Data processing system, data processing method, and data processing program

Abstract

To enable efficient transfer of projection data of three or more energy bands with reproducibility ensured in a data processing system, a data processing method, and a data processing program.SOLUTION: A data processing system comprises a first data processing apparatus that processes projection data from a photon-counting detector, and a second data processing apparatus, wherein the first data processing apparatus derives at least one first compressed projection data by reducing a resolution of at least one first projection data of at least one energy band among a plurality of projection data to be lower than resolutions of projection data of other plurality of energy bands, and transmits the first compressed projection data and the projection data of the other plurality of energy bands to the second data processing apparatus, and the second data processing apparatus acquires the first compressed projection data and other plurality of projection data, and derives first restored projection data by restoring the first compressed projection data based on the other plurality of projection data and the first compressed projection data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a data processing system, a data processing method, and a data processing program. [Background technology]

[0002] In recent years, photon-counting computed tomography (PCCT) devices, which are radiographic imaging devices equipped with photon-counting detectors, have become well known. PCCT devices are capable of obtaining high-resolution images, i.e., cross-sectional images, with higher resolution than conventional computed tomography (CT) devices. In addition, they can measure the energy of each photon and obtain energy information for each of multiple energy bands. Therefore, PCCT devices can obtain more information than conventional CT devices.

[0003] However, due to the structure of the PCCT device, the detector is placed on a rotating plate along with the X-ray source, and during imaging, the detector detects signals that must be transmitted as projection data to the console while the rotating plate is rotating. For this reason, projection data is transferred from the detector to the console via slip rings instead of wires.

[0004] However, compared to conductive wires, slip rings make data transfer more difficult. Therefore, various methods for compressing projection data output from a detector have been proposed to improve transfer efficiency by reducing the amount of data. For example, Patent Document 1 proposes a method in which, of first and second projection data in two energy bands, the resolution of the second projection data is reduced to compress the second projection data, the compressed second projection data and the first projection data are transferred, and the second projection data is restored using the first projection data at the transfer destination. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2018 / 0146938 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, the photon counting detector may be capable of measuring not only two but three or more energy bands.

[0007] The present disclosure has been made in consideration of the above circumstances, and has as its object to enable efficient transfer of projection data for three or more energy bands while ensuring reproducibility. [Means for solving the problem]

[0008] The data processing system according to the present disclosure includes: a first data processing device that processes projection data from a photon counting detector that detects radiation emitted from a radiation source and transmitted through a subject, and outputs a plurality of projection data items assigned to three or more energy bands corresponding to the number of photons in the radiation; a second data processing device; the first data processing device comprises at least one first processor; the first processor derives at least one first compressed projection data by reducing the resolution of at least one first projection data in at least one energy band among the plurality of projection data relatively to the resolution of projection data in other plurality of energy bands other than the at least one energy band; transmitting at least one of the first compressed projection data and the projection data of the other plurality of energy bands to a second data processing device; the second data processing device comprises at least one second processor; a second processor for acquiring at least one first compressed projection data and a plurality of other projection data; The first compressed projection data is reconstructed based on the other plurality of projection data and the first compressed projection data to derive the first reconstructed projection data.

[0009] In the data processing system according to the present disclosure, the energy band of the first projection data may be relatively higher in energy than the energy band of at least one of the other projection data.

[0010] In addition, in the data processing system according to the present disclosure, the second processor derives the first restored compressed projection data by restoring the first compressed projection data based on a relationship between the first projection data and a plurality of other projection data, which has been derived in advance; The first reconstructed projection data may be derived by modifying the first reconstructed compressed projection data to match the first compressed projection data.

[0011] In addition, in the data processing system according to the present disclosure, the photon counting detector outputs three projection data items assigned to three energy bands, respectively; the first processor derives first compressed projection data from first projection data of the three projection data, and transmits second projection data and third projection data other than the first projection data of the three projection data to the second data processing device together with the first compressed projection data as other multiple projection data; The second processor may derive the first restored compressed projection data by restoring the first compressed projection data based on the relationship between the first projection data and the second and third projection data.

[0012] In addition, in the data processing system according to the present disclosure, the second processor may derive the first restored compressed projection data by restoring the first compressed projection data based on the relationship between a first ratio of the second projection data to the third projection data and a second ratio of the first projection data to the third projection data.

[0013] The data processing method according to the present disclosure includes: a first data processing device that processes projection data from a photon counting detector that detects radiation emitted from a radiation source and transmitted through a subject, and outputs a plurality of projection data assigned to three or more energy bands corresponding to the number of photons in the radiation; a second data processing device; and a data processing method in a data processing system including the second data processing device, In the first data processing device, a computer derives at least one first compressed projection data by lowering the resolution of at least one first projection data in at least one energy band among the plurality of projection data relatively to the resolution of projection data in a plurality of energy bands other than the at least one energy band; At least one of the first compressed projection data and the projection data of the other plurality of energy bands is transmitted to a second data processing device.

[0014] In the data processing method according to the present disclosure, in the second data processing device, a computer acquires at least one of the first compressed projection data and the projection data of the other multiple energy bands transmitted by the data processing method according to the present disclosure; The first reconstructed projection data may be derived by reconstructing the first compressed projection data based on the other plurality of projection data and the first compressed projection data.

[0015] A data processing program according to the present disclosure includes: a first data processing device that processes projection data from a photon counting detector that detects radiation emitted from a radiation source and transmitted through a subject, and outputs a plurality of projection data assigned to each of three or more energy bands corresponding to the number of photons of the radiation; a data processing program that causes a computer to execute data processing in a data processing system including a second data processing device, a step of deriving at least one first compressed projection data by lowering the resolution of at least one first projection data in at least one energy band among the plurality of projection data relatively to the resolution of projection data in a plurality of energy bands other than the at least one energy band; and transmitting at least one of the first compressed projection data and the projection data of the other plurality of energy bands to a second data processing device.

[0016] The data processing program according to the present disclosure includes a procedure in which, in a second data processing device, the at least one first compressed projection data and projection data of other multiple energy bands transmitted by the data processing program according to the present disclosure are acquired; and deriving first restored projection data by restoring the first compressed projection data based on the other plurality of projection data and the first compressed projection data. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to efficiently transfer projection data for three or more energy bands while ensuring reproducibility. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram illustrating a data processing system according to an embodiment of the present disclosure. [Figure 2] A flowchart showing the processing performed in this embodiment [Figure 3] FIG. 1 is a diagram for explaining compression and decompression of first projection data; [Figure 4] A diagram showing the relationship between the first ratio and the second ratio DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic configuration diagram of a data processing system according to this embodiment. As shown in Fig. 1, a data processing system 10 according to this embodiment includes a CT device 1 and a console 2.

[0020] The CT device 1 is a PCCT device that detects radiation emitted from a radiation source and generates projection data for generating a tomographic image based on a detection signal corresponding to the number of photons of the radiation. In this embodiment, the case where the radiation is X-rays will be described as an example. The CT device 1 includes an X-ray source 11, an X-ray detector 12, a gantry 13, a bed 14, and a DAS (Data Acquisition System) 15.

[0021] A circular opening 13A is provided in the center of the gantry 13 for placing a bed 14 on which the subject H is placed. The gantry 13 also has a rotating plate 13B fixed at a position where the X-ray source 11 and the X-ray detector 12 (hereinafter simply referred to as the detector 12) face each other, and a drive mechanism (not shown) for rotating the rotating plate 13B.

[0022] The X-ray source 11 includes an X-ray tube 11A, an X-ray filter 11B, and a bowtie filter 11C. The X-ray tube 11A generates X-rays and irradiates the generated X-rays onto the subject H. The X-ray filter 11B adjusts the dose of X-rays irradiated from the X-ray tube 11A. To suppress the dose of radiation in the peripheral area, the bowtie filter 11C increases the dose near the center and decreases the dose in the periphery, thereby optimizing the dose of radiation.

[0023] The detector 12 has a detection surface on which a plurality of detection elements are arranged two-dimensionally, detects X-rays that have passed through the subject H, and outputs a detection signal for each detection element. This makes it possible to detect a detection signal for each transmission position of radiation that passes through a structure of the subject H. The detector 12 is an example of a photon-counting detector disclosed herein.

[0024] The photon-counting detector can measure the energy of each photon and output energy information for each of a plurality of energy bands as a detection signal. In this embodiment, the detector 12 outputs a detection signal for each of, for example, three energy bands. The energy bands can be, for example, 30 keV or more and less than 50 keV, 50 keV or more and less than 100 keV, and 100 keV or more, but are not limited thereto.

[0025] The DAS 15 collects detection signals for each energy band output by the detector 12, generates projection data for each energy band at each position around the rotation axis of the rotating plate 13B based on the collected detection signals, and transmits the generated projection data to the console 2. The DAS 15 is an example of a first data processing device of the present disclosure. On the detection surface of the detector 12, the projection data are arranged such that the direction along the periphery of the rotating plate 13B is the X direction and the direction along the rotation axis is the Y direction. In this embodiment, the projection data are arranged in descending order of energy band as the first projection data P1, the second projection data P2, and the third projection data P3.

[0026] In this embodiment, the DAS 15 has a processor 16 and a storage 17 to perform first data processing, which will be described later. The processor 16 is configured, for example, by a central processing unit (CPU) and a memory such as a random access memory (RAM). The storage 17 is a data storage that stores a first data processing program 17A executed by the DAS 15. Examples of the storage 17 include a hard disk drive (HDD) and a solid state drive (SSD). The processor 16 loads the first data processing program 17A from the storage 17 into the memory and executes the loaded program, thereby performing the first data processing.

[0027] The console 2 includes a display 21, an input device 22, a storage 23, a communication unit 24, and a processor 25. The console 2 is configured, for example, based on a personal computer or the like, and its hardware configuration is similar to that of a general computer. The display 21 is, for example, a liquid crystal display or the like, and displays an operation screen and captured tomographic images, etc. The input device 22 is a device through which an operator inputs operation instructions, and is configured by a keyboard, a mouse, etc. The console 2 is an example of a second data processing device of the present disclosure.

[0028] The storage 23 is a data storage that stores various programs such as a control program that controls each part of the console 2. The various programs include an application program that includes a second data processing program 23A that causes the console 2 to function as a second data processing device. Examples of the storage 23 include an HDD and an SSD. The storage 23 also temporarily stores projection data acquired from the CT device 1.

[0029] The communication unit 24 is a communication interface for communication between the CT device 1 and the console 2. The communication unit 24 is connected to a network (not shown) such as a LAN (Local Area Network) and / or a WAN (Wide Area Network), and performs transmission control in accordance with communication protocols defined by various wired or wireless communication standards.

[0030] The processor 25 is configured by, for example, a CPU and a memory such as a RAM, etc. The processor 25 loads various programs including the second data processing program 23A from the storage 23 into the memory and executes the loaded programs to perform the second data processing.

[0031] Furthermore, the processor 25 controls each part of the CT device 1 in accordance with instructions from the operator inputted from the input device 22, and causes the parts to perform imaging of the subject H. Furthermore, the processor 25 performs a reconstruction process to generate a tomographic image by reconstructing the tomographic image based on the projection data acquired from the CT device 1.

[0032] Next, the processing performed in this embodiment will be described. Fig. 2 is a flowchart showing the processing performed in this embodiment. Here, the first data processing performed by the DAS 15 in the CT device 1 and the second data processing performed by the processor 25 of the console 2 will be described. First, in the CT device 1, the detector 12 acquires first to third projection data P1 to P3 in three energy bands at each position around the rotation axis of the detector 12 based on the detection signal at each pixel (step ST1).

[0033] Next, the DAS 15 derives first compressed projection data PC1 by lowering the resolution of the first projection data P1 in the highest energy band relatively compared to the resolutions of the second projection data P2 and the third projection data P3 (step ST2). Fig. 3 is a diagram for explaining the derivation of the first compressed projection data. Note that Fig. 3 shows the values ​​of detection signals for six pixels arranged in the X direction of each projection data for the first projection data P1 to the third projection data P3, i.e., pixel values.

[0034] The DAS 15 derives first compressed projection data PC1 by compressing the first projection data P1 in the X direction by adding the pixel values ​​of two adjacent pixels for the first projection data P1 and reducing the resolution of the first projection data P1 in the X direction by half. Specifically, as shown in FIG. 3, the pixel values ​​of the two pixels on the left side of the first projection data P1 are 9 and 17, respectively, so the leftmost pixel value of the first compressed projection data PC1 is 26. The pixel values ​​of the two middle pixels of the first projection data P1 are 13 and 34, respectively, so the middle pixel value of the first compressed projection data PC1 is 47. The pixel values ​​of the two rightmost pixels of the first projection data P1 are 30 and 43, respectively, so the rightmost pixel value of the first compressed projection data PC1 is 73.

[0035] The first projection data P1 may be compressed in the Y direction, or in both the X and Y directions.

[0036] The DAS 15 transmits the first compressed projection data PC1, the second projection data P2, and the third projection data P3 to the console 2 (data transmission: step ST3). Note that the second projection data P2 and the third projection data P3 are not compressed. Steps ST1 to ST3 correspond to the first data processing.

[0037] The processor 25 of the console 2 derives the first restored projection data PD1 by restoring the first compressed projection data PC1 based on the second projection data P2 and the third projection data P3. In this embodiment, the processor 25 derives the first restored projection data PD1 by restoring the first compressed projection data PC1 based on the relationship between a first ratio R1 of the second projection data P2 to the third projection data P3 and a second ratio R2 of the first projection data P1 to the third projection data P3.

[0038] The relationship between the first ratio R1 and the second ratio R2 will be described below. In this embodiment, a large number of first projection data P1, second projection data P2, and third projection data P3 are acquired in advance. The processor 25 derives the first ratio R1 (=P2 / P3) and the second ratio R2 (=P1 / P3) for each pixel value of the first projection data P1, second projection data P2, and third projection data P3 acquired during the same imaging session.

[0039] The magnitude of the energy of the energy bands of the first projection data P1, the second projection data P2, and the third projection data P3 is P1>P2>P3. Therefore, the first ratio R1 and the second ratio R2 represent the radiation quality of the X-rays that pass through the subject H and are irradiated onto the detector 12. Here, the X-rays emitted from the X-ray source 11 are attenuated differently depending on the thickness and composition of the subject H, and therefore the detector 12 detects X-rays of different radiation qualities (i.e., spectral hardness).

[0040] FIG. 4 is a diagram showing an example of the relationship between the first ratio R1 and the second ratio R2. In FIG. 4, the horizontal axis represents the first ratio R1, and the vertical axis represents the second ratio R2. As shown in FIG. 4, the relationship between the first ratio R1 and the second ratio R2 is roughly expressed by a linear function. Therefore, the relationship between the first ratio R1 and the second ratio R2 is expressed by the following equation (1). In equation (1), a is the slope of the straight line in FIG. 4, and b is the value at the intersection of the straight line and the R2 axis. R2=a×R1+b (1)

[0041] 4, it can be seen that when the first ratio R1 is large (i.e., the radiation quality is hard), the second ratio R2 also becomes large. Note that the relationship between the first ratio R1 and the second ratio R2 is derived in advance and stored in the storage 23.

[0042] The relationship between the first ratio R1 and the second ratio R2 is derived by actually measuring the first projection data P1, the second projection data P2, and the third projection data P3. Therefore, the relationship between the first ratio R1 and the second ratio R2 may be expressed not only by a linear function, but also by a multidimensional function, a nonlinear function, or the like.

[0043] The processor 25 restores the first compressed projection data by referring to the relationship between the first ratio R1 and the second ratio R2, and derives the first restored compressed projection data PCD1 (step ST4). When the first ratio R1 and the second ratio R2 have the relationship shown in the above formula (1), formula (1) can be transformed into the following formula (2). (P1 / P3)=a×(P2 / P3)+b (2)

[0044] Therefore, the pixel value PCD1 of the first restored compressed projection data PCD1 can be derived by the following equation (3). PCD1=a×P2+b×P3 (3)

[0045] For example, when a=3.32 and b=−2.78, the pixel values ​​of the first restored compressed projection data PCD1 are derived as 8.6, 13.5, 14.1, 36.0, 30.0, and 44.8 from the left, as shown in FIG.

[0046] Next, the processor 25 derives the first restored projection data PD1 by correcting the first restored compressed projection data PCD1 to match the first compressed projection data PC1 (step ST5). Here, as shown in FIG. 3, the two pixel values ​​on the left side of the first restored compressed projection data PCD1 are 8.6 and 13.5, and their sum is 22.1. Comparing the sum, 22.1, with the leftmost pixel value, 26, of the first compressed projection data PC1, the pixel value of the first compressed projection data PC1 is 18% larger. Therefore, the processor 25 increases the two pixel values ​​on the left side of the first restored compressed projection data PCD1 by 18%, thereby correcting the left pixel values ​​of the first restored projection data PD1 to 10.1 and 15.9, respectively.

[0047] Similarly, the processor 25 corrects the two central pixel values ​​of 14.1 and 36.0 of the first restored compressed projection data PCD1 to 13.2 and 33.8 based on the central pixel value of 47 of the first compressed projection data PCD1. Furthermore, the processor 25 corrects the two right pixel values ​​of 30.0 and 44.8 of the first restored compressed projection data PCD1 to 29.3 and 43.7 based on the right pixel value of 73 of the first compressed projection data PCD1. Steps ST4 and ST5 correspond to the second data processing.

[0048] Then, the processor 25 derives a tomographic image by reconstructing it using the first restored projection data PD1, the second projection data P2, and the third projection data P3 (step ST6), and ends the process. That is, the processor 25 generates a tomographic image for the energy band of the first projection data P1 by using the first restored projection data PD1. For the energy band of the second projection data P2, it generates a tomographic image by using the second projection data P2. For the energy band of the third projection data P3, it generates a tomographic image by using the third projection data P3.

[0049] As described above, in this embodiment, by making the resolution of at least one first projection data P1 in at least one energy band among the plurality of projection data P1 to P3 relatively lower than that of the projection data in the other energy bands, at least one first compressed projection data PC1 is derived, and the first compressed projection data PC1 and the plurality of projection data other than the at least one first compressed projection data PC1 among the plurality of projection data (i.e., the second projection data P2 and the third projection data P3) are transmitted to the console 2. This makes it possible to reduce the amount of projection data transmitted from the CT apparatus 1 to the console 2. Therefore, it is possible to efficiently transfer projection data in three or more energy bands.

[0050] In this embodiment, the first restored projection data PD1 is derived by restoring the first compressed projection data PC1 based on at least one first compressed projection data PC1 and a plurality of projection data (i.e., the second projection data P2 and the third projection data P3). This allows the transfer of projection data in three or more energy bands to be performed efficiently while ensuring reproducibility.

[0051] In the above embodiment, the relationship between the first ratio R1 and the second ratio R2 is derived by an equation, but this is not limiting. For example, the relationship between the first projection data P1 and the second projection data P2 and the third projection data P3 may be derived in advance as a lookup table and stored in the storage 23, and the first projection data P1 may be derived by referring to the lookup table.

[0052] In the above embodiment, the first projection data P1 in the highest energy band is compressed, but this is not limiting. The third projection data P3 in the lowest energy band may be compressed, or the second projection data P2 in the intermediate energy band may be compressed.

[0053] Furthermore, in the above embodiment, the photon-counting detector outputs detection signals in three energy bands, but this is not limited thereto. Detection signals in three or more energy bands may be derived. In this case, the DAS 15 compresses projection data in at least one of the multiple energy bands and transmits it to the console 2. Note that the console 2 may derive in advance a relationship between the projection data in the compressed energy band and the projection data in the other energy bands, and restore the projection data of the compressed energy band by referring to this relationship.

[0054] In addition, in the above embodiment, the processors 16 and 25 include a CPU, which is a general-purpose processor that executes software (programs) and functions as various processing units, as well as a PLD (Programmable Logic Device) such as an FPGA (Field-Programmable Gate Array) whose circuit configuration can be changed after manufacture, and a dedicated electrical circuit, which is a processor having a circuit configuration designed specifically to execute specific processing such as an ASIC.

[0055] The various processes described above 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). Furthermore, 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).

[0056] The following are appendices to the present disclosure. [Explanation of symbols]

[0057] 1 CT device 2 Console 11 X-ray source 11A X-ray tube 11B X-ray filter 11C Bowtie Filter 12 X-ray detector 13 Gantry 13A opening 13B Rotating Plate 14 berths 15 DAS 16 processors 17. Storage 17A First Data Processing Program 21 Display 22 Input Devices 23 Storage 23A Second Data Processing Program 24 Communications Department 25 processors H Subject P1~P3 1st to 3rd projection data PC1 First compressed projection data PCD1 First restored compressed projection data PD1 First restored projection data

Claims

1. a first data processing device that detects radiation emitted from a radiation source and transmitted through a subject, and processes the projection data from a photon counting detector that outputs a plurality of projection data items assigned to three or more energy bands corresponding to the number of photons of the radiation; a second data processing device; the first data processing device comprises at least one first processor; the first processor derives at least one first compressed projection data by reducing the resolution of at least one first projection data in at least one energy band among the plurality of projection data relatively to projection data in a plurality of energy bands other than the at least one energy band; transmitting the at least one first compressed projection data and the projection data of the other plurality of energy bands to the second data processing device; the second data processing device comprises at least one second processor; the second processor acquires the at least one first compressed projection data and the other plurality of projection data; a data processing system that derives first reconstructed projection data by reconstructing the first compressed projection data based on the other plurality of projection data and the first compressed projection data;

2. 2. The data processing system of claim 1, wherein an energy band of the first projection data is relatively higher in energy than an energy band of at least one of the other plurality of projection data.

3. the second processor derives first restored compressed projection data by restoring the first compressed projection data based on a relationship between the first projection data and the other plurality of projection data, which has been derived in advance; 3. A data processing system according to claim 1, wherein said first reconstructed projection data is derived by modifying said first reconstructed compressed projection data to match said first compressed projection data.

4. the photon-counting detector outputs three projection data items assigned to three energy bands, respectively; the first processor derives the first compressed projection data from the first projection data of the three projection data, and transmits second projection data and third projection data other than the first projection data of the three projection data to the second data processing device together with the first compressed projection data as the other plurality of projection data; 4. The data processing system of claim 3, wherein the second processor derives first restored compressed projection data by restoring the first compressed projection data based on a relationship between the first projection data and the second projection data and the third projection data.

5. 5. The data processing system of claim 4, wherein the second processor derives first restored compressed projection data by restoring the first compressed projection data based on a relationship between a first ratio of the second projection data to the third projection data and a second ratio of the first projection data to the third projection data.

6. a first data processing device that detects radiation emitted from a radiation source and transmitted through a subject, and processes the projection data from a photon counting detector that outputs a plurality of projection data items assigned to three or more energy bands corresponding to the number of photons of the radiation; a second data processing device, wherein a computer in the first data processing device derives at least one first compressed projection data by lowering a resolution of at least one first projection data in at least one energy band among the plurality of projection data relatively to projection data in a plurality of energy bands other than the at least one energy band; a data processing method for transmitting the at least one first compressed projection data and the projection data of the other plurality of energy bands to the second data processing device;

7. In the second data processing device, a computer acquires the at least one first compressed projection data and the projection data of the other plurality of energy bands transmitted by the data processing method according to claim 6, a data processing method for deriving first reconstructed projection data by reconstructing the first compressed projection data based on the other plurality of projection data and the first compressed projection data;

8. a first data processing device that detects radiation emitted from a radiation source and transmitted through a subject, and processes the projection data from a photon counting detector that outputs a plurality of projection data items assigned to three or more energy bands corresponding to the number of photons of the radiation; a data processing program for causing a computer to execute data processing in a data processing system including a second data processing device, a step of deriving at least one first compressed projection data by lowering the resolution of at least one first projection data in at least one energy band among the plurality of projection data relatively to the resolution of projection data in a plurality of energy bands other than the at least one energy band; and transmitting the at least one first compressed projection data and the projection data in the other plurality of energy bands to the second data processing device.

9. a step of acquiring, in the second data processing device, the at least one first compressed projection data and the projection data of the other plurality of energy bands transmitted by the data processing program according to claim 8; and a procedure of deriving first restored projection data by restoring the first compressed projection data based on the other plurality of projection data and the first compressed projection data.

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