Phantom and method for calibrating a radiation imaging apparatus and a photon counting detector

Abstract

The present application provides a phantom and a correction method for a radiation imaging apparatus and a photon counting type detector, which can shorten the time required for obtaining correction data even for a large irradiation field. The phantom is used when obtaining correction data of a photon counting type detector that outputs an electric signal corresponding to a photon energy of an incident radiation, and includes a first base substance and a second base substance as known substances, the first base substance having a smaller attenuation coefficient for the radiation than the second base substance, the thickness of the first base substance varying in steps in a direction orthogonal to an irradiation field of the radiation, and the thickness of each step becoming thinner as a distance from a center of the irradiation field becomes longer in a direction in which detection elements of the photon counting type detector are arranged.

Description

TECHNICAL FIELD

[0001] The present application relates to a radiation imaging apparatus equipped with a photon counting type detector, and to a phantom used in correction of a photon counting type detector. BACKGROUND

[0002] Development of a PCCT (Photon Counting Computed Tomography) apparatus equipped with a detector employing a photon counting method, i.e., a photon counting type detector, is being advanced. The photon counting type detector is capable of measuring energy of a radiation photon, i.e., photon energy, of an incident radiation, and therefore, in a PCCT apparatus, a medical image that discriminates between substances of different compositions can be obtained, for example, a medical image that discriminates between an iodine contrast agent used in angiography and a calcified plaque in a blood vessel can be obtained. In addition, in order to obtain a medical image that discriminates between substances, it is necessary to obtain, as correction data, a relationship between output and photon energy when a phantom composed of combinations of a plurality of base substances of known composition and thickness is measured by a photon counting type detector, and to obtain this in advance for each detector element.

[0003] In Non-Patent Literature 1, it is disclosed that 25 kinds of correction data are obtained using a stepped phantom composed of 0 to 4 acrylic plates of 2.54 cm thickness and 0 to 4 aluminum plates of 0.635 cm thickness.

[0004] PRIOR ART DOCUMENTS

[0005] NON-PATENT LITERATURE

[0006] Non-Patent Literature 1: Taly Gilat Schmidt et al. “A Spectral CT method to directly estimate basis material maps from experimental photon-counting data”, in IEEE Transactions on Medical Imaging, vol. 36, no. 6, pp. 1808-1819, September 2017

[0007] However, Non-Patent Literature 1 only discloses a phantom used in a small irradiation field of 13 cm. In the case where the stepped phantom of Non-Patent Literature 1 is expanded to a large irradiation field of 50 cm, the phantom becomes one having a weight that is difficult to handle, and obtaining correction data of a photon counting type detector takes time. SUMMARY

[0008] Therefore, an object of the present application is to provide a phantom, a radiation imaging apparatus, and a correction method for a photon counting detector, which can shorten the time required for acquiring correction data even for a large irradiation field.

[0009] To achieve the above object, the present application is a phantom used when acquiring correction data for a photon counting detector that outputs an electric signal corresponding to the photon energy of an incident radiation, characterized by including a first base substance and a second base substance that are known substances, the first base substance having a smaller attenuation coefficient for the radiation than the second base substance, the thickness varying in steps in a direction orthogonal to the irradiation field of the radiation, and the thickness becoming thinner as the distance from the center of the irradiation field becomes longer in the direction in which the detection elements of the photon counting detector are arranged at each step.

[0010] Further, the present application is a radiation imaging apparatus provided with a photon counting detector that outputs an electric signal corresponding to the photon energy of an incident radiation, characterized by including a storage unit that stores correction data acquired using the phantom.

[0011] Further, the present application is a correction method for a photon counting detector that outputs an electric signal corresponding to the photon energy of an incident radiation, characterized by acquiring correction data for the photon counting detector using a phantom that includes a first base substance and a second base substance that are known substances, the first base substance having a smaller attenuation coefficient for the radiation than the second base substance, the thickness varying in steps in a direction orthogonal to the irradiation field of the radiation, and the thickness becoming thinner as the distance from the center of the irradiation field becomes longer in the direction in which the detection elements of the photon counting detector are arranged at each step.

[0012] Effects of Invention

[0013] According to the present application, a phantom, a radiation imaging apparatus, and a correction method for a photon counting detector, which can shorten the time required for acquiring correction data even for a large irradiation field, can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a diagram showing the overall structure of the PCCT device.

[0015] Figure 2 is a diagram explaining the correction of the photon counting detector.

[0016] Figure 3 is a diagram explaining a conventional stepped phantom.

[0017] Figure 4is a diagram showing the relationship of the existing step phantom and the opening of the gantry.

[0018] Figure 5A is a perspective view showing the elliptical connected phantom of Example 1.

[0019] Figure 5B is a side view showing the elliptical connected phantom of Example 1.

[0020] Figure 5C is a diagram showing the relationship of the elliptical connected phantom of Example 1 and the opening of the gantry.

[0021] Figure 6 is a chart showing the transmission length of the elliptical connected phantom of Example 1 per each channel.

[0022] Figure 7A is a diagram showing the X-ray transmission length in the irradiation field.

[0023] Figure 7B is a diagram showing the 1st distribution phantom of Example 2.

[0024] Figure 7C is a diagram showing the 2nd distribution phantom of Example 2.

[0025] Figure 7D is a diagram showing the 3rd distribution phantom of Example 2.

[0026] Figure 8 is a chart showing the transmission length of the distribution phantom connected phantom of Example 2 per each channel.

[0027] Figure 9 is a diagram showing the drive of the phantom.

[0028] Figure 10 is a diagram showing a configuration example of the 2nd base material phantom.

[0029] Explanation of Reference Numerals

[0030] 101: X-ray CT apparatus, 102: gantry, 103: X-ray tube, 104: bowtie filter, 105: bed, 106: subject, 107: detector panel, 108: arithmetic device, 109: input device, 110: display device, 111: X-ray, 112: opening, 201: combination of base materials, 202: 1st base material, 203: 2nd base material, 204: correction data, 301: step phantom, 401: trolley, 402: drive unit, 404: irradiation field, 501: elliptical connected phantom, 701: 1st distribution phantom, 702: 2nd distribution phantom, 703: 3rd distribution phantom, 710: focal point, 711: tangent point, 712: circular arc, 901: support unit, 902: 2nd base material phantom DETAILED DESCRIPTION

[0031] Embodiments of the present application will be described below with reference to the accompanying drawings. The present application is applied to a radiation imaging apparatus equipped with a radiation source and a photon counting type detector. In the following description, an example in which the radiation is X-rays and the radiation imaging apparatus is an X-ray CT apparatus will be described.

[0032] [Example 1]

[0033] In Figure 1 An overall configuration of an X-ray CT apparatus 101 of the present embodiment is shown. In addition, a lateral direction of a paper surface is set as an X-axis, a longitudinal direction is set as a Y-axis, and a direction orthogonal to the XY plane is set as a Z-axis. The X-ray CT apparatus 101 is equipped with a gantry 102, an X-ray tube 103, a bowtie filter 104, a table 105, a detector panel 107, a computing apparatus 108, an input apparatus 109, and a display apparatus 110.

[0034] A subject 106 is placed on the table 105, which is disposed in an opening 112 provided in the gantry 102. X-rays 111 radiated from the X-ray tube 103 are shaped into a beam shape suitable for the size of the subject 106 by the bowtie filter 104, and are irradiated to the subject 106, and are detected by the detector panel 107 after passing through the subject 106. The X-ray tube 103 and the detector panel 107 are installed to the gantry 102 in a manner of being disposed in opposition to each other with the subject 106 interposed therebetween, and are rotated around the subject 106 by a rotation driving portion of the gantry 102. By repeating X-ray irradiation from the X-ray tube 103 and X-ray measurement in the detector panel 107 together with rotation of the X-ray tube 103 and the detector panel 107, projection data under various projection angles are acquired.

[0035] A tomographic image of the subject 106 is generated by performing image reconstruction processing on the acquired projection data by the computing apparatus 108, and is displayed on the display apparatus 110. Further, if the projection data is acquired while the table 105 on which the subject 106 is placed and the gantry 102 relatively move in the Z-axis direction, a volumetric image of the subject 106 is generated. In addition, the amount of X-rays irradiated from the X-ray tube 103, the rotation speed of the gantry 102, and the relative movement speed of the gantry 102 and the table 105 are set based on a scan condition input by an operator via the input apparatus 109. Further, the computing apparatus 108 is a hardware configuration similar to a general computer apparatus, and is equipped with a CPU (Central Processing Unit), a memory, an HDD (Hard Disk Drive), and the like, and performs correction processing on the projection data and the like, and control of each portion.

[0036] The detector panel 107 is configured by arranging a plurality of detection elements P in a circular arc shape centered on the X-ray focus of the X-ray tube 103. The detection element P is a photon counting type detector that measures the energy of the incident X-ray photons, i.e., the photon energy, and performs an output corresponding to the photon energy.

[0037] In the X-ray CT apparatus 101 provided with the photon counting type detector, since the photon energy spectrum related to the projection data of the object 106 can be acquired, a medical image that discriminates substances of different compositions, a medical image divided into a plurality of energy components can be generated. In addition, in order to obtain a medical image that discriminates substances of different compositions and the like, it is necessary to correct in advance the relationship between the output and the photon energy when the photon counting type detector measures a plurality of combinations of base substances of known composition and thickness.

[0038] The use of Figure 2 will be described for the correction of the photon counting type detector. The correction of the photon counting type detector uses a plurality of combinations 201 of base substances of known composition and thickness, such as two base substances of the first base substance 202 and the second base substance 203. The combination 201 of base substances can use a plurality of different thicknesses of plates for each base substance. For example, if the thickness of the first base substance 202 is J kinds and the thickness of the second base substance 203 is K kinds, J x K kinds of combinations 201 of base substances are used, and the photon energy spectrum is acquired for each combination for each detector element. In Figure 2 , since J = 3 and K = 3, nine kinds of photon energy spectra are shown as the correction data 204. The acquired correction data 204 is stored in a storage section of the arithmetic device 108 and used in the correction of the projection data of the object 106.

[0039] The use of Figure 3 will be described for the existing stepped phantom 301 exemplified in Non-Patent Literature 1. The stepped phantom 301 includes the first base substance 202 and the second base substance 203, the first base substance 202 uses acrylic acid, and the second base substance 203 uses aluminum having a larger attenuation coefficient for X-rays than acrylic acid. In addition, the first base substance 202 forms four levels of steps, and the second base substance 203 that forms four levels of steps is placed on each step of the first base substance 202. That is, 25 kinds of combinations of base substances are formed by the stepped phantom 301 in which the first base substance 202 and the second base substance 203 of five kinds of thicknesses including zero thickness are arranged in the Z-axis direction. In addition, the length in the Z-axis direction of each step of the second base substance 203 is set to be longer than the length in the Z-axis direction of the X-rays 111 incident to the detector panel 107, so that the X-rays 111 incident to the detector panel 107 are transmitted through the base substances of the same thickness.

[0040] The stepped phantom 301 is mounted on the dolly 401 via the drive section 402, and is moved in the Z-axis direction by the drive section 402. By the movement of the stepped phantom 301 in the Z-axis direction, a given combination of base substances is arranged in the irradiation field 404 of the X-rays 111. In order to generate a tomographic image of a general examinee, the irradiation field 404 has a diameter of 50 cm or so, and therefore the first base substance 202 also needs a maximum thickness of the same order. Further, the second base substance 203 needs a thickness that attenuates X-rays to the same extent as the first base substance 202 of the maximum thickness. The stepped phantom 301 including the first base substance 202 of the maximum thickness of 50 cm or so becomes a weight of over 100 kg, and becomes difficult to handle, and the acquisition of the correction data takes time.

[0041] The use of Figure 4 will be described with respect to the relationship between the stepped phantom 301 and the opening 112 of the gantry 102. If the stepped phantom 301 is expanded in conformity with the irradiation field 404, the stepped phantom 301 becomes larger than the opening 112 and cannot pass through the opening 112. That is, the stepped phantom 301 is difficult to handle not only in terms of weight but also in terms of size. Therefore, in Embodiment 1, the time required for the acquisition of the correction data is shortened by making the phantom lightweight or small-sized.

[0042] The use of Figures 5A-5C will be described with respect to the phantom of Embodiment 1, that is, the elliptical connection phantom 501. In addition, Figure 5A is a perspective view of the elliptical connection phantom 501, Figure 5B is a side view, Figure 5C is a front view, and is a view for explaining the relationship between the elliptical connection phantom 501 and the opening 112.

[0043] The elliptical connection phantom 501 is formed of the first base substance 202 having a smaller attenuation coefficient for X-rays than the second base substance 203, and the thickness changes in steps in the direction orthogonal to the irradiation field 404, that is, the Z-axis direction. Further, each step of the elliptical connection phantom 501 in the Z-axis direction is thinned as the distance from the center of the irradiation field 404 becomes longer in the direction in which the detection elements P of the detector panel 107 are arrayed.

[0044] More specifically, the elliptical connection phantom 501 is formed by connecting a plurality of elliptical cylinders having equal lengths of major axes and different lengths of minor axes in the Z-axis direction. In addition, it is preferable that one of the plurality of elliptical cylinders be a circular cylinder having equal lengths of major axis and minor axis. As Figure 5CAs illustrated, since the elliptical connecting body mold 501 is of a size that fits in the irradiation field 404, it does not have a weight that is difficult to handle, and the time required to acquire correction data can be shortened. Furthermore, since the elliptical cylinder is similar in shape to the detected body 106, the influence of scattered rays generated by the detected body 106 is included in the correction data.

[0045] In addition, when N is the number of elliptical cylinders, that is, the number of steps in the Z-axis direction, it is preferable that the length of the minor axis of the i-th elliptical cylinder from one end in the Z-axis direction be i / N times the length of the major axis. By making the ratio of the minor axis to the major axis of the i-th elliptical cylinder i / N, since the difference in the X-ray transmission length between adjacent elliptical cylinders in the Z-axis direction becomes approximately equal, the processing of the acquired correction data becomes easy.

[0046] Figure 6 is an example of a graph that indicates the X-ray transmission length of the elliptical connecting body mold 501 in each channel of the detector panel 107. In Figure 6 In the illustrated graph, the vertical axis is the X-ray transmission length that has been normalized, and the horizontal axis is the channel of the detector panel 107. In addition, the elliptical connecting body mold 501 is formed by connecting four elliptical cylinders, and the ratio of the minor axis to the major axis of each elliptical cylinder is 1 / 4, 2 / 4, 3 / 4, and 4 / 4. Furthermore, since the detector panel 107 is left-right symmetrical, the left end of the horizontal axis is made to correspond to the center of the irradiation field 404, and the vertical axis is normalized using the diameter, which is the maximum thickness of the cylinder whose ratio of the minor axis to the major axis is 4 / 4. As Figure 6 As illustrated, since the difference in the X-ray transmission length between adjacent elliptical cylinders in the Z-axis direction is approximately equal in most of the channels of the detector panel 107, the correction data acquired using the elliptical connecting body mold 501 can be easily processed.

[0047] As explained above, the elliptical connecting body mold 501 of Embodiment 1 does not have a weight that is difficult to handle, and the time required to acquire correction data can be shortened. Furthermore, if the length of the minor axis of the i-th elliptical cylinder from one end in the Z-axis direction is i / N times the length of the major axis, the processing of the acquired correction data becomes easy. In addition, the correction data acquired using the elliptical connecting body mold 501 is stored in the storage section of the arithmetic device 108, and is used in the correction of the projection data of the detected body 106.

[0048]

Embodiment 2

[0049] In Embodiment 1, the elliptical connecting body mold 501 in which a plurality of elliptical cylinders are connected in the Z-axis direction was explained. In Embodiment 2, a distribution body connecting body mold in which distribution bodies having thicknesses that are assigned X-ray transmission lengths in the irradiation field 404, that is, thicknesses multiplied by a coefficient of 1 or less, are connected in the Z-axis direction is explained.

[0050] The distribution body joint body mold 501 is also formed of the first base material 202, and the thickness changes in steps in the direction orthogonal to the irradiation field 404, that is, the Z-axis direction. Further, each step of the distribution body joint body mold in the Z-axis direction is thinned as the distance from the center of the irradiation field 404 becomes longer in the direction in which the detection elements P of the detector panel 107 are arranged.

[0051] The distribution body joint body mold 501 is also formed of the first base material 202, and the thickness changes in steps in the direction orthogonal to the irradiation field 404, that is, the Z-axis direction. Further, each step of the distribution body joint body mold in the Z-axis direction is thinned as the distance from the center of the irradiation field 404 becomes longer in the direction in which the detection elements P of the detector panel 107 are arranged. Figures 7A-7D The distribution body joint body mold 501 is also formed of the first base material 202, and the thickness changes in steps in the direction orthogonal to the irradiation field 404, that is, the Z-axis direction. Further, each step of the distribution body joint body mold in the Z-axis direction is thinned as the distance from the center of the irradiation field 404 becomes longer in the direction in which the detection elements P of the detector panel 107 are arranged. Figure 7A is a view illustrating the X-ray transmission length in the irradiation field 404, Figure 7B is a view illustrating the first distribution body 701 that is a part of the distribution body joint body mold, Figure 7C is a view illustrating the second distribution body 702, Figure 7D is a view illustrating the third distribution body 703.

[0052] As shown in Figure 7A , the X-ray transmission length in the irradiation field 404 differs for each detection element of the detector panel 107, and L0, which passes through the center of the irradiation field 404, is the longest, and as L1, L2, it becomes shorter as it moves away from the center. Figures 7B-7D The first distribution body 701, the second distribution body 702, and the third distribution body 703 shown in have thicknesses that are multiplied by a coefficient of 1 or less with respect to the X-ray transmission length in the irradiation field 404. That is, the distribution body joint body mold, like the elliptical joint body mold 501, is contained in the size of the irradiation field 404, and thus does not have a weight that is difficult to handle, and the time required to acquire the correction data can be shortened. Further, since each distribution body is similar in shape to the detected body 106, the influence of the scattered rays generated by the detected body 106 is included in the correction data.

[0053] Further, when N is the number of distribution bodies, that is, the number of steps in the Z-axis direction, it is preferable that the X-ray transmission length of the i-th distribution body from one end in the Z-axis direction be i / N times the X-ray transmission length in the irradiation field 404. For example, the first distribution body 701 among the four distribution bodies is set to have an X-ray transmission length of 1 / 4 times the irradiation field 404, the second distribution body 702 is set to have an X-ray transmission length of 2 / 4 times, and the third distribution body 702 is set to have an X-ray transmission length of 3 / 4 times. By making the ratio of the X-ray transmission length of the i-th distribution body to the X-ray transmission length in the irradiation field 404 i / N, the difference in the X-ray transmission length between adjacent distribution bodies in the Z-axis direction becomes uniform in all channels of the detector panel 107, and thus the processing of the acquired correction data becomes easy.

[0054] Further, the X-ray transmission length of each distribution body is preferably set with reference to a circular arc 712 centered on the focal point 710 of the X-rays that passes through a tangent 711 of the irradiation field 404 that passes through the focal point 710 of the X-rays and a tangent point of the irradiation field 404. More specifically, the length of half of the X-ray transmission length of each distribution body is preferably set on each of the focal point 710 side and the opposite side of the circular arc 712. By setting the X-ray transmission length of each distribution body with reference to the circular arc 712, the channels in which the X-ray transmission length of each distribution body becomes zero are aligned.

[0055] Figure 8 is an example of a graph that indicates the X-ray transmission length of the distribution body joint body pattern in each channel of the detector panel 107. Figure 8 The example graph is the same as Figure 6 Also, the vertical axis is the X-ray transmission length that has been normalized, and the horizontal axis is the channel of the detector panel 107. In addition, the distribution body joint body pattern is formed by joining the first distribution body 701, the second distribution body 702, the third distribution body 703, and a cylinder, and the X-ray transmission length of each distribution body is 1 / 4, 2 / 4, and 3 / 4 of the X-ray transmission length of a cylinder having an outer diameter equal to the diameter of the irradiation field 404. Further, since the detector panel 107 is left-right symmetrical, the left end of the horizontal axis is made to correspond to the center of the irradiation field 404, and the vertical axis is normalized using the maximum thickness, i.e., the diameter, of the cylinder. As shown in Figure 8 The difference in the X-ray transmission length between each distribution body adjacent in the Z-axis direction is equal in all channels of the detector panel 107, and the channels in which the X-ray transmission length becomes zero are also aligned. As a result, the correction data obtained using the distribution body joint body pattern can be easily processed.

[0056] As explained above, the distribution body joint body pattern of Embodiment 2 does not have a weight that is difficult to handle, and the time required to obtain the correction data can be shortened. Further, if the X-ray transmission length of the i-th distribution body from one end in the Z-axis direction is i / N times the X-ray transmission length of the irradiation field 404, the processing of the obtained correction data becomes easy. In addition, the correction data obtained using the distribution body joint body pattern is stored in the storage section of the arithmetic device 108 and used in the correction of the projection data of the object 106.

[0057] The elliptical joint body pattern 501 of Embodiment 1 and the distribution body joint body pattern of Embodiment 2 are formed of the first base material 202, and are used in combination with the second base material body pattern formed of the second base material 203 in the obtaining of the correction data. When the first base material 202 and the second base material 203 are used in combination, it is preferable to drive them separately.

[0058] The elliptical joint body pattern 501 of Embodiment 1 and the distribution body joint body pattern of Embodiment 2 are formed of the first base material 202, and are used in combination with the second base material body pattern formed of the second base material 203 in the obtaining of the correction data. When the first base material 202 and the second base material 203 are used in combination, it is preferable to drive them separately. Figure 9The driving of the phantom will be described. In Figure 9 The elliptical connection phantom 501 formed of the first base material 202 is installed in the bed 105 via the support portion 901, and the second base material phantom 902 formed of the second base material 203 is installed in the driving portion 402. That is, the elliptical connection phantom 501 is moved by the driving of the bed 105, and the second base material phantom 902 is moved by the driving of the driving portion 402, and is disposed in the irradiation field 404 in the opening portion 112 of the stand 102. By moving the elliptical connection phantom 501 and the second base material phantom 902 separately, the moving distance in the Z-axis direction can be shortened compared to the stepped phantom 301.

[0059] The second base material phantom 902 will be described using Figure 10 The second base material 203 is thinner than the elliptical connection phantom 501 because the attenuation coefficient with respect to X-rays is smaller than that of the first base material 202. In addition, the second base material phantom 902 can be a shape of a distribution body connection phantom that does not include a cylinder. In the case where the second base material phantom 902 is disposed closer to the X-ray tube 103, the size of the second base material phantom 902 in the X-axis direction can be made smaller.

[0060] The embodiments of the phantom and the correction method of the radiation imaging apparatus and the photon counting type detector according to the present application have been described above. In addition, the phantom and the correction method of the radiation imaging apparatus and the photon counting type detector according to the present application are not limited to the above-described embodiments, and the constituent elements can be modified and embodied within the scope of the gist of the present application. Furthermore, the plurality of constituent elements disclosed in the above-described embodiments can be appropriately combined. Furthermore, several constituent elements can be deleted from all the constituent elements shown in the above-described embodiments.

Claims

1. A phantom used when correction data of a photon counting type detector that outputs an electric signal corresponding to a photon energy of an incident radiation line is acquired, the phantom characterized by, comprising a first base substance and a second base substance as known substances, the first base substance having a smaller attenuation coefficient for the radiation line than the second base substance, the thickness varying in steps in a direction orthogonal to an irradiation field of the radiation line, at each step, the thickness becoming thinner as a distance from a center of the irradiation field becomes longer in a direction in which detection elements of the photon counting type detector are arranged, a cross-sectional shape of the first base substance in the irradiation field being an ellipse having a minor axis along the radiation line passing through the center of the irradiation field, the length of the minor axis being different for each step in the direction orthogonal to the irradiation field, the length of a major axis of the ellipse being equal in all steps in the direction orthogonal to the irradiation field.

2. The phantom according to claim 1, characterized in that, the length of the minor axis of the i-th ellipse from one end in the direction orthogonal to the irradiation field is i / N times the length of the major axis when N is the number of steps in the direction orthogonal to the irradiation field.

3. The phantom according to claim 1, characterized in that, the thickness of the first base substance in the direction in which the radiation line transmits the first base substance is i / N times the length in which the radiation line transmits the irradiation field at the i-th step from one end in the direction orthogonal to the irradiation field when N is the number of steps in the direction orthogonal to the irradiation field.

4. The phantom according to claim 3, characterized in that, the center of the thickness of the first base substance in the direction in which the radiation line transmits the first base substance forms a circular arc that passes through a tangent of the irradiation field by a focal point of the radiation line and a tangent point of the irradiation field and is centered on the focal point.

5. The phantom according to claim 1, characterized in that, the first base substance and the second base substance are individually moved in the direction orthogonal to the irradiation field.

6. A radiation imaging apparatus provided with a photon counting type detector that outputs an electric signal corresponding to a photon energy of an incident radiation line, the radiation imaging apparatus characterized by, comprising: a storage section that stores correction data acquired using the phantom according to claim 1.

7. A correction method of a photon counting type detector that outputs an electric signal corresponding to a photon energy of an incident radiation line, the correction method characterized by, acquiring correction data of the photon counting type detector using a phantom, the phantom comprising a first base substance and a second base substance as known substances, the first base substance having a smaller attenuation coefficient for the radiation line than the second base substance, the thickness varying in steps in a direction orthogonal to an irradiation field of the radiation line, at each step, the thickness becoming thinner as a distance from a center of the irradiation field becomes longer in a direction in which detection elements of the photon counting type detector are arranged, The cross-sectional shape of the first base substance in the irradiation field is an ellipse having a minor axis along a radial line passing through the center of the irradiation field, The length of the minor axis differs for each step in the direction orthogonal to the irradiation field, The length of the major axis of the ellipse is equal in all steps in the direction orthogonal to the irradiation field.

Images