Radiation imaging apparatus, method, program, and photon counting detector

Abstract

To satisfactorily perform material decomposition regardless of whether a material included in the body of a subject has a discontinuous structure of absorption such as a K edge in a measurement energy region, in a radiation imaging apparatus, method and program, and a photon counting type detector.SOLUTION: Processing is performed on projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins. Substance decomposition of a subject is performed on the basis of a plurality of pieces of calibration data representing an energy spectrum of a predetermined calibration member and an energy spectrum of an energy region on at least one side with reference to an absorption edge of photon energy of a substance assumed to be present in a body of the subject at the time of imaging of the subject in projection data acquired by measuring the subject with a photon counting detector.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a radiographic apparatus, a method and a program, and a photon-counting detector. [Background technology]

[0002] Photon-counting computed tomography (PCCT) systems equipped with photon-counting detectors, which employ the photon-counting method, are known. Photon-counting detectors can measure photon energy, which is the energy of incident radiation photons. Therefore, PCCT systems can obtain material-resolved images in which materials with different compositions are resolved, such as medical images in which iodine contrast agents used in angiography and calcified plaques in blood vessels are resolved into material-resolved images. To obtain material-resolved images, the detector is calibrated. For this purpose, calibration is performed in advance for each detector element, in which the relationship between output and photon energy measured by the photon-counting detector for combinations of multiple base materials with known compositions and thicknesses is obtained as calibration data.

[0003] For example, Patent Documents 1 and 2 disclose a calibration method using a calibration member containing a substance with a relatively small effective atomic number, such as acrylic or polyethylene, as a first basis substance, and a substance with a relatively large effective atomic number, such as aluminum, a calcium mixture, an iodine mixture, or tin, as a second basis substance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-108073 [Patent Document 2] Patent Publication No. 2021-108954 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, the photon absorption (attenuation) of a material generally tends to decrease as the photon energy increases, but it is known that there are singular points such as the K absorption edge (also called K edge) that show a discontinuous structure in absorption at certain photon energies. The energy position of the K edge varies depending on the material, and the larger the atomic number, the higher the K edge appears at energy.

[0006] Here, the subject may contain substances other than those of the human body due to the injection of a drug as a contrast agent into the subject, the presence of artificial objects (gold teeth, bolts for fixing bones, embolization coils for blood clots, etc.) within the subject's body, etc. Since each of these substances has a different absorption edge, it is preferable to perform calibration using these substances individually in order to perform material decomposition with high accuracy.

[0007] However, it is extremely time-consuming to calibrate for all substances, such as drugs that may be used during imaging and metals that may be present in the subject's body. Furthermore, it is possible that more substances will be used as contrast agents in the future. For example, the use of gadolinium (atomic weight 64), gold (atomic weight 79), and barium (atomic weight 83) is being considered.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to enable good material decomposition regardless of whether or not the material contained in the body of the subject has a discontinuous absorption structure such as a K-edge within the measurement energy range. [Means for solving the problem]

[0009] A radiation imaging apparatus according to the present disclosure is a radiation imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, a storage unit configured to store a plurality of calibration data representing energy spectra of a plurality of types of calibration members each formed of a combination of one or more types of base materials differing in at least one of composition and thickness, the calibration data being obtained by measuring the calibration members using a photon counting detector; a processor; The processor performs material decomposition of the subject based on the calibration data and the energy spectrum of the energy region on at least one side of the absorption edge of the photon energy of a substance assumed to be present inside the subject at the time of imaging, in the projection data acquired by measuring the subject with a photon counting detector.

[0010] In the radiation imaging apparatus according to the present disclosure, the processor may perform material decomposition of the object based on an energy spectrum on the high energy side of the absorption edge and an energy spectrum on the low energy side of the absorption edge in the projection data.

[0011] In the radiation imaging apparatus according to the present disclosure, the processor may perform material decomposition of the object based on the energy spectrum on the high energy side of the absorption edge in the projection data and the energy spectrum in the entire energy range in the projection data.

[0012] In the radiation imaging apparatus according to the present disclosure, the processor may perform material decomposition of the object based on the energy spectrum on the low energy side of the absorption edge in the projection data and the energy spectrum in the entire energy range in the projection data.

[0013] In the radiographic imaging apparatus according to the present disclosure, the processor may perform material decomposition of the subject based on the energy spectrum on the high-energy side of the absorption edge in the projection data, the energy spectrum on the low-energy side of the absorption edge, and the energy spectrum in the entire energy range in the projection data.

[0014] In the radiation imaging apparatus according to the present disclosure, the number of the plurality of energy bins may be 3 or more and 8 or less.

[0015] A radiation imaging apparatus according to the present disclosure is a radiation imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, A radiographic imaging method for a radiographic imaging apparatus including a storage unit that stores a plurality of calibration data representing energy spectra of a plurality of types of calibration members each made of a combination of one or more types of base materials that differ in at least one of composition and thickness, the calibration data being obtained by measuring the calibration members using a photon counting detector, the method comprising: The material decomposition of the subject is performed based on the energy spectrum of at least one energy region on either side of the absorption edge of the photon energy of a substance assumed to be present inside the subject at the time of imaging, in the calibration data and projection data acquired by measuring the subject with a photon counting detector.

[0016] A radiography program according to the present disclosure is a radiography apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, A radiographic imaging program that causes a computer to function as a radiographic imaging apparatus having a storage unit that stores a plurality of calibration data representing energy spectra of a plurality of types of calibration members each formed of a combination of one or more types of base materials that differ in at least one of composition and thickness, the calibration data being obtained by measuring the calibration members using a photon counting detector, the program comprising: The computer executes a procedure for decomposing materials in the subject based on the calibration data and the energy spectrum in at least one energy region on either side of the absorption edge of the photon energy of a substance assumed to be present inside the subject at the time of imaging the subject, in projection data acquired by measuring the subject with a photon counting detector.

[0017] The technology of the present disclosure can also be applied to programs and program products. [Effects of the Invention]

[0018] According to the present disclosure, material decomposition can be performed satisfactorily regardless of whether the material contained in the body of the subject has a discontinuous absorption structure such as a K-edge within the measurement energy range. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic configuration diagram of a medical image capturing system including a radiation imaging apparatus according to an embodiment of the present disclosure; [Figure 2] Diagram for explaining an example of energy bin settings [Figure 3] FIG. 1 is a diagram showing the hardware configuration of a radiation imaging apparatus according to an embodiment of the present invention. [Figure 4] FIG. 1 is a diagram showing the functional configuration of a radiation imaging apparatus according to an embodiment of the present invention. [Figure 5] Diagram for explaining the detector calibration method [Figure 6] Diagram showing the K-edge of gadolinium [Figure 7] FIG. 1 is a diagram for explaining material decomposition according to this embodiment. [Figure 8] A flowchart showing the processing performed in this embodiment [Figure 9] Another example of how to divide the energy range [Figure 10] Another example of how to divide the energy range [Figure 11] Another example of how to divide the energy range [Figure 12] FIG. 10 is a diagram illustrating another example of energy bin settings. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. First, an example of the configuration of a medical image capturing system including a radiation imaging apparatus according to the present embodiment will be described. Fig. 1 is a schematic diagram of the configuration of a medical image capturing system including a radiation imaging apparatus according to the present embodiment.

[0021] As shown in Fig. 1, a medical imaging system 1 of this embodiment includes a CT device 2 and a console 3. The CT device 2 includes a gantry 4 and a bed 8. In the following description, the horizontal direction in Fig. 1 is defined as the X-axis, the vertical direction as the Y-axis, and the direction perpendicular to the XY plane as the Z-axis.

[0022] The gantry 4 has an opening 4A, and the subject H to be imaged is placed inside the opening 4A while being placed on a bed 8. The gantry 4 and the bed 8 are capable of moving relatively in the Z-axis direction.

[0023] Inside the gantry 4, a radiation source 5 having a radiation tube 6 and a bowtie filter 7, and a detector 9 are arranged facing each other with the subject H in between. The bowtie filter 7 optimizes the radiation exposure by increasing the dose near the center and decreasing the dose on the periphery to reduce the radiation exposure in the peripheral area. The radiation emitted from the radiation tube 6 is shaped by the bowtie filter 7 into a beam suitable for the size of the subject H and is then irradiated onto the subject H. The detector 9 detects the radiation that has passed through the subject H and generates projection data according to the count of photons of the detected radiation. As an example, the detector 9 in this embodiment is a photon-counting detector in which a plurality of detection elements 9P that detect photon energy, which is the energy of photons of the incident radiation, are arranged in an arc shape centered on the focal point of the radiation tube 6.

[0024] In this embodiment, X-rays are used as an example of radiation, but the radiation is not limited to this and gamma rays or the like may also be used.

[0025] In this embodiment, the detector 9 detects the photon energy of the incident radiation by dividing it into a plurality of energy bins. In particular, in this embodiment, one boundary of the plurality of energy bins of the detector 9 is set to coincide with the absorption edge of the photon energy of a substance that is expected to be present inside the body of the subject H when the subject H is imaged.

[0026] Fig. 2 is a diagram for explaining an example of setting energy bins. Fig. 2 shows the relationship between radiation energy and attenuation coefficient for a certain substance that is assumed to be present inside the body of subject H. In Fig. 2, the horizontal axis represents radiation energy (keV) and the vertical axis represents attenuation coefficient.

[0027] Substances that are expected to be present in the body of subject H include iodine, gadolinium, barium, and gold used as contrast agents, embolization coils (platinum and tungsten), gold teeth, and bolts (titanium) for fixing bones. Figure 2 shows the attenuation coefficient of gadolinium, which is used as a contrast agent, and shows a K-absorption edge (also called K-edge) around 50 keV, which indicates a sudden change in the attenuation coefficient.

[0028] In this embodiment, a gadolinium contrast agent is present in the subject. In this case, energy bins are set so that one boundary of the energy bins coincides with the K-edge of gadolinium. For example, in FIG. 2, energy bins B1 and B2 are set at 20 to 35 keV and 35 to 50 keV, respectively, which are lower in energy than the K-edge, and energy bins B3 and B4 are set at 50 to 85 keV and 85 keV to 120 keV, respectively, which are higher in energy than the K-edge. This results in a total of four energy bins. In this embodiment, "coinciding with the K-edge" does not necessarily mean that the boundary coincides exactly with the energy of the K-edge, but may also include a deviation of, for example, approximately ±1 keV. Furthermore, the energy of the K-edge may be included in either energy bin B1 or energy bin B2.

[0029] For the energy bin B3 of 50 to 85 keV, the lower limit is 50 keV, which is the K edge.

[0030] The radiation tube 6 and the detector 9 are rotated around the subject H by a rotation drive unit (not shown) of the gantry 4. By repeating the irradiation of radiation from the radiation tube 6 and the detection of radiation by the detector 9 as they both rotate, data about the subject H (hereinafter referred to as projection data) is acquired for each projection path of the radiation. The projection data acquired by the detector 9 is output to the console 3 and stored in the storage of the console 3. The data value corresponding to each detection element 9P, which is the smallest unit of projection data, is the count number of photons detected by the detection element 9P. Projection data is acquired individually for each energy bin.

[0031] The dose of radiation emitted from the radiation tube 6, the rotation speed of the gantry 4, and the relative movement speed between the gantry 4 and the bed 8 are set by the console 3 based on the acquisition conditions for acquiring projection data input by a user such as a technician.

[0032] The console 3 of this embodiment performs control related to acquisition of projection data, generation of medical images, control related to material decomposition, etc. The console 3 is an example of a radiation imaging apparatus of the present disclosure.

[0033] Next, a radiographic imaging apparatus according to this embodiment will be described. First, the hardware configuration of the radiographic imaging apparatus according to this embodiment will be described with reference to Fig. 3. As shown in Fig. 3, the radiographic imaging apparatus 10 is a computer such as a workstation, a server computer, or a personal computer, and includes a CPU (Central Processing Unit) 11, nonvolatile storage 13, and memory 16 as a temporary storage area.

[0034] The radiation imaging apparatus 10 also includes a display 14, an input device 15, and an I / F (Interface) 17. The CPU 11, the storage 13, the display 14, the input device 15, the memory 16, and the I / F 17 are connected to a bus 18. The CPU 11 is an example of a processor in the present disclosure.

[0035] The storage 13 is realized by a hard disk drive (HDD), a solid state drive (SSD), a flash memory, or the like. The storage 13 as a storage medium stores a radiography program 12 installed in the radiography apparatus 10. The CPU 11 reads the radiography program 12 from the storage 13, expands it in the memory 16, and executes the expanded radiography program 12. The storage 13 also stores calibration data, which will be described later. The storage 13 is an example of a storage unit of the present disclosure.

[0036] The display 14 is a device that displays various screens, and is, for example, a liquid crystal display or an EL (Electro Luminescence) display.

[0037] The input device 15 is used by the user to input scan conditions for acquiring projection data, instructions and various information regarding image generation and display, etc. Examples of the input device 15 include various switches, buttons, a touch panel, a touch pen, a keyboard, and a mouse. The display 14 and the input device 15 may be integrated into a touch panel display.

[0038] The I / F 17 communicates various types of information with a rotation drive unit (not shown) of the gantry 4, the radiation source 5, and the detector 9 via wired or wireless communication.

[0039] The radiation imaging program 12 is stored in a state accessible from the outside in a storage device of a server computer connected to a network or in a network storage, and is downloaded and installed in response to a request into a computer constituting the radiation imaging apparatus 10. Alternatively, the program is recorded on a recording medium such as a DVD (Digital Versatile Disc) or a CD-ROM (Compact Disc Read Only Memory) and distributed, and is installed from the recording medium into a computer constituting the radiation imaging apparatus 10.

[0040] Next, the functional configuration of the radiation imaging apparatus according to this embodiment will be described. Fig. 4 is a diagram showing the functional configuration of the radiation imaging apparatus according to this embodiment. As shown in Fig. 4, the radiation imaging apparatus 10 includes an information acquisition unit 21, a material decomposition unit 22, and a display control unit 23. The CPU 11 executes the radiation imaging program 12 to function as the information acquisition unit 21, the material decomposition unit 22, and the display control unit 23.

[0041] The information acquisition unit 21 receives the projection data P0 and the calibration data C0 from the CT apparatus 2 via the I / F 17. The calibration data C0 is acquired by calibrating the detector 9 using a calibration member. The calibration will be described below.

[0042] A medical imaging system 1 equipped with a detector 9 that is a photon-counting detector can acquire projection data for each energy bin of the subject H (i.e., the energy spectrum for each projection path), thereby generating material decomposition images in which materials with different compositions are decomposed, and medical images separated into multiple energy components. In order to obtain such material decomposition images, it is necessary to acquire calibration data C0 that represents the relationship between the output and photon energy when a combination of multiple basis materials, which are materials with known compositions and thicknesses, is measured by the detector 9. Calibration refers to the acquisition of such calibration data C0.

[0043] An example of a method for calibrating the detector 9, which is a photon-counting detector, will be described below. FIG. 5 is a diagram illustrating the detector calibration method. A calibration member made of a combination of one or more basis materials with known compositions and thicknesses is used to calibrate the detector 9, which is a photon-counting detector. In FIG. 5, the calibration member 30 is made of a combination of two types of basis materials, a first basis material 30A and a second basis material 30B. The first basis material 30A and the second basis material 30B have different attenuation coefficients for radiation. In this embodiment, the second basis material 30B has a larger attenuation coefficient than the first basis material 30A. For example, the first basis material 30A can be acrylic (a soft tissue-equivalent material), and the second basis material 30B can be aluminum (a bone-equivalent material), which has a larger attenuation coefficient than acrylic.

[0044] 5, two first basis materials 30A each having a unit thickness are combined with two second basis materials 30B each having a unit thickness. In this manner, calibration data C0 is obtained for each combination 32 of the thicknesses of the first basis materials 30A and the second basis materials 30B in the radiation transmission direction. For example, if there are M different thicknesses of the first basis materials 30A and N different thicknesses of the second basis materials 30B, M×N sets of calibration data C0 can be obtained by combining 32 the M×N types of basis materials.

[0045] Specifically, in the example shown in FIG. 5, if a calibration member 30 that does not use the first basis material 30A is defined as a calibration member 30 in which the thickness of the first basis material 30A is "0 (zero)," there are M = 3 different thicknesses of the first basis material 30A. Similarly, if a calibration member 30 that does not use the second basis material 30B is defined as a calibration member 30 in which the thickness of the second basis material 30B is "0 (zero)," there are K = 3 different thicknesses of the second basis material 30B. Therefore, in this case, there are 3 × 3 = 9 different calibration members that combine basis materials. Note that "Air" in FIG. 5 corresponds to a calibration member 30 that does not use either the first basis material 30A or the second basis material 30B, i.e., a calibration member 30 in which the thickness of both the first basis material 30A and the second basis material 30B is "0 (zero)."

[0046] In this embodiment, radiation is irradiated from the radiation source 5 for each of the nine combinations 32, and the detector 9 detects the radiation that has passed through the combination 32, thereby obtaining the photon energy spectrum (i.e., the relationship between the radiation energy and the number of photon counts) as calibration data C0 for each combination 32. The nine types of calibration data C0 obtained in this manner are output to the console 3.

[0047] In the console 3, the calibration data C0 acquired from the CT apparatus 2 is stored in the storage 13 in association with the type of combination 32 used to acquire the calibration data C0. The stored calibration data C0 is used for material decomposition using the projection data P0 of the subject H.

[0048] In this embodiment, four energy bins B1 to B4 are set in the detector 9. Therefore, the calibration data C0 may be stored as a map showing the number of photon counts for each of the four energy bins B1 to B4 for each of the nine combinations 32 of the basis materials 30A and 30B described above. Alternatively, the calibration data C0 may be represented by a graph or a formula and stored in the storage 13.

[0049] The material decomposition unit 22 derives a material decomposition image by performing material decomposition using the projection data P0 acquired by the CT apparatus 2 by imaging the subject H. Material decomposition will be described below.

[0050] The projection data P0 is acquired at various projection angles by the CT device 2, and has a radiation energy spectrum for each detector element 9P included in the detector 9. The material decomposition unit 22 searches for the energy spectrum represented by the calibration data C0 that has the closest shape to the energy spectrum for each detector element 9P in each projection data P0, and obtains a combination of thicknesses of basis materials corresponding to the energy spectrum found. Estimating the thickness of the basis materials using this method is equivalent to fitting the energy spectrum represented by the calibration data C0 to the energy spectrum for each detector element 9P. Projection data for each basis material is generated from the combination of thicknesses of the basis materials.

[0051] If the first basis material 30A used when acquiring the calibration data C0 is acrylic and the second basis material 30B is aluminum, the thickness of the acrylic and the thickness of the aluminum are obtained for each detection element 9P in the projection data P0 at various projection angles. Furthermore, the projection data of the acrylic and the projection data of the aluminum are obtained. The material decomposition unit 22 then derives a material decomposition image by reconstructing a tomographic image for each basis material from the obtained multiple projection data for each basis material.

[0052] In this embodiment, the detector 9 detects the photon energy of the incident radiation divided into four energy bins B1 to B4 as shown in Fig. 2. In this embodiment, when performing material decomposition using the projection data P0, the energy band of the projection data P0 is divided into a high-energy region higher than the K-edge of the material assumed to be present inside the body of the subject H (i.e., energy bins B3 to B4) and a low-energy region lower than the K-edge (i.e., energy bins B1 to B2), and the material decomposition is performed.

[0053] In this embodiment, a contrast agent made of gadolinium, for example, is used as a substance assumed to be present inside the body of the subject H. FIG. 6 is a diagram showing the energy spectrum of gadolinium. Note that the horizontal axis of the energy spectrum shown in FIG. 6 represents the radiation energy, and the vertical axis represents the photon count. When the count in air is C0, the energy spectrum can be calculated by C0exp(-attenuation). For ease of explanation, in FIG. 6, C0 is set to a uniform value (10,000) for each energy bin. Therefore, the attenuation shown in FIG. 2 corresponds to the energy spectrum shown in FIG. 6, and both have a K-edge around 50 keV.

[0054] As shown in Figure 6, when a K-edge is observed in the energy spectrum 40 of the projection data P0, if material decomposition is performed using the calibration data C0 over the entire energy range of the projection data P0, the K-edge cannot be properly decomposed, as indicated by the dashed line 41. As a result, over the entire energy range of the projection data P0, the material decomposition result obtained is intermediate between the spectrum of energies above the K-edge and the spectrum of energies below the K-edge. As such, the material decomposition result obtained by calibration using a basis material whose K-edge structure does not match that of the specimen H cannot accurately represent the actual elemental composition. Furthermore, while it would be ideal to use each element that can exist in the specimen H as a basis for calibration, this approach has the drawback of requiring a large amount of effort and time.

[0055] In this embodiment, as described above, the material decomposition unit 22 performs material decomposition using the energy spectrum of the projection data P0 and the calibration data C0 in the higher energy region than the K-edge and the lower energy region than the K-edge of the material assumed to be present in the body of the subject H. As a result, as shown in FIG. 7 , in the higher energy region than the K-edge of the projection data P0, material decomposition can be performed satisfactorily using the calibration data C0 similar to the projection data P0, as indicated by the dashed-dotted line 42. Furthermore, in the lower energy region than the K-edge of the projection data P0, material decomposition can be performed satisfactorily using the calibration data C0 similar to the projection data P0, as indicated by the dashed-two-dot line 43. Therefore, even if the material assumed to be present in the body of the subject H has an absorption edge such as the K-edge, good material decomposition can be performed by calibration using a basis material that does not have a significant K-edge structure in the photon energy region (e.g., approximately 20 to 140 keV) of the radiation used in the CT device 2.

[0056] Here, if there is no significant K-edge structure on the subject H side, material decomposition can be performed well even in the entire energy range of the projection data P0 without being affected by the K-edge.

[0057] In this embodiment, four energy bins B1 to B4 are set in the detector 9, and therefore the average photon energy (i.e., the number of counts) in each of the energy bins B1 to B4 is obtained as the energy spectrum of the projection data P0. The calibration data C0 also represents the photon energy in each of the energy bins B1 to B4. Therefore, material decomposition is performed using the photon energy in each of the energy bins B1 to B4 in the projection data P0 and the photon energy in each of the energy bins B1 to B4 in the calibration data C0.

[0058] The display control unit 23 displays the derived tomographic image on the display 14.

[0059] Next, the processing performed in this embodiment will be described. FIG. 8 is a flowchart showing the processing performed in this embodiment. It is assumed that the calibration data C0 has been acquired in advance and stored in the storage 13. First, the information acquisition unit 21 acquires a plurality of projection data P0 derived by imaging the subject H with the CT device 2 (step ST1). Next, in the entire energy range detectable by the detector 9, in a region higher in energy than the K-edge of a material assumed to be present in the body of the subject H, the material decomposition unit 22 performs material decomposition using the energy spectrum represented by the calibration data C0 and the energy spectrum for each detection element 9P included in each of the plurality of projection data P0 (step ST2). Furthermore, the material decomposition unit 22 performs material decomposition in the entire energy range detectable by the detector 9, in a region lower in energy than the K-edge of a material assumed to be present in the body of the subject H (step ST3).

[0060] Next, the material decomposition unit 22 derives a material decomposition image by reconstructing a tomographic image for each basis material from the plurality of projection data P0 for each basis material obtained by material decomposition (step ST4).Then, the display control unit 23 displays the material decomposition image on the display 14 (step ST5), and the process ends.

[0061] As described above, in this embodiment, material decomposition of the subject H is performed based on the energy spectrum of at least one energy region on either side of the absorption edge in the projection data P0 acquired by measuring the subject H with the detector 9 and the calibration data C0. Therefore, material decomposition can be performed well regardless of whether or not the material contained in the subject has a discontinuous absorption structure such as a K-edge within the measurement energy region.

[0062] In the above embodiment, material decomposition is performed by dividing the energy band of the projection data P0 into a high-energy region (i.e., energy bins B3 to B4) higher than the K-edge of a substance assumed to be present in the body of the subject H and a low-energy region (i.e., energy bins B1 to B2) lower than the K-edge of a substance assumed to be present in the body of the subject H, but this is not limited to this. As shown in Fig. 9, material decomposition may be performed by dividing the energy band of the projection data P0 into a full energy region (i.e., energy bins B1 to B4) and a high-energy region (i.e., energy bins B3 to B4) higher than the K-edge of a substance assumed to be present in the body of the subject H.

[0063] In this way, by performing material decomposition of the subject H using calibration data based on the energy spectrum of the entire energy region of the projection data P0, it is possible to perform good material decomposition of the subject H for materials that do not have a singular point such as a K-edge. In addition, it is possible to compare the results of material decomposition in the entire energy region of the projection data P0 with those in a region higher in energy than the K-edge.

[0064] 10, material decomposition may be performed by dividing the energy band of the projection data P0 into a full energy region (i.e., energy bins B1 to B4), a low energy region (i.e., energy bins B1 to B2) lower than the K-edge of a material assumed to be present in the body of the subject H, and a high energy region (i.e., energy bins B3 to B4) higher than the K-edge. Furthermore, as shown in FIG. 11, material decomposition may be performed by dividing the energy band of the projection data P0 into a full energy region (i.e., energy bins B1 to B4) and a low energy region (i.e., energy bins B1 to B2) lower than the K-edge of a material assumed to be present in the body of the subject H.

[0065] Furthermore, in the above embodiment, four energy bins B1 to B4 are set for the detector 9, but the number of bins is not limited to this. Any number of energy bins equal to or greater than two can be set as long as the boundaries of the energy bins coincide with the K-edges of materials that are expected to be present in the body of the subject H. Note that if the number of energy bins is too small, material decomposition cannot be performed well, and if the number is too large, the amount of calculation required for material decomposition increases, so the number is preferably between 3 and 8.

[0066] In the above embodiment, the energy bins of the detector 9 are set so that one boundary of the energy bins coincides with the K-edge of the material, but this is not limiting. The boundary of the energy bins does not have to coincide with the K-edge. For example, as shown in FIG. 12, if the energy of the K-edge is 50 keV, one energy bin B11 may be set from 30 to 60 keV, which includes the K-edge, and three energy bins, B12 and B13, may be set at 60 to 90 keV and 90 keV to 120 keV, respectively, which are higher in energy than the K-edge.

[0067] Here, when performing material decomposition using the projection data of energy bin B11, the material decomposition can be performed by regarding the bin as belonging to the wider energy band (in this case, the lower energy side than the K-edge) based on the K-edge energy. Since information from two or more bins is required for material decomposition into two materials, in this case, material decomposition can be performed in two systems: the entire energy region (energy bins B11 to B13) and the upper edge energy region (energy bins B12 to B13).

[0068] Furthermore, in the above embodiment, the hardware structure of the radiation imaging apparatus 10 can use various processors as shown below. The various processors include a CPU, which is a general-purpose processor that executes software (programs) and functions as various processing units, as well as dedicated electrical circuits, such as a PLD (Programmable Logic Device) whose circuit configuration can be changed after manufacture, such as an FPGA (Field-Programmable Gate Array), and an ASIC, which is a processor having a circuit configuration designed specifically for executing specific processing.

[0069] The above-mentioned various processes may be executed by one of these various processors, or may be executed by a combination of two or more processors of the same or different types (for example, a plurality of FPGAs, or a combination of a CPU and an FPGA). Also, a plurality of processing units may be configured by a single processor. An example of configuring a plurality of processing units by a single processor is a form in which a processor is used that realizes the functions of an entire system including a plurality of processing units by a single IC (Integrated Circuit) chip, such as an SoC (System on a Chip).

[0070] The following are appendices to the present disclosure. (Additional note 1) A radiographic imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, a storage unit configured to store a plurality of calibration data representing energy spectra of a plurality of types of calibration members each made of a combination of one or more types of base materials differing in at least one of composition and thickness, the calibration data being acquired by measuring the calibration members with the photon counting detector; a processor; The processor is a radiation imaging device that performs material decomposition of the subject based on the calibration data and an energy spectrum in at least one energy region on either side of the absorption edge of the photon energy of a substance that is expected to be present inside the subject at the time of imaging, in projection data obtained by measuring the subject using the photon counting detector. (Additional note 2) 2. The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the subject based on an energy spectrum on the high energy side of the absorption edge and an energy spectrum on the low energy side of the absorption edge in the projection data. (Additional note 3) 2. The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the subject based on an energy spectrum on the high energy side of the absorption edge in the projection data and an energy spectrum in the entire energy range in the projection data. (Additional note 4) 2. The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the subject based on an energy spectrum on the low energy side of the absorption edge in the projection data and an energy spectrum in the entire energy range in the projection data. (Additional note 5) The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the subject based on an energy spectrum on the high-energy side of the absorption edge in the projection data, an energy spectrum on the low-energy side of the absorption edge, and an energy spectrum in the entire energy range in the projection data. (Additional note 6) 6. The radiographic imaging apparatus according to any one of appended items 1 to 5, wherein the number of the plurality of energy bins is 3 or more and 8 or less. (Additional note 7) A radiographic imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, A radiation imaging method for a radiation imaging apparatus including a storage unit that stores a plurality of calibration data representing energy spectra of a plurality of types of calibration members each made of a combination of one or more types of base materials that differ in at least one of composition and thickness, the calibration data being acquired by measuring the calibration members using the photon counting detector, the method comprising: A radiation imaging method for performing material decomposition of the subject based on the energy spectrum of at least one energy region on either side of the absorption edge of the photon energy of a substance assumed to be present inside the subject at the time of imaging, in the calibration data and projection data obtained by measuring the subject with the photon counting detector. (Additional note 8) A radiographic imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, a radiation imaging program that causes a computer to function as a radiation imaging apparatus having a storage unit that stores a plurality of calibration data representing energy spectra of a plurality of types of calibration members each made of a combination of one or more types of base materials that differ in at least one of composition and thickness, the calibration data being acquired by measuring the calibration members using the photon counting detector, the radiation imaging program comprising: A radiography program that causes a computer to execute a procedure for decomposing materials in the subject based on the calibration data and the energy spectrum in at least one energy region on either side of the absorption edge of the photon energy of a material that is assumed to be present inside the subject at the time of imaging the subject, in projection data obtained by measuring the subject with the photon counting detector. [Explanation of symbols]

[0071] 1 Medical imaging system 2 CT device 3 Console 4 Gantry 4A opening 5 Radiation source 6 Radiation tube 7 Bowtie Filter 8 berths 9 Detector 9P detector element 10 Radiography equipment 11 CPU 12 Radiography Program 13. Storage 14 Display 15 Input Devices 16 memory 17 Interfaces 18 Bus 21 Information Acquisition Department 22 Material Decomposition Department 23 Display control unit 30 Calibration member 30A,30B Base material 32 combinations 40 Energy Spectrum 41 Dashed lines showing material decomposition results across the entire energy range The dashed-dotted line shows the material decomposition results in the energy region higher than the 42 K edge. The dashed-dotted line shows the material decomposition results in the energy region below the 43 K edge. B1~B4, B11~B13 Energy Bins H Subject

Claims

1. A radiographic imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, a storage unit configured to store a plurality of calibration data representing energy spectra of a plurality of types of calibration members each made of a combination of one or more types of base materials differing in at least one of composition and thickness, the calibration data being acquired by measuring the calibration members with the photon counting detector; a processor; The processor is a radiation imaging device that performs material decomposition of the subject based on the calibration data and an energy spectrum in at least one energy region on either side of the absorption edge of the photon energy of a substance that is expected to be present inside the subject at the time of imaging, in projection data obtained by measuring the subject using the photon counting detector.

2. 2. The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the object based on an energy spectrum on the high energy side of the absorption edge and an energy spectrum on the low energy side of the absorption edge in the projection data.

3. 2. The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the object based on an energy spectrum on the high energy side of the absorption edge in the projection data and an energy spectrum in the entire energy range in the projection data.

4. 2. The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the object based on an energy spectrum on the low energy side of the absorption edge in the projection data and an energy spectrum in the entire energy range in the projection data.

5. 2. The radiographic imaging apparatus according to claim 1, wherein the processor performs material decomposition of the subject based on an energy spectrum on the high-energy side of the absorption edge in the projection data, an energy spectrum on the low-energy side of the absorption edge, and an energy spectrum in the entire energy range in the projection data.

6. The radiographic imaging apparatus according to claim 1 , wherein the number of the plurality of energy bins is 3 or more and 8 or less.

7. A radiographic imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, A radiation imaging method for a radiation imaging apparatus including a storage unit that stores a plurality of calibration data representing energy spectra of a plurality of types of calibration members each made of a combination of one or more types of base materials that differ in at least one of composition and thickness, the calibration data being acquired by measuring the calibration members using the photon counting detector, the method comprising: A radiation imaging method for performing material decomposition of the subject based on the energy spectrum of at least one energy region on either side of the absorption edge of the photon energy of a substance assumed to be present inside the subject at the time of imaging, in the calibration data and projection data obtained by measuring the subject with the photon counting detector.

8. A radiographic imaging apparatus that processes projection data acquired by a photon counting detector that converts incident radiation into the number of detected photons for each of a plurality of energy bins, a radiation imaging program that causes a computer to function as a radiation imaging apparatus having a storage unit that stores a plurality of calibration data representing energy spectra of a plurality of types of calibration members each made of a combination of one or more types of base materials that differ in at least one of composition and thickness, the calibration data being acquired by measuring the calibration members using the photon counting detector, the radiation imaging program comprising: A radiography program that causes a computer to execute a procedure for decomposing materials in the subject based on the calibration data and the energy spectrum in at least one energy region on either side of the absorption edge of the photon energy of a material that is assumed to be present inside the subject at the time of imaging the subject, in projection data obtained by measuring the subject with the photon counting detector.

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