Photon-counting CT apparatus

Abstract

To make it possible to acquire objective data while suppressing a data size of counting data collected by using an X-ray detector of a photon counting type.SOLUTION: A photon-counting CT apparatus includes: an X-ray generator for generating X-ray; a photon counting type X-ray detector for detecting the X-ray passing a subject; a collection part for collecting counting data counting an X-ray photon number every energy band on the basis of a detection result of the X-ray by the X-ray detector; a setting part for setting a first condition and a second condition as a band setting of the energy band; and a control part continuously performing first scan to be conducted under the first condition and second scan to be conducted under the second condition with respect to the subject mounted on a top board.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and drawings relate to a photon-counting CT device. [Background technology]

[0002] Photon-counting X-ray detectors are known. In an examination using a photon-counting X-ray detector, count data indicating the X-ray intensity for each energy band (bin) is collected. By processing this count data, various data can be generated, such as material decomposition images.

[0003] The more energy bands that are set when collecting counting data using a photon-counting X-ray detector, the more diverse data can be generated in subsequent processing. However, the data size of the counting data increases depending on the number of energy bands set, which increases the burden on data transmission and storage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-42604 Summary of the Invention [Problem to be solved by the invention]

[0005] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to enable acquisition of target data while suppressing the data size of count data collected using a photon-counting X-ray detector. However, the problems to be solved by the embodiments disclosed in this specification and the drawings 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. [Means for solving the problem]

[0006] The photon-counting CT device according to the embodiment includes an X-ray generator that generates X-rays, a photon-counting X-ray detector that detects the X-rays that have passed through a subject, a collection unit that collects counting data that counts the number of X-ray photons for each energy band based on the X-ray detection results from the X-ray detector, a setting unit that sets first and second conditions as band settings that are settings for the energy bands, and a control unit that successively executes a first scan under the first conditions and a second scan under the second conditions on the subject placed on a tabletop. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a photon-counting CT apparatus according to the first embodiment. [Figure 2] FIG. 2 is a flowchart for explaining a series of processing steps of the photon-counting CT apparatus according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing an example of setting the first condition and the second condition according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing an example of setting the first condition and the second condition according to the first embodiment. [Figure 5] FIG. 5 is a diagram illustrating an example of a band setting according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of a photon-counting CT apparatus will be described in detail with reference to the accompanying drawings.

[0009] (First embodiment) The following description will be given taking as an example a photon-counting CT (Photon Counting Computed Tomography: PCCT) device 10 shown in Fig. 1. The photon-counting CT device 10 is a type of X-ray CT device, and includes a photon-counting X-ray detector 112. For example, the photon-counting CT device 10 includes a gantry device 110, a bed device 130, and a console device 140.

[0010] In Fig. 1, the rotation axis of the rotating frame 113 in a non-tilted state or the longitudinal direction of the tabletop 133 of the bed device 130 is defined as the Z-axis direction. The axis direction that is perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction. The axis direction that is perpendicular to the Z-axis direction and vertical to the floor surface is defined as the Y-axis direction. Note that Fig. 1 depicts the gantry device 110 from multiple directions for the purpose of explanation, and shows a case where the photon-counting CT device 10 has one gantry device 110.

[0011] The gantry device 110 includes an X-ray tube 111 , an X-ray detector 112 , a rotating frame 113 , an X-ray high voltage device 114 , a control device 115 , a wedge 116 , a collimator 117 , and a DAS (Data Acquisition System) 118 .

[0012] The X-ray tube 111 is a vacuum tube having a cathode (filament) that generates thermoelectrons and an anode (target) that generates X-rays upon impact of the thermoelectrons. The X-ray tube 111 generates X-rays to be irradiated onto the subject P by irradiating thermoelectrons from the cathode toward the anode when a high voltage is applied from the X-ray high voltage device 114. The X-ray tube 111 is an example of an X-ray generator.

[0013] The X-ray detector 112 is a photon-counting type X-ray detector, which outputs a signal capable of measuring the energy value of an X-ray photon each time an X-ray photon is incident on the detector 112. The X-ray photons incident on the detector 112 are irradiated from the X-ray tube 111 and transmitted through the subject P. The X-ray detector 112 has a plurality of detecting elements that output one pulse of an electric signal (analog signal) each time an X-ray photon is incident on the detector 112. By counting the number of electric signals (pulses), it is possible to count the number of X-ray photons incident on each detecting element. Furthermore, by performing a predetermined arithmetic process on this signal, it is possible to measure the energy value of the X-ray photon that caused the output of the signal. For example, the X-ray detector 112 is an area detector in which a plurality of detecting elements are arranged in the channel direction and the slice direction.

[0014] The above-mentioned detection element is composed of, for example, a scintillator and an optical sensor such as a photomultiplier tube. In this case, the X-ray detector 112 is an indirect conversion type detector that converts incident X-ray photons into scintillator light using the scintillator, and then converts the scintillator light into an electrical signal using an optical sensor such as a photomultiplier tube. As another example, the above-mentioned detection element is a semiconductor detection element such as CdTe (cadmium telluride) or CdZnTe (cadmium zinc telluride) with electrodes arranged on it. In this case, the X-ray detector 112 is a direct conversion type detector that directly converts incident X-ray photons into an electrical signal.

[0015] The rotating frame 113 is an annular frame that supports the X-ray tube 111 and the X-ray detector 112 so that they face each other and rotates the X-ray tube 111 and the X-ray detector 112 using a control device 115. For example, the rotating frame 113 is an aluminum casting. Note that the rotating frame 113 can also support an X-ray high voltage device 114, a wedge 116, a collimator 117, a DAS 118, and the like in addition to the X-ray tube 111 and the X-ray detector 112. Furthermore, the rotating frame 113 can also support various components not shown in FIG. 1 . Hereinafter, the rotating frame 113 and the parts of the gantry device 110 that rotate together with the rotating frame 113 will also be referred to as a rotating unit.

[0016] The X-ray high voltage device 114 has electrical circuits such as a transformer and a rectifier, and includes a high voltage generator that generates a high voltage to be applied to the X-ray tube 111, and an X-ray control device that controls the output voltage according to the X-rays generated by the X-ray tube 111. The high voltage generator may be of a transformer type or an inverter type. The X-ray high voltage device 114 may be provided on the rotating frame 113, or on a fixed frame (not shown).

[0017] The control device 115 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 control device 115 receives input signals from the input interface 143 and controls the operation of the gantry device 110 and the bed device 130. For example, the control device 115 controls the rotation of the rotating frame 113, the tilt of the gantry device 110, the operation of the bed device 130 and the tabletop 133, etc. The control device 115 may be provided in the gantry device 110 or in the console device 140.

[0018] The wedge 116 is a filter for adjusting the amount of X-rays irradiated from the X-ray tube 111. Specifically, the wedge 116 is a filter that transmits and attenuates the X-rays irradiated from the X-ray tube 111 so that the X-rays irradiated from the X-ray tube 111 to the subject P have a predetermined distribution. For example, the wedge 116 is a wedge filter or a bow-tie filter, which is a filter made of processed aluminum or the like so as to have a predetermined target angle and a predetermined thickness.

[0019] The collimator 117 is a lead plate or the like for narrowing the irradiation range of the X-rays that have passed through the wedge 116, and a slit is formed by combining a plurality of lead plates or the like. The collimator 117 is also sometimes called an X-ray aperture. Although FIG. 1 shows a case where the wedge 116 is disposed between the X-ray tube 111 and the collimator 117, the collimator 117 may also be disposed between the X-ray tube 111 and the wedge 116. In this case, the wedge 116 transmits and attenuates the X-rays that are emitted from the X-ray tube 111 and whose irradiation range has been limited by the collimator 117.

[0020] The DAS 118 collects count data by counting the number of X-ray photons for each energy band based on the X-ray detection result by the X-ray detector 112. For example, the DAS 118 has an amplifier that amplifies the electrical signals output from each detection element of the X-ray detector 112 and an A / D converter that converts the electrical signals into digital signals, and collects the count data. The DAS 118 is an example of a collection unit.

[0021] The counting data collected by the DAS 118 is transmitted by optical communication from a transmitter having a light emitting diode (LED) provided on the rotating frame 113 to a receiver having a photodiode provided on a non-rotating portion of the gantry 110 (for example, a fixed frame, etc., not shown in FIG. 1), and then transferred to the console device 140. Here, the non-rotating portion is, for example, a fixed frame that rotatably supports the rotating frame 113. Note that the method of transmitting data from the rotating frame 113 to the non-rotating portion of the gantry 110 is not limited to optical communication, and any non-contact data transmission method or a contact data transmission method may be employed.

[0022] The bed device 130 is a device on which the subject P, who is the subject of the scan, is placed and moved, and includes a base 131, a bed driving device 132, a top plate 133, and a support frame 134. The base 131 is a housing that supports the support frame 134 so that it can move in the vertical direction. The bed driving device 132 is a drive mechanism that moves the top plate 133, on which the subject P is placed, in the longitudinal direction of the top plate 133, and includes a motor, an actuator, etc. The top plate 133, which is provided on the upper surface of the support frame 134, is a plate on which the subject P is placed. Note that the bed driving device 132 may move the support frame 134 in addition to the top plate 133 in the longitudinal direction of the top plate 133.

[0023] The console device 140 includes a memory 141, a display 142, an input interface 143, and a processing circuit 144. Although the console device 140 will be described as being separate from the gantry device 110, the gantry device 110 may include the console device 140 or some of the components of the console device 140.

[0024] The memory 141 is realized by, for example, a semiconductor memory element such as RAM or flash memory, a hard disk, an optical disk, etc. The memory 141 stores, for example, counting data and image data generated based on the counting data. Furthermore, for example, the memory 141 stores a program that enables a circuit included in the photon-counting CT apparatus 10 to realize its function. The memory 141 may also be realized by the cloud.

[0025] The display 142 displays various types of information. For example, the display 142 displays various images generated by the processing circuit 144, or displays a GUI for receiving various operations from the operator. For example, the display 142 is a liquid crystal display or a CRT display. The display 142 may be a desktop type, or may be configured as a tablet terminal or the like capable of wireless communication with the console device 140 main body.

[0026] The input interface 143 accepts various input operations from an operator, converts the accepted input operations into electrical signals, and outputs the electrical signals to the processing circuit 144. For example, the input interface 143 may be implemented by a mouse, keyboard, trackball, switch, button, joystick, a touchpad that performs input operations by touching the operation surface, a touchscreen that integrates a display screen and a touchpad, a non-contact input circuit using an optical sensor, a voice input circuit, or the like. The input interface 143 may be provided in the gantry device 110. The input interface 143 may also be configured as a tablet terminal or the like that can wirelessly communicate with the console device 140 main body. The input interface 143 is not limited to those that include physical operation components such as a mouse and keyboard. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the console device 140 and outputs the electrical signal to the processing circuit 144 is also included as an example of the input interface 143.

[0027] The processing circuitry 144 executes a setting function 144a, a control function 144b, and an output function 144c to control the overall operation of the photon-counting CT apparatus 10. The setting function 144a is an example of a setting unit, and the control function 144b is an example of a control unit.

[0028] For example, the processing circuitry 144 sets various scan conditions by reading and executing a program corresponding to the setting function 144a from the memory 141. Examples of the scan conditions include a band setting, which is a setting of an energy band when collecting count data. Details of the band setting will be described later.

[0029] Furthermore, the processing circuitry 144 reads out from the memory 141 and executes a program corresponding to the control function 144b, thereby performing a scan on the subject P. For example, the control function 144b controls the X-ray high voltage device 114 to supply a high voltage to the X-ray tube 111. As a result, the X-ray tube 111 generates X-rays to be irradiated onto the subject P. The control function 144b also controls the bed driving device 132 to move the subject P into the imaging opening of the gantry device 110. The control function 144b also adjusts the opening and position of the collimator 117. The control function 144b also rotates the rotating unit by controlling the control device 115. While the scan is being performed by the control function 144b, the DAS 118 collects X-ray signals from each detection element in the X-ray detector 112 and generates count data.

[0030] Furthermore, the control function 144b may execute various processes using the count data. For example, the control function 144b performs preprocessing on the count data and performs reconstruction processing on the preprocessed data to generate image data (volume data).

[0031] For example, the control function 144b performs preprocessing such as logarithmic conversion, offset correction, inter-channel sensitivity correction, and beam hardening correction on the count data output from the DAS 118. The count data after preprocessing is also referred to as raw data. The count data before preprocessing and the raw data after preprocessing are also collectively referred to as projection data. Furthermore, the control function 144b reconstructs image data by performing reconstruction processing on the projection data using a filtered back projection method, an iterative reconstruction method, or the like. Furthermore, the control function 144b may perform various image processing based on the collected count data, such as material decomposition processing, which will be described later.

[0032] The processing circuitry 144 also reads out a program corresponding to the output function 144c from the memory 141 and executes it to output various types of information. For example, the output function 144c controls the display on the display 142. For example, the output function 144c also transmits various types of data collected by executing a scan on the subject P to another device. For example, the output function 144c transmits projection data and image data to a PACS (Picture Archiving and Communication System) via a network (not shown) for registration.

[0033] 1, each processing function is stored in the form of a program executable by a computer in memory 141. Processing circuitry 144 is a processor that realizes the function corresponding to each program by reading and executing the program from memory 141. In other words, once a program has been read, processing circuitry 144 has the function corresponding to the read program.

[0034] 1, the setting function 144a, the control function 144b, and the output function 144c are realized by a single processing circuit 144. However, the processing circuit 144 may be configured by combining multiple independent processors, and each processor may execute a program to realize the functions. Furthermore, each processing function of the processing circuit 144 may be realized by being distributed or integrated as appropriate in a single or multiple processing circuits.

[0035] The term "processor" used in the above description refers to circuits 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), and a field programmable gate array (FPGA)). The processor realizes its functions by reading and executing programs stored in memory 141.

[0036] 1, a single memory 141 is described as storing a program corresponding to each processing function. However, the embodiment is not limited to this. For example, a configuration may be adopted in which a plurality of memories 141 are distributed and the processing circuit 144 reads out the corresponding program from each memory 141. Furthermore, instead of storing the program in the memory 141, the program may be directly embedded in the circuit of the processor. In this case, the processor realizes the function by reading and executing the program embedded in the circuit.

[0037] The processing circuitry 144 may also realize its functions by using a processor in an external device connected via a network NW. For example, the processing circuitry 144 reads and executes a program corresponding to each function from the memory 141, and realizes each function shown in FIG. 1 by using a group of servers (cloud) connected to the photon-counting CT apparatus 10 via the network NW as a computational resource.

[0038] The overall configuration of the photon-counting CT device 10, which is a PCCT device, has been described above. Various data can be generated from the count data obtained by counting the number of X-ray photons for each energy band, but the appropriate energy band setting varies depending on the application. Furthermore, while the count data can be converted to combine information from different energy bands, the combined data cannot be divided into energy bands. Given these factors, it is conceivable to set multiple energy bands in advance so that the desired data can be generated later. However, since the data size increases with the number of energy bands, it is preferable to have a small number of energy bands, considering the load of data transmission and storage.

[0039] Therefore, the photon-counting CT apparatus 10 dynamically changes the number of energy bands through processing by the processing circuitry 144, making it possible to acquire target data while suppressing the data size of the count data.

[0040] A series of processes performed by the processing circuitry 144 will be described below with reference to the flowchart shown in Fig. 2. Fig. 2 is a flowchart for explaining the flow of a series of processes performed by the photon-counting CT apparatus according to the first embodiment. Fig. 2 describes a case in which a main scan and a pre-scan for determining the timing to start the main scan are executed consecutively.

[0041] A main scan is a scan performed on a region of interest, including a region suspected of having a disease or a region to be treated, with the purpose of acquiring diagnostic images. A contrast agent may be used in the main scan. By injecting contrast agent into the subject P and performing a main scan when the region of interest is sufficiently filled with contrast agent, diagnostic images of the region of interest can be acquired. A main scan is an example of a second scan.

[0042] When performing a main scan using a contrast agent, it is preferable to start the scan by identifying the timing when the region of interest is filled with the contrast agent. Using a large amount of contrast agent increases the period during which the region of interest is filled with the contrast agent, making it easier to obtain image data showing the region of interest filled with the contrast agent. However, using a large amount of contrast agent can cause side effects on the subject P. Performing a CT scan over a long period of time also makes it easier to obtain image data showing the region of interest filled with the contrast agent, but this increases the subject P's radiation exposure. Therefore, in order to reduce the amount of contrast agent used and the subject P's radiation exposure, it is preferable to start the scan by identifying the appropriate timing when the region of interest is filled with the contrast agent and complete the scan in a short time. For these reasons, in FIG. 2, a pre-scan is performed to determine the timing to start the main scan. The pre-scan is an example of a first scan.

[0043] Specifically, the pre-scan collects data for estimating the amount of contrast agent present in a monitoring region set near the region of interest. For example, when a contrast agent is injected into a blood vessel, the monitoring region is set upstream of the region of interest in the blood flow. By transitioning to the main scan when the contrast agent reaches the monitoring region, diagnostic images can be collected with the region of interest sufficiently enhanced.

[0044] First, the setting function 144a sets a first condition as the setting of the energy band during the pre-scan (step S101). The first condition is a condition suitable for generating data for estimating the amount of contrast agent present. For example, for a substance in which the k-absorption edge (k-edge) appears, such as an iodine-based contrast agent, an enhanced image can be generated by K-edge imaging. Therefore, the setting function 144a sets two energy bands with the k-absorption edge as a threshold as the first condition.

[0045] Next, the control function 144b starts a pre-scan under the first condition set by the setting function 144a (step S102). Specifically, the control function 144b causes the X-ray tube 111 to irradiate an area including a monitoring region of the subject P with X-rays. The pre-scan may be performed while rotating the rotating unit in the photon-counting CT apparatus 10, or may be performed without rotating the rotating unit.

[0046] While the pre-scan is being performed, the DAS 118 collects count data of the monitoring area under a first condition (step S103) based on the X-ray detection result by the X-ray detector 112. For example, the DAS 118 collects count data by counting the number of X-ray photons for each of two energy bands with the k-absorption edge as a threshold.

[0047] The control function 144b also estimates the amount of contrast agent present in the monitoring region based on the count data collected during the pre-scan (step S104), and determines whether to proceed to the main scan based on the result of estimating the amount of contrast agent present (step S105).

[0048] For example, the control function 144b calculates the difference between the count values ​​(count numbers) in two energy bands set with the k-absorption edge as a threshold. When a contrast agent flows into the monitoring region and a substance having the k-absorption edge is present on the X-ray path, the difference between the count values ​​increases. This difference value is an index indicating the amount of contrast agent present, and can be used to determine whether to proceed to a main scan by comparing it with a threshold, for example. This difference value may be acquired based on reconstructed image data or on projection data before reconstruction. This means that the reconstruction process can be omitted when determining whether to proceed to a main scan.

[0049] If the main scan is not to be started (No in step S105), the process returns to step S103, where the collection of counting data and the estimation of the amount of contrast agent are continued. On the other hand, if the main scan is to be started (Yes in step S105), the setting function 144a sets a second condition as the setting of the energy band during the main scan (step S106). Furthermore, the control function 144b starts the main scan under the second condition (step S107) and collects counting data in the region of interest (step S108). Note that the timing for setting the second condition is not limited to the example shown in FIG. 2, and it may be set before step S105. For example, step S101 and step S106 may be integrated, and the first and second conditions may be set before the start of the pre-scan.

[0050] The second condition is set according to the purpose of diagnosis. For example, the setting function 144a sets the second condition according to the tissues and parts included in the region of interest. Also, for example, the setting function 144a sets the second condition according to the disease that the subject P is suffering from or is suspected of suffering from. For example, the setting function 144a sets the second condition so that the signal-to-noise ratio (SN) of fatty organs can be optimized.

[0051] An example of setting the first and second conditions is shown in Figure 3. In each graph in Figure 3, the horizontal axis represents the energy (keV) of the X-rays, and the vertical axis represents the photon count value. As shown by the curves in Figure 3, the X-rays used in CT scans are polychromatic X-rays with a range of energies.

[0052] 3 shows an example of setting the first condition, in which two energy bands are set with a threshold value Th11 as the threshold value. The threshold value Th11 is set, for example, to match the k-absorption edge of a substance contained in the contrast agent.

[0053] On the other hand, the right diagram in Fig. 3 shows an example of setting the second condition, in which two energy bands are set with a threshold value Th12 as the threshold. For example, when transitioning from pre-scan to main scan, the control function 144b changes the energy band settings as shown in Fig. 3. For example, the threshold value Th12 is set so that data that meets the purpose of diagnosis can be generated.

[0054] When multiple energy bands are set and a main scan is performed, it is possible to optimize the contrast of a specific medium or obtain functional images such as K-edge imaging depending on the diagnostic purpose. For example, when two energy bands are set as shown in Figure 3, the control function 144b can perform material decomposition processing to estimate the abundance of each of the two reference materials. The material decomposition processing can be performed, for example, by solving the following equations (1) and (2).

[0055]

number

[0056]

number

[0057] In Equations (1) and (2), "N(bin1)" is the count value of the energy bin "bin1." That is, "N(bin1)" is the number of X-ray photons having the X-ray energy included in the energy bin "bin1" among the X-ray photons incident on the X-ray detector 112. Similarly, "N(bin2)" is the count value of the energy bin "bin2." "u1(bin1)" indicates the linear attenuation coefficient of the first reference material at the energy bin "bin1," "u2(bin1)" indicates the linear attenuation coefficient of the second reference material at the energy bin "bin1," "u1(bin2)" indicates the linear attenuation coefficient of the first reference material at the energy bin "bin2," and "u2(bin2)" indicates the linear attenuation coefficient of the second reference material at the energy bin "bin2." The values ​​of these linear attenuation coefficients are known. "L1" is the path length through which material 1 exists, and "L2" is the path length through which material 2 exists. "L1" and "L2" can be obtained by solving the simultaneous equations of Equation (1) and Equation (2). Note that the material decomposition process may be performed on the projection data or on the reconstructed image data.

[0058] The control function 144b can generate, for example, a reference material image in which the reference material is emphasized as a result of the material decomposition process. For example, when two energy bands are set, a reference material image in which the first reference material is emphasized and a reference material image in which the second reference material is emphasized can be generated, respectively. Note that the selection of the reference material can be predicted based on the purpose of diagnosis, and the setting function 144a can set the energy band in the main scan according to the reference material. For example, when the disease of the subject P is bone marrow edema, the setting function 144a can set two energy bands so as to improve the separation ability between "calcium" and "water."

[0059] Furthermore, the control function 144b can generate various images such as a virtual monochromatic X-ray image (also referred to as a monochromatic image) at a predetermined energy, a density image, an effective atomic number image, etc. by performing weighting calculation processing based on the mixing ratio of each reference material using a plurality of reference material images. In addition, the output function 144c can display the generated various image data on the display 142.

[0060] As described above, the photon-counting CT apparatus 10 according to the first embodiment includes the X-ray tube 111, the X-ray detector 112, the DAS 118, a setting function 144a, and a control function 144b. The X-ray tube 111 generates X-rays. The X-ray detector 112 is a photon-counting X-ray detector that detects X-rays that have passed through the subject P. The DAS 118 collects count data that counts the number of X-ray photons for each energy band based on the X-ray detection results from the X-ray detector 112. The setting function 144a sets first and second conditions as band settings that set the energy bands. The control function 144b consecutively performs a first scan under the first conditions and a second scan under the second conditions on the subject P placed on the top board 133. This allows the photon-counting CT apparatus 10 to acquire target data while suppressing the data size of count data collected using the photon-counting X-ray detector 112.

[0061] For example, as described with reference to Figures 2 and 3, the photon-counting CT device 10 can acquire data according to the purpose of the pre-scan and data according to the purpose of the main scan. That is, the photon-counting CT device 10 can set an energy band suitable for determining the accumulation state of the contrast agent in the pre-scan, and set an energy band according to the diagnostic purpose in the main scan, and collect count data. Furthermore, the number of energy bands (number of bins) set in the pre-scan and main scan is two, which can be said to be the minimum data size for count data obtained by PCCT. In this way, the photon-counting CT device 10 can reduce the data size of the count data and reduce the burden associated with data transmission and storage while capturing images advantageous for PCCT.

[0062] Reducing the data size of count data can provide various benefits. First, by reducing storage and line usage, data management costs can be reduced. Furthermore, reducing data size shortens the time required to transmit and process count data, improving the real-time nature of processing based on count data. For example, reducing the data size of count data collected in a pre-scan speeds up the process of estimating the amount of contrast agent present, enabling more accurate determination of the timing to transition to a main scan.

[0063] Furthermore, the number of energy bands is not the only parameter that affects the data size of the counting data. For example, the pixel size, the number of views, the dynamic range, and other parameters also affect the data size of the counting data.

[0064] The pixel size is a condition for binning the detector elements of the X-ray detector 112. Binning is a process in which multiple detector elements (detector element group) in the X-ray detector 112 are treated as one pixel, and signals collected by the detector element group are bundled together and handled as a single signal. The more detector elements in a detector element group, the smaller the data size of the count data. The number of views is the number of data in the time direction. For example, the more frequently the DAS 118 reads signals from the X-ray detector 112, the greater the number of views and the larger the data size of the count data. The dynamic range is the data area assigned to each count value. For example, if the dynamic range is excessively small and a high dose of X-rays is incident, the count value may overflow, making it impossible to properly collect the count data. It is preferable to set the dynamic range so that overflow does not occur, but the larger the dynamic range, the larger the data size of the count data.

[0065] In the photon-counting CT apparatus 10, an increase in data size due to reducing the pixel size, increasing the number of views, or widening the dynamic range may be offset by a reduction in data size due to reducing the number of energy bands. That is, the photon-counting CT apparatus 10 may reduce the data size of the count data according to the above-described embodiment, or may adjust various scan conditions while suppressing an increase in data size.

[0066] 3 shows an example in which the number of energy bands is maintained and only the thresholds between the energy bands are changed when transitioning from pre-scan to main scan. However, the embodiment is not limited to this, and the number of energy bands may also be changed.

[0067] For example, as the second condition, the setting function 144a sets four energy bands, with the thresholds between the energy bands being thresholds Th13, Th14, and Th15, as shown in the right diagram of FIG. 4. That is, the photon-counting CT apparatus 10 acquires detailed information only in the main scan so as to ensure necessary information. In this case, although the data size of the count data collected in the main scan increases, information necessary for diagnosis should be collected. Also, in the case shown in FIG. 4, only two energy bands are set for the pre-scan, and the data size of the count data is suppressed.

[0068] (Second embodiment) In the first embodiment described above, a case where a pre-scan and a main scan are executed consecutively has been described as an example. However, the embodiment is not limited to this, and can be similarly applied to other cases where a plurality of scans are executed consecutively on the subject P.

[0069] The photon-counting CT device 10 according to the second embodiment has a configuration similar to that of the photon-counting CT device 10 shown in Fig. 1, with some differences in the processing by the setting function 144a and the control function 144b. Hereinafter, the same reference numerals as in Fig. 1 will be used to designate the points described in the first embodiment, and further description will be omitted.

[0070] For example, a case may be assumed in which multiple regions of interest are set for the subject P, and diagnostic images for each region of interest are acquired. Alternatively, a case may be assumed in which multiple diagnostic images are acquired for one region of interest under different scan conditions. That is, a case may be assumed in which multiple main scans are performed consecutively. In such a case, the setting function 144a can set first conditions according to the diagnostic purpose of the first scan, and set second conditions according to the diagnostic purpose of the second scan.

[0071] In addition, a positioning scan may be performed before the main scan to determine the scan range for the main scan. The positioning scan is also called scanogram or scout scan. In this case, the setting function 144a sets a first condition to obtain data suitable for the positioning process, and can set a second condition depending on the purpose of diagnosis. For example, if the purpose of the main scan is to collect diagnostic images of a specific organ, the setting function 144a can improve the accuracy of the positioning process by setting a first condition to optimize the contrast of the organ.

[0072] The first and second conditions may differ only in the thresholds between energy bands, or in the number of energy bands. For example, if the first scan is more important than the second scan, the first condition may be set to have a larger number of energy bands.

[0073] Furthermore, each of the multiple scans executed consecutively may be a full scan that collects projection data over a 360° view range, or a half scan that collects projection data over a view range that is 180° greater than the X-ray fan angle. The fan angle is an angle that indicates the spread of X-rays emitted from the X-ray tube 111 and detected by the X-ray detector 112. Specifically, as shown by the dotted line in FIG. 1, the X-rays emitted from the X-ray tube 111 spread in a fan shape on the XY plane (the axial plane of the subject P), and the fan angle corresponds to the central angle of the fan shape. While the specific value of the fan angle when performing a half scan is not particularly limited, the fan angle is often about 45°. In this case, half reconstruction can be performed by collecting projection data over a view range of about 225°.

[0074] In the various examples described in the first and second embodiments, the switching between the first and second conditions may be performed for each rotation of the rotating part, or may be performed for one or more views. For example, when a half scan is performed as the first scan, the second scan can be performed as soon as data in the view range required for half reconstruction is collected, without waiting for one rotation of the rotating part.

[0075] (Third embodiment) In the above-described first and second embodiments, examples have been described in which a plurality of scans are successively performed on the subject P placed on the tabletop 133, and an energy band is set for each scan. However, the embodiments are not limited to this. In the third embodiment, an example in which a plurality of energy bands are set for one scan will be described.

[0076] The photon-counting CT device 10 according to the third embodiment has a configuration similar to that of the photon-counting CT device 10 shown in Fig. 1, with some differences in the processing by the setting function 144a and the control function 144b. Hereinafter, the same reference numerals as in Fig. 1 will be used to designate the same parts as those described in the first and second embodiments, and further description will be omitted.

[0077] Specifically, the setting function 144a sets a reference condition and an opposing condition as the setting of the energy bands in one scan. The reference condition and the opposing condition will be described with reference to FIG. 5. FIG. 5 is a diagram showing an example of band setting according to the third embodiment. In FIG. 5, energy band S, energy band T, and energy band U are set as the reference condition. Furthermore, energy band V, energy band W, and energy band Z are set as the opposing condition.

[0078] In the following description, an arbitrary view is defined as the first view, and a view at a position opposite to the first view (a position 180° opposite) is defined as the second view. When a reference condition is set for the first view, an opposite condition is set for the second view. For example, the control function 144b can switch between the reference condition and the opposite condition every time the rotating unit rotates 180°, thereby executing a scan such that the reference condition is set for the first view and the opposite condition is set for the second view. Alternatively, the control function 144b can switch between the reference condition and the opposite condition for each one or more views, thereby executing a scan such that the reference condition is set for the first view and the opposite condition is set for the second view.

[0079] Comparing the first and second views, we can see that although the X-ray irradiation directions are opposite, the paths along which the X-rays pass overlap. This means that by post-processing the counting data collected in the first and second views, it is possible to obtain information about a finer energy band.

[0080] 5 can be divided into six smaller energy bands (energy band a, energy band b, energy band c, energy band d, energy band e, and energy band f). The count values ​​in energy bands S to U are known from the count data collected in the first view, and the count values ​​in energy bands V to Z are known from the count data collected in the second view, but the count values ​​in energy bands a to f are unknown.

[0081] Here, the sum of the count value in energy band a and the count value in energy band b matches the count value in energy band S. That is, an equation can be set for the relationship between energy bands a and b and energy band S. Similarly, an equation can be set for the relationship between energy bands c and d and energy band T. Similarly, an equation can be set for the relationship between energy bands e and f and energy band U. Similarly, an equation can be set for the relationship between energy bands b and c and energy band V. Similarly, an equation can be set for the relationship between energy bands d and e and energy band W. Similarly, an equation can be set for the relationship between energy band f and energy band Z. In this way, in the example shown in FIG. 5, six equations can be set and there are six unknowns, so the count values ​​in the energy bands a to f can each be calculated by solving simultaneous equations.

[0082] 5, although the number of energy bands of counting data collected in each view is three (energy bands S to U or energy bands V to Z), count values ​​for each of six energy bands (energy bands a to f) can be obtained by post-processing. That is, the photon-counting CT apparatus 10 according to the third embodiment can appropriately obtain target data by post-processing while suppressing the data size of the collected counting data.

[0083] The processing according to the third embodiment may be performed in combination with the processing according to the first and second embodiments, or may be performed separately. For example, when multiple scans are performed consecutively, the control function 144b performs some or all of the multiple scans so that the reference conditions are set for the first view and the opposing conditions are set for the second view. Alternatively, when only one scan is performed, the control function 144b performs the one scan so that the reference conditions are set for the first view and the opposing conditions are set for the second view.

[0084] (Fourth embodiment) In the third embodiment described above, an example in which reference conditions and opposing conditions are set as a case in which multiple energy bands are set for one scan is described. In the fourth embodiment, another example in which multiple energy bands are set for one scan is described.

[0085] The photon-counting CT device 10 according to the fourth embodiment has a configuration similar to that of the photon-counting CT device 10 shown in Fig. 1, with some differences in the processing by the setting function 144a and the control function 144b. Hereinafter, the same reference numerals as in Fig. 1 will be used to designate the same parts as those described in the first to third embodiments, and further description will be omitted.

[0086] Even when only one scan is performed, there may be multiple targets of interest. For example, multiple types of contrast agents may be injected into the subject P, and the accumulation of each agent may be of interest. For example, a first iodine-based contrast agent and a second gadolinium-based contrast agent may be injected into the subject P.

[0087] In this case, the setting function 144a sets a first contrast agent condition according to the first contrast agent and a second contrast agent condition according to the second contrast agent, and the control function 144b executes a scan on the subject P while switching between the first contrast agent condition and the second contrast agent condition. For example, control function 144b performs a scan while switching between the first contrast agent condition and the second contrast agent condition every time the rotating unit rotates 180°. Also, for example, control function 144b performs a scan while switching between the first contrast agent condition and the second contrast agent condition for one or more views. Control function 144b may switch between the first contrast agent condition and the second contrast agent condition so that the first contrast agent condition is used for a first view and the second contrast agent condition is used for a second view opposite to the first view.

[0088] The components of each device according to the above-described embodiments are conceptual and functionally independent, and are not necessarily physically configured as shown in the drawings. In other words, the specific form of distribution and integration of each device is not limited to that shown in the drawings, and all or part of each device can be functionally or physically distributed and integrated in any unit depending on various loads, usage conditions, etc. Furthermore, all or any part of the processing functions performed by each device can be realized by a CPU and a program analyzed and executed by the CPU, or can be realized as hardware using wired logic.

[0089] The methods described in the above embodiments can be realized by executing a prepared program on a computer such as a personal computer or a workstation. This program can be distributed via a network such as the Internet. This program can also be recorded on a non-transitory computer-readable recording medium such as a hard disk, flexible disk (FD), CD-ROM, MO, or DVD, and executed by being read from the recording medium by a computer.

[0090] According to at least one of the embodiments described above, it is possible to obtain target data while suppressing the data size of count data collected using a photon counting X-ray detector.

[0091] 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, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0092] 10: Photon counting CT device 111:X-ray tube 112: X-ray detector 118:DAS 144: Processing circuit 144a: Setting function 144b: Control function 144c: Output function

Claims

1. an X-ray generator that generates X-rays; a photon counting X-ray detector that detects the X-rays that have passed through the subject; a collection unit that collects count data obtained by counting the number of X-ray photons for each energy band based on the detection result of the X-rays by the X-ray detector; a setting unit that sets a first condition and a second condition as a band setting that is a setting of the energy band; a control unit that successively executes a first scan under the first conditions and a second scan under the second conditions on the subject placed on a top plate; A photon-counting CT device comprising:

2. the first scan is a pre-scan for determining a timing to start the second scan; the second scan is a main scan for acquiring a diagnostic image in which a region of interest in the subject is enhanced with a contrast agent; the setting unit sets a condition according to a type of the contrast agent as the first condition, and sets a condition according to a diagnostic purpose for the region of interest as the second condition; 2. The photon-counting CT apparatus according to claim 1, wherein the control unit determines the timing by detecting the contrast agent based on the projection data collected in the first scan, and performs the first scan and the second scan consecutively.

3. The photon-counting CT apparatus according to claim 2 , wherein the setting unit sets, as the second condition, a condition in which the number of the energy bands is greater than that of the first condition.

4. the setting unit sets a reference condition and an opposing condition as the band setting, 2. The photon-counting CT apparatus according to claim 1, wherein the control unit executes scanning such that, in at least one of the first scan and the second scan, the reference condition is satisfied in a first view and the opposing condition is satisfied in a second view at a position opposite to the first view.

5. 2. The photon-counting CT device according to claim 1, wherein the control unit performs the first scan and the second scan consecutively by switching between the first condition and the second condition within a view range that is 180° greater than the fan angle of the X-rays.

6. the setting unit sets, as the band setting, a first contrast agent condition according to a first contrast agent injected into the body of the subject, and a second contrast agent condition according to a second contrast agent injected into the body of the subject; The photon-counting CT apparatus according to claim 1 , wherein the control unit executes at least one of the first scan and the second scan while switching between a first contrast agent condition and a second contrast agent condition.

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