Radiation imaging apparatus and radiation imaging system

Abstract

To provide a technology advantageous for achieving both a low dosage and improvement of quality of an energy subtraction image.SOLUTION: A radiation imaging apparatus includes a detection panel for acquiring a radiation image, a detection unit for detecting a radiation dose incident on the detection panel, and a control circuit. First imaging for acquiring an energy subtraction image and second imaging following the first imaging are performed. The control circuit determines a target dose to stop irradiation of a radioactive ray on the basis of information according to the radiation dose detected by the detection unit during imaging in at least one of the first imaging and the second imaging.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a radiation imaging apparatus and a radiation imaging system. [Background technology]

[0002] Radiation imaging devices including an imaging panel in which pixels are arranged in an array, each pixel combining a conversion element that converts radiation into an electric charge and a switching element such as a thin film transistor (TFT), are widely used as imaging devices for medical image diagnosis and non-destructive testing. A method is known in which such a radiation imaging device is used to acquire multiple radiation images using radiation of different energies, and an energy subtraction image is acquired by isolating or highlighting a specific subject portion based on the difference between the acquired radiation images. Patent Document 1 discloses that an energy subtraction image is acquired by performing two imaging operations using radiation of different energies. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-151009 Summary of the Invention [Problem to be solved by the invention]

[0004] When two scans are taken to obtain an energy subtraction image, the radiation exposure is high, so reducing the radiation dose becomes an issue. However, reducing the radiation dose may result in a decrease in the image quality of the resulting energy subtraction image.

[0005] An object of the present invention is to provide a technique that is advantageous in achieving both a lower dose and improved image quality of energy subtraction images. [Means for solving the problem]

[0006] In view of the above problems, a radiation imaging device according to an embodiment of the present invention is a radiation imaging device comprising a detection panel for acquiring a radiation image, a detection unit for detecting the amount of radiation incident on the detection panel, and a control circuit, wherein a first imaging is performed to obtain an energy subtraction image, and a second imaging is performed following the first imaging, and the control circuit determines a target dose at which to stop irradiation of radiation based on information corresponding to the amount of radiation detected by the detection unit during imaging during at least one of the first imaging and the second imaging. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technique that is advantageous in achieving both a low dose and an improvement in the quality of energy subtraction images. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a radiation imaging system including a radiation imaging apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of the radiation imaging apparatus of FIG. 1. [Figure 3] FIG. 2 is a diagram showing an example of the configuration of an amplifier unit of the radiation imaging apparatus of FIG. 1. [Figure 4] 2 is a diagram showing an example of the operation of the radiation imaging apparatus of FIG. 1; [Figure 5] 2 is a diagram for explaining the accumulation operation of the radiation imaging apparatus of FIG. 1. [Figure 6] 2 is a diagram showing an example of the operation of the radiation imaging apparatus of FIG. 1; [Figure 7] 2 is a diagram showing an example of a radiation image obtained by the radiation imaging apparatus of FIG. 1; [Figure 8] 2 is a diagram showing an example of a method for deriving bone density using the radiation imaging apparatus of FIG. 1; [Figure 9] 2 is a diagram showing an example of the operation of the radiation imaging apparatus of FIG. 1; [Figure 10] 2 is a diagram showing an example of the operation of the radiation imaging apparatus of FIG. 1; [Figure 11] FIG. 2 is a diagram showing an example of a lookup table of the radiation imaging apparatus of FIG. [Figure 12] FIG. 2 is a diagram showing an example of a lookup table of the radiation imaging apparatus of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] A radiation imaging apparatus according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 12. FIG. 1 is a diagram showing an example of the configuration of a radiation imaging system 500 including a radiation imaging apparatus 100 according to this embodiment. The radiation imaging system 500 includes the radiation imaging apparatus 100, a radiation source 501, a radiation source interface 502, a communication interface 503, and a controller 504, and performs imaging of, for example, a subject 700. In the configuration shown in FIG. 1, an example is shown in which communication is performed using wired communication among the radiation imaging apparatus 100, the radiation source 501, the radiation source interface 502, the communication interface 503, and the controller 504. However, this is not limiting, and communication may be performed wirelessly among some or all of the radiation imaging apparatus 100, the radiation source 501, the radiation source interface 502, the communication interface 503, and the controller 504.

[0011] In the radiation imaging system 500, the controller 504 can perform overall control of the radiation imaging system 500. In accordance with a user's setting, the controller 504 causes the radiation source 501 to generate radiation of a desired energy via the radiation source interface 502. For example, when performing two imaging operations to obtain an energy subtraction image, the controller 504 sends a control signal to the radiation source interface 502 so that the radiation source 501 successively generates multiple types of radiation with different energies. In accordance with the control signal, the radiation source interface 502 controls the radiation source 501 so that the radiation source 501 successively generates multiple types of radiation with different energies.

[0012] For example, settings such as the radiation dose, irradiation time (ms), tube current (mA), tube voltage (kV), and radiation detection field, which is an area for detecting radiation, are input by a user (e.g., a technician) via a user interface of the controller 504. When a user operates an exposure switch attached to the radiation source 501 or the controller 504, the controller 504 transmits a start request signal to the radiation imaging apparatus 100. The start request signal is a signal requesting the start of radiation irradiation. In response to receiving the start request signal, the radiation imaging apparatus 100 begins preparations for receiving radiation irradiation. When preparations are complete, the radiation imaging apparatus 100 transmits a start ready signal to the radiation source interface 502 via the communication interface 503. The start ready signal is a signal notifying that radiation irradiation can be started. The start ready signal may be transmitted from the radiation imaging apparatus 100 to the controller 504, and a signal equivalent to the start ready signal may be transmitted from the controller 504 to the radiation source interface 502. In response to receiving the start enable signal, the radiation source interface 502 causes the radiation source 501 to start emitting radiation.

[0013] When the cumulative amount of irradiated radiation reaches the target dose, the radiation imaging apparatus 100 transmits a stop notification to the radiation source interface 502 via the communication interface 503. The stop notification is a signal requesting termination of radiation irradiation. Upon receiving the stop notification, the radiation source interface 502 causes the radiation source 501 to terminate radiation irradiation. The target dose can be determined based on the radiation dose input by the user, the radiation irradiation intensity, communication delays between the components of the radiation imaging system 500, processing delays, etc.

[0014] In order to transmit the stop notification, the radiation imaging apparatus 100 includes a detection unit for detecting the amount of radiation (accumulated amount) incident on a detection panel for acquiring a radiation image. Pixels arranged on a detection panel (described later) may function as the detection unit, or the radiation imaging apparatus 100 may include a detection device such as an ion chamber as the detection unit.

[0015] FIG. 2 is a diagram showing an example of the configuration of a radiation imaging apparatus 100 according to this embodiment. The radiation imaging apparatus 100 includes a detection panel DP in which a plurality of pixels PIX are arranged in a matrix to form a plurality of rows and a plurality of columns. The radiation imaging apparatus 100 also includes a power supply circuit 140, a drive circuit 150, a readout circuit 160, a processing circuit 170, a control circuit 180, and a communication unit 190. The drive circuit 150 drives the plurality of pixels PIX via a plurality of drive lines 110 arranged corresponding to each pixel row of the plurality of pixels PIX arranged on the detection panel DP. Signals output from the plurality of pixels PIX are supplied to the readout circuit 160 via a plurality of signal lines 120 arranged corresponding to each pixel column of the plurality of pixels PIX arranged on the detection panel DP.

[0016] The multiple pixels PIX may include multiple imaging pixels 101, one or more detection pixels 104, and one or more correction pixels 107. The imaging pixels 101 may be pixels used to acquire a radiation image. The detection pixels 104 may be used to monitor the amount of radiation exposure. The correction pixels 107 may be used to correct the amount of radiation exposure. The sensitivity of the correction pixels 107 to radiation is lower than the sensitivity of the detection pixels 104 to the same radiation. The detection pixels 104 and the correction pixels 107 may function as a detection unit for detecting the amount of radiation incident on the detection panel DP. This makes it possible to detect the amount of radiation incident on the detection panel DP without providing an ion chamber or the like as a detection unit. The amount of radiation exposure may be monitored using only the signals output from the detection pixels 104, without providing the correction pixels 107.

[0017] Each imaging pixel 101 includes a conversion element 102 that converts radiation into an electrical signal and a switch element 103 that connects a signal line 120 and the conversion element 102 to each other. Each detection pixel 104 includes a conversion element 105 that converts radiation into an electrical signal and a switch element 106 that connects the signal line 120 and the conversion element 105 to each other. The detection pixel 104 is arranged so as to be included in a row and column formed by a plurality of imaging pixels 101. Each correction pixel 107 includes a conversion element 108 that converts radiation into an electrical signal and a switch element 109 that connects the signal line 120 and the conversion element 108 to each other. The correction pixel 107 is arranged so as to be included in a row and column formed by a plurality of imaging pixels 101. In FIG. 2, the imaging pixels 101, the detection pixels 104, and the correction pixels 107 are distinguished from each other by applying different hatching to the conversion elements 102, 105, and 108.

[0018] The conversion elements 102, 105, and 108 may each be configured with a scintillator that converts incident radiation into light and a photoelectric conversion element that converts the light converted by the scintillator into an electrical signal. The scintillator is generally formed in a sheet shape so as to cover the detection panel DP and is shared by multiple pixels PIX. Alternatively, the conversion elements 102, 105, and 108 may each be configured with a conversion element that directly converts incident radiation into an electrical signal.

[0019] The switch element 103 of each imaging pixel 101 may include a thin film transistor (TFT) whose active region is made of a semiconductor such as amorphous silicon or polycrystalline silicon. A first terminal of each conversion element 102 is connected to a first main terminal of the switch element 103, and a second terminal of the conversion element 102 is connected to a bias line 130. The bias line 130 extends in a direction along the pixel column and is commonly connected to the second terminals of the conversion elements 102 of the PIXs constituting each pixel column. A bias voltage Vs is supplied to the bias line 130 from a power supply circuit 140. The power supply circuit 140 may be configured to amplify and read the bias voltage Vs. A second main terminal of the switch element 103 of one or more imaging pixels 101 included in one pixel column is connected to a corresponding signal line 120. A control terminal of the switch element 103 of one or more imaging pixels 101 included in one pixel row is connected to a corresponding drive line 110.

[0020] The detection pixels 104 and the correction pixels 107 also have the same configuration as the imaging pixels 101, and are connected to the corresponding drive lines 110 and the corresponding signal lines 120. The detection pixels 104 and the correction pixels 107 may be exclusively connected to the signal lines 120. That is, the correction pixel 107 may not be connected to the signal line 120 to which the detection pixel 104 is connected. Also, the detection pixel 104 may not be connected to the signal line 120 to which the correction pixel 107 is connected. The imaging pixel 101 may be connected to the same signal line 120 as the detection pixel 104 or the correction pixel 107.

[0021] The drive circuit 150 is configured to supply drive signals to the pixels PIX to be driven via multiple drive lines 110 in accordance with signals supplied from the control circuit 180. In this embodiment, the drive signals are signals for turning on the switch elements 103, 106, and 109 included in the pixels PIX to be driven. For example, the switch elements 103, 106, and 109 of each pixel PIX are turned on by a high-level signal and turned off by a low-level signal. Therefore, these high-level signals are sometimes referred to as drive signals. By supplying the drive signals to the pixels PIX, signals accumulated in the conversion elements 102, 105, and 108 of the pixels PIX become readable by the readout circuit 160. When a drive line 110 is connected to at least one of the detection pixel 104 and the correction pixel 107, the drive line 110 is sometimes referred to as a detection drive line 111.

[0022] The readout circuit 160 is configured to read out signals from the plurality of pixels PIX through the plurality of signal lines 120. The readout circuit 160 includes a plurality of amplifier circuits 161, a multiplexer 162, and an analog-to-digital (AD) converter 163. Each of the plurality of signal lines 120 is connected to a corresponding one of the plurality of amplifier circuits 161 arranged in the readout circuit 160. One signal line 120 corresponds to one amplifier circuit 161. The multiplexer 162 selects the plurality of amplifier circuits 161 in a predetermined order, and supplies the signal of the selected amplifier circuit 161 to the AD converter 163. The AD converter 163 converts the supplied analog signal into a digital signal and outputs it.

[0023] The signals read out from the imaging pixels 101 are supplied to the processing circuit 170. The processing circuit 170 performs processes such as arithmetic and storage on the signals read out from the imaging pixels 101 under the control of the control circuit 180. The processing circuit 170 includes an arithmetic circuit 171 and a memory 172. The arithmetic circuit 171 generates data for a radiation image based on the signals read out from the imaging pixels 101 and supplies the data to the control circuit 180. The signals read out from the detection pixels 104 and the correction pixels 107 are supplied to the processing circuit 170. The processing circuit 170 performs processes such as arithmetic and storage on the signals read out from the detection pixels 104 and the correction pixels 107 under the control of the control circuit 180. The processing circuit 170 outputs information about radiation incident on the radiation imaging device 100 (detection panel DP) based on the signals read out from the detection pixels 104 and the correction pixels 107. For example, the processing circuitry 170 may detect the start and end of irradiation of the radiation imaging device 100 based on signals read out from the detection pixels 104 and the correction pixels 107. The processing circuitry 170 may also calculate the radiation dose and integrated dose based on the signals read out from the detection pixels 104 and the correction pixels 107.

[0024] The control circuit 180 controls each component of the radiation imaging device 100, including the drive circuit 150 and the readout circuit 160. The control circuit 180 can control, for example, the start and end of exposure (accumulation of electric charges corresponding to radiation incident on the imaging pixels 101) based on information from the processing circuit 170. The control circuit 180 may be configured with a general-purpose processing circuit such as a microprocessor, or may be configured with a dedicated processing circuit such as an Application Specific Integrated Circuit (ASIC). When the control circuit 180 is configured with a general-purpose processing circuit, the control circuit 180 may further include a memory.

[0025] In order to detect the amount of radiation incident on the detection panel DP, the control circuit 180 controls the drive circuit 150 to scan only the detection drive lines 111 and enable signals to be read out from the detection pixels 104 and the correction pixels 107. Next, the control circuit 180 controls the readout circuit 160 to read out signals from the pixel columns corresponding to the detection pixels 104 and the correction pixels 107 and output them as information indicating the amount of radiation exposure. Through such operations, the radiation imaging device 100 can obtain radiation exposure information on the detection panel DP during radiation exposure.

[0026] The communication unit 190 is controlled by the control circuit 180 and has a function of communicating between the radiation imaging apparatus 100 and an external device. Although not shown in Fig. 2, the communication unit 190 communicates with the communication interface 503 shown in Fig. 1. The communication unit 190 is not limited to a specific standard as long as it can realize communication between the radiation imaging apparatus 100 and an external device, such as wired communication or wireless communication. Furthermore, multiple communication units 190 may be provided to support multiple communication standards.

[0027] The communication unit 190 is connected to the signal processing unit 270. The signal processing unit 270 is a component of the radiation imaging system 500 and may be incorporated in the controller 504 shown in FIG. 1 or may be arranged separately from the controller 504. The signal processing unit 270 performs processing such as calculation and storage on the radiographic image data generated by the arithmetic circuit 171. The signal processing unit 270 includes the arithmetic circuit 271 and a memory 272. The arithmetic circuit 271 performs image processing on the radiographic image data, and the radiographic image is displayed on a monitor using the image-processed data. The monitor may be incorporated in the controller 504 or arranged separately from the controller 504, for example. The arithmetic circuit 271 of the signal processing unit 270 may also generate energy subtraction image data from the radiographic image data as part of the image processing. Furthermore, the arithmetic circuit 271 may derive bone mineral content (bone mineral quantification) or bone density from the energy subtraction image data. The derived bone mineral content, bone density, etc. may be displayed on the monitor described above.

[0028] FIG. 3 is a diagram showing an example configuration of the amplifier circuit 161. The amplifier circuit 161 may include a differential amplifier circuit AMP and a sample-and-hold circuit SH. The differential amplifier circuit AMP amplifies and outputs a signal supplied to the signal line 120. The control circuit 180 can reset the potential of the signal line 120 by supplying a signal φR to the switch element of the differential amplifier circuit AMP. The output from the differential amplifier circuit AMP can be held by the sample-and-hold circuit SH. The control circuit 180 causes the sample-and-hold circuit SH to hold the signal by supplying a signal φSH to the switch element of the sample-and-hold circuit SH. The signal held in the sample-and-hold circuit SH is read out by the multiplexer 162.

[0029] 4 is a timing chart illustrating an example of the operation of the radiation imaging device of the present invention. In this embodiment, the radiation imaging device 100 performs an operation of outputting signals from the pixels PIX on a pixel row basis. Here, one frame period includes an accumulation period and a readout period. The accumulation period is a period during which the imaging pixels 101 perform an accumulation operation of accumulating signals corresponding to irradiated radiation. The readout period is a period during which the readout circuit 160 performs a readout operation of reading out one frame's worth of signals from the detection panel DP while the drive circuit 150 scans multiple rows.

[0030] The radiation imaging device 100 repeatedly performs a pixel reset operation until the exposure switch is pressed and radiation (X-rays) is irradiated. The pixel reset operation is performed by repeatedly scanning pixel rows by the drive circuit 150, similar to the readout operation performed during the readout period. The pixel reset operation resets each of the pixels PIX arranged on the entire surface of the detection panel DP.

[0031] In imaging to obtain an energy subtraction image for separating bone and soft tissue, analyzing bone density, etc., when the exposure switch is pressed, accumulation and readout operations for offset correction are performed. Subsequently, an accumulation and readout operation are performed in which a first radiation irradiation is performed, followed by an accumulation and readout operation in which radiation of a different energy from the first irradiation is performed. Imaging (accumulation and readout operations) in which radiation of three or more different energies is irradiated may be performed. This allows data for multiple radiographic images using radiation of different energies to be obtained. The accumulation and readout operations for offset correction may be performed after imaging in which radiation is irradiated, or may be performed between imaging in which radiation is irradiated multiple times.

[0032] FIG. 5 is a diagram illustrating the accumulation operation of irradiating radiation by the radiation imaging apparatus 100. When the cumulative amount of irradiated radiation reaches the target dose, the radiation imaging apparatus 100 transmits a stop notification to the radiation source interface 502 via the communication interface 503. The stop notification is a signal requesting the radiation source interface 502 to stop irradiating radiation. In response to receiving the stop notification, the radiation source interface 502 causes the radiation source 501 to terminate radiation irradiation. By using such automatic exposure control (AEC), the amount of radiation incident on the subject 700 can be reduced. For example, AEC may be used in at least one of the multiple imaging operations performed to obtain an energy subtraction image. Data for multiple types of radiation images with different energies obtained through this operation can be used to analyze bone density and the like in the signal processing unit 270.

[0033] 6 is a diagram illustrating a flow of generating energy subtraction image data and analyzing bone density (bone mineral content) in the signal processing unit 270 after imaging using radiation of different energies in the radiation imaging device 100. First, in S601, the arithmetic circuit 271 of the signal processing unit 270 generates a material separation image, which is a material characteristic image. Specifically, the arithmetic circuit 271 generates the material separation image based on the following equations (1) and (2) from a high-energy radiation image XH as shown in FIG. 7(a) and a low-energy radiation image XL as shown in FIG. 7(b), both of which are captured using the radiation imaging device 100. -lnX L =μ LA d A +μ LB d B ··· (1) -lnX H =μ HA d A +μ HB d B (2) Here, μ is the linear attenuation coefficient, d is the thickness of the material, the subscripts H and L represent high energy and low energy, respectively, and the subscripts A and B represent fat (soft tissue) and bone, respectively. Here, fat and bone are used as material examples, but this is not particularly limited and any material can be used. By solving the simultaneous equations of equations (1) and (2), a material-separated image dA of fat shown in FIG. 7(c) and a material-separated image dB of bone shown in FIG. 7(d) can be obtained.

[0034] Next, in S602, the arithmetic circuitry 271 calculates the bone region from the bone material separation image dB calculated in S601. The bone region may be calculated using histogram analysis or deep learning. Here, the bone region is calculated using the bone material separation image dB. However, this is not limiting, and the bone region may also be calculated using the high-energy radiation image XH shown in FIG. 7(a) or the low-energy radiation image XL shown in FIG. 7(b).

[0035] After calculating the bone region, in S603, the arithmetic circuit 271 determines a soft tissue region in the bone material property image dB. The arithmetic circuit 271 determines the soft tissue region as a region including pixels positioned a predetermined number of pixels apart from the edge of the bone region in the horizontal direction, excluding the bone region B, as shown in Fig. 8. As shown in Fig. 8, if there are multiple bone regions, multiple soft tissue regions S are determined.

[0036] Next, in S604, the arithmetic circuit 271 calculates pixel values ​​of bone regions in the bone material property image dB. As shown in Fig. 8, when there are multiple bone regions B, the arithmetic circuit 271 calculates the average value of pixel values ​​of each of the bone regions B1 to B4.

[0037] Furthermore, in S605, the arithmetic circuitry 271 calculates pixel values ​​of soft tissue regions in the bone material property image dB. As shown in Fig. 8, when there are multiple soft tissue regions S, the arithmetic circuitry 271 calculates the average pixel values ​​of each of the soft tissue regions S1a to S4b. In the flow shown in Fig. 6, S605 is performed after S604, but S604 may also be performed after S605.

[0038] After calculating the pixel values ​​of bone region B and soft tissue region S, in S606, the arithmetic circuit 271 calculates bone density (or bone mineral content) based on the pixel values ​​of bone region B calculated in S604 and the pixel values ​​of soft tissue region S calculated in S605. For example, bone density can be derived using a DXA method or the like. In this case, bone density may be derived only from the pixel values ​​of bone region B, without using the pixel values ​​of soft tissue region S.

[0039] When the subject 700 being imaged has a large body thickness, the quality of the resulting energy subtraction image may be degraded. This degradation in the quality of the energy subtraction image may result in a decrease in the accuracy of bone density analysis. This is due to factors such as a decrease in the signal-to-noise ratio of the radiation image obtained by the radiation imaging device 100 and the influence of scattered radiation when the subject 700 has a large body thickness. On the other hand, if the exposure conditions are uniformly set regardless of the body thickness of the subject 700, overexposure may occur when the subject has a small body thickness. Therefore, the radiation imaging device 100 of this embodiment controls the radiation exposure time and the target dose according to the body thickness. This allows the radiation imaging device 100 of this embodiment to simultaneously reduce the radiation dose and improve the quality of the energy subtraction image (improve the accuracy of bone density derivation). The specific operation of the radiation imaging device will be described with reference to FIG. 9 .

[0040] FIG. 9 is a diagram illustrating the operation of the radiation imaging apparatus 100 of this embodiment. In FIG. 9, the horizontal axis represents the radiation exposure time, and the vertical axis represents the accumulated amount of radiation. The control circuit 180 of the radiation imaging apparatus 100 uses the processing circuit 170 to acquire real-time information corresponding to the amount of radiation detected by the detection unit using the detection pixels 104 and correction pixels 107 described above during imaging. More specifically, as shown in FIG. 9, the processing circuit 170 calculates a change in a signal indicating the accumulated amount of radiation detected by the detection unit during imaging. With the horizontal axis representing the exposure time and the vertical axis representing the accumulated amount of radiation, the change in the signal indicating the accumulated amount is calculated as a rate of change (slope shown in FIG. 9). The rate of change (slope) varies depending on the body thickness of the subject 700 to be imaged. For example, a thick subject 700 absorbs a large amount of radiation, resulting in a smaller rate of change (slope) of signal 901A indicating the accumulated amount of radiation incident on the radiation imaging apparatus 100 and detected by the detection unit. On the other hand, for a subject 700 with a thin body thickness, the rate of change (slope) of signal 901C indicating the integrated amount of radiation incident on radiation imaging apparatus 100 and detected by the detection unit increases.

[0041] When the body thickness of the subject 700 is thin, the radiation exposure time is short. On the other hand, the influence of the radiation wave tail included in the radiation accumulation operation is greater than when the radiation exposure time is long. The radiation wave tail is radiation generated between the time when the radiation source interface 502 issues an instruction to the radiation source 501 to stop radiation exposure and the time when the radiation actually stops. This can reduce the image quality of the energy subtraction image and cause errors in the bone density obtained from the energy subtraction image. Therefore, it is necessary to reduce the target dose. Conversely, when the body thickness is thick, scattered radiation increases and the signal-to-noise ratio of the obtained image decreases, so it is necessary to increase the target dose.

[0042] Therefore, the control circuit 180 of the radiation imaging device 100 of this embodiment may determine a target dose at which to stop irradiation of radiation based on real-time information corresponding to the amount of radiation detected during imaging by a detection unit using an ion chamber, the detection pixels 104, and the correction pixels 107. As described above, the processing circuit 170 calculates a change in a signal indicating the integrated amount of radiation. When the rate of change of the signal indicating the integrated amount of radiation calculated by the processing circuit 170 is a first rate (e.g., signal 901C), the control circuit 180 controls the irradiation time of radiation so that the integrated amount of radiation incident on the detection panel DP is smaller than when the rate of change is a second rate (e.g., signal 901A) that is smaller than the first rate. In other words, when the rate of change of the signal indicating the integrated amount of radiation is a first rate (e.g., signal 901C), the control circuit 180 lowers the target dose than when the rate of change is a second rate (e.g., signal 901A) that is smaller than the first rate. This facilitates both a reduction in radiation dose and an improvement in the image quality of the energy subtraction image (improvement in the accuracy of bone density analysis). The above-described control of target dose determination may be performed in all of the multiple radiographic imaging sessions for generating the energy subtraction image. Alternatively, for example, the control of target dose determination may be performed in one of the two imaging sessions, and normal AEC may be used in the other. It is sufficient that the control of target dose determination is performed in at least one of the multiple radiographic imaging sessions.

[0043] Furthermore, even when the body is thick, the radiation wave tail can degrade the image quality of the energy subtraction image and reduce the accuracy of bone density analysis. Radiation wave tails contain radiation of various energies, which can reduce the accuracy of bone density analysis. Radiation wave tails, whether large or small, occur regardless of the energy of the radiation being irradiated. However, the inventors have experimentally demonstrated that a combination of exposure conditions for capturing multiple types of radiation images with different energies can enable high-precision bone density analysis without degrading the image quality of the energy subtraction image. One possible reason for this is that the response of the radiation wave tail varies depending on radiation exposure conditions, such as tube voltage and tube current. Therefore, the radiation imaging device 100 may include multiple lookup tables that correspond to information related to the radiation dose detected by the detection unit during imaging in order to determine the radiation exposure conditions. For example, the control circuit 180 selects an appropriate lookup table based on information obtained in capturing a previous radiation image and determines the radiation exposure conditions for capturing a subsequent radiation image by referring to the lookup table. The lookup table may be stored, for example, in the memory 172 of the processing circuitry 170. By using the lookup table, even when the body is thick and susceptible to the effects of radiation wave tails, imaging can be performed under exposure conditions that do not reduce the accuracy of the bone density analysis, which has been experimentally determined in advance.

[0044] Fig. 10 is a diagram showing an example of a flow of capturing an energy subtraction image using the radiation imaging apparatus 100 when a lookup table is used. In the flow shown in Fig. 10, imaging using low-energy radiation to obtain an energy subtraction image, and imaging using high-energy radiation following the imaging using low-energy radiation are performed. In other words, the energy of the radiation in the earlier imaging is lower than the energy of the radiation in the later imaging.

[0045] First, as shown in S1001, imaging using low-energy radiation is performed. The imaging conditions for imaging using low-energy radiation may be determined appropriately by the user depending on the body thickness of the subject 700, etc. Alternatively, for example, the control circuit 180 may determine the radiation irradiation conditions based on at least one parameter selected from the thickness of the imaging target, the radiation transmittance of the imaging target, the region of the imaging target, and the imaging protocol. These parameters may be input by the user via a user interface of the controller 504. Alternatively, for example, the radiation imaging system 500 may include a camera or the like to detect the body thickness and imaging region of the subject 700, etc. Alternatively, for example, a high tube current condition may be set as the irradiation condition for imaging using low-energy radiation. This is because a bone density is more likely to be derived with higher accuracy when the body thickness is thick than when the tube current is low.

[0046] Imaging using low-energy radiation continues until the target dose is reached (YES in S1002). At this time, the control circuit 180 uses the processing circuit 170 to calculate the rate of change of the signal indicating the integrated dose of radiation shown in FIG. 9. The control circuit 180 may also determine the target dose for imaging using low-energy radiation from the rate of change of the signal. The target dose may be set, for example, according to a signal corresponding to a bone region. When the target dose is reached, the control circuit 180 outputs a stop notification as described above, and radiation irradiation stops (S1003).

[0047] Next, in S1004, the control circuit 180 selects a lookup table to be used. An appropriate lookup table is selected from a plurality of lookup tables based on information corresponding to the radiation dose detected by the detection unit in imaging using low-energy radiation, i.e., the rate of change in the signal indicating the integrated amount of radiation. For example, if the change (slope) in the signal indicating the integrated amount of radiation is large, the lookup table for a subject with a thin body thickness shown in FIG. 11 is used. On the other hand, if the change (slope) in the signal indicating the integrated amount of radiation is small, the lookup table for a subject with a thick body thickness shown in FIG. 12 is used. The relationship between the change (slope) in the signal indicating the integrated amount of radiation and the body thickness may be obtained in advance using a phantom, for example.

[0048] Next, imaging using high-energy radiation is performed. At this time, the control circuit 180 may determine, as the irradiation condition, a tube current having many radiation irradiation time candidates from the lookup table selected in S1004. In the case of the lookup table shown in FIG. 11, the control circuit 180 selects 20 mA as the setting of the tube current of the radiation source for irradiating radiation to the radiation imaging device. In the case of the lookup table shown in FIG. 12, the control circuit 180 selects 50 mA as the setting of the tube current of the radiation source for irradiating radiation to the radiation imaging device. Once the radiation irradiation conditions for imaging using high-energy radiation have been determined, radiation irradiation is started (S1005).

[0049] Imaging using high-energy radiation continues until the target dose is reached (YES in S1006). At this time, the control circuit 180 may use the processing circuit 170 to calculate the rate of change of the signal indicating the integrated dose of radiation shown in FIG. 9 and determine the target dose for imaging using high-energy radiation. The target dose may be set, for example, according to a signal corresponding to a bone region. When the target dose is reached, the control circuit 180 outputs a stop notification as described above, and radiation irradiation stops (S1007).

[0050] When imaging using low-energy and high-energy radiation is completed, in S1008, the arithmetic circuit 271 of the signal processing unit 270 generates an energy subtraction image using the obtained radiographic image data using radiation of two types of energy, and derives bone density. As described above, the arithmetic circuit 271 calculates bone density based on pixel values ​​of the bone region and pixel values ​​of the soft tissue region.

[0051] In this way, by using the radiation imaging device 100 of this embodiment, it is possible to achieve a low radiation dose according to the body thickness of the subject when performing multiple imaging operations to generate energy subtraction images. Furthermore, degradation in the image quality of the obtained energy subtraction images is suppressed, making it possible to derive bone density and bone mineral content with high accuracy. In other words, it is possible to achieve both a low radiation dose and improved image quality of the energy subtraction images (improved accuracy in deriving bone density (bone mineral content)).

[0052] The disclosure of the present specification includes the following radiation imaging apparatus and radiation imaging system.

[0053] (Item 1) A radiation imaging device comprising: a detection panel for acquiring a radiation image; a detection unit for detecting a radiation amount incident on the detection panel; and a control circuit, a first imaging step for obtaining an energy subtraction image and a second imaging step following the first imaging step are performed; The control circuit determines a target dose at which to stop the irradiation of radiation based on information corresponding to the radiation dose detected by the detection unit during at least one of the first imaging and the second imaging.

[0054] (Item 2) 2. The radiation imaging device according to item 1, wherein the information includes a change in a signal indicating an integrated amount of radiation detected by the detection unit during imaging.

[0055] (Item 3) The radiation imaging device described in item 2 is characterized in that the control circuit controls the radiation irradiation time so that when the rate of change is a first rate, the accumulated amount of radiation incident on the detection panel is less than when the rate of change is a second rate that is smaller than the first rate.

[0056] (Item 4) The radiation imaging device described in item 2 or 3, characterized in that the control circuit reduces the target dose when the rate of change is a first rate compared to when the rate of change is a second rate that is smaller than the first rate.

[0057] (Item 5) 5. The radiation imaging device according to any one of items 1 to 4, wherein the control circuit outputs a signal to stop irradiation of radiation in response to a signal indicating an integrated amount of radiation detected by the detection unit during imaging reaching the target dose.

[0058] (Item 6) The radiation imaging device described in any one of items 1 to 5, characterized in that the control circuit determines the radiation irradiation conditions for the first imaging from at least one parameter of the thickness of the imaging target, the radiation transmittance of the imaging target, the part of the imaging target, and the imaging protocol.

[0059] (Item 7) 7. The radiation imaging device according to claim 1, wherein the control circuit determines the target dose for the first imaging and the radiation irradiation conditions for the second imaging based on the information for the first imaging.

[0060] (Item 8) 8. The radiation imaging apparatus according to item 7, wherein the control circuit determines the target dose in the second imaging based on the information in the second imaging.

[0061] (Item 9) Further provided with memory, Item 9. The radiation imaging device according to item 7 or 8, wherein the memory stores a plurality of lookup tables corresponding to the information in the first imaging, so that the control circuit can determine the irradiation conditions in the second imaging from the information in the first imaging.

[0062] (Item 10) 10. The radiation imaging device according to any one of items 7 to 9, wherein the irradiation conditions in the second imaging include a setting of a tube current of a radiation source for irradiating the radiation imaging device with radiation.

[0063] (Item 11) 11. The radiation imaging apparatus according to any one of items 1 to 10, wherein the energy of the radiation in the first imaging is lower than the energy of the radiation in the second imaging.

[0064] (Item 12) A plurality of pixels are arranged in a matrix on the detection panel, 12. The radiation imaging device according to any one of items 1 to 11, wherein the plurality of pixels include a pixel that functions as the detection unit.

[0065] (Item 13) A radiation imaging device according to any one of items 1 to 12, a signal processing unit that processes a signal output from the radiation imaging device; A radiation imaging system comprising:

[0066] (Item 14) Item 14. The radiation imaging system according to item 13, wherein the signal processing unit derives at least one of bone mineral content and bone density from data of the energy subtraction image.

[0067] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0068] 100: Radiation imaging device, 180: Control circuit, DP: Detection panel

Claims

1. A radiation imaging device comprising: a detection panel for acquiring a radiation image; a detection unit for detecting a radiation amount incident on the detection panel; and a control circuit, a first imaging step for obtaining an energy subtraction image, and a second imaging step subsequent to the first imaging step; The control circuit determines a target dose at which to stop the irradiation of radiation based on information corresponding to the radiation dose detected by the detection unit during at least one of the first imaging and the second imaging.

2. 2. The radiation imaging apparatus according to claim 1, wherein the information includes a change in a signal indicating an integrated amount of radiation detected by the detection unit during imaging.

3. 3. The radiation imaging device according to claim 2, wherein the control circuit controls the radiation irradiation time so that when the rate of change is a first rate, the accumulated amount of radiation incident on the detection panel is smaller than when the rate of change is a second rate that is smaller than the first rate.

4. 3. The radiation imaging apparatus according to claim 2, wherein the control circuit reduces the target dose when the rate of change is a first rate compared to when the rate of change is a second rate that is smaller than the first rate.

5. 2. The radiation imaging device according to claim 1, wherein the control circuit outputs a signal to stop irradiation of radiation in response to a signal indicating an integrated amount of radiation detected by the detection unit during imaging reaching the target dose.

6. 2. The radiation imaging device according to claim 1, wherein the control circuit determines radiation irradiation conditions for the first imaging from at least one parameter selected from the group consisting of a thickness of the imaging target, a radiation transmittance of the imaging target, a region of the imaging target, and an imaging protocol.

7. 2. The radiation imaging apparatus according to claim 1, wherein the control circuit determines the target dose in the first imaging and radiation irradiation conditions in the second imaging based on the information in the first imaging.

8. 8. The radiation imaging apparatus according to claim 7, wherein the control circuit determines the target dose in the second imaging based on the information in the second imaging.

9. Further provided with memory, 8. The radiation imaging device according to claim 7, wherein the memory stores a plurality of lookup tables corresponding to the information in the first imaging, for the control circuit to determine the irradiation conditions in the second imaging from the information in the first imaging.

10. 8. The radiation imaging apparatus according to claim 7, wherein the irradiation conditions in the second imaging include a setting of a tube current of a radiation source for irradiating the radiation imaging apparatus with radiation.

11. 2. The radiation imaging apparatus according to claim 1, wherein the energy of the radiation in the first imaging is lower than the energy of the radiation in the second imaging.

12. A plurality of pixels are arranged in a matrix on the detection panel, The radiation imaging apparatus according to claim 1 , wherein the plurality of pixels include a pixel that functions as the detection unit.

13. A radiation imaging apparatus according to any one of claims 1 to 12; a signal processing unit that processes a signal output from the radiation imaging device; A radiation imaging system comprising:

14. 14. The radiation imaging system according to claim 13, wherein the signal processing unit derives at least one of bone mineral content and bone density from data of the energy subtraction image.

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