Radiographic imaging control device, method, and program
Patent Information
- Application Number
- JP2024574283
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Priority Date
- 2023-11-29
- Filing Date
- 2023-11-29
- Publication Date
- 2025-10-16
Abstract
Description
Radiography control device, method and program
[0001] The present disclosure relates to a radiography control device, method, and program.
[0002] Conventionally, radiation that has passed through a subject is detected by a radiation detector such as an FPD (Flat Panel Detector) to obtain a radiographic image for use in diagnosis. In such systems, a radiographic imaging system has been proposed that includes an auto exposure control (AEC) mechanism that detects the amount of radiation that reaches the radiation detector and stops the irradiation of radiation when a certain amount of radiation is reached (see, for example, Japanese Patent Application Laid-Open No. 2013-233420). By using such a system, the amount of radiation that reaches the radiation detector can be controlled to a constant level, thereby enabling radiographic images suitable for diagnosis to be obtained at all times.
[0003] Meanwhile, energy subtraction processing is known, which utilizes the difference in attenuation of transmitted radiation depending on the material constituting the subject, and uses two radiological images obtained by irradiating the subject with two types of radiation with different energy distributions. A layered detector has been proposed as a radiation detector for performing this energy subtraction processing. A layered detector is formed, for example, by stacking two radiation detectors in a layered configuration. By using such a layered detector, energy subtraction imaging can be performed with a single radiation exposure. Furthermore, by acquiring a radiological image using only the radiation detector closest to the radiation source, simple imaging similar to that using only one radiation detector can be performed.
[0004] However, when a layered detector is used, the radiation dose irradiated to the radiation detector farther from the radiation source is smaller than the radiation dose irradiated to the radiation detector closer to the radiation source. Therefore, unless the dose is appropriately set when performing energy subtraction processing, the radiation dose irradiated to the radiation detector farther from the radiation source will be too small, reducing the signal-to-noise ratio (S / N) and, as a result, reducing the image quality of the radiographic image obtained by energy subtraction processing.
[0005] The present disclosure has been made in consideration of the above circumstances, and has an object to make it possible to acquire high-quality radiographic images when performing radiography using a layer structure detector.
[0006] The radiation imaging control device according to the present disclosure is a radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, and includes: a layered detector configured by stacking a plurality of radiation detectors, each having a plurality of dose detection pixels that detect the dose during radiation imaging; and at least one processor, wherein the processor acquires the imaging purpose, determines, according to the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the radiation dose during radiation imaging, and performs dose control according to the dose detected by the dose detection pixels of the determined radiation detector.
[0007] In addition, in the radiation imaging control device according to the present disclosure, when the purpose of imaging is simple imaging, the processor may determine that, among multiple radiation detectors, the radiation detector closest to the radiation source is the radiation detector that will perform dose control.
[0008] Furthermore, in the radiation imaging control device according to the present disclosure, when the imaging purpose is energy subtraction imaging, the processor may determine, among the multiple radiation detectors, a radiation detector other than the radiation detector closest to the radiation source as the radiation detector that will perform dose control.
[0009] Furthermore, in the radiation imaging control device according to the present disclosure, when the imaging purpose is energy subtraction imaging, the processor may determine all of the plurality of radiation detectors as radiation detectors that perform dose control.
[0010] In addition, in the radiation imaging control device according to the present disclosure, the processor may determine a target dose when performing radiation imaging in accordance with the imaging purpose, and stop driving the radiation source when the dose detected by the determined dose detection pixels of the radiation detector reaches the target dose.
[0011] Furthermore, in the radiation imaging control device according to the present disclosure, the processor may identify a region of interest in the imaging subject in accordance with the imaging purpose, and perform dose control in accordance with the dose detected by a dose detection pixel located at least at a position corresponding to the region of interest in the radiation detector determined to be the radiation detector for controlling the radiation dose.
[0012] The radiation imaging control method according to the present disclosure is a radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, and is a radiation imaging control method in a radiation imaging control device that has a layered detector configured by stacking a plurality of radiation detectors, each having a plurality of dose detection pixels that detect the dose during radiation imaging, and includes the steps of: acquiring an imaging purpose; determining, according to the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the radiation dose during radiation imaging; and performing dose control according to the dose detected by the dose detection pixels of the determined radiation detector.
[0013] The radiation imaging control program according to the present disclosure is a radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, and is a radiation imaging control program that causes a computer to execute a radiation imaging control method in a radiation imaging control device that has a layered detector configured by stacking a plurality of radiation detectors, each having a plurality of dose detection pixels that detect the dose during radiation imaging, and causes the computer to execute the following steps: acquiring the imaging purpose; determining, according to the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the radiation dose during radiation imaging; and performing dose control according to the dose detected by the dose detection pixels of the determined radiation detector.
[0014] According to the present disclosure, when performing radiography using a layer structure detector, a high-quality radiographic image can be obtained.
[0015] Schematic block diagram showing the configuration of a radiographic image capturing system to which a radiographic image capturing control device according to an embodiment of the present disclosure is applied. FIG. Schematic diagram showing the configuration of a radiation detector. FIG. Illustrates the distribution of dose detection pixels. FIG. Schematic diagram showing the configuration of a radiographic image capturing control device according to this embodiment. FIG. Illustrates the functional configuration of a radiographic image capturing control device according to this embodiment. FIG. Illustrates a region of interest in the chest. Flowchart showing the processing performed in this embodiment. Flowchart showing the processing performed in other embodiments.
[0016]
[0023] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic block diagram showing the configuration of a radiographic image capturing system to which a radiographic image capturing control device according to an embodiment of the present disclosure is applied. As shown in Fig. 1, the radiographic image capturing system according to this embodiment includes an image capturing device 1 and a radiographic image capturing control device 10 according to this embodiment.
[0017] The imaging device 1 includes a radiation source 3 and a layered detector 4. The layered detector 4 is configured by stacking, in order from the side closest to the radiation source 3, a first radiation detector 5, a radiation energy conversion filter 7 made of a copper plate or the like, and a second radiation detector 6.
[0018] By using such a layer structure detector 4, the imaging device 1 can perform energy subtraction using a so-called one-shot method in which radiation such as X-rays that is emitted from the radiation source 3 and has passed through the subject H, which is the imaging target, is irradiated at different energies to the first radiation detector 5 and the second radiation detector 6. Furthermore, by using only the first radiation detector 5 of the layer structure detector 4, it is possible to obtain a radiographic image by simply imaging the subject H.
[0019] Here, energy subtraction is a process that takes advantage of the fact that the amount of attenuation of transmitted radiation differs depending on the material that makes up the subject, and uses two radiological images obtained by irradiating the subject with two types of radiation with different energy distributions to generate images that extract different tissues within the subject (e.g., soft tissue and bone).
[0020] 2 is a diagram showing a schematic configuration of the first and second radiation detectors. When there is no need to distinguish between the first and second radiation detectors, they may be simply referred to as radiation detectors. As shown in FIG. 2, the radiation detectors 5 and 6 each include a pixel region 30, a gate driver 31, a signal processing circuit 32, a control unit 34, and a communication interface (I / F) 35.
[0021] The pixel region 30 has a plurality of normal pixels 40A arranged in a matrix along the X and Y directions, which are orthogonal to each other. The normal pixels 40A are pixels for image generation that detect radiation and generate a radiographic image. In addition to the normal pixels 40A, the pixel region 30 also has a plurality of dose detection pixels 40B. The dose detection pixels 40B are pixels for detecting the dose of radiation irradiated onto the radiation detectors 5 and 6.
[0022] Each normal pixel 40A includes a photoelectric conversion unit 41 that generates and accumulates electric charges by photoelectrically converting visible light converted by the scintillator, and a thin-film transistor (TFT) 42 that serves as a switching element. The photoelectric conversion unit 41 includes, for example, a p-intrinsic-n (PIN) type semiconductor layer, an upper electrode disposed above the semiconductor layer, and a lower electrode disposed below the semiconductor layer. A bias voltage is applied to the upper electrode. The lower electrode is connected to the thin-film transistor (TFT) 42.
[0023] Like the normal pixels 40A, the dose detection pixels 40B have a photoelectric conversion unit 41 and a TFT 42. However, in the dose detection pixels 40B, the source electrode and drain electrode of the TFT 42 are short-circuited. The dose detection pixels 40B are pixels used to detect the amount of radiation that reaches the radiation detectors 5 and 6 after passing through the subject H, and function as AEC sensors for stopping the irradiation of radiation, as will be described later.
[0024] The dose detection pixels 40B account for approximately a few percent of the pixels included in the imaging surface of the radiation detectors 5 and 6. The dose detection pixels 40B are preferably provided so as to be evenly scattered across the imaging surface without being locally biased within the imaging surface. For example, as shown in FIG. 3, the dose detection pixels 40B are preferably provided so as to be evenly distributed across the imaging surface at intervals of several pixels. The positions of the dose detection pixels 40B are known during the manufacture of the radiation detectors 5 and 6, and are preferably stored in advance in a non-volatile memory, which will be described later. Note that the dose detection pixels 40B may be arranged in a concentrated manner in a local area, and the arrangement of the dose detection pixels 40B can be changed as appropriate. Hereinafter, when there is no need to distinguish between the normal pixels 40A and the dose detection pixels 40B, these will be simply referred to as pixels 40.
[0025] 2, the dose detection pixels 40B are arranged vertically and horizontally at intervals of several pixels in place of the normal pixels for image detection of the radiation detectors 5 and 6, but this is not limiting and the dose detection pixels 40B may be arranged in the gaps between the normal pixels 40A. In this case, the positions of the normal pixels do not need to be used as the dose detection pixels 40B, and therefore the pixel density can be increased accordingly.
[0026] The pixel region 30 has a plurality of scanning lines 43 extending in the X direction and a plurality of signal lines 44 extending in the Y direction. The scanning lines 43 and the signal lines 44 are wired in a grid pattern. Each pixel 40 is connected to an intersection of the scanning line 43 and the signal line 44. Specifically, in each pixel 40, the gate electrode of the TFT 42 is connected to the scanning line 43, and the source electrode of the TFT 42 is connected to the signal line 44. The drain electrode of the TFT 42 is connected to the photoelectric conversion unit 41.
[0027] Each scanning line 43 is commonly connected to one pixel row's worth of pixels 40. Each signal line 44 is commonly connected to one pixel column's worth of pixels 40. Each scanning line 43 is connected to the gate driver 31. Each signal line 44 is connected to the signal processing circuit 32.
[0028] The gate driver 31 sequentially supplies gate pulses as scanning signals to each scanning line 43. The gate pulses supplied to the scanning lines 43 are applied to the gate electrodes of the TFTs 42 included in the pixels 40 connected to the scanning lines 43.
[0029] When the TFT 42 is turned on, the charge accumulated in the photoelectric conversion unit 41 of the normal pixel 40A is output to the signal line 44. In the radiation amount detection pixel 40B, the source electrode and drain electrode of the TFT 42 are short-circuited, so the charge generated in the photoelectric conversion unit 41 of the radiation amount detection pixel 40B is output to the signal line 44 regardless of the switching state of the TFT 42.
[0030] The signal processing circuit 32 has an integrator as a charge amplifier, a CDS (correlated double sampling) circuit, and an analog-to-digital (A / D) converter. The signal processing circuit 32 integrates the charges input from each pixel 40 via the signal line 44 using the integrator, and then performs correlated double sampling using the CDS circuit. The signal processing circuit 32 then converts the pixel signals, from which reset noise components have been removed by correlated double sampling, into digital signals using the A / D converter.
[0031] The signal processing circuit 32 generates image data of a radiographic image based on pixel signals read out from each normal pixel 40A in the pixel region 30. Meanwhile, charges generated in the dose detection pixels 40B constantly flow into an integrator on a signal line to which the dose detection pixels 40B are connected in the signal processing circuit 32. The signal processing circuit 32 generates dose data for performing dose control, as will be described later, based on the pixel signals read out from the dose detection pixels 40B.
[0032] The control unit 34 is configured by a microcomputer and includes a CPU (Central Processing Unit), a memory, and a storage device. The control unit 34 performs control for radiographic imaging by causing the CPU to execute a program stored in the memory. The control unit 34 controls each of the gate driver 31, the signal processing circuit 32, and the communication I / F 35.
[0033] When imaging begins, the control unit 34 controls the gate driver 31 and the signal processing circuit 32 to perform a reset operation on the charges accumulated in the normal pixels 40A. Specifically, the control unit 34 causes the gate driver 31 to supply gate pulses to each scanning line 43, thereby outputting the accumulated charges in each normal pixel 40A to the signal line 44 and discarding the charges in the signal processing circuit 32. After the reset operation is completed, the control unit 34 turns off all the TFTs 42, thereby putting the normal pixels 40A into a charge accumulation state.
[0034] The control unit 34 puts the normal pixels 40A into a charge accumulation state, and after radiation irradiation is stopped as described below, controls the gate driver 31 to read pixel signals from the normal pixels 40A to the signal processing circuit 32, thereby generating image data for the radiographic image. Furthermore, when imaging is started, the control unit 34 controls the signal processing circuit 32 to generate dose data from the charges generated in the dose detection pixels 40B. The control unit 34 outputs the radiographic image and dose data to the radiography control device 10 via the communication I / F 35.
[0035] In the radiation imaging control device 10 according to this embodiment, the first and second radiation detectors 5 and 6 included in the layer structure detector 4 described above are switched and used depending on the imaging purpose. That is, when the imaging purpose is simple imaging to obtain one radiation image of the subject H, only the first radiation detector 5, which is closer to the radiation source 3, is used. On the other hand, when the imaging purpose is energy subtraction imaging, both the first radiation detector 5 and the second radiation detector 6 are used.
[0036] Next, a radiation imaging control device according to this embodiment will be described. First, the hardware configuration of the radiation imaging control device according to this embodiment will be described with reference to FIG. 4. As shown in FIG. 4, the radiation imaging control device 10 is a computer such as a workstation, server computer, or personal computer, and includes a CPU (Central Processing Unit) 11, non-volatile storage 13, and memory 16 as a temporary storage area. The radiation imaging control device 10 also includes a display 14 such as a liquid crystal display, input devices 15 such as a keyboard and a mouse, and a network I / F (Interface) 17 connected to a network (not shown). The radiation imaging control device 10 also includes a high-voltage generator 18 and an exposure switch 19 connected to the radiation source 3. The CPU 11, storage 13, display 14, input devices 15, memory 16, network I / F 17, high-voltage generator 18, and exposure switch 19 are connected to a bus 20. The radiation detectors 5 and 6 are also connected to the bus 20. The CPU 11 is an example of a processor in the present disclosure.
[0037] The storage 13 is realized by a hard disk drive (HDD), a solid state drive (SSD), a flash memory, etc. The storage 13 as a storage medium stores the radiation imaging control program 12 installed in the radiation imaging control device 10. The CPU 11 reads the radiation imaging control program 12 from the storage 13, loads it into the memory 16, and executes the loaded radiation imaging control program 12.
[0038] The high voltage generator 18 generates a high tube voltage by boosting the input voltage using a transformer, and supplies the high tube voltage to the radiation source 3 through a high voltage cable.
[0039] The irradiation switch 19 is, for example, a two-stage switch operated by an operator such as a radiologist. When pressed in the first stage, it generates a warm-up start signal for starting the warm-up of the radiation source 3, and when pressed in the second stage, it generates an irradiation start signal for starting irradiation by the radiation source 3.
[0040] The radiation imaging control program 12 is stored in an externally accessible state in a storage device of a server computer connected to a network or in network storage, and is downloaded and installed in response to a request into a computer constituting the radiation imaging control device 10. Alternatively, the program is recorded on a recording medium such as a DVD (Digital Versatile Disc) or CD-ROM (Compact Disc Read Only Memory) and distributed, and is installed from the recording medium into a computer constituting the radiation imaging control device 10.
[0041] Next, the functional configuration of the radiation imaging control device according to this embodiment will be described. Fig. 5 is a diagram showing the functional configuration of the radiation imaging control device according to this embodiment. As shown in Fig. 5, the radiation imaging control device 10 includes a dose control unit 21, a device control unit 22, a subtraction unit 23, and a display control unit 24. The CPU 11 executes the radiation imaging control program 12 to function as the dose control unit 21, the device control unit 22, the subtraction unit 23, and the display control unit 24.
[0042] The dose control unit 21 controls radiography by irradiating radiation onto the subject H. Specifically, the dose control unit 21 drives the radiation source 3 by controlling the tube voltage that determines the energy spectrum of the radiation emitted by the radiation source 3, the tube current that determines the irradiation dose per unit time, the start, stop or termination of irradiation by the radiation source 3, and the radiation irradiation time. That is, the dose control unit 21 starts the supply of power from the high voltage generator 18 to the radiation source 3 when it receives an irradiation start signal from the irradiation switch 19, and stops the supply of power from the high voltage generator 18 to the radiation source 3 when the irradiated dose reaches the target dose, thereby stopping the irradiation of radiation by the radiation source 3.
[0043] The storage 13 stores several types of imaging conditions, such as tube voltage and tube current, in advance, depending on the imaging region, etc. The imaging conditions are manually set by the operator via the input device 15. The dose control unit 21 irradiates radiation at the tube voltage and tube current-irradiation-time product of the set imaging conditions. Meanwhile, as described below, when it detects that the irradiation dose based on the dose data has reached a necessary and sufficient dose, the dose control unit 21 functions to stop the radiation irradiation even if the irradiation time is less than the tube current-irradiation-time product (irradiation time) intended for irradiation based on the imaging conditions. To prevent a dose shortage caused by ending radiation irradiation before reaching the target dose and receiving a radiation irradiation stop signal, a maximum value of the tube current-irradiation-time product (or irradiation time) is set as an imaging condition for the radiation source 3. It is preferable that the set tube current-irradiation-time product be a value corresponding to the imaging region.
[0044] On the other hand, the dose control unit 21 acquires an imaging purpose for dose control. Imaging purposes include, for example, simple imaging, which acquires one radiographic image of the subject H, and energy subtraction imaging. The imaging purpose is set by the operator via the input device 15. When the imaging purpose is simple imaging, only the first radiation detector 5, which is closer to the radiation source 3 in the layered structure detector 4, is used to acquire a radiographic image. On the other hand, when the imaging purpose is energy subtraction imaging, both the first radiation detector 5 and the second radiation detector 6 are used, and a first radiographic image G1 is acquired by the first radiation detector 5 and a second radiographic image G2 is acquired by the second radiation detector 6.
[0045] The dose control unit 21 determines the radiation detector to be used for dose control depending on the imaging purpose. If the imaging purpose is simple imaging, the dose control unit 21 determines the first radiation detector 5 as the radiation detector to be used for dose control. If the imaging purpose is energy subtraction imaging, the dose control unit 21 determines the second radiation detector 6 as the radiation detector to be used for dose control so that the second radiation detector 6, which is farther from the radiation source 3, is irradiated with a sufficient dose of radiation.
[0046] It is also possible to determine a target dose for radiography in accordance with the purpose of radiography, and to control the dose so that the target dose of radiation is irradiated onto the subject H. For example, when the radiography site is the chest and the purpose of radiography is simple radiography, the lung field is the region of interest. Therefore, the target dose is determined so that the lung field has the desired image quality in the radiographic image acquired by simple radiography. This results in the generation of a radiographic image in which the lung field has high image quality.
[0047] In this case, the target dose may be set as follows: Chest phantoms of various thicknesses, made of materials such as acrylic having a radiation attenuation coefficient similar to that of the human body, are imaged while varying the dose. Then, when the lung field in the radiographic image acquired by the first radiation detector 5 has a desired image quality, the average delivered dose in the lung field region is set as the target dose and stored in storage 13. When actually performing imaging, the target dose corresponding to the imaging purpose stored in storage 13 may be read from storage 13 and used.
[0048] Furthermore, when the imaging site is the chest and the imaging purpose is energy subtraction imaging, the target dose is determined so that the lung field, which is the region of interest, has the desired image quality in the radiographic image acquired by the second radiation detector 6 farther from the radiation source 3. This ensures the image quality of the lung field in the radiographic images acquired by both the first radiation detector 5 and the second radiation detector 6. Therefore, energy subtraction processing can derive bone images in the lung field from which soft tissue has been sufficiently removed, and soft tissue images in the lung field from which bone has been sufficiently removed.
[0049] In this case, the target dose may be set as follows: Chest phantoms having various thicknesses are imaged while varying the dose, and when the lung field in the radiographic image acquired by the second radiation detector 6 achieves the desired image quality, the average delivered dose in the lung field region is set as the target dose and saved in storage 13. When actually performing imaging, the target dose according to the imaging purpose that has been saved in storage 13 may be read from storage 13 and used.
[0050] Note that when the imaging objective is energy subtraction imaging, if only the image quality of the lung field, which is the region of interest, is considered, the dose may be insufficient in the mediastinum and subdiaphragm. In this case, even if a bone image is derived by energy subtraction processing, it may be impossible to accurately separate the vertebrae and soft tissue present in the mediastinum and subdiaphragm. Therefore, when the imaging target is the chest and the imaging objective is energy subtraction imaging, the mediastinum and subdiaphragm, other than the lung field, may be used as the region of interest in the radiographic image acquired by the second radiation detector 6 farther from the radiation source 3, and a target dose may be determined so that the mediastinum and subdiaphragm have desired image quality. This ensures the image quality of the entire image in the radiographic images acquired by both the first radiation detector 5 and the second radiation detector 6. Therefore, the energy subtraction processing can be used to derive bone images from which soft tissue has been sufficiently removed even for the vertebrae included in the mediastinum and subdiaphragm, and soft-tissue images from which bone has been sufficiently removed in the mediastinum and subdiaphragm.
[0051] Here, in the energy subtraction process, whether the lung field or the mediastinum and subdiaphragm are to be the regions of interest may be set based on an input from the input device 15 by the operator.
[0052] It is also possible to specify a region of interest in the subject H depending on the purpose of imaging, and in the radiation detector used for dose control, perform dose control according to the dose detected by the dose detection pixels 40B located at positions corresponding to the region of interest. For example, if the region of interest is the lung field, as shown in Figure 6, in the radiation detectors 5 and 6, dose control is performed according to the dose detected by the dose detection pixels 40B located at positions within a region 51 corresponding to the lung field in the radiographic image.
[0053] On the other hand, when the region of interest is the mediastinum and below the diaphragm, as shown in Figure 6, dose control is performed in the radiation detectors 5, 6 according to the dose detected by the dose detection pixel 40B located within a region 52 in the radiation image corresponding to the mediastinum and below the diaphragm.
[0054] When the purpose of imaging is simple imaging, the dose control unit 21 derives a cumulative histogram of dose data for each dose detection pixel 40B and identifies the subject region based on the cumulative histogram. When using dose detection pixels 40B corresponding to the lung field, the dose control unit 21 derives a cumulative histogram of dose data for each dose detection pixel 40B in the identified subject region and performs dose control using the dose data acquired by the dose detection pixels 40B on the high dose side, which corresponds to 80 to 90% of the cumulative histogram.
[0055] On the other hand, when the purpose of imaging is energy subtraction imaging and the dose detection pixels 40B corresponding to the mediastinum and below the diaphragm are used, a cumulative histogram of dose data is derived for each dose detection pixel 40B in the identified subject region, and dose control is performed using the dose data acquired by the dose detection pixels 40B on the low dose side, which corresponds to 20 to 40% in the cumulative histogram.
[0056] Furthermore, the dose detection pixels 40B corresponding to the lung field or the mediastinum and below the diaphragm may be specified in advance, and the dose control may be performed using the dose detection pixels 40B specified according to the region of interest.
[0057] In addition, when the imaging site is an extremity or the like, if the imaging purpose is simple imaging, the first radiation detector 5 may be selected as the radiation detector for dose control, and if the imaging purpose is energy subtraction imaging, the second radiation detector 6 may be selected as the radiation detector for dose control. In this case, the region of interest is often a bone. Therefore, the subject region is identified based on the cumulative histogram of dose data, and in the identified subject region, a cumulative histogram of dose data is derived for each dose detection pixel 40B, and dose control is performed using the dose data acquired by the dose detection pixels 40B on the low-dose side, which corresponds to 20 to 40% of the cumulative histogram.
[0058] The device control unit 22 controls the operations of the first and second radiation detectors 5, 6 in response to input operations from the operator via the input device 15. Specifically, the device control unit 22 performs various controls such as turning the power of the radiation detectors 5, 6 on and off, and switching between standby mode and imaging mode. In addition, the device control unit 22 preferably has a function of performing various image processing such as offset correction, sensitivity correction, and defect correction on the radiation images acquired by the first and second radiation detectors 5, 6.
[0059] When the purpose of radiography is energy subtraction radiography, the subtraction unit 23 performs weighted subtraction between corresponding pixels on the first radiographic image G1 acquired by the first radiation detector 5 and the second radiographic image G2 acquired by the second radiation detector 6, as shown in the following equations (1) and (2), to derive a bone image Gb from which only the bones of the subject H contained in the first radiographic image G1 and the second radiographic image G2 are extracted, and a soft tissue image Gs from which only the soft tissue is extracted. Note that α1 and α2 in the following equations (1) and (2) are weighting coefficients, which are derived based on attenuation coefficients corresponding to the radiation energy of the soft and bone tissues of the subject H. Gb(x,y)=G1(x,y)-α1×G2(x,y) (1) Gs(x,y)=G2(x,y)-α2×G1(x,y) (2)
[0060] The display control unit 24 displays the acquired radiographic image on the display 14. That is, when the purpose of imaging is plain radiography, the display control unit 24 displays the radiographic image acquired by the first radiation detector 5 on the display 14. When the purpose of imaging is energy subtraction imaging, the display control unit 24 displays the bone image Gb and the soft tissue image Gs on the display 14.
[0061] Next, the processing performed in this embodiment will be described. Fig. 7 is a flowchart showing the processing performed in this embodiment. First, the dose control unit 21 acquires the imaging purpose input by the operator via the input device 15 (step ST1), and identifies at least one radiation detector to be used for dose control (step ST2). The dose control unit 21 also determines a target dose to be irradiated to the subject H according to the imaging purpose (step ST3), and identifies a region of interest in the subject H according to the imaging purpose (step ST4).
[0062] Next, when the exposure switch 19 is operated, the dose control unit 21 drives the radiation source 3 to start irradiating radiation (step ST5).The dose control unit 21 then determines whether the dose during imaging has reached the target dose based on the dose data detected by the dose detection pixel 40B located at a position corresponding to the region of interest in the radiation detector for dose control (step ST6).
[0063] If the result of step ST6 is negative, the radiation irradiation continues. If the result of step ST6 is positive, the dose control unit 21 stops the radiation irradiation by the radiation source 3 (step ST7).
[0064] Next, the device control unit 22 acquires radiographic images from the radiation detector according to the purpose of imaging, and performs energy subtraction processing if necessary. The display control unit 24 then displays the acquired radiographic images or bone images and soft tissue images on the display 14 (image display: step ST8), and the process ends.
[0065] As described above, in this embodiment, of the multiple radiation detectors 5 and 6 included in the layer structure detector 4, at least one radiation detector to be used for radiation dose control is determined in accordance with the imaging purpose, and dose control is performed in accordance with the dose detected by the dose detection pixels 40B of the determined radiation detector. Therefore, when performing radiography using the layer structure detector 4, high-quality plain radiographic images, bone images, or soft tissue images can be obtained. Note that, hereinafter, when there is no need to distinguish between plain radiographic images, bone images, and soft tissue images, they may simply be referred to as radiological examination images.
[0066] In particular, when the purpose of imaging is simple imaging, a high-quality simple radiographic image can be obtained by determining the first radiation detector 5, which is closest to the radiation source 3 among the multiple radiation detectors 5 and 6, as the radiation detector that controls the radiation dose.
[0067] Furthermore, when the purpose of imaging is energy subtraction imaging, by determining the second radiation detector 6, other than the first radiation detector 5 that is closest to the radiation source 3, among the multiple radiation detectors 5, 6 as the radiation detector that performs radiation dose control, it is possible to irradiate the second radiation detector 6 that is farther from the radiation source 3 with a sufficient dose of radiation. Therefore, it is possible to acquire high-quality bone images and soft tissue images.
[0068] Furthermore, by determining a target dose according to the purpose of imaging and controlling the dose so that the subject H is irradiated with the target dose of radiation, it is possible to obtain a radiographic image of higher quality.
[0069] In addition, by identifying a region of interest in the subject H according to the purpose of imaging and performing dose control according to the dose detected by the dose detection pixel 40B corresponding to the region of interest, a radiological image with high image quality for the region of interest can be obtained.
[0070] In the above embodiment, when the imaging purpose is energy subtraction imaging, the second radiation detector 6 farther from the radiation source 3 is determined to be the radiation detector to be used for radiation source control, but this is not limited to this. Both the first radiation detector 5 and the second radiation detector 6 may be determined to be the radiation detectors to be used for radiation source control. This will be described below as another embodiment.
[0071] Here, the first radiation detector 5, which is closer to the radiation source 3, receives a larger radiation dose than the second radiation detector 6, and therefore pixel values on the high-density side may become saturated in the radiation image acquired by the first radiation detector 5. On the other hand, the S / N ratio of the radiation image acquired by the second radiation detector 6 may deteriorate due to an insufficient radiation dose.
[0072] For this reason, when the imaging site is the chest, controlling the dose to improve the image quality of the mediastinum and below the diaphragm in the radiographic image acquired by the second radiation detector 6 may result in saturation of pixel values in the lung field in the radiographic image acquired by the first radiation detector 5. Therefore, in another embodiment, the dose control unit 21 may determine both the first radiation detector 5 and the second radiation detector 6 as the radiation detectors for dose control.
[0073] In another embodiment, when the imaging site of the subject H is the chest and the region of interest is the lung field, the dose control unit 21 performs dose control in accordance with the dose detected by the dose detection pixels 40B located in a region corresponding to the lung field in the first radiation detector 5. Furthermore, the dose control unit 21 performs dose control in accordance with the dose detected by the dose detection pixels 40B located in a region corresponding to the mediastinum and below the diaphragm in the second radiation detector 6.
[0074] Specifically, the dose control unit 21 presets an upper limit dose, which is the upper limit at which pixel values of the radiographic image do not become saturated, and controls the driving of the radiation source 3 to stop irradiating radiation when the dose detected by the dose detection pixels 40B corresponding to the lung field region in the first radiation detector 5 reaches the upper limit dose, or when the dose detected by the dose detection pixels 40B corresponding to the mediastinum and below the diaphragm in the second radiation detector 6 reaches a target dose.
[0075] Next, a process performed in another embodiment will be described. FIG. 8 is a flowchart showing a process performed in another embodiment. First, the dose control unit 21 acquires the imaging purpose input by the operator via the input device 15 (step ST11) and identifies at least one radiation detector to be used for dose control (step ST12). In this embodiment, since the imaging purpose is energy subtraction imaging, both the first radiation detector 5 and the second radiation detector 6 are identified as the radiation detectors to be used for dose control. Furthermore, the dose control unit 21 determines a target dose to be irradiated to the subject H in accordance with the imaging purpose (step ST13) and identifies a region of interest in the subject H in accordance with the imaging purpose (step ST14). In this embodiment, the region of interest is the lung field.
[0076] Next, when the exposure switch 19 is operated, the dose control unit 21 drives the radiation source 3 to start irradiating radiation (step ST15). The dose control unit 21 then determines whether the dose irradiated to the subject H has reached the upper limit dose based on the dose data detected by the dose detection pixels 40B located in the first radiation detector 5 at positions corresponding to the region of interest (step ST16). If the result in step ST16 is negative, the dose control unit 21 determines whether the dose during imaging has reached the target dose based on the dose data detected by the dose detection pixels 40B located in the second radiation detector 6 at positions corresponding to the mediastinum and below the diaphragm (step ST17).
[0077] If step ST17 is negative, the process returns to step ST16 to continue the irradiation of radiation. If steps ST16 and ST17 are positive, the dose control unit 21 stops the irradiation of radiation by the radiation source 3 (step ST18).
[0078] Next, the device control unit 22 acquires radiographic images from the radiation detector according to the purpose of imaging, and the subtraction unit 23 performs energy subtraction processing. The display control unit 24 then displays the bone image and soft tissue image derived by the energy subtraction processing on the display 14 (image display: step ST19), and the processing ends.
[0079] In this way, according to another embodiment, the dose can be controlled so that areas of high density in the radiological image do not become saturated, as occurs when the region of interest is the lung field. Therefore, high-quality radiological images can be obtained.
[0080] The radiation in the above embodiment is not particularly limited, and in addition to X-rays, α rays, γ rays, etc. can be used.
[0081] In the above embodiment, the following various processors can be used as the hardware structure of processing units that perform various processes, such as the dose control unit 21, the device control unit 22, the subtraction unit 23, and the display control unit 24. As described above, the various processors include a CPU, which is a general-purpose processor that executes software (programs) and functions as various processing units, as well as dedicated electrical circuits that are processors having a circuit configuration specifically designed to perform specific processes, such as a programmable logic device (PLD) that is a processor whose circuit configuration can be changed after manufacture, such as an FPGA (Field Programmable Gate Array), and an ASIC (Application Specific Integrated Circuit).
[0082] A single processing unit may be configured with one of these various processors, or may be configured with a combination of two or more processors of the same or different types (for example, a combination of multiple FPGAs or a combination of a CPU and an FPGA).Furthermore, multiple processing units may be configured with a single processor.
[0083] Examples of configuring multiple processing units with a single processor include: first, a form in which one processor is configured with a combination of one or more CPUs and software, as typified by client and server computers, and this processor functions as multiple processing units; second, a form in which a processor is used to realize the functions of an entire system including multiple processing units with a single IC (Integrated Circuit) chip, as typified by a system on chip (SoC); thus, various processing units are configured using one or more of the above-mentioned various processors as a hardware structure.
[0084] Furthermore, more specifically, the hardware structure of these various processors can be an electric circuit that combines circuit elements such as semiconductor elements.
[0085] The following are supplementary items of the present disclosure. (Supplementary Item 1) A radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, comprising: a layered detector configured by stacking a plurality of radiation detectors, each having a plurality of dose detection pixels that detect a dose during the radiation imaging; and at least one processor, wherein the processor acquires an imaging purpose, and determines, in accordance with the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for dose control of the radiation during the radiation imaging, and performs the dose control in accordance with the dose detected by the dose detection pixels of the determined radiation detector. (Supplementary Item 2) The radiation imaging control device according to Supplementary Item 1, wherein, when the imaging purpose is simple imaging, the processor determines, in accordance with the dose detection pixels of the determined radiation detector, the radiation detector that is closest to the radiation source from the plurality of radiation detectors to be the radiation detector that will perform the dose control. (Supplementary Item 3) The radiation imaging control device according to Supplementary Item 1, wherein the processor, when the imaging purpose is energy subtraction imaging, determines a radiation detector among the plurality of radiation detectors other than a radiation detector closest to the radiation source as the radiation detector that will perform the dose control. (Supplementary Item 4) The radiation imaging control device according to Supplementary Item 1, wherein the processor, when the imaging purpose is energy subtraction imaging, determines all of the plurality of radiation detectors as the radiation detectors that will perform the dose control. (Supplementary Item 5) The radiation imaging control device according to any one of Supplementary Items 1 to 4, wherein the processor determines a target dose for performing the radiation imaging in accordance with the imaging purpose, and stops driving the radiation source when the dose detected by the dose detection pixels of the determined radiation detector reaches the target dose. (Supplementary Item 6) The radiation imaging control device according to any one of Supplementary Items 1 to 5, wherein the processor identifies a region of interest in the imaging subject in accordance with the imaging purpose, and performs the dose control in accordance with the dose detected by the dose detection pixel located at least at a position corresponding to the region of interest in the radiation detector determined to be the radiation detector that controls the dose of the radiation.(Supplementary Item 7) A radiation imaging control method in a radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, the radiation imaging control method including a layered detector configured by stacking a plurality of radiation detectors, each having a plurality of dose detection pixels that detect a dose during the radiation imaging, the method comprising: acquiring an imaging purpose; determining, according to the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the dose of the radiation during the radiation imaging; and performing the dose control according to the dose detected by the dose detection pixels of the determined radiation detector. (Supplementary Item 8) A radiation imaging control program that causes a computer to execute a radiation imaging control method in a radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, the radiation imaging control device having a layered detector configured by stacking a plurality of radiation detectors, each having a plurality of dose detection pixels that detect a dose during the radiation imaging, the radiation imaging control program causing a computer to execute the following steps: acquiring an imaging purpose; determining, according to the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the dose of the radiation during the radiation imaging; and performing the dose control according to the dose detected by the dose detection pixels of the determined radiation detector.
[0086] REFERENCE SIGNS LIST 1 Imaging device 3 Radiation source 4 Layer structure detector 5, 6 Radiation detector 7 Radiation energy conversion filter 10 Radiation imaging control device 11 CPU 12 Radiation imaging control processing program 13 Storage 14 Display 15 Input device 16 Memory 17 Network I / F 18 High voltage generator 19 Exposure switch 20 Bus 21 Radiation source control unit 22 Device control unit 23 Subtraction unit 24 Display control unit 30 Pixel area 31 Gate driver 32 Signal processing circuit 34 Control unit 35 Communication I / F 40 Pixel 40A Normal pixel 40B Detection pixel 41 Photoelectric conversion unit 42 TFT 43 Scanning line 44 Signal line 51 Region corresponding to lung field 52 Region corresponding to mediastinum and subdiaphragm G1, G2 Radiation image Gb Bone image Gs Soft tissue image H Subject
Claims
1. A radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, comprising: a layered detector configured by stacking a plurality of radiation detectors, each having a plurality of dose detection pixels that detect the dose during the radiation imaging; and at least one processor, wherein the processor acquires the imaging purpose, and determines, according to the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the dose of the radiation during the radiation imaging, and performs the dose control according to the dose detected by the dose detection pixels of the determined radiation detector.
2. A radiation imaging control device as described in claim 1, wherein when the imaging purpose is simple imaging, the processor determines the radiation detector among the plurality of radiation detectors that is closest to the radiation source as the radiation detector that will perform the dose control.
3. A radiation imaging control device as described in claim 1, wherein, when the imaging purpose is energy subtraction imaging, the processor determines, among the plurality of radiation detectors, a radiation detector other than the radiation detector closest to the radiation source as the radiation detector that will perform the dose control.
4. A radiation imaging control device according to claim 1, wherein said processor determines all of said plurality of radiation detectors as radiation detectors that perform said dose control when said imaging purpose is energy subtraction imaging.
5. A radiation imaging control device according to any one of claims 1 to 4, wherein the processor determines a target dose when performing the radiation imaging in accordance with the imaging purpose, and stops driving the radiation source when the determined dose detected by the dose detection pixel of the radiation detector reaches the target dose.
6. A radiation imaging control device as described in claim 1, wherein the processor identifies a region of interest in the subject to be imaged according to the imaging purpose, and performs the dose control in accordance with the dose detected by the dose detection pixel located at least at a position corresponding to the region of interest in the radiation detector determined to be the radiation detector that controls the radiation dose.
7. A radiation imaging control method in a radiation imaging control device that controls radiation imaging of an object by irradiating the object with radiation emitted from a radiation source, the radiation imaging control device having a layered detector configured by stacking a plurality of radiation detectors each having a plurality of dose detection pixels that detect the dose during the radiation imaging, the method comprising: acquiring an imaging purpose; determining, according to the imaging purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the dose of the radiation during the radiation imaging; and performing the dose control according to the dose detected by the dose detection pixels of the determined radiation detector.
8. A radiography control program that causes a computer to execute a radiography control method in a radiography control device that controls radiography of an object by irradiating the object with radiation emitted from a radiation source, the radiography control device having a layered detector configured by stacking a plurality of radiation detectors each having a plurality of dose detection pixels that detect the dose during the radiography, the radiography control program causing a computer to execute the following steps: acquiring the radiography purpose; determining, according to the radiography purpose, at least one radiation detector from the plurality of radiation detectors to be used for controlling the dose of the radiation during the radiography; and performing the dose control according to the dose detected by the dose detection pixels of the determined radiation detector.