determination function59. Further, the notification information41-6may include information on a notification destination (target).

The display42displays various types of information. For example, the display42outputs a medical image (CT image) generated by the processing circuitry50, a graphical user interface (GUI) for receiving various operations by an operator, and the like. The display42is, for example, a liquid crystal display, a cathode ray tube (CRT) display, an organic electroluminescence (EL) display, or the like. The display42may be provided on the gantry device10. The display42may be of a desktop type or may be a display device (for example, a tablet terminal) capable of wireless communication with the main body of the console device40. Further, the display42is an example of a display unit.

The input interface43receives various input operations by the operator and outputs an electrical signal representing the content of a received input operation to the processing circuitry50. For example, the input interface43receives input operations such as collection conditions at the time of collecting detection data or projection data, reconstruction conditions at the time of reconstructing a CT image, and image processing conditions at the time of generating a post-processed image from a CT image. For example, the input interface43is realized by a mouse, a keyboard, a touch panel, a trackball, a switch, a button, a joystick, a camera, an infrared sensor, a microphone, and the like. The input interface43may be provided in the gantry device10. Further, the input interface43may be realized by a display device (for example, a tablet terminal) capable of wireless communication with the main body of the console device40.

The network connection circuitry44includes, for example, a network card having a printed circuit board, a wireless communication module, or the like. The network connection circuitry44implements an information communication protocol in accordance with the form of a network that is a connection target. Networks include, for example, a local area network (LAN), a wide area network (WAN), the Internet, a cellular network, a dedicated line, and the like.

The processing circuitry50controls the overall operation of the X-ray CT apparatus1. The processing circuitry50includes, for example, a system control function51, a preprocessing function52, a reconstruction processing function53, an image processing function54, a scan control function55, a display control function56, an adjustment function57, an acquisition function58, a determination function59, a notification function60and the like. The processing circuitry50realizes these functions by a hardware processor executing a program stored in the memory41, for example.

The hardware processor refers to, for example, a circuitry such as a CPU, a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a programmable logic device (e.g., a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), or a field programmable gate array (FPGA)). Instead of storing the program in the memory41, the program may be directly embedded in the circuitry of the hardware processor. In this case, the hardware processor realizes the functions by reading and executing the program embedded in the circuitry. The hardware processor is not limited to being configured as a single circuit and may be configured as one hardware processor by combining a plurality of independent circuits to realize each function. Further, a plurality of components may be integrated into one hardware processor to realize each function. In addition, the processing circuitry50is an example of a processing unit. The acquisition function58is an example of an acquisition unit. The determination function59is an example of a determination unit. The notification function60is an example of a notification unit.

Each component of the console device40or the processing circuitry50may be distributed and realized by a plurality of pieces of hardware. The processing circuitry50may be realized by a processing device that can communicate with the console device40instead of being a component included in the console device40. The processing device is, for example, a workstation connected to one X-ray CT apparatus, or a device (e.g., a cloud server) connected to a plurality of X-ray CT apparatuses and collectively executing processing equivalent to that of the processing circuitry50which will be described below. That is, the configuration of the present embodiment can also be realized as an X-ray CT system (medical diagnostic system) in which an X-ray CT apparatus and other processing devices are connected via a network.

The system control function51controls various functions of the processing circuitry50on the basis of input operations received through the input interface43, for example.

The preprocessing function52performs preprocessing such as logarithmic conversion processing, offset correction processing, inter-channel sensitivity correction processing, and beam hardening correction on detection data output from the DAS16to generate projection data41-2and causes the memory41to store the generated projection data41-2. Data before preprocessing (detection data) and data after preprocessing may be collectively referred to as projection data.

The reconstruction processing function53performs reconstruction processing on the projection data41-2generated by the preprocessing function52using a filtered back projection method, an iterative approximation reconstruction method, or the like to generate reconstructed image data (CT image data)41-3and causes the memory41to store the generated reconstructed image data41-3.

The image processing function54converts the reconstructed image data41-3into three-dimensional image data or cross-sectional image data of an arbitrary cross-section by a known method on the basis of an input operation received through the input interface43. Generation of three-dimensional image data may be performed by the reconstruction processing function53.

The scan control function55controls detection data collection processing in the gantry device10by instructing the X-ray high voltage device14, the DAS16, the control device18, and the bed driving device32. The scan control function55controls the operation of each unit at the time of capturing an alignment image, an actual captured image, and an image used for diagnosis.

The display control function56controls a display mode of the display42. For example, the display control function56controls the display42to display a reconstructed image generated by the processing circuitry50, a GUI image for receiving various operations by the operator, and the like.

The adjustment function57controls adjustment processing when the X-ray CT apparatus1is shipped and when parts such as the X-ray tube11are exchanged. Adjustment processing includes, for example, calibration processing, IF adjustment (adjustment of a filament current value (IF value) of the X-ray tube11) processing, seasoning (operation of preliminarily applying a load to the X-ray tube with a low voltage to increase the degree of vacuum inside the X-ray tube to remove residues, etc.) processing, and the like. The adjustment function57executes the above-described adjustment processing when an execution instruction from a user is received through the input interface43, at a timing at which exchange of a target object (for example, an X-ray tube) is detected, a tube warm-up timing, or at a predetermined cycle.

The acquisition function58acquires data for determining design differences and a degree of deterioration of the X-ray tube11and the like. For example, the acquisition function58acquires the first energy spectrum information acquired by detecting X-rays at a timing (first timing) of adjusting operating conditions of equipment when the X-ray CT apparatus1is shipped and causes the memory41to store the acquired first energy spectrum information as sample data41-4. Further, the acquisition function58may acquire the sample data41-4including the first energy spectrum information acquired from an external device via the network connection circuitry44and causes the memory41to store the first energy spectrum information.

In addition, the acquisition function58acquires second energy spectrum information acquired by detecting X-rays at a timing (for example, a second timing after the first timing) such as at the time of exchanging the X-ray tube11. The acquisition function58may acquire the first energy spectrum information or the second energy spectrum information by being triggered by execution of predetermined adjustment processing (for example, IF adjustment) among the one or more types of adjustment processing executed by the adjustment function57. In addition, the acquisition function58may execute processing of acquiring the first energy spectrum information or the second energy spectrum information when an execution instruction from the user is received through the input interface43.

The determination function59determines the state of an object such as the X-ray tube11on the basis of the first energy spectrum information and the second energy spectrum information acquired by the acquisition function58. Further, the determination function59causes the memory41to store the determination result as a determination result41-5. Details of the determination function59will be described later.

The notification function60notifies a target of a notification content (warning and the like) according to the state of the X-ray tube determined by the determination function59among a plurality of notification contents included in notification information41-6stored in the memory41. For example, the notification function60may display warning information on the display42and may notify a terminal (for example, a portable terminal such as a smartphone or a tablet terminal, or a fixed terminal) used by the target of the warning information via the network connection circuitry44.

(Determination Function)

Next, the determination function59will be described in detail. The determination function59determines whether or not an object such as the X-ray tube11is a non-genuine product and determines a degree of deterioration of the object by determining the state of the object. In the following, the X-ray tube11is used as an example of the object. Further, in the following processing, it is assumed that the first energy spectrum information using a genuine product that is the X-ray tube11(genuine tube) has already been acquired at the first timing such as at the time of shipment and stored in the memory41as sample data41-4.

FIG.3is a flowchart showing an example of determination processing for determining whether or not an X-ray tube11after exchange is a non-genuine tube. In the example ofFIG.3, after the X-ray tube11is exchanged, the adjustment function57executes adjustment processing of the X-ray CT apparatus1after exchange of the X-ray tube11(step S100). Next, the acquisition function58acquires the second energy spectrum information by being triggered by execution of predetermined processing in adjustment processing after exchange (step S102). Next, the acquisition function58acquires the first energy spectrum information which is the sample data41-4stored in the memory41(step S104). Next, the determination function59acquires a count value of an energy bin containing specific X-rays from each of the first energy spectrum information and the second energy spectrum information (step S106).

FIG.4is a diagram for describing comparison of count values of energy bins containing specific X-rays. In the example ofFIG.4, the horizontal axis represents energy (keV) and the vertical axis represents a count value (cnt) of photon counting. The example ofFIG.4also shows the first energy spectrum ES1obtained from the sample data41-4and the second energy spectrum ES2acquired after exchange.

In the example ofFIG.4, energy bins (energy bands) B1to B7are set at predetermined intervals for each of the first energy spectrum ES1and the second energy spectrum ES2. The energy bin intervals may be different intervals for each bin instead of the predetermined interval and may be arbitrarily set according to interval to be determined.

For example, the determination function59performs determination using a count value of an energy bin containing characteristic X-rays of the first energy spectrum ES1obtained from the X-ray tube11which is a genuine tube among the energy bines shown inFIG.4. Characteristic X-rays correspond to a portion in which a count value greatly varies depending on the material included in the X-ray tube11, for example. The determination function59may perform comparison using a count value of an energy bin containing the energy of a K absorption edge regarding the anode material in the X-ray tube11. In the example ofFIG.4, the determination function59acquires a count value (hereinafter referred to as a first count value) C11of the energy bin B4containing specific X-rays. Similarly, the determination function59acquires a count value (hereinafter referred to as a second count value) C12of the energy bin B4from the second energy spectrum ES2.

Referring back toFIG.3, the determination function59determines whether or not the difference (difference value) between the first count value C11and the second count value C12is equal to or greater than a threshold value (step S108). When it is determined that the difference is equal to or greater than the threshold value, the determination function59determines that the X-ray tube after exchange is a non-genuine tube (step S110). Further, the determination function59may determine that the X-ray tube corresponding to the first energy spectrum information and the X-ray tube corresponding to the second energy spectrum information have different performances instead of determining that the X-ray tube after exchange is a non-genuine tube.

Next, the notification function60notifies a target of information (warning information) indicating that the exchanged X-ray tube is a non-genuine tube (step S112). Accordingly, processing of this flowchart ends. Further, in processing of step S108, if the difference between the first count value and the second count value is less than the threshold value, processing of this flowchart ends assuming that the X-ray tube after exchange is a genuine tube. In this case, the notification function60may notify the target of information indicating that the X-ray tube after exchange is a genuine tube.

As described above, the determination function59can determine the state of the X-ray tube more efficiently by narrowing down among all energy bins B1to B7to energy bins that change greatly due to the design of the X-ray tube11and performing determination. In determination processing described above, a difference in a target material may be determined on the basis of a determination result using energy bins containing characteristic X-rays with different energies emitted by the material of the X-ray tube target. Further, in the above-described processing, when a count value of an energy bin differs due to differences in a filter material, thickness, and target angle, the energy bin may be used for determination. Moreover, the determination function59is not limited to a specific energy bin and may perform determination using all energy bins or may perform determination by comparing the first energy spectrum and the second energy spectrum.

Next, processing of determining a degree of deterioration of the X-ray tube in the determination function59will be described.FIG.5is a flowchart showing a flow of a series of processing for determining a degree of deterioration. It is assumed that the sample data41-4is stored in the memory41in advance in the example ofFIG.5.

In the example ofFIG.5, the determination function59determines whether or not the number of times of scanning (number of times of slicing) of the X-ray CT apparatus1is equal to or greater than a predetermined number of times or whether a predetermined time has elapsed from execution of the previous determination processing (step S200). If it is determined that the number of times of scanning is equal to or greater than the predetermined number of times or the predetermined time has elapsed from the previous processing, the acquisition function58acquires second energy spectrum information (step S202). Next, the acquisition function58acquires the sample data (first energy spectrum information)41-4from the memory41(step S204). Next, the determination function59acquires count values of two different energy bins from the acquired first energy spectrum information and second energy spectrum information (step S206).

FIG.6is a diagram for describing acquisition of count values of two different energy bins. In the example ofFIG.6, energy bins B1to B7are assigned to each of the first energy spectrum ES1and the second energy spectrum ES2as inFIG.4. The determination function59obtains count values of two different energy bins from each of the first energy spectrum ES1and the second energy spectrum ES2. In the two different energy bins, the energy bin with a lower energy is called the low energy bin and the energy bin with a higher energy is called the high energy bin.

In the example ofFIG.6, the determination function59acquires a count value C12of the energy bin B2and a count value C13of the energy bin B6of the first energy spectrum ES1. Similarly, the determination function also acquires a count value C22of the energy bin B2and a count value C23of the energy bin B6from the second energy spectrum ES2.

Referring back toFIG.5, subsequently, the determination function59calculates the ratio of the count value of the low energy bin to the count value of the high energy bin in the first energy spectrum ES1(for example, output ratio C12/C13) and the ratio of the count value of the low energy bin to the count value of the high energy bin in the second energy spectrum ES2(for example, output ratio C22/C23) (step S208). Next, the determination function59determines whether or not the difference between the count ratios is equal to or greater than a threshold value (step S210). If it is determined that the difference is equal to or greater than the threshold value, the determination function59determines a degree of deterioration in accordance with the difference (step S212). In processing of step S212, the determination function59determines that the greater the difference, the greater the degree of deterioration, for example. Further, when the determination function59determines a degree of deterioration of the anode material, the determination function59may store a correspondence table of output ratios between low energy bins and high energy bins and anode thicknesses is stored in the memory41in advance and determine a degree of deterioration of the anode material with reference to the correspondence table. For example, the correspondence table is generated in advance through simulation, actual measurement, or the like before shipment of the X-ray CT apparatus1. Further, the correspondence table may be stored in the sample data41-4. Moreover, when a similar correspondence table is generated in advance for materials other than the anode material, the determination function59may determine a degree of deterioration for other materials in the same manner.

Next, the notification function60notifies the target of information based on the determination result (for example, information indicating a degree of deterioration or information indicating that maintenance is required) (step S214). Accordingly, processing of this flowchart ends. Further, if it is determined that the number of times of scanning is not equal to or greater than the predetermined number of times and that the predetermined time has not elapsed from the previous processing in processing of step S200, or it is determined that the difference between the count ratios is not equal to or greater than the threshold value in processing of step S210, processing of this flowchart ends.

In processing of step S200, processing after step S202may be performed at any timing of the user (for example, at a timing indicated by a service person through the console). In determination processing described above, a degree of deterioration can be determined more efficiently and the target can be notified of a more accurate state.

Modified Examples

The above-described embodiment may be performed using a PCD as a reference (Ref) detector of a CT apparatus instead of using a main detector of a PCCT apparatus. Further, the sample data in the embodiment may be downloaded via a network or installed or updated by a recording medium such as a magnetic memory after shipment. In the embodiment, the determination function59may perform determination by changing (narrowing) the energy width of a bin such that an area including characteristic X-rays and an area including scattered X-rays are focused according to content to be determined.

According to at least one embodiment described above, the X-ray CT apparatus of the embodiment can determine the state of an X-ray tube more efficiently by including a photon counting X-ray detector that detects X-rays radiated from the X-ray tube in units of photons, a storage unit that stores first energy spectrum information acquired by detecting X-rays at a first timing, an acquisition unit that acquires second energy spectrum information by detecting X-rays at a second timing after the first timing, and a determination unit that determines the state of the X-ray tube on the basis of the first energy spectrum information and the second energy spectrum information.

Specifically, according to the present embodiment, an air radiation spectrum can be easily inspected, and an X-ray tube having an air radiation spectrum different from a recommended value can be detected, for example. Further, according to the embodiment, it is possible to detect an X-ray tube that provides an inappropriate air radiation spectrum that causes artifacts such as CT value shift and notify a target of the detected X-ray tube by comparing count of energy bins of energy spectrum sample data and the energy spectrum of the mounted X-ray tube. In addition, it is not necessary to introduce an external device that performs the conventional collation method in which an electronic board on which an individual ID number is recorded in an X-ray tube is built in and collation is performed in order to compare air radiation spectra using a PCD mounted in a PCCT apparatus, and it is possible to curb a change in the external shape of the apparatus, an increase in weight, and an increase in manufacturing costs.

The embodiment described above can be represented as follows.

An X-ray CT apparatus including:a memory configured to store a program; anda processor,wherein the memory stores first energy spectrum information acquired by detecting X-rays at a first timing, andby executing the program, the processor detects X-rays radiated from an X-ray tube in units of photons by a photon counting X-ray detector, acquires second energy spectrum information by detecting X-rays at a second timing after the first timing, and determines a state of the X-ray tube on the basis of the first energy spectrum information and the second energy spectrum information.

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