JP7624831B2 - X-ray computed tomography apparatus, anode deterioration estimation method, and anode deterioration estimation program - Google Patents

Description

This embodiment relates to an X-ray computed tomography apparatus, an anode deterioration estimation method, and an anode deterioration estimation program.

A photon counting type X-ray computed tomography (PCCT) device calculates the ratio of the count number of X-ray photons that have passed through a subject to the spectrum of the X-ray photons before passing through the subject (hereinafter referred to as the air irradiation spectrum) for each of multiple energy bins. Through this calculation, the PCCT device calculates the linear attenuation coefficient for each of multiple energy bins and reconstructs a cross-sectional image of the subject.

On the other hand, the anode material in the X-ray tube (hereafter referred to as anode material) deteriorates with long-term use of the X-ray tube in the PCCT device. Deterioration of the anode material attenuates the soft X-ray output in the X-ray output irradiated from the X-ray tube. This causes the air irradiation spectrum to change. If the linear attenuation coefficient cannot be calculated correctly due to changes in the air irradiation spectrum, this causes artifacts such as CT value shifts in the reconstructed cross-sectional images. In order to avoid CT value shifts, it is necessary to know the net air irradiation spectrum during CT scanning.

On the other hand, the width of the energy bins in the X-ray detector of a PCCT device is variable. In order to know the change in the air irradiation spectrum by setting the threshold of an arbitrary energy bin, it is necessary to obtain a spectrum at fine energy bins. For this, it is necessary to set the width of the energy bins for measuring X-ray photons finely and to measure X-ray photons many times while gradually shifting the energy bin area for measurement, which takes a lot of time.

US Patent Application Publication No. 2019/0099149

One of the problems that the embodiments disclosed in this specification and the drawings attempt to solve is to easily determine at least one of the X-ray spectrum that has changed due to deterioration of the X-ray tube and the degree of deterioration of the X-ray tube. However, the problems that the embodiments disclosed in this specification and the drawings attempt to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems.

The X-ray computed tomography apparatus according to this embodiment includes a storage unit, an acquisition unit, and a determination unit. The storage unit stores at least one of a first output from a first detection element at a first position in the channel direction of the X-ray detector, which is acquired at a first timing, a second output from a second detection element at a second position that is an end side of the channel direction from the first position, which is acquired at the first timing, a first output ratio based on the first output and the second output, and a first irradiation spectrum of the X-ray tube at the first timing. The acquisition unit acquires a third output from the first detection element and a fourth output from the second detection element at a second timing that is later than the first timing. The determination unit determines at least one of a second irradiation spectrum of the X-ray tube at the second timing and a deterioration degree of the X-ray tube based on at least one of the first output and the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output.

FIG. 1 is a diagram showing an example of the arrangement of an X-ray CT apparatus according to an embodiment. FIG. 2 is a diagram illustrating an example of a first detection element at a first position and a second detection element at a second position in the embodiment. FIG. 3 is a diagram showing an example of a first output ratio and a plurality of second output ratios according to the degree of deterioration of an anode material in the embodiment. FIG. 4 is a diagram showing an example of an irradiation spectrum RS relating to a first timing and a second timing according to the embodiment. FIG. 5 is a flowchart illustrating an example of a procedure of a deterioration estimation process according to the embodiment.

Hereinafter, with reference to the drawings, an embodiment of an X-ray computed tomography apparatus, an anode deterioration estimation method, and an anode deterioration estimation program will be described in detail. In the following embodiments, parts with the same reference numerals perform the same operation, and duplicated descriptions will be omitted as appropriate. For the sake of specificity, the X-ray computed tomography apparatus according to the embodiment will be described as a photon counting type X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT (computed tomography) apparatus) capable of performing photon counting CT. The X-ray CT apparatus is an apparatus capable of reconstructing X-ray CT image data with a high signal-to-noise 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 type X-ray detector). Note that the X-ray computed tomography apparatus according to the embodiment may have an integral type (current mode measurement type) X-ray detector instead of a photon counting type X-ray detector.

(Embodiment)
FIG. 1 is a diagram showing an example of the configuration of an X-ray CT device 1 according to this embodiment. As shown in FIG. 1, the X-ray CT device 1 includes a gantry device 10, a bed device 30, and a console device 40. In this embodiment, the rotation axis of the rotating frame 13 in a non-tilted state or the longitudinal direction of the top plate 33 of the bed device 30 is defined as the Z-axis direction, the axial direction perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction, and the axial direction perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction. In FIG. 1, a plurality of gantry devices 10 are drawn for convenience of explanation, but the actual configuration of the X-ray CT device 1 includes only one gantry device 10.

The gantry device 10 and the bed device 30 operate based on user operations via the console device 40, or on user operations via an operation unit provided on the gantry device 10 or the bed device 30. The gantry device 10, the bed device 30, and the console device 40 are connected to each other by wire or wirelessly so that they can communicate with each other.

The gantry device 10 is a device having an imaging system that irradiates X-rays onto the subject P and collects projection data from the detection data of the X-rays that have passed through the subject P. The gantry device 10 has an X-ray tube 11 (X-ray generator), an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a bow-tie filter 16, a collimator 17, and a DAS (Data Acquisition System) 18.

The X-ray tube 11 is a vacuum tube that generates X-rays by irradiating thermoelectrons from a cathode (filament) to an anode (target) through the application of high voltage from the X-ray high voltage device 14 and the supply of filament current. X-rays are generated when the thermoelectrons collide with the target. X-rays generated at the tube focus in the X-ray tube 11 pass through an X-ray emission window in the X-ray tube 11, are shaped into a cone beam via a collimator 17, and are irradiated onto the subject P. The X-ray tube 11 may be, for example, a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons.

The X-ray detector 12 is, for example, a photon counting X-ray detector. The photon counting X-ray detector 12 counts the photons of the X-rays generated by the X-ray tube 11. Specifically, the photon counting X-ray detector 12 detects the X-rays irradiated from the X-ray tube 11 and passing through the subject P in photon units, and outputs an electrical signal corresponding to the amount of X-ray to the DAS 18. The photon counting X-ray detector 12 has, for example, multiple detection element rows in which multiple detection elements are arranged in the channel direction along one arc centered on the focus of the X-ray tube 11. The photon counting X-ray detector 12 has, for example, a structure in which multiple detection element rows are arranged in the slice direction (row direction). The photon counting X-ray detector 12 is also called a main detector that detects the X-rays that have passed through the subject P.

Specifically, the photon counting type X-ray detector 12 is an indirect conversion type detector having, for example, a grid, a scintillator array, and an optical sensor array. The scintillator array has multiple scintillators. The scintillator has scintillator crystals that output light with a photon amount corresponding to the amount of incident X-rays. The grid is arranged on the X-ray incident side of the scintillator array and has an X-ray shielding plate that has the function of absorbing scattered X-rays. The optical sensor array has multiple optical sensor groups. The optical sensor group has multiple optical sensors. The optical sensor has the function of amplifying the light received from the scintillator and converting it into an electrical signal. The optical sensor is, for example, an APD (Avalanche Photo-Diode) or a SiPM (Silicon Photo Multiplier). In other words, the optical sensor receives light from the scintillator and outputs an electrical signal (pulse) corresponding to the incident X-ray photons. The electrical signal output by each detection element is also called a detection signal. The peak value (voltage) of this electrical signal (pulse) correlates with the energy value of the X-ray photon. The photon counting X-ray detector 12 may be a direct conversion detector having a semiconductor element that converts the incident X-rays into an electrical signal.

The rotating frame 13 supports the X-ray tube 11 and the photon counting X-ray detector 12 so that they can rotate around a rotation axis. Specifically, the rotating frame 13 is an annular frame that supports the X-ray tube 11 and the photon counting X-ray detector 12 facing each other and rotates the X-ray tube 11 and the photon counting X-ray detector 12 using a control device 15 described below. The rotating frame 13 is rotatably supported by a fixed frame made of a metal such as aluminum. More specifically, the rotating frame 13 is connected to the edge of the fixed frame via a bearing. The rotating frame 13 receives power from a drive mechanism of the control device 15 and rotates at a constant angular velocity around the rotation axis Z.

The rotating frame 13 further includes and supports the X-ray high voltage device 14 and the DAS 18 in addition to the X-ray tube 11 and the photon counting X-ray detector 12. Such a rotating frame 13 is housed in a substantially cylindrical housing in which an opening (bore) 131 that forms the imaging space is formed. The opening 131 substantially coincides with the FOV. The central axis of the opening 131 coincides with the rotation axis Z of the rotating frame 13. The detection data generated by the DAS 18 is transmitted, for example, from a transmitter having a light-emitting diode (LED) to a receiver having a photodiode provided in a non-rotating part (for example, a fixed frame) of the gantry 10 by optical communication, and is then transferred to the console device 40. The method of transmitting the detection data from the rotating frame 13 to the non-rotating part of the gantry 10 is not limited to the optical communication described above, and any method of non-contact data transmission may be used.

The X-ray high voltage device 14 has electrical circuits such as a transformer and a rectifier, and includes a high voltage generator having the function of generating a high voltage to be applied to the X-ray tube 11 and a filament current to be supplied to the X-ray tube 11, and an X-ray control device that controls the output voltage according to the X-rays emitted 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, or on the fixed frame (not shown) side of the gantry device 10.

The control device 15 has a processing circuit having a CPU (Central Processing Unit) and the like, and a driving mechanism such as a motor and an actuator. The processing circuit has, as hardware resources, a processor such as a CPU or an MPU (Micro Processing Unit) and a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The control device 15 may also be realized by an ASIC, a Field Programmable Gate Array (FPGA), another Complex Programmable Logic Device (CPLD), or a Simple Programmable Logic Device (SPLD). The control device 15 controls the X-ray high voltage device 14 and the DAS 18, etc., according to instructions from the console device 40. The processor realizes the above control by reading and executing a program stored in the memory.

The control device 15 also has a function of receiving an input signal from the console device 40 or an input interface attached to the gantry 10 and controlling the operation of the gantry 10 and the bed device 30. For example, the control device 15 receives an input signal and controls the rotation of the rotating frame 13, the tilt of the gantry 10, and the operation of the bed device 30 and the tabletop 33. The control of tilting the gantry 10 may be realized by the control device 15 rotating the rotating frame 13 around an axis parallel to the X-axis direction based on inclination angle (tilt angle) information input by an input interface attached to the gantry 10. The control device 15 may be provided in the gantry 10 or in the console device 40. The control device 15 may be configured to directly incorporate a program into the circuit of the processor instead of storing the program in the memory. In this case, the processor realizes the above control by reading and executing the program incorporated in the circuit.

The bowtie filter 16 is placed in front of the X-ray emission window of the X-ray tube 11. The bowtie filter 16 is a filter for adjusting the amount of X-rays irradiated from the X-ray tube 11. Specifically, the bowtie filter 16 is a filter that transmits and attenuates the X-rays irradiated from the X-ray tube 11 so that the X-rays irradiated from the X-ray tube 11 to the subject P have a predetermined distribution. The bowtie filter 16 is a filter made of processed aluminum to have a predetermined target angle and a predetermined thickness.

The collimator 17 is a lead plate or the like that focuses the X-rays that have passed through the bowtie filter 16 into the X-ray irradiation range 113, and a slit is formed by combining multiple lead plates or the like.

The DAS 18 has a plurality of counting circuits. Each of the plurality of counting circuits has an amplifier that performs an amplification process on the electrical signal output from each detection element of the photon counting type X-ray detector 12, and an A/D converter that converts the amplified electrical signal into a digital signal, and generates detection data that is the result of counting process using the detection signal of the photon counting type X-ray detector 12. The detection data that is the result of the counting process is data that assigns the number of X-ray photons to each energy bin. For example, the DAS 18 counts photons (X-ray photons) derived from X-rays irradiated from the X-ray tube 11 and transmitted through the subject P, and discriminates the energy of the counted photons to obtain the result of the counting process. The detection data generated by the DAS 18 is transferred to the console device 40. The detection data is a set of data including the channel number and column number of the detector pixel from which the detection data was generated, the view number indicating the collected view (also called the projection angle), and a value indicating the dose of the detected X-ray. The view number may be the order in which the views were collected (collection time), or a number (e.g., 1 to 1000) representing the rotation angle of the X-ray tube 11. Each of the multiple counting circuits in the DAS 18 is realized, for example, by a group of circuits equipped with circuit elements capable of generating detection data.

The bed device 30 is a device for placing and moving the subject P to be scanned, and includes a base 31, a bed drive device 32, a top plate 33, and a top plate support frame 34. The base 31 is a housing that supports the top plate support frame 34 so that it can move in the vertical direction. The bed drive device 32 is a motor or actuator that moves the top plate 33 on which the subject P is placed in the longitudinal direction of the top plate 33. The bed drive device 32 moves the top plate 33 under the control of the console device 40 or the control of the control device 15. The top plate 33, which is provided on the upper surface of the top plate support frame 34, is a plate on which the subject P is placed. Note that the bed drive device 32 may move the top plate support frame 34 in the longitudinal direction of the top plate 33 in addition to the top plate 33.

The console device 40 has a memory 41 (storage unit), a display 42 (display unit), an input interface 43 (input unit), and a processing circuit 44 (processing unit). Data communication between the memory 41, the display 42, the input interface 43, and the processing circuit 44 is performed via a bus (BUS).

The memory 41 is a storage device such as a HDD (Hard Disk Drive), SSD (Solid State Drive), or integrated circuit storage device that stores various information. The memory 41 stores, for example, projection data and reconstructed image data. In addition to an HDD or SSD, the memory 41 may be a drive device that reads and writes various information to and from portable storage media such as a CD (Compact Disc), a DVD (Digital Versatile Disc), or a flash memory, or a semiconductor memory element such as a RAM (Random Access Memory). The storage area of the memory 41 may be located within the X-ray CT device 1, or may be located within an external storage device connected via a network.

The memory 41 stores various programs according to this embodiment. For example, the memory 41 stores programs related to the execution of each of the system control function 441, the preprocessing function 442, the reconstruction processing function 443, the acquisition function 444, and the determination function 445 executed by the processing circuitry 44.

The memory 41 also stores at least one of the first output, the second output, the first output ratio, and the first irradiation spectrum. The first output is acquired at a first timing and is an output value from a first detection element at a first position in the channel direction of the X-ray detector 12. The second output is acquired at the first timing and is an output value from a second detection element at a second position that is closer to the end of the channel direction than the first position. The first timing corresponds to, for example, any timing before the shipment of the X-ray CT device 1. The first output ratio is, for example, a value indicating the ratio of the first output to the second output. The first irradiation spectrum corresponds to the spectrum of the X-rays irradiated from the X-ray tube 11 at the first timing. That is, the first irradiation spectrum is generated before the shipment of the X-ray CT device 1.

Figure 2 is a diagram showing an example of a first detector element 121 at a first position and a second detector element 122 at a second position. As shown in Figure 2, the second detector element 122 is located closer to the end in the channel direction than the first detector element 121 at the first position. In addition, the transmission distance s of the bowtie filter 16 of the X-ray R1 incident on the first detector element 121 is shorter than the transmission distance t of the bowtie filter 16 of the X-ray R2 incident on the second detector element 122 (s < t).

The memory 41 stores the third output and the fourth output acquired by the acquisition function 444. The third output is an output value from the first detection element 121 at a second timing that is later than the first timing. The fourth output is an output value from the second detection element 122 at the second timing. The second timing is, for example, a timing at which a calibration scan (such as air calibration) is performed before performing a scan on the subject P. Note that, instead of storing the third output and the fourth output, the memory 41 may store a second output ratio based on the third output and the fourth output. In this case, the second output ratio is generated by the acquisition function 444 based on the third output and the fourth output.

The memory 41 stores a program related to a process (hereinafter referred to as a deterioration estimation process) for determining at least one of the second irradiation spectrum of the X-ray tube 11 at the second timing and the deterioration degree of the X-ray tube 11 based on at least one of the first output and the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output. The deterioration estimation process will be described in the description of the determination function 445. The memory 41 also stores a predetermined period for determining whether or not a warning regarding maintenance of the X-ray tube 11 according to the deterioration degree is required, according to the deterioration degree.

The display 42 displays various information. For example, the display 42 outputs medical images (CT images) generated by the processing circuit 44, a GUI (Graphical User Interface) for accepting various operations from the user, and the like. The display 42 displays a predetermined warning under the control of the decision function 445. As the display 42, for example, a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescence display (OELD), a plasma display, or any other display can be used as appropriate. The display 42 may also be provided on the pedestal device 10. The display 42 may also be a desktop type, or may be configured as a tablet terminal or the like capable of wireless communication with the console device 40 main body. The display 42 corresponds to the display unit.

The input interface 43 accepts various input operations from the user, converts the accepted input operations into electrical signals, and outputs them to the processing circuit 44. For example, the input interface 43 accepts from the user the collection conditions when collecting projection data, the reconstruction conditions when reconstructing CT images, and the image processing conditions when generating post-processed images from CT images. As the input interface 43, for example, a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad, a touch panel display, and the like can be used as appropriate.

In this embodiment, the input interface 43 is not limited to having physical operation parts such as a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display. For example, an example of the input interface 43 includes an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs the electrical signal to the processing circuit 44. The input interface 43 is also an example of an input unit. The input interface 43 may be provided in the pedestal device 10. The input interface 43 may be configured as a tablet terminal or the like that can wirelessly communicate with the console device 40 main body. The input interface 43 corresponds to an input unit.

The processing circuitry 44 controls the operation of the entire X-ray CT apparatus 1 in response to the electrical signal of the input operation output from the input interface 43. For example, the processing circuitry 44 has a processor such as a CPU, MPU, or GPU (Graphics Processing Unit) and a memory such as a ROM or RAM as hardware resources. The processing circuitry 44 executes the system control function 441, the preprocessing function 442, the reconstruction processing function 443, the acquisition function 444, and the decision function 445 by a processor that executes a program deployed in the memory. The processing circuitry 44 that realizes the system control function 441, the preprocessing function 442, the reconstruction processing function 443, the acquisition function 444, and the decision function 445 corresponds to the system control unit, the preprocessing unit, the reconstruction processing unit, the acquisition unit, and the decision unit. Note that each of the functions 441 to 445 is not limited to being realized by a single processing circuit. A processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to realize each of the functions 441 to 445.

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

The pre-processing function 442 generates data by performing pre-processing such as logarithmic conversion, offset correction, inter-channel sensitivity correction, and beam hardening correction on the detection data output from the DAS 18. Note that data before pre-processing is called raw data, and data after pre-processing is called projection data.

The reconstruction processing function 443 performs reconstruction processing using the filtered back projection method (FBP method) or the iterative reconstruction method on the projection data generated by the preprocessing function 442 to generate CT image data. The reconstruction processing function 443 stores the reconstructed CT image data in the memory 41. The projection data generated from the counting results obtained by the photon counting CT contains information on the energy of X-rays attenuated by passing through the subject P. Therefore, the reconstruction processing function 443 can reconstruct X-ray CT image data of a specific energy component, for example. The reconstruction processing function 443 can also reconstruct X-ray CT image data of each of a plurality of energy components, for example.

The reconstruction processing function 443 can also generate image data in which a color tone according to the energy component is assigned to each pixel of the X-ray CT image data of each energy component, and multiple X-ray CT image data color-coded according to the energy component are superimposed. The reconstruction processing function 343 can also generate image data that allows identification of the substance, for example, by using the K-absorption edge (K-edge) specific to the substance. Other image data generated by the reconstruction processing function 443 include monochromatic X-ray image data, density image data, and effective atomic number image data.

The acquisition function 444 acquires a third output from the first detection element 121 and a fourth output from the second detection element 122 at a second timing that is later than the first timing. The acquisition function 444 calculates a second output ratio based on the third output and the fourth output. The acquisition function 444 may be realized as the DAS 18. In this case, the DAS 18 acquires the third output from the first detection element 121 and the fourth output from the second detection element 122, for example, in an air calibration scan.

The determination function 445 determines (generates) a first irradiation spectrum before shipping the X-ray CT device 1 based on the detection data for each energy bin acquired at the first timing. The determination function 445 executes a program related to the deterioration estimation process to determine at least one of the second irradiation spectrum of the X-ray tube 11 at the second timing and the deterioration degree of the X-ray tube 11 based on at least one of the first output and the second output, the first output ratio, and the first irradiation spectrum, and the third output and the fourth output. For example, the determination function 445 determines the linear attenuation coefficient of the anode material (hereinafter referred to as the anode material) of the X-ray tube 11 at the second timing based on the third output and the fourth output or the second output ratio, and determines the second irradiation spectrum based on the determined linear attenuation coefficient and the first irradiation spectrum. The determination function 445 may calculate the second output ratio based on the third output and the fourth output.

Specifically, the determination function 445 determines the thickness of the anode material of the X-ray tube 11 (hereinafter referred to as the anode thickness) based on the second output ratio. For example, the determination function 445 determines the anode thickness at the second timing by comparing the second output ratio with a correspondence table of anode thicknesses for the first output ratio, i.e., the second output ratio stored in the memory 41 for each X-ray tube 11 (hereinafter referred to as the output ratio-thickness table). The output ratio-thickness table is generated in advance by simulation, actual measurement, etc., before shipment of the X-ray CT device 1.

The determination function 445 determines the degree of deterioration based on the determined anode thickness. The degree of deterioration is modeled based on the increase in X-ray stopping power associated with an increase in the thickness of the anode material, such as tungsten. The degree of deterioration is related to the relative change in the irradiation spectrum from the first timing to the second timing. Therefore, the second irradiation spectrum can be estimated using a deterioration model based on the first irradiation spectrum measured before the shipment of the X-ray CT device 1 and the second output ratio at the second timing when the anode material has deteriorated. The determination function 445 may determine the degree of deterioration by indexing the second output ratio to the first output ratio, or may determine the degree of deterioration of the X-ray tube 11 by applying the second output ratio to the deterioration model.

In addition, the determination function 445 determines the linear attenuation coefficient of the anode material (hereinafter referred to as the anode attenuation coefficient) based on the determined thickness. The distribution of the anode attenuation coefficient with respect to the anode thickness is, for example, a table (hereinafter referred to as the thickness-attenuation coefficient table). The thickness-attenuation coefficient table is determined in advance using a simulation or the like according to the thickness of the anode material, and is stored in the memory 41. The determination function 445 determines the second irradiation spectrum by multiplying the determined anode attenuation coefficient by the first irradiation spectrum. The determination function 445 stores the determined second irradiation spectrum in the memory 41. The second irradiation spectrum is used to generate projection data in the main scan.

Based on the determined deterioration level, the determination function 445 determines the period from the second timing to the time when maintenance of the X-ray tube 11 is recommended (hereinafter referred to as the recommended maintenance period). The determination function 445 determines whether the recommended maintenance period is equal to or shorter than a predetermined period. If the recommended maintenance period is equal to or shorter than the predetermined period, the determination function 445 causes a predetermined warning to be displayed on the display 42.

When the first irradiation spectrum is not stored in the memory 41, the determination function 445 generates the first irradiation spectrum based on the first output and the second output, or the first output ratio. At this time, the memory 41 stores the first output and the second output, or the first output ratio. In addition, the memory 41 stores a table (hereinafter referred to as the output ratio-spectrum table) that is modeled in advance to derive the irradiation spectrum based on the first output and the second output, or the first output ratio. With these, the determination function 445 determines the first irradiation spectrum based on the first output and the second output, or the first output ratio and the output-spectrum table. Next, the determination function 445 determines the second irradiation spectrum based on the first irradiation spectrum, the third output, and the fourth output.

Also, if the first output, the second output, and the first output ratio are not stored in the memory 41, the determination function 445 generates the first output and the second output, or the first output ratio, based on the first irradiation spectrum. For example, the determination function 445 determines the first output and the second output, or the first output ratio, based on the first irradiation spectrum and the output-spectrum table. Then, the determination function 445 determines the deterioration degree of the X-ray tube 11 based on the first output and the second output, or the first output ratio, the third output, and the fourth output.

The configuration of the X-ray CT scanner 1 according to the embodiment has been described above. Below, an overview of the deterioration estimation process executed by the X-ray CT scanner 1 will be described using FIG. 2, and then the procedure for the deterioration estimation process will be described.

The X-ray flux at the first timing, i.e., before the anode material is deteriorated (hereinafter referred to as pre-deterioration X-rays), is denoted by X. Also, the linear attenuation coefficient of the bowtie filter 16 corresponding to the energy of the pre-deterioration X-rays is denoted by μ. In this case, the first output x from the first detection element 121 at the first timing is expressed by the following formula (1) using the transmission distance s of the bowtie filter 16, with reference to FIG. 2 .
x=exp(-μs)X (1)

Furthermore, with reference to FIG. 2, the second output x′ from the second detection element 122 at the first timing is expressed by the following equation (2) using the transmission distance t of the bowtie filter 16.
x'=exp(-μt)X (2)

By taking the ratio of equation (1) to equation (2), the following equation (3) is obtained as the first output ratio.
x/x'=exp(-μ(s-t)) (3)

Moreover, the X-ray flux at the second timing, i.e., after the anode material has deteriorated (hereinafter referred to as "deteriorated X-rays"), is denoted as Y. Moreover, the linear attenuation coefficient of the bowtie filter 16 corresponding to the energy of the deteriorated X-rays is denoted as μ'. In this case, with reference to FIG. 2 , the second output y from the first detection element 121 at the second timing is expressed by the following equation (4) using the transmission distance s of the bowtie filter 16.
y=exp(-μ's)Y (4)

Furthermore, with reference to FIG. 2, a second output y′ from the second detection element 122 at a second timing is expressed by the following equation (5) using the transmission distance t of the bowtie filter 16.
y'=exp(-μ't)Y (5)

By taking the ratio of equation (4) to equation (5), the following equation (6) is obtained as the second output ratio.
y/y'=exp(-μ'(s-t)) (6)
do.

By solving −(s−t) in equations (3) and (6), the following equation (7) is obtained.
(1/μ)ln(x/x')=-(s-t)=(1/μ')ln(y/y')
(x/x') ^μ' = (y/y') ^μ (7)

In general, the output of the soft X-rays is attenuated in the degraded X-rays Y compared to the undegraded X-rays X. The attenuation of the soft X-rays is due to the increase in the thickness of the anode material and the absorption of the soft X-rays by fine cracks in the anode material. In other words, the degraded X-rays are harder than the undegraded X-rays. For these reasons, for example, in a comparison of the effective energies of X-rays, the energy of the degraded X-rays Y is greater than the energy of the undegraded X-rays X. On the other hand, the linear attenuation coefficient is smaller in proportion to the effective energy. For these reasons, the linear attenuation coefficient μ' of the bowtie filter 16 corresponding to the energy of the degraded X-rays is smaller than the linear attenuation coefficient μ of the bowtie filter 16 corresponding to the energy of the undegraded X-rays (μ>μ'...(8)).

From equations (7) and (8), the relationship between the first output ratio (x/x') and the second output ratio (y/y') is expressed as follows:
(x/x')>(y/y')

In other words, the second output ratio (y/y') after the anode material of the X-ray tube 11 has deteriorated is smaller than the first output ratio (x/x') before the anode material of the X-ray tube 11 has deteriorated. Therefore, the degree of decrease in the second output ratio (y/y') corresponds to the degree of deterioration of the anode material.

Figure 3 is a diagram showing an example of a first output ratio OR1 and a plurality of second output ratios corresponding to the degree of deterioration (deterioration level) of the anode material. As shown in Figure 3, the second output ratio decreases according to the deterioration of the anode material. In other words, the value of the second output ratio corresponds to the deterioration level of the anode material, with the first output ratio as the reference. The deterioration level of the anode material corresponds to an increase in the thickness of the surface of the anode material and the surface of the anode material becoming rough due to cracks or the like. In other words, for example, the ratio of the second output ratio to the first output ratio corresponds to the deterioration level of the anode material, i.e., the thickness of the anode material.

Deterioration of the anode material corresponds to a decrease in the linear attenuation coefficient of the bowtie filter 16, as shown in formula (8). The degree of decrease in the linear attenuation coefficient depends on the attenuation of soft X-rays, and therefore contributes to a decrease in the number of counts in the detection element. The first irradiation spectrum changes according to the ratio of the linear attenuation coefficient at the second timing, i.e., after the anode material has deteriorated, to the linear attenuation coefficient at the first timing, i.e., before the anode material has deteriorated.

The degree of deterioration of the anode material can be modeled by the increase in the stopping power of soft X-rays due to an increase in the thickness of the anode material. Specifically, the memory 41 stores a correspondence table of the degree of deterioration of the anode material with respect to the second output ratio according to the first output ratio (hereinafter referred to as the output ratio-deterioration degree table). The output ratio-deterioration degree table according to the first output ratio corresponds to a table that estimates the degree of deterioration in consideration of individual differences in the X-ray tube 11. The determination function 445 determines the degree of deterioration of the anode material based on the third output and the fourth output or the second output ratio and the output ratio-deterioration degree table.

OR2L shown in FIG. 3 indicates the second output ratio. OR2M shown in FIG. 3 indicates the second output ratio at the time when the anode material has further deteriorated, i.e., the anode thickness has further increased, since the time when the second output ratio OR2L was obtained. As shown in FIG. 3, as the degree of deterioration of the anode material increases, the second output ratio decreases from the first output ratio OR1. When the anode material deteriorates and the anode thickness increases, the linear attenuation coefficient of the anode material changes. The change in the linear attenuation coefficient affects the reduction in soft X-rays among the X-rays generated by the anode material. As a result, the number of soft X-ray counts decreases in the spectrum of X-rays irradiated from the X-ray tube 11.

Figure 4 shows an example of the irradiation spectrum RS for the first timing and the second timing. In Figure 4, the first irradiation spectrum RS1 is shown by a solid line. In Figure 4, the irradiation spectrum RS2L for the second output ratio OR2L is shown by a dotted line, and in Figure 4, the irradiation spectrum RS2M for the second output ratio OR2M is shown by a dashed line. As shown in Figure 4, the number of soft X-ray counts in the irradiation spectrum decreases with deterioration of the anode material. The deterioration estimation process estimates the second irradiation spectrum (RS2L or RS2M) at the second timing based on the second output ratio and the first irradiation spectrum RS1.

Figure 5 is a flowchart showing an example of the procedure for the deterioration estimation process. The deterioration estimation process is performed after shipment of the X-ray CT device 1, for example, during air calibration before execution of a main scan on the subject P. Therefore, in performing the deterioration estimation process, at least one of the first output x and the second output x', the first output ratio OR1, and the first irradiation spectrum is already stored in the memory 41. The deterioration estimation process is appropriately performed at a preset timing, such as six months or one year after shipment of the X-ray CT device 1. The interval for executing the deterioration estimation process and the timing for executing the deterioration estimation process can be appropriately set or changed by the user's instruction via the input interface 43.

(Deterioration Estimation Processing)
(Step S501)
The system control function 441 executes air calibration before the main scan. The acquisition function 444 acquires a third output and a fourth output by the air calibration. The acquisition function 444 stores the third output and the fourth output in the memory 41. The energy bins in the first output, the second output, the third output, and the fourth output are, for example, a total energy bin obtained by adding up a plurality of energy bins, or a low energy bin among the plurality of energy bins that corresponds to soft X-rays related to the influence of deterioration of the X-ray tube 11, or an energy bin (hereinafter referred to as a K-edge bin) among the plurality of energy bins that includes the energy of the K-absorption edge related to the material of the anode in the X-ray tube 11.

(Step S502)
The acquisition function 444 calculates the second output ratio based on the third output and the fourth output. Note that instead of the acquisition function 444, the determination function 445 may calculate the second output ratio based on the third output and the fourth output. The acquisition function 444 stores the second output ratio in the memory 41.

(Step S503)
The determination function 445 converts the second output ratio into an anode thickness. Specifically, the determination function 445 determines the anode thickness at the second timing by comparing the second output ratio with an output ratio-thickness table corresponding to the first output ratio. The determination function 445 stores the determined anode thickness in the memory 41.

(Step S504)
The determination function 445 determines the anode attenuation coefficient by comparing the determined anode thickness with a thickness-attenuation coefficient table. The determination function 445 stores the determined anode attenuation coefficient in the memory 41. The output ratio-thickness table and the thickness-attenuation coefficient table may be integrated as an output ratio-attenuation coefficient table corresponding to the first output ratio and stored in the memory 41. At this time, the determination function 445 determines the anode attenuation coefficient by comparing the output ratio-attenuation coefficient table with the second output ratio. In this case, step S503 is unnecessary.

(Step S505)
The determination function 445 multiplies the determined anode attenuation coefficient by the first irradiation spectrum to determine the second irradiation spectrum. The determination function 445 stores the determined second irradiation spectrum in the memory 41. The memory 41 may store a power ratio-spectrum table, which is a correspondence table of the second irradiation spectrum to the second output ratio, according to the first output ratio, i.e., the first irradiation spectrum and the second output ratio, for the X-ray tube 11. At this time, the determination function 445 determines the second irradiation spectrum by collating the second output ratio with the power ratio-spectrum table. In this case, the processes of steps S503 and S504 are unnecessary. If the type of the X-ray detector 12 is an integral type, the processes of steps S503 to S505 are unnecessary.

(Step S506)
The determination function 445 determines the deterioration degree of the anode material by comparing the output ratio-deterioration degree table corresponding to the first output ratio with the second output ratio. The determination function 445 stores the determined deterioration degree in the memory 41. The various tables described in the above steps S503 to S506 may be realized by various calculations that input data to be compared with the tables and output the comparison results. For example, since the degree of the second output ratio decreases depending on the degree of deterioration of the X-ray tube 11, the second irradiation spectrum can be calculated from the second output ratio by modeling the change in the spectrum according to the degree of deterioration. Furthermore, since the degree of deterioration of the X-ray tube 11 can be modeled by the increase in X-ray stopping power due to the increase in the anode thickness, the deterioration degree can be calculated from the increase in the anode pressure.

(Step S507)
The determination function 445 determines the recommended maintenance period for the X-ray tube 11 at the second timing based on the deterioration degree. For example, as shown in Fig. 3, the greater the deterioration degree, the shorter the recommended maintenance period. That is, the closer the second output ratio is to the first output ratio, the longer the recommended maintenance period. The maximum value of the recommended maintenance period is preset based on the elapsed time since shipment of the CT apparatus 1, the number of scans, etc., and is stored in the memory 41.

(Step S508)
The determination function 445 determines whether the recommended maintenance period is equal to or shorter than a predetermined period. If the recommended maintenance period is equal to or shorter than the predetermined period (Yes in step S508), the process proceeds to step S509. If the recommended maintenance period is not equal to or shorter than the predetermined period (No in step S508), the process proceeds to step S510.

(Step S509)
The determination function 445 displays a predetermined warning on the display 42. The predetermined warning is, for example, a character string (for example, "It is time for maintenance of the X-ray tube") that prompts the user to perform maintenance of the X-ray tube 11. Note that the predetermined warning is not limited to the character string, and may be, for example, a blinking light of a predetermined hue, a sound, or the like.

(Step S510)
The system control function 441 executes a main scan on the subject P in accordance with a user's instruction at a third timing that is later than the second timing. The DAS 18 generates detection data by executing the main scan. The DAS 18 transfers the generated detection data to the console device 40.

(Step S511)
The pre-processing function 442 generates projection data for a plurality of energy bins based on the detection data and the second illumination spectrum. For example, the pre-processing function 442 performs various pre-processing operations, such as dividing the detection data by the second illumination spectrum, in each of the plurality of energy bins to generate projection data.

(Step S512)
The reconstruction processing function 443 generates a plurality of cross-sectional images corresponding to a plurality of energy bins based on the projection data. Specifically, the reconstruction processing function 443 generates volume data for each of the plurality of energy bins by executing reconstruction on the projection data for each of the plurality of energy bins. The reconstruction processing function 443 generates a cross-sectional image for each of the plurality of energy bins based on various image processes on the generated volume data.

The X-ray CT device 1 according to the embodiment described above stores at least one of the first output, the second output, the first output ratio, and the first irradiation spectrum, acquires the third output and the fourth output, and determines at least one of the second irradiation spectrum and the deterioration degree of the X-ray tube 11 based on at least one of the first output, the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output. For example, the X-ray CT device 1 determines the linear attenuation coefficient of the anode of the X-ray tube 11 at the second timing based on the second output ratio using the third output and the fourth output, and determines the second irradiation spectrum based on the determined linear attenuation coefficient and the first irradiation spectrum.

Specifically, the X-ray CT device 1 according to the embodiment determines the thickness of the anode based on the second output ratio, determines the linear attenuation coefficient based on the thickness, and determines the degree of deterioration based on the thickness. In addition, in the present X-ray CT device 1, the X-ray detector 12 is a photon counting detector, and generates projection data for multiple energy bins based on the detection data generated by the main scan performed at the third timing and the second irradiation spectrum, and generates multiple cross-sectional images corresponding to the multiple energy bins based on the projection data.

As a result, the X-ray CT device 1 according to the embodiment can estimate the irradiation spectrum in a short time using a simple method of performing one air calibration scan, and can calculate the correct linear attenuation coefficient in image reconstruction. As a result, the X-ray CT device 1 can suppress the occurrence of artifacts such as CT value shifts in the reconstructed cross-sectional image. Furthermore, the X-ray CT device 1 according to the embodiment does not require a new two-channel Ref detector for estimating the degree of deterioration of the X-ray tube 11, so the deterioration estimation process can be performed without incurring additional costs.

In addition, according to the X-ray CT device 1 of the embodiment, the recommended maintenance period is determined based on the deterioration degree of the X-ray tube 11, and if the recommended maintenance period is equal to or shorter than a predetermined period, a predetermined warning is displayed on the display 42. This makes it possible to monitor long-term changes in the radiation spectrum from the X-ray tube 11, and to notify the user of the need for maintenance of the X-ray tube 11 at an appropriate timing according to the deterioration degree of the X-ray tube 11.

In addition, according to the X-ray CT device 1 of the embodiment, the energy bins in the first output, the second output, the third output, and the fourth output are a total energy bin obtained by adding up multiple energy bins, or a low energy bin among the multiple energy bins that corresponds to soft X-rays related to the influence of deterioration of the X-ray tube 11, or an energy bin (K edge bin) among the multiple energy bins that includes the energy of the K absorption edge related to the anode material in the X-ray tube 11. For example, when a low energy bin or a K edge bin is used, the influence of deterioration of the X-ray tube 11 in relation to deterioration of the anode can be detected more sensitively, and the accuracy of the timing of execution of the deterioration estimation process can be improved.

As described above, the X-ray CT device 1 according to this embodiment can estimate the degree of deterioration of the X-ray tube 11 and adjust the irradiation spectrum used for image reconstruction in a short time, at low cost, and in a simple manner, and can notify the user when it is time to perform maintenance on the deterioration of the X-ray tube 11 and generate a CT image with reduced artifacts due to CT value shifts.

(First Modification)
The first modified example is to execute the deterioration estimation process using the output from a reference detector arranged at the end of the bowtie filter 16. That is, in the deterioration estimation process in this modified example, the output used in steps S501 to S506 is the output from the reference detector.

The X-ray CT apparatus 1 further includes a reference detector in addition to the X-ray detector 12 that detects X-rays transmitted through the subject P. The reference detector is disposed at the end of the bowtie filter 16 that is disposed in front of the X-ray radiation window in the X-ray tube 11. The reference detector is realized, for example, by the above-mentioned photon counting type X-ray detector. The photon counting type X-ray detector as the reference detector has, for example, two channels capable of detecting X-rays at multiple energy bins. The reference detector may also be an integral type X-ray detector.

A filter having a thickness that varies depending on the channel is provided on the X-ray incidence side of the reference detector. Specifically, the filter is disposed at a first position and a second position on the reference detector on the incidence side of the X-rays generated by the X-ray tube 11, and has a different thickness at the first position and the second position.

The degradation estimation process performed by the first modified example is similar to that described in the embodiment, and therefore a detailed description is omitted. In addition, the effects of the first modified example are similar to those of the embodiment, except for cost reduction, and therefore a detailed description is omitted.

(Second Modification)
The second modification is to execute the deterioration estimation process using outputs from a plurality of detection elements arranged along the channel direction in the X-ray detector 12 .

The memory 41 stores at least one of a plurality of fifth outputs obtained at a first timing and including the first output and the second output, a plurality of third output ratios based on the plurality of fifth outputs including the first output ratio and a first irradiation spectrum by a plurality of detection elements in the channel direction in the X-ray detector 12. The plurality of detection elements in the channel direction are three or more detection elements along the channel direction, and may be, for example, all detection elements along the channel direction.

The acquisition function 444 acquires a plurality of sixth outputs by the plurality of detection elements, including a third output and a fourth output, at a second timing. The plurality of detection elements related to the plurality of sixth outputs are in the same position as the plurality of detection elements related to the plurality of fifth outputs. For example, the acquisition function 445 may calculate a plurality of output ratios, including the second output ratio, based on the plurality of fifth outputs and the plurality of sixth outputs, in which the positions of the detection elements are different. In the calculated output ratio, the positions of the detection elements related to the numerator and denominator are different.

The determination function 445 determines at least one of the second irradiation spectrum and the deterioration degree based on at least one of the plurality of fifth outputs, the plurality of third output ratios, and the first irradiation spectrum, and the plurality of sixth outputs. The various tables described in the embodiment include combinations of the plurality of fifth outputs and the plurality of sixth outputs, and are stored in advance in the memory 41. For example, the various tables are set by modeling the output distribution in the channel direction according to the deterioration of the anode material.

The deterioration estimation process performed by the second modified example is similar to that described in the embodiment, and therefore a description thereof will be omitted. In addition to the effects of the embodiment, the second modified example has the effect of improving the accuracy of the deterioration degree and the second irradiation spectrum because the amount of data used in the deterioration estimation process is increased. As a result, the X-ray CT device 1 according to the second modified example can improve the accuracy of the maintenance timing for deterioration of the X-ray tube 11 and generate CT images with further reduced artifacts due to CT value shifts.

(Third Modification)
The third modified example is to execute the deterioration estimation process using outputs from a plurality of detection elements along the channel direction and slice direction in the X-ray detector 12. That is, the deterioration estimation process in the third modified example further uses outputs from a plurality of detection elements along the slice direction in addition to the description in the second modified example.

The memory 41 stores at least one of a plurality of seventh outputs by a plurality of detection elements in the channel direction and slice direction in the X-ray detector 12, a plurality of fourth output ratios based on the plurality of seventh outputs, and a first irradiation spectrum, which are acquired at a first timing. The plurality of seventh outputs include a first output and a second output. The plurality of fourth output ratios include a first output ratio. The plurality of detection elements in the channel direction and slice direction may be three or more detection elements along the channel direction and a plurality of detection elements along the slice direction, and may be, for example, all detection elements in the X-ray detector 12.

The acquisition function 444 acquires, at the second timing, multiple eighth outputs by multiple detection elements in the channel direction and slice direction. The eighth output includes a third output and a fourth output. The multiple detection elements for the multiple eighth outputs are in the same positions as the multiple detection elements for the multiple seventh outputs. For example, the acquisition function 445 may calculate multiple output ratios based on the multiple seventh outputs and the multiple eighth outputs, which have different positions of the detection elements. The positions of the detection elements in the numerator and denominator in the calculated output ratio are different.

The determination function 445 determines at least one of the second irradiation spectrum and the deterioration degree based on at least one of the multiple seventh outputs, multiple fourth output ratios, and first irradiation spectrum, and the eighth output. The various tables described in the embodiment include combinations of multiple seventh outputs and multiple eighth outputs, and are stored in advance in the memory 41. For example, the various tables are set by modeling the output distribution including the channel direction and slice direction according to the deterioration of the anode material.

The deterioration estimation process performed by the third modified example is similar to that described in the embodiment, and therefore a description thereof will be omitted. In addition to the effects of the embodiment, the third modified example has the effect of improving the accuracy of the deterioration degree and the second irradiation spectrum because the number of data used in the deterioration estimation process is increased. Furthermore, in this modified example, the heel effect at the anode in the X-ray tube 11 can improve the accuracy of the deterioration degree and the second irradiation spectrum even if the influence of the deterioration of the X-ray tube 11 on the output ratio differs depending on the cone angle direction. In other words, the X-ray CT device 1 according to the third modified example can further improve the accuracy of the maintenance timing for the deterioration of the X-ray tube 11 and generate CT images with even further reduced artifacts due to CT value shifts.

When the technical idea of the embodiment is realized by an anode deterioration estimation method, the anode deterioration estimation method stores at least one of a first output by a first detection element 121 at a first position in the channel direction of the X-ray detector 12, which is acquired at a first timing, a second output by a second detection element 122 at a second position that is acquired at the first timing and is closer to the end side in the channel direction than the first position, a first output ratio based on the first output and the second output, and a first irradiation spectrum of the X-ray tube 11 at the first timing, and acquires a third output by the first detection element 121 and a fourth output by the second detection element 122 at a second timing that is later than the first timing, and determines at least one of a second irradiation spectrum of the X-ray tube 11 at the second timing and a deterioration degree of the X-ray tube 11 based on at least one of the first output and the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output. The procedure and effects of the deterioration estimation process performed by the anode deterioration estimation method are the same as those in the embodiment, so a description will be omitted.

When the technical idea of the embodiment is realized by an anode deterioration estimation program, the anode deterioration estimation program causes a computer to store at least one of a first output by a first detection element 121 at a first position in the channel direction of the X-ray detector 12, which is acquired at a first timing, a second output by a second detection element 122 at a second position that is closer to the end side in the channel direction than the first position, a first output ratio based on the first output and the second output, and a first irradiation spectrum of the X-ray tube 11 at the first timing, and acquire a third output by the first detection element 121 and a fourth output by the second detection element 122 at a second timing that is later than the first timing, and determine at least one of a second irradiation spectrum of the X-ray tube 11 at the second timing and a deterioration degree of the X-ray tube 11 based on at least one of the first output and the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output.

For example, the anode deterioration estimation program can be installed in a computer in a server device (processing device) connected to an X-ray CT scanner and deployed in memory, thereby realizing the deterioration estimation process. At this time, the program that can cause the computer to execute the method can also be stored and distributed on a storage medium such as a magnetic disk (hard disk, etc.), optical disk (CD-ROM, DVD, etc.), or semiconductor memory. The processing procedure and effects of the anode deterioration estimation program are similar to those of the first embodiment, so a description thereof will be omitted.

In other embodiments, the X-ray CT scanner 1 does not need to have a bed device 30. For example, if the opening 131 of the gantry device 10 of the X-ray CT scanner 1 has a generally cylindrical shape extending vertically, the subject P is imaged in an upright position, and therefore the bed device 30 is not required.

According to at least one of the embodiments described above, it is possible to easily determine at least one of the X-ray spectrum that has changed due to deterioration of the X-ray tube 11 and the degree of deterioration of the X-ray tube 11.

Although several embodiments of the present invention 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 gist of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and gist of the invention.

REFERENCE SIGNS LIST 1 X-ray CT device 10 Mount device 11 X-ray tube 12 X-ray detector 13 Rotating frame 14 X-ray high voltage device 15 Control device 16 Bowtie filter 17 Collimator 18 DAS (Data Acquisition System)
30 Bed device 31 Base 32 Bed driving device 33 Top plate 34 Top plate support frame 40 Console device 41 Memory 42 Display 43 Input interface 44 Processing circuit 113 X-ray irradiation range 121 First detection element 122 Second detection element 131 Opening 441 System control function 442 Pre-processing function 443 Reconstruction processing function 444 Acquisition function 445 Decision function

Claims (12)

a storage unit that stores at least one of a first output from a first detection element at a first position in a channel direction of the X-ray detector, which is acquired at a first timing, a second output from a second detection element at a second position that is closer to an end in the channel direction than the first position, which is acquired at the first timing, a first output ratio based on the first output and the second output, and a first irradiation spectrum of the X-ray tube at the first timing;
an acquisition unit that acquires a third output from the first detection element and a fourth output from the second detection element at a second timing that is later than the first timing;
a determination unit that determines at least one of a second irradiation spectrum of the X-ray tube at the second timing and a deterioration degree of the X-ray tube based on at least one of the first output, the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output;
Equipped with
The determination unit is
determining a linear attenuation coefficient of an anode of the X-ray tube at the second timing based on a second output ratio using the third output and the fourth output;
determining the second illumination spectrum based on the linear attenuation coefficient and the first illumination spectrum;
determining a thickness of the anode based on the second power ratio;
determining the linear attenuation coefficient based on the thickness;
determining the degree of deterioration based on the thickness;
X-ray computed tomography equipment. The X-ray detector is a photon counting detector that counts photons of X-rays generated by the X-ray tube,
a pre-processing unit that generates projection data for a plurality of energy bins based on detection data generated by a scan executed at a third timing that is later than the second timing and the second irradiation spectrum;
a reconstruction processing unit that generates a plurality of cross-sectional images corresponding to the plurality of energy bins based on the projection data;
The X-ray computed tomography apparatus according to claim 1 , further comprising: the determination unit determines a period from the second timing to a time when maintenance of the X-ray tube is recommended based on the deterioration degree; and
A display unit that displays a predetermined warning when the period is equal to or shorter than a predetermined period.
3. An X-ray computed tomography apparatus according to claim 1 or 2. the energy bins in the first output, the second output, the third output, and the fourth output are all energy bins obtained by adding up a plurality of energy bins, or a low energy bin among the plurality of energy bins that is related to the influence of deterioration of the X-ray tube, or an energy bin among the plurality of energy bins that includes a K-absorption edge energy related to a material of an anode in the X-ray tube.
4. An X-ray computed tomography apparatus according to claim 1. The determination unit is
If the first irradiation spectrum is not stored in the storage unit, generating the first irradiation spectrum based on the first output and the second output or the first output ratio;
determining the second illumination spectrum based on the first illumination spectrum, the third output, and the fourth output;
5. An X-ray computed tomography apparatus according to claim 1. The determination unit is
When the first output, the second output, and the first output ratio are not stored in the storage unit, determining the first output and the second output, or the first output ratio, based on the first irradiation spectrum;
determining the deterioration degree based on the first output and the second output, or based on a ratio of the first output to the third output and the fourth output;
5. An X-ray computed tomography apparatus according to claim 1. a bowtie filter disposed in front of an X-ray emission window in the X-ray tube;
The X-ray detector is a main detector that detects X-rays that have passed through a subject.
7. An X-ray computed tomography apparatus according to claim 1. The X-ray detector is a reference detector disposed at an end of a bowtie filter disposed in front of an X-ray radiation window in the X-ray tube,
the reference detector further includes a filter disposed at the first position and the second position on an incident side of the X-rays generated by the X-ray tube, the filter having a different thickness at the first position and the second position;
2. An X-ray computed tomography apparatus according to claim 1. the storage unit stores at least one of a plurality of fifth outputs obtained at the first timing, the plurality of fifth outputs including the first output and the second output, and the plurality of detection elements in the X-ray detector arranged in the channel direction; a plurality of third output ratios including the first output ratio and based on the plurality of fifth outputs; and the first irradiation spectrum;
the acquisition unit acquires, at the second timing, a plurality of sixth outputs including the third output and the fourth output from the plurality of detection elements;
the determination unit determines at least one of the second irradiation spectrum and the deterioration degree based on at least one of the plurality of fifth outputs, the plurality of third output ratios, and the first irradiation spectrum, and the plurality of sixth outputs.
9. An X-ray computed tomography apparatus according to claim 1. the storage unit stores at least one of a plurality of seventh outputs by a plurality of detection elements in the channel direction and a slice direction in the X-ray detector, a plurality of fourth output ratios based on the plurality of seventh outputs, the plurality of seventh outputs being acquired at the first timing, and the first irradiation spectrum;
the acquiring unit acquires, at the second timing, a plurality of eighth outputs by the plurality of detector elements in the channel direction and the slice direction;
the determination unit determines at least one of the second irradiation spectrum and the deterioration degree based on at least one of the plurality of seventh outputs, the plurality of fourth output ratios, and the first irradiation spectrum, and the eighth output.
9. An X-ray computed tomography apparatus according to claim 1. storing at least one of a first output by a first detection element at a first position in a channel direction of the X-ray detector, which is acquired at a first timing, a second output by a second detection element at a second position that is acquired at the first timing and is closer to an end in the channel direction than the first position, a first output ratio based on the first output and the second output, and a first irradiation spectrum of the X-ray tube at the first timing;
At a second timing that is later than the first timing, a third output from the first detection element and a fourth output from the second detection element are obtained;
determining at least one of a second irradiation spectrum of the X-ray tube at the second timing and a deterioration degree of the X-ray tube based on at least one of the first output, the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output ;
determining a linear attenuation coefficient of an anode of the X-ray tube at the second timing based on a second output ratio using the third output and the fourth output;
determining the second illumination spectrum based on the linear attenuation coefficient and the first illumination spectrum;
determining a thickness of the anode based on the second power ratio;
determining the linear attenuation coefficient based on the thickness;
determining the degree of deterioration based on the thickness ;
The anode deterioration estimation method includes: On the computer,
storing at least one of a first output by a first detection element at a first position in a channel direction of the X-ray detector, which is acquired at a first timing, a second output by a second detection element at a second position that is acquired at the first timing and is closer to an end in the channel direction than the first position, a first output ratio based on the first output and the second output, and a first irradiation spectrum of the X-ray tube at the first timing;
At a second timing that is later than the first timing, a third output from the first detection element and a fourth output from the second detection element are obtained;
determining at least one of a second irradiation spectrum of the X-ray tube at the second timing and a deterioration degree of the X-ray tube based on at least one of the first output, the second output, the first output ratio, and the first irradiation spectrum, the third output, and the fourth output ;
determining a linear attenuation coefficient of an anode of the X-ray tube at the second timing based on a second output ratio using the third output and the fourth output;
determining the second illumination spectrum based on the linear attenuation coefficient and the first illumination spectrum;
determining a thickness of the anode based on the second power ratio;
determining the linear attenuation coefficient based on the thickness;
determining the degree of deterioration based on the thickness ;
This is an anode deterioration estimation program that realizes this.

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