Photon counting ct device and method of correction of material discrimination map

Abstract

Provided are a photon counting CT device and a method for correcting a material discrimination map. In the PCCT device, material discrimination is performed with high accuracy even if a change in X-ray spectrum occurs. In a state in which no object is disposed in an imaging space of the photon counting CT device and / or in a state in which one or more kinds of correction materials are disposed at a position through which X-rays emitted from an X-ray tube pass, X-rays are emitted from the X-ray tube, X-ray photons are counted for each of a plurality of energy bands, and a correction count value is measured. A count value of the material discrimination map is corrected based on the measured correction count value.

Description

TECHNICAL FIELD

[0001] The present application relates to an X-ray CT (Computed Tomography) apparatus having a photon counting mode (hereinafter referred to as a PCCT apparatus), and particularly relates to a technique for statistical noise suppression on a low-energy side in the PCCT apparatus. BACKGROUND

[0002] An X-ray CT apparatus rotates a subject around a pair of an X-ray tube and an X-ray detector arranged in opposition to each other while holding a positional relationship therebetween, and obtains X-ray transmission data of the subject, and reconstructs a tomographic image (hereinafter referred to as a CT image) thereof by computation, and is used as an inspection apparatus for industry and security, an image diagnostic apparatus for medical care, and the like.

[0003] A PCCT apparatus equipped with a photon counting mode is being researched and developed for a medical X-ray CT apparatus. In the PCCT apparatus, a detector of the photon counting system counts X-ray photons (X-ray photons) that have transmitted a subject for each detection element. Thereby, for example, a spectrum (spectrum) that estimates an element constituting an internal tissue of a subject that has transmitted X-rays can be obtained, and an X-ray CT image in which a material discrimination of a tissue of a subject is performed can be obtained (see Patent Literature 1).

[0004] In addition, in the PCCT apparatus, by discriminating each X-ray photon counted by an energy value, an X-ray intensity of each energy band (energy bin) can be obtained. With this X-ray intensity, in the PCCT apparatus, sometimes only X-rays of a specific energy range are extracted and imaged, and are used in diagnosis.

[0005] On the other hand, in Patent Literature 2, an invention is disclosed in which, in order to improve the accuracy of material discrimination in a PCCT apparatus, detection data of a response of a detector due to nonlinearity of detection of photons is calculated by computation. Then, the calculated data of the non-linear response is subtracted from the data actually detected by the detector, and the detection data after the subtraction is used for material discrimination.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: JP Patent No. 2019-176988

[0009] Patent Literature 2: JP Patent No. 2016-193174

[0010] In the PCCT device, the data counted by the X-ray detecting element per energy band is subjected to a correction process. For example, linearity correction of a reference correction circuit, correction of a logarithmic transformation process, correction of a bias process, sensitivity correction, beam hardening correction, water phantom calibration, CT value correction, and the like are performed. An object is not arranged, and X-rays are irradiated to air, and data counted per energy band (Air data) is obtained by the detecting element, and based on this data, correction data used for the correction is calculated. Normally, the Air data is obtained to determine the correction data before the PCCT device is shipped, or at the time of maintenance.

[0011] However, the above-described Air data deviates at the time of calculation of the correction data and at the time of actual imaging of the object, and if the correction data calculated based on the Air data in which the deviation has occurred is used to correct the counted data obtained at the time of imaging of the object, there is a problem that the accuracy of material discrimination is reduced. The inventors have noted that the reason for the deviation in the Air data depending on the imaging day is that the spectrum of the X-rays generated by the X-ray tube changes due to heat generated by the X-ray tube, air temperature, secular change, and the like.

[0012] In Patent Document 2, data of a non-linear response is calculated and subtracted from the detection data, but since the change in the spectrum of the X-rays due to heat and the like is also affected by the air temperature of the place where the PCCT device is installed, the time from when the power is turned on, and the like, it is not easy to accurately calculate by calculation. SUMMARY

[0013] The object of the present application is to accurately perform material discrimination even if a change in the spectrum of the X-rays occurs in the PCCT device.

[0014] To achieve the above object, a photon counting device according to the present application is provided. That is, the present photon counting device has: an X-ray tube that irradiates an X-ray to an imaging space; an X-ray detector that counts a plurality of X-ray photons that have passed through the imaging space, corresponding to energy levels thereof, in each of a plurality of energy bands; a mapping storage section that stores a substance discrimination mapping that shows count values of the plurality of energy bands, which is obtained in advance for a product of combining two or more substances whose respective thicknesses are variously different; a substance discrimination section that refers to the substance discrimination mapping to obtain a combination of thicknesses of the two or more substances corresponding to count values counted by the X-ray detector for the plurality of energy bands in a state in which a subject is disposed in the imaging space; and a mapping correction section that corrects the substance discrimination mapping. The mapping correction section irradiates the X-ray from the X-ray tube to count the X-ray photons in each of the plurality of energy bands, thereby obtaining a correction-use count value, in a state in which the subject is not disposed in the imaging space and / or in a state in which one or more correction-use substances are disposed at a position through which the X-ray irradiated from the X-ray tube passes, and corrects the count values of the substance discrimination mapping based on the correction-use count value.

[0015] Effects of the Invention

[0016] According to the present application, even if a change in X-ray spectrum occurs in the PCCT device, the mapping correction section obtains a correction-use count value to correct the count values of the mapping, so that substance discrimination can be performed with good accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a block diagram showing the configuration of a photon counting CT device according to Embodiment 1 of the present application.

[0018] Figure 2 is a diagram explaining the case where count values are measured for a plurality of energy bands per detection element (channel) in the photon counting CT device according to Embodiment 1.

[0019] Figure 3 is a diagram showing an example of a substance discrimination mapping (table) in the photon counting CT device according to Embodiment 1.

[0020] Figure 4 is a diagram showing the case where X-ray photons are measured by the X-ray detector 321 without disposing the subject 101 in the imaging range 103 for correction of the substance discrimination mapping, the case where the correction-use substance 104 is disposed and X-ray photons are measured by the X-ray detector 321 for correction of the substance discrimination mapping, and the case where the subject is imaged and substance discrimination is performed using the corrected substance discrimination mapping, in the photon counting CT device according to Embodiment 1.

[0021] Figure 5are explanatory diagrams each showing (a) a correction substance map generated in advance, (b) a correction substance map at a current time point, (c) a full point correction substance map at the current time point of the photon counting CT apparatus of Embodiment 1.

[0022] Figure 6 are explanatory diagrams each showing (a) a correction substance map generated in advance, (b) a correction substance map at a current time point, (c) a full point correction substance map at the current time point of the photon counting CT apparatus of Embodiment 1.

[0023] Figure 7 is a functional block diagram of the arithmetic unit 400 of the photon counting CT apparatus of Embodiment 1.

[0024] Figure 8 is a flowchart showing a flow of the imaging processing of Embodiment 1.

[0025] Figure 9 is a flowchart showing a flow of the imaging processing of Embodiment 1.

[0026] Figure 10 (a) and (b) of are explanatory diagrams each showing a part of the structure of the photon counting CT apparatus of Embodiment 3.

[0027] Figure 11 (a) and (b) of are explanatory diagrams each showing a part of the structure of the photon counting CT apparatus of Embodiment 3.

[0028] Figure 12 is a block diagram showing a part of the structure of the photon counting CT apparatus of Embodiment 4.

[0029] Explanation of Reference Numerals

[0030] 100: PCCT apparatus, 101: subject, 102: bed, 200: UI unit, 210: input device, 220: output device, 300: measurement unit, 310: X-ray irradiation unit, 311: X-ray tube, 312: X-ray filter, 313: bowtie filter, 320: X-ray detection unit, 321: X-ray detector, 322: detection element, 330: gantry, 331: opening, 332: rotating plate, 340: control unit, 341: irradiation controller, 342: gantry controller, 343: bed controller, 344: detection controller, 400: arithmetic unit, 401: central processing device, 402: memory, 403: HDD device, 404: map correction unit, 405: imaging unit, 406: correction unit, 407: image generation unit, 408: substance discrimination unit, 409: map storage unit, 410: substance discrimination map. DETAILED DESCRIPTION

[0031] An example of a photon counting CT apparatus of an embodiment of the present application will be described below. In all the drawings used to describe the embodiment of the present application below, the same reference numerals are assigned to elements having the same function, and repeated description thereof will be omitted.

[0032] Embodiment 1

[0033] The outline of the PCCT apparatus of the present embodiment 1 will be described below using Figure 1 .

[0034] In the present embodiment, the count value based on X-rays at the imaging time point of the subject 101 is measured under given conditions, and the mapping (table in this case) 410 used in the material discrimination is corrected using the measured count. Thereby, even in the case where the X-ray tube 311, the surrounding structure, or the like is affected by the temperature rise of the X-ray tube 311 and thus a change is generated in the spectrum of the X-rays, the material discrimination can be performed with good accuracy.

[0035] The PCCT apparatus of the present embodiment has the overall structure as shown in Figure 1 , and has the X-ray tube 311 that irradiates X-rays, the X-ray detector 321, the rotating section (rotating plate) 332, the mapping storage section 409, the material discrimination section 408, and the mapping correction section 404 in the imaging space 103.

[0036] The X-ray tube 311 is a structure in which a cathode and an anode are arranged in a tube in vacuum. Hot electrons generated from the cathode collide with the rotating anode, and X-rays are generated.

[0037] The X-ray detector 321 includes a plurality of detection elements (channels Ch1 to n) arranged in a row and a counting circuit, and counts the number of X-ray photons that have passed through the imaging space 103 in each of a plurality of energy bands (bin1 to k) corresponding to the energy levels thereof as shown in Figure 2 .

[0038] The rotating section 332 rotates the X-ray tube 311 and the X-ray detector 321 around the imaging space 103.

[0039] The material discrimination mapping 410 used in the material discrimination process is stored in the mapping storage section 409. One example of the material discrimination mapping 410 is as shown in Figure 3 , and is a mapping in which the thicknesses (lengths through which X-rays pass) of a plurality of kinds of materials (bone and fat in this case) of two or more kinds that are desired to be discriminated are prepared, and the count values of the X-ray detector 321 counted for a plurality of energy bands (bin1 to k) are obtained in advance by measurement or calculation in a case where a product in which they are combined is arranged between the X-ray tube 311 and the X-ray detector 321. As the mapping 410, this is as shown inFigure 3 The mapping 410 is shown as being expressed using a table, but can also be expressed using a graph, an equation, or the like.

[0040] The substance discrimination section 408 refers to the mapping 410 to find a combination of thicknesses (transmission distances) of two or more substances corresponding to the count values counted by the X-ray detector 321 for the plurality of energy bands, in a state in which the subject 101 is arranged in the imaging space 103.

[0041] The mapping correction section 404 irradiates the X-ray from the X-ray tube 311 to count each of the plurality of energy bands in a state in which the subject 101 is not arranged in the imaging space 103 (Air) before, after, or at a desired timing such as when the switch of the apparatus is turned on, and / or in a state in which one or more correction substances 104 are arranged between the X-ray tube 311 and the X-ray detector 321 (b) of (a)), and acquires correction count values 412 (b) of (a)). The mapping correction section 404 corrects the count values of the substance discrimination mapping 410 based on the acquired correction count values 412. Figure 4 Figure 4 Figure 5

[0042] The one or more correction substances 104 referred to here means one or more substances that differ in element or composition, or one or more objects that differ in shape.

[0043] The element or composition of the correction substance 104 can be the same as the substances of the substance discrimination mapping 410 (for example, bone and fat), or can be different. In the case where the element or composition of the correction substance 104 is different from the substances of the substance discrimination mapping 410, the relationship 61 between the correction count values 411 counted for the correction substance 104 for each of the plurality of energy bands (a) of (a), (b) of (a)) and the count values counted for the substances of the substance discrimination mapping 410 for each of the plurality of energy bands (count values of the substance discrimination mapping 410) (c) of (a)) is measured in advance by the same X-ray spectroscopy. The mapping correction section 404 corrects the count values of the substance discrimination mapping 410 (c) of (c)) using this relationship 61, based on the correction count values 412 or 412-1 (b) of (b), (b) of (b)) of the correction substance 104, and can create a corrected substance discrimination mapping 410-1 (d) of (d)). Figure 5 Figure 6 Figure 3 Figure 6 Figure 5 Figure 6 Figure 3 Figure 6 Figure 6 For example, as shown in FIG. 6, the mapping correction section 404 can correct the count values of the substance discrimination mapping 410 (c) of (c)) based on the correction count values 412-1 (b) of (b)) of the correction substance 104, and can create a corrected substance discrimination mapping 410-1 (d) of (d)).

[0044] For example, as shown in FIG. 6, the mapping correction section 404 can correct the count values of the substance discrimination mapping 410 (c) of (c)) based on the correction count values 412-1 (b) of (b)) of the correction substance 104, and can create a corrected substance discrimination mapping 410-1 (d) of (d)). Figure 5 ​​​​​​​​​​​(a), (b) and Figure 6 As in (a) and (b) above, at least one of aluminum (Al) and acrylic resin plates is used as the calibration material 104 .

[0045] In addition, when the elements or composition of the calibration material 104 are different from those of the material identification map 410, it is desirable to store in the map storage unit 409 a previously generated calibration material map 411 ( Figure 5 (a) Figure 6 (a)) A calibration material map 411 is generated in advance as follows Figure 5 (a) Figure 6 As shown in (a), when the thickness of two or more types of calibration materials (Al and acrylic resin) 104 is varied in various ways and the combination thereof is arranged between the X-ray tube 311 and the X-ray detector 321, the X-ray detector 321 is determined in advance by actual measurement or calculation for multiple energy bands (bin1 to k: Figure 5 (a) Figure 6 The calibration material map 411 is generated in advance by maintenance personnel before shipment of the PCCT apparatus and when the X-ray tube 311 or X-ray detector 321 is replaced, and is stored in the map storage unit 409 .

[0046] The mapping correction unit 404 expects to measure the calibration counter value 412 ( Figure 5 (b)) to generate, for example, a map (hereinafter referred to as calibration material map 412 at the current time). Calibration material map 412 at the current time, like calibration material map 411 generated previously, is a map of count values ​​for each energy band obtained by combining two or more types of calibration materials (Al and acrylic resin) 104 with varying thicknesses. Since at least some of the count values ​​are generated by actual measurement at the current time, the X-ray spectrum at the current time can be reflected in the count values.

[0047] For example, the calibration count value for each energy band is measured for at least two combinations of the calibration material map 412 at the current time point (two columns in the table). Specifically, for example, the empty state ( Figure 4 The calibration count value of each energy band measured under (a) is used as Figure 5the column of the mapping 412 of (b) for which the thickness of the correction substance (Al and acrylic resin) 104 is 0 cm. In addition, the correction count value of each energy band actually measured under the condition where only the acrylic resin having a thickness of 10 cm as the correction substance 104 is arranged (b) is used as the correction count value of the column of the mapping 412 of (b) for which the thickness of the acrylic resin is 10 cm and the thickness of Al is 0 cm. Figure 5 the correction count value of each energy band actually measured under the condition where only the acrylic resin having a thickness of 10 cm as the correction substance 104 is arranged (b) is used as the correction count value of the column of the mapping 412 of (b) for which the thickness of the acrylic resin is 10 cm and the thickness of Al is 0 cm.

[0048] Thus, the mapping correction section 404, after obtaining the correction count values by actually measuring at least two places (three places in (b)) of the correction substance mapping 412 of the current time point of (b), refers to the correction substance mapping 411 (a) generated in advance as in (a), whereby the count values of the remaining empty columns of the correction substance mapping 412 of the current time point of (b) are calculated by interpolation or extrapolation. Figure 5 Figure 5 the correction count value of each energy band actually measured under the condition where only the acrylic resin having a thickness of 10 cm as the correction substance 104 is arranged (b) is used as the correction count value of the column of the mapping 412 of (b) for which the thickness of the acrylic resin is 10 cm and the thickness of Al is 0 cm. Figure 5 Figure 5 the correction count value of each energy band actually measured under the condition where only the acrylic resin having a thickness of 10 cm as the correction substance 104 is arranged (b) is used as the correction count value of the column of the mapping 412 of (b) for which the thickness of the acrylic resin is 10 cm and the thickness of Al is 0 cm. Figure 5

[0049] An example of the calculation in the mapping correction section 404 is shown. The values of the columns of the mapping of (a) are expressed as Ak_ac#x_al#y. k is the bin number (1-3 in the figure), x of ac#x is the length (mm) of the X-ray passing direction of the acrylic resin, and y of al#y is the length (mm) of the X-ray passing direction of the aluminum. In addition, the values of the columns of the mapping of (b) are similarly shown as Bk_ac#x_al#y. Further, in the mapping of (b), the values of the columns not measured are set to Ck_ac#x_al#y. As an example, the value C of the position of the acrylic resin 50 mm and the aluminum 0 mm of (b) can be obtained by the following equation (1). Figure 5 Figure 5 Figure 5 Figure 5

[0050] Ck_ac#50_al#0 = Ak_ac#50_al#0 x (Bk_ac#100_al#0 / Ak_ac#100_al#0 + Bk_ac#0_al#0 / Ak_ac#0_al#0) / 2... Equation (1)

[0051] Thus, the count values of the positions within the information of the positions measured at the current time point can be obtained by interpolation, and in the case where this is not possible, the ratio of A and B is calculated by extrapolation, and the result is multiplied to the original value of A to perform correction.

[0052] Thus, the count values of the positions within the information of the positions measured at the current time point can be obtained by interpolation, and in the case where this is not possible, the ratio of A and B is calculated by extrapolation, and the result is multiplied to the original value of A to perform correction. Figure 5 ​​​​​​​​Figure 5 (c)). Figure 6 The material map 412 - 1 for all-point correction at the current time point in (c) reflects the X-ray spectrum at the current time point.

[0053] Therefore, if Figure 6 As shown in (a) and (b) of FIG. 1 , by comparing the calibration material map 412-1 ( Figure 6 (b)) and the previously generated calibration material map 411 ( Figure 6 (a)), the change of X-ray spectrum during this period can be grasped as the change of count value. By correcting the change of X-ray spectrum Figure 6 The count value of the material discrimination map 410 of (c) can be used to obtain the material discrimination map 410-1 ( Figure 6 (d)).

[0054] use Figure 6 A method of calibrating the count value of the substance discrimination map 410 to generate the calibrated substance discrimination map 410 - 1 will be described.

[0055] First, we calculate Figure 6 The respective positions of the material identification map 410 (e.g., fat 50 mm, bone 2 mm) in (c) are Figure 6 Which position (ratio of acrylic resin to aluminum) is in the previously generated calibration material map 411 of (a)? Figure 6 The material discrimination map 410 of (c) obtains the attenuation results of each bin of each signal that has penetrated 50mm of fat and 2mm of bone, so the ratio of the attenuation results is obtained. Figure 6 The point where the attenuation result that matches the ratio is found in the calibration material map 411 generated in advance (a). Since there is no perfect match, there is an error, but the point where the error is minimized is found. The minimum error is defined, for example, as the point where the sum of the squares of the differences in the counts of each bin is minimized. Figure 6 The correction value is obtained by calculation at the position on the calibration material map 411 generated in advance in (a).

[0056] Correction value = ( Figure 6 (b) The count value of the corresponding position of the material map 412-1 for all points of the current time point) / ( Figure 1 (a) The count value at that position of the calibration material map 411 generated in advance)

[0057] Multiply this correction value by Figure 4the value of the corresponding position of the material discrimination map 410 of (c). The calculation is repeated to make the corrected material discrimination map 410-1 for the case of different materials. Figure 7

[0058] The material discrimination section 408 uses the corrected material discrimination map 413 to perform material discrimination on the count values of the subject.

[0059] Therefore, in the PCCT apparatus of the present embodiment, even if a change in the spectrum of the irradiated X-rays occurs due to a temperature rise of the X-ray tube 311 or the like, the mapping correction section 404 acquires the correction count values and corrects the count values of the material discrimination map 410, so the material discrimination section 408 can perform material discrimination with good accuracy.

[0060] In addition, the mapping correction section 404 can also measure the correction count values by irradiating X-rays from the X-ray tube 311 in three states, in which Air, which is not configured in the imaging space 103, a first correction material (e.g., Al) of a given thickness is configured between the X-ray tube 311 and the X-ray detector 321, and a second correction material (acrylic resin) of a given thickness is configured between the X-ray tube and the X-ray detector, respectively, and counting for each of a plurality of energy bands, in order to generate the correction material map 412 of the current time point. The mapping correction section 404 corrects the count values of the material discrimination map 410 using the correction count values measured in the three states, respectively.

[0061] <Detailed Configuration>

[0062] The PCCT apparatus 100 of the present embodiment will be described in further detail below. As shown in FIG. 1, the PCCT apparatus 100 of the present embodiment includes a measurement section 300, a calculation section 400, and a UI section 200. Figure 8 The PCCT apparatus 100 of the present embodiment includes a measurement section 300, a calculation section 400, and a UI section 200.

[0063] The measurement section 300 irradiates X-rays to the subject 101 in accordance with the control performed by the calculation section 400, and measures X-ray photons that have transmitted the subject 101. The measurement section 300 includes, in addition to the X-ray tube 311 and the X-ray detection section 320, a gantry 330, a control section 340, and a table 102 on which the subject 101 is placed. The control section 340 includes an irradiation controller 341, a gantry controller 342, a table controller 343, and a detection controller 344.

[0064] ​An opening 331 is provided in the center of the gantry 330, within which the subject 101 and the bed 102 are placed. Inside the gantry 330, a rotating plate 332 is mounted with the X-ray tube 311 and the X-ray detector 321, and a drive mechanism (not shown) for rotating the rotating plate 332 is located. When the rotating plate 332 rotates a given angle, the gantry controller 342 outputs a signal to the detection controller 344, which in turn outputs a signal to the X-ray detector 320. The counting circuit of the X-ray detector 321 then outputs count data as data corresponding to one degree of rotation. As an example, the diameter of the opening 331 of the gantry 330 is 700 mm. The distance between the X-ray generation point of the X-ray tube 311 and the X-ray incident surface of the X-ray detector 321 is, for example, 1000 mm.

[0065] The time required for one rotation of the rotating plate 332 is set by parameters input by the user via the UI unit 200. For example, it can be set to 1.0 s / rotation, and the number of images captured per rotation can be set to 900. In this specification, the circumferential direction of the opening 331 is referred to as the x-direction, and the radial direction is referred to as the y-direction. The z-direction (the body axis of the subject 101) is perpendicular to the x- and y-directions.

[0066] An X-ray filter 312 for adjusting the X-ray spectrum and a bowtie filter 313 for suppressing the peripheral irradiation dose are arranged between the X-ray tube 311 and the imaging space 103, forming an X-ray irradiation unit 310. A high voltage is supplied to the X-ray tube 311 under the control of an irradiation controller 341.

[0067] The X-ray detector 321 is a structure in which a plurality of detection elements are arranged. The plurality of X-ray detectors 321 are arranged in an arc shape to form the X-ray detection unit 320. Figure 9 As shown in (a) to (c) above, a collimator 323 is provided on the incident surface side of the X-ray detector 321 to limit the incident direction of the X-rays. The detection elements of the X-ray detector 321 are semiconductor elements. The x-direction dimension of the detection elements is, for example, 1 mm.

[0068] The operation unit 400 controls the overall operation of the PCCT device 100 and processes the data obtained by the measurement unit 300 to perform imaging. The operation unit 400 includes a central processing unit (CPU) 401, a memory 402, and a HDD (Hard disk drive) device 403. Figure 4 As shown in its functional block diagram in FIG, it has functions of a mapping correction unit 404, an imaging unit 405, a count data correction unit 406, a substance identification unit 408, and an image generation unit 407.

[0069] The CPU 401 realizes the above-described functions by software by loading a program previously stored in the HDD device 403 into the memory 402 and executing it. In addition, all or a part of the functions of the arithmetic portion 400 can be realized by, for example, an integrated circuit such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or the like.

[0070] The imaging portion 405 is caused to perform CT imaging, positioning scanning, or the like. The count value data correction portion 406 performs a correction process on the count value data collected for each energy band. The correction process performed here is, for example, linearity correction of a reference correction circuit, logarithmic transformation processing, bias processing, sensitivity correction, beam hardening correction, water phantom calibration, CT value correction, or the like.

[0071] The material discrimination portion 408 transforms the corrected count value data from the count value data correction portion 406 into the transmission distance of the material constituting the subject 102 (for example, 1 cm for bone and 5 cm for fat).

[0072] The image generation portion 407 virtually reconstructs an image in which only bone is extracted, an image in which only fat is extracted, a CT image in which X-rays of a specific energy band are irradiated, using the transformation result of the material discrimination portion 408.

[0073] Data used in the saving process in the HDD device 403, data of the result of the process, or the like are saved.

[0074] The Ul portion 200 is provided with an input device 210 such as a keyboard, a mouse, and the like, and an output device 220 such as a display device, and receives from the user the timing at which the material discrimination map 410 is corrected, the kind of image that is desired to be output, the imaging conditions, or the like, and outputs them to the arithmetic portion 400. The imaging conditions are, for example, the tube current, the tube voltage of the X-ray tube 311, the imaging range of the subject 101, or the like.

[0075] Next, the imaging process of the arithmetic portion 400 will be described using the flow of Figure 4

[0076] <Step S1101>

[0077] First, the map correction portion 404 determines whether or not the current time point is the timing at which correction of the predetermined material discrimination map 410 is performed, and in the case where it is the timing at which map correction is performed, proceeds to Step S1102 (Step S1101). In the case where it is not the timing at which map correction is performed, proceeds to Step S1104.

[0078] ​Here, the predetermined timing of mapping correction is a timing set by the user, and can be set before imaging, during imaging, after imaging, or when the switch is turned on in the morning.

[0079] <Step S1102>

[0080] When it is time to calibrate the material discrimination map 410 , the map correction unit 404 measures the count values ​​for the two types of calibration materials (Al and acrylic resin) 104 at the current time point and generates a calibration material map 412 .

[0081] use Figure 5 The specific step S1102 is further explained in the following process.

[0082] (Step S2001)

[0083] The mapping correction unit 404 performs the following operation in an empty state (Air) in which the subject 101 is not arranged in the imaging space 103: Figure 5 As in (a) of FIG. 1 , X-rays are irradiated from the X-ray tube 311 , and the detector 321 measures the correction count value for each of the plurality of energy bands.

[0084] (Step S2002)

[0085] The mapping correction unit 404 causes the output device (display device) 220 to display a message urging the user to place only a 10 cm acrylic resin plate as the calibration material 104 between the X-ray tube 311 and the imaging space 103. If the user places the acrylic resin plate, the image is displayed in this state ( Figure 5 Under (b)), X-rays are irradiated from the X-ray tube 311, and a correction count value 412 for each of a plurality of energy bands is measured in the detector 321.

[0086] (Step S2003)

[0087] The count values ​​obtained in steps S2001 and S2002 are used as calibration count values ​​for the columns of the calibration material map 412 at the current time point for the calibration material (Al and acrylic resin) 104, each with a thickness of 0 cm, and the columns of the combination of acrylic resin thickness 10 cm and Al thickness 0 cm. The count values ​​of the remaining empty columns are calculated by interpolation and extrapolation. In this way, the calibration material map 412 at the current time point ( Figure 3 (b)).

[0088] <Step S1103>

[0089] The map correction unit 404 generates the calibration material map 412 ( Figure 6 (b)) and the previously generated calibration material map 411 (Figure 4 (a) of FIG. 10, the material discrimination map 410 is corrected in accordance with the count value of (c) of FIG. 10. Figure 9 , Figure 8

[0090] <Step S1104, S1105>

[0091] When the imaging section 405 receives an instruction to start imaging from the user via the UI section 200, it proceeds to step S1105, and as shown in (c) of FIG. 11, X-rays are radiated from the X-ray tube 311 to the subject 101 arranged in the imaging range 103, and the count value is measured for a plurality of energy bands by the X-ray detector 321. Figure 10

[0092] <Step S1106>

[0093] The material discrimination section 408 refers to the material discrimination map 410 corrected in step S1103 to find a combination of thicknesses (transmission distances) of two or more materials corresponding to the coefficients for the subject 101 acquired in step S1105.

[0094] <Step S1106, S1107>

[0095] The image generation section 407 generates an image in which only a desired material (for example, only bone, only fat) is extracted, or an X-ray CT image of a case in which X-rays of a specific energy (for example, 60 eV) are radiated, by computation based on the transmission distances of the materials found by the material discrimination section 408 in step S1106. The image generation section 407 causes the generated image to be displayed on the output section 220.

[0096] In the present embodiment, even in the case where the X-ray spectrum has changed due to temperature rise of the X-ray tube 311 or the like, the change in the count value at the current time point is actually measured to correct the material discrimination map, so the accuracy of material discrimination can be improved. Thus, the physician can perform diagnosis with good accuracy by looking at the image subjected to material discrimination.

[0097] <Embodiment 2>

[0098] A PCCT device according to Embodiment 2 will be described.

[0099] In Embodiment 2, as the correction material 104, a cylindrical resin-made phantom in which the attenuation is approximately the same as that of the subject 101 is used. For example, a cylindrical phantom made of polyethylene is used.

[0100] The map correction section 404 corrects the material discrimination map 410 in Embodiment 1 in accordance with the count value of (c) of FIG. 10. Figure 10 ​​The step S2001 of the flowchart measures the count value in the state where the subject 101 is not arranged in the imaging range 103 (Air), and in step S2002, a cylindrical resin phantom is arranged in the imaging range 103, and the count value is measured. The mapping correction section 404 generates the correction substance map 412 of the current time point in which the count value data measured in the state where the subject 101 is not arranged (Air) and the count value data measured in the state where the cylindrical resin phantom is arranged are elements in step S2003.

[0101] The correction substance map 411 generated in advance is also the same, and the map is generated in which the two of the count value data of the count values measured in the state of Air and the state where the cylindrical phantom is arranged are elements.

[0102] In Figure 3 In step S1102 of the flowchart, the mapping correction section 404 corrects the substance discrimination map 410 based on the difference between the correction substance map 412 of the current time point and the correction substance map 411 generated in advance, and obtains the corrected substance discrimination map 413.

[0103] The other configurations, processing actions, and effects are the same as those of Embodiment 1.

[0104] Embodiment 3

[0105] The PCCT device of Embodiment 3 is explained using (a) and (b) of Figure 6

[0106] In the PCCT device of Embodiments 1 and 2, the configuration in which the correction count value is measured by the X-ray detector 321, but in Embodiment 3, the mapping correction section 404 further has a reference detector 902 separately from the X-ray detector 321, and the correction count value is measured by the reference detector 902.

[0107] As shown in (a) of Figure 10 The reference detector 902 is arranged at a position reached by the X-rays emitted from the X-ray source 311 and passing through the outside of the imaging range 103. Therefore, by measuring the correction measurement value by the reference detector 902, the correction measurement value can be measured even in the imaging of the subject, and the substance discrimination map 410 can be corrected in real time (c) of Figure 11 、 Figure 12

[0108] ​​In addition, since the reference detector 902 is located outside the imaging range 103, even if nothing is placed between the reference detector 902 and the X-ray source 311, the count value in the air state can be obtained. If a calibration material 104 of a predetermined thickness is placed in front of the reference detector 902, the count value of the calibration material 104 can be obtained. ​ As in (b), using reference detector 902 having multiple detection elements 902-1 to 902-3, with nothing placed in front of detection element 902-1 and calibration materials 104-1 and 104-2 of different thicknesses or materials placed in front of detection elements 902-1 and 902-3, respectively, calibration count values ​​for air and two types of calibration materials can be obtained simultaneously. This allows for rapid generation of the calibration material map 412 at the current time.

[0109] In addition, since the reference detector 902 is arranged outside the imaging range 103, the subject 101 can be imaged while maintaining the same configuration. Therefore, there is an advantage that the material discrimination map 410 can be automatically calibrated without requiring the user to assemble or disassemble the X-ray source 311 at the position where it passes through the calibration material 104.

[0110] Furthermore, since the reference detector 902 is located outside the subject, it is not affected by the subject 101. This can also be used, such as ​ As shown in (a) and (b) of FIG. 1 , the end portion of the detector 321 that detects X-rays that have passed through the subject is used as the reference detector 902. In this case, there is an advantage in that the detector 321 and the detector 902 can be integrated.

[0111] In this embodiment, it is also desirable to use the calibration substance map 411 generated in advance, the map of count values ​​detected by the reference detector 902 .

[0112] Since the other structures are the same as those in the first embodiment, the description thereof will be omitted.

[0113] Implementation Method 4

[0114] use ​ The PCCT apparatus according to the fourth embodiment will be described.

[0115] In the PCC devices of Embodiments 1 to 3, the map correction unit 404 generates the calibration material map 41 at the current time point through calculation after measuring the calibration count value, and further generates the calibration material discrimination map 410. However, in Embodiment 4, the map correction unit 404 uses a learned learning model 920. The measured calibration count value can be input to the learning model 920, and the calibrated material discrimination map 413 can be directly output. The learning model 920 can use a known scheme, such as a neural network.

[0116] In learning the learning model 920 , the calibration count values ​​obtained by the methods of Embodiments 1 and 2 are used as input data, and the calibrated material discrimination map 413 is used as correct answer data. It is sufficient to learn in advance through machine learning or deep learning.

[0117] Thus, the map correction unit 404 can obtain the corrected material discrimination map 413 simply by measuring the calibration count value and inputting it into the learning model 920 . Therefore, the material discrimination map 410 can be corrected in a short time and with high accuracy.

[0118] The correction count value input to the learning model 920 by the mapping correction unit 404 only needs to be 1 or above. For example, it can be the count value of multiple energy bands measured only in the empty state (Air) of the camera range 103 without a subject, or it can be the count value measured by further configuring one or more correction substances 104.

[0119] Alternatively, the data output by the learned model may be used as the calibration material map 412 at the current time point, rather than the material discrimination map 410. In this case, the map correction unit 404 uses the obtained calibration material map 412 to correct the material discrimination map 410 through the same process as in the first embodiment, thereby obtaining a corrected material discrimination map 413.

[0120] In the third embodiment, the configuration, processing operation, and effects other than the process of obtaining the corrected material discrimination map 413 by the map correction unit 404 are the same as those in the first and second embodiments, and therefore detailed descriptions are omitted.

Claims

1. A photon counting CT device, characterized in that: have: An X-ray tube that irradiates an imaging space with X-rays; an X-ray detector for counting a plurality of X-ray photons having passed through the imaging space in correspondence with energy levels of the plurality of X-ray photons for each of a plurality of energy bands; a map storage unit storing a material discrimination map indicating count values ​​of a plurality of energy bands obtained in advance for a product of combining the thicknesses of two or more materials while varying the thicknesses of the two or more materials in a plurality of ways; a material identification unit that refers to the material identification map to determine a combination of thicknesses of two or more materials corresponding to count values ​​obtained by the X-ray detector for the plurality of energy bands when the subject is arranged in the imaging space; and a map correction unit that corrects the substance discrimination map, The mapping correction unit irradiates X-rays from the X-ray tube to count X-ray photons in each of the multiple energy bands and measures a correction count value in a state where no subject is arranged in the imaging space and / or in a state where one or more correction substances are arranged at a position where the X-rays irradiated from the X-ray tube pass through, and corrects the count value of the material discrimination mapping based on the correction count value.

2. The photon counting CT device according to claim 1, characterized in that: The mapping correction unit uses the X-ray detector to measure the correction count value at a timing before or after imaging the subject.

3. The photon counting CT device according to claim 1, characterized in that: The mapping correction unit has a reference detector for counting X-ray photons, which is arranged at a position where X-rays irradiated from the X-ray tube and passing through the outside of the imaging space arrive, and measures the correction count value at any time before, during, or after imaging of the subject.

4. The photon counting CT device according to claim 1, characterized in that: The one or more calibration substances are one or more substances having different elements or compositions, or substances having one or more different shapes.

5. The photon counting CT device according to claim 1, characterized in that: The calibration substance is different from the substance of the substance discrimination map. The mapping correction unit uses a relationship between a previously obtained correction count value for the correction material counted in each of the multiple energy bands and a count value for the two or more substances in the material identification map counted in each of the multiple energy bands, and corrects the count value of the material identification map based on the correction count value.

6. The photon counting CT device according to claim 1, characterized in that: The mapping correction unit irradiates X-rays from the X-ray tube to count each of the multiple energy bands under three conditions: an empty state in which no object is arranged in the imaging space, a state in which a first correction material of a given thickness is arranged between the X-ray tube and the X-ray detector, and a state in which a second correction material of a given thickness is arranged between the X-ray tube and the X-ray detector, thereby measuring a correction count value, and uses the correction count values ​​respectively measured under the three conditions to correct the count value of the material discrimination mapping.

7. The photon counting CT device according to claim 1, characterized in that: The material discrimination map is generated using count values ​​obtained by irradiating X-rays from the X-ray tube in an empty state in which no subject is arranged in the imaging space, and count values ​​obtained by irradiating X-rays from the X-ray tube in a state in which the thicknesses of the two or more substances are made different in multiple ways and a combination of the thicknesses of the two or more substances is arranged between the X-ray tube and the X-ray detector.

8. The photon counting CT device according to claim 1, characterized in that: The thicknesses of the two or more substances in the substance discrimination map include a thickness of zero.

9. The photon counting CT device according to claim 1, characterized in that: The mapping correction unit uses the count value data measured in the empty state where no subject is arranged in the imaging space and in the state where one or more correction materials are arranged at the position through which X-rays pass, as the count value data for mapping that combines the thicknesses of two or more correction materials differently, and generates a mapping by obtaining the measurement value data for the combination of thicknesses for which there is no count value data by interpolation and / or extrapolation.

10. The photon counting CT device according to claim 1, characterized in that: The mapping correction unit uses a cylindrical resin phantom as the one or more correction substances.

11. The photon counting CT device according to claim 1, characterized in that: The map correction unit includes a learned model, inputs the correction count value as input data to the learning model, and obtains the corrected substance discrimination map as output data.

12. A method for calibrating material discrimination mapping of a photon counting CT device, characterized in that: The steps are as follows: Irradiating the imaging space with X-rays through an X-ray tube; counting, by an X-ray detector, a plurality of X-ray photons that have passed through the imaging space and corresponding to the energy levels of the plurality of X-ray photons for each of a plurality of energy bands; The map storage unit stores a material discrimination map indicating count values ​​of a plurality of energy bands obtained in advance for a product of combining the thicknesses of two or more materials while making the thicknesses of the two or more materials different in a plurality of ways; obtaining, with reference to the material discrimination map, a combination of thicknesses of two or more materials corresponding to count values ​​obtained by the X-ray detector for the plurality of energy bands when the subject is arranged in the imaging space; In an empty state where no subject is arranged in the imaging space and / or in a state where one or more calibration substances are arranged at a position where X-rays irradiated from the X-ray tube pass through, irradiating X-rays from the X-ray tube to count X-ray photons for each of a plurality of energy bands, thereby measuring a calibration count value; and The count value of the substance discrimination map is corrected based on the actually measured count value for correction.

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