JP7262237B2 - Radiation imaging device and radiation imaging system - Google Patents

Description

The present invention relates to a radiation imaging apparatus and a radiation imaging system.

2. Description of the Related Art In medical image diagnosis and non-destructive inspection, radiation imaging apparatuses using flat panel detectors (FPDs) made of semiconductor materials are widely used. In such a radiation imaging apparatus, it is known to monitor radiation incident on the radiation imaging apparatus. By detecting radiation dose in real time, it is possible to detect the start and end of radiation irradiation, grasp the cumulative dose of incident radiation during radiation irradiation, and perform automatic exposure control (AEC). becomes. Japanese Patent Application Laid-Open No. 2003-100001 discloses a radiographic image capturing apparatus that instructs a radiation generating apparatus to terminate radiation irradiation when image data read from a radiation detection element reaches or exceeds a predetermined threshold value. Further, in Patent Document 1, when a user presses an exposure switch, acquisition of an offset component caused by dark current or the like generated in a radiation detection element is started, and after acquisition of the offset component, radiation is generated. Sending a signal to irradiate the device is shown. By removing the offset component from the image data read from the radiation detection element during radiation irradiation, it is possible to improve the accuracy of AEC.

JP 2015-213546 A

The accuracy of the offset component required when measuring the cumulative dose of radiation depends on the signal value when the signal is sampled. That is, when the signal value is small, the influence of the accuracy of the offset component can be relatively greater than when the signal value is large. Therefore, depending on the radiation irradiation conditions, the accuracy of the offset component may not be sufficient. In addition, depending on the radiation irradiation conditions, the offset components may be sampled more than necessary in order to increase the accuracy of the offset components. be.

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique that is advantageous in obtaining offset components suitable for imaging conditions.

In view of the above problems, a radiation imaging apparatus according to an embodiment of the present invention is arranged in a detection unit for acquiring a radiographic image, and includes a detection element for detecting incident radiation, and an output from the detection element during radiation irradiation. and a calculation unit for measuring the amount of incident radiation based on the signal obtained, wherein the calculation unit detects, before irradiation with radiation, estimated from set imaging information. The number of times the offset component of the detection element is sampled is determined according to the signal value that the element outputs in one sampling during radiation irradiation, and the offset correction value is calculated from the offset component of the detection element sampled over the number of sampling times. The amount of incident radiation is measured based on a correction value obtained by correcting the signal value output from the detection element according to the offset correction value during radiation irradiation.

The above means provide an advantageous technique for acquiring an offset component suitable for imaging conditions.

1 is a block diagram showing a configuration example of a system using a radiation imaging apparatus according to the present invention; FIG. FIG. 2 is a circuit diagram showing a configuration example of a detection unit of the radiation imaging apparatus in FIG. 1; 2A and 2B are a plan view and a cross-sectional view showing a configuration example of a pixel of the radiation imaging apparatus of FIG. 1; FIG. 2 is a flowchart showing an operation example of a system using the radiation imaging apparatus of FIG. 1; FIG. 2 is a timing chart showing an operation example of a system using the radiation imaging apparatus of FIG. 1; FIG. 6 is a diagram showing a modification of the timing diagram of FIG. 5; The figure which shows the modification of the flowchart of FIG. 1 is a diagram for explaining a configuration example of a radiation imaging system using a radiation imaging apparatus according to the present invention; FIG.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. It should be noted that the following embodiments do not limit the invention according to the scope of claims. Although multiple features are described in the embodiments, not all of these multiple features are essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant description is omitted.

Radiation in the present invention includes alpha rays, beta rays, and gamma rays, which are beams produced by particles (including photons) emitted by radioactive decay, as well as beams having energy equal to or higher than the same level, such as X rays. It can also include rays, particle rays, and cosmic rays.

First Embodiment A radiation imaging apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1A is a diagram showing a configuration example of a radiation imaging system SYS using a radiation imaging apparatus 200 according to the first embodiment of the present invention. The radiation imaging system SYS includes a radiation imaging device 200 and a radiation source 227 for irradiating the radiation imaging device 200 with radiation.

The radiation imaging apparatus 200 includes a detector 223 , a signal processor 224 , a controller 225 and a power supply circuit 226 . The control unit 225 supplies a control signal to each of the detection unit 223 , the signal processing unit 224 and the power supply circuit 226 to control each component of the radiation imaging apparatus 200 . The detection section 223 includes a support substrate 100 , a pixel array 228 , a drive circuit 221 and a readout circuit 222 . The pixel array 228 is arranged on the support substrate 100 of the detection section 223 . A plurality of pixels for generating a radiographic image are arranged in the pixel array 228 . A detection element for detecting incident radiation is arranged in the detection unit 223 for acquiring a radiographic image. The control unit 225 controls the detector elements during radiation irradiation to acquire signals for measuring the amount of incident radiation. In this embodiment, the sensing elements are arranged in a pixel array 228 as described below. Also, for example, any one of a plurality of pixels for generating a radiographic image may function as a detection element. Also, the detection elements may be arranged in the periphery of the pixel array 228 of the detection section 223 instead of in the pixel array 228 .

The drive circuit 221 drives the pixel array 228 according to the controller 225 . The readout circuit 222 reads, as an electric signal, a signal generated by radiation incident on each pixel of the pixel array 228 and the detection element according to the control unit 225 . The signal processing unit 224 transfers the electric signal of the detection element read out from the readout circuit 222 to the control unit 225 . The control unit 225 outputs a signal for controlling the radiation sampling operation in the detection unit 223 and the irradiation of radiation from the radiation source 227 according to the electric signal from the detection element. In addition, the signal processing unit 224 transmits the electrical signal read from the readout circuit 222 to an image processing unit (not shown) provided outside the radiation imaging apparatus 200 according to a control signal supplied from the control unit 225. supply. An image processing unit (not shown) supplied with the electric signal may generate an image from the electric signal and output it to a display (not shown) or the like. This allows the user of the radiation imaging apparatus 200 to observe the captured radiation image. Also, the image processing of the electrical signal may be performed by the signal processing unit 224 . A power supply circuit 226 supplies a bias voltage to each component of the radiation imaging apparatus 200 . In this embodiment, the signal processing unit 224 and the control unit 225 have different configurations, but for example, the control unit 225 may have an integrated configuration that performs the processing performed by the signal processing unit 224. .

A radiation source 227 that emits radiation and a radiation control unit 229 that controls the radiation source 227 are connected to the radiation imaging apparatus 200 . The radiation controller 229 controls the radiation source 227 according to control signals supplied from the controller 225 . Although the radiation source 227 is controlled by the radiation controller 229 in this embodiment, the controller 225 may directly supply the control signal to the radiation source 227 without going through the radiation controller 229 . Further, for example, in the present embodiment, the radiation imaging apparatus 200 and the radiation control unit 229 are arranged separately, but the radiation imaging apparatus 200 performs the functions of the radiation control unit 229 described below. At least a part may be included. Alternatively, the radiation imaging apparatus 200 and the radiation control unit 229 may be integrated. In other words, the radiation imaging apparatus 200 and the radiation control unit 229 may be collectively referred to as the "radiation imaging apparatus" of the present invention.

Conditions such as tube current and tube voltage can be input to the radiation control unit 229 from the outside during radiographic imaging. Conditions such as radiation irradiation time can also be externally input to the radiation control unit 229 and used to control the radiation source 227 . Imaging information such as tube current, tube voltage, and irradiation time may be input directly into the radiation control unit 229 by the user. Alternatively, the imaging information may be preset for each imaging mode, and may be selected by the user from a recipe of imaging information stored in the radiation control unit 229, for example. The radiation control unit 229 has a user interface for accepting input of information such as imaging conditions from the user. control console.

Next, the detector 223 will be described with reference to FIG. The detection unit 223 includes the support substrate 100 on which the pixel array 228 is arranged, the drive circuit 221, and the readout circuit 222, as described above. Pixel array 228 includes a plurality of pixels arranged in a matrix. In this embodiment, the plurality of pixels includes pixels 101 and pixels 121 having different shapes.

In order to acquire a radiographic image, the pixel 101 includes a conversion element 102 that converts incident radiation or light into electric charge corresponding to the amount of incident light, and a switch element 103 that outputs the electric charge generated by the conversion element 102 to a signal line. including. The conversion element 102 may be an indirect conversion element using, for example, a scintillator that converts radiation into light and a photoelectric conversion element that converts the light converted by the scintillator into charge. In this case, the scintillator may be shared by multiple pixels 101 . Further, as the conversion element 102, for example, a direct conversion element that directly converts radiation into an electric charge may be used. A thin film transistor (TFT) using amorphous silicon or polycrystalline silicon, for example, can be used as the switch element 103 . For example, polycrystalline silicon may be used depending on the characteristics required for the TFT. Further, the semiconductor material used for the TFT is not limited to silicon, and other semiconductor materials such as germanium and compound semiconductors may be used.

A first main electrode of the switching element 103 is electrically connected to the first electrode of the conversion element 102 , and a bias line 108 is electrically connected to the second electrode of the conversion element 102 . A bias line 108 is commonly connected to the second electrodes of the plurality of conversion elements 102 arranged along the columns. A common bias voltage is supplied to the bias lines 108 arranged in each column. Bias line 108 receives a bias voltage from power supply circuit 226 shown in FIG.

A signal line 106 is electrically connected to the second main electrode of the switch element 103 . The signal line 106 is commonly connected to the second main electrodes of the switching elements 103 of the pixels arranged along the columns. The signal line 106 is arranged for each column of pixels. Each signal line 106 is electrically connected to a readout circuit 222 . A drive line 104 is electrically connected to the control electrode of the switch element 103 . The drive line 104 is commonly connected to the control electrodes of the switch elements 103 of the plurality of pixels 101 arranged along the row, and the drive circuit 221 applies gate control voltages Vg1 to Vgn to the drive line 104 .

The pixel 121 includes a detector element 122 that converts the incident radiation or light into an electric charge corresponding to the incident amount, and the electric charge generated by the detector element 122 in order to obtain the total amount of incident radiation during radiation irradiation. and a switch element 123 that outputs to the signal line. Pixels 121 may also include conversion elements 102 and switch elements 103 for generating radiographic images, as shown in FIG. The detection element 122 and the switch element 123 may have the same configuration as the conversion element 102 and the switch element 103, respectively.

The first electrode of the detection element 122 is electrically connected to the first main electrode of the switch element 123, and the second electrode of the detection element 122 is electrically connected to the bias line 108 arranged for each column. be. The detection line 110 is connected to the second main electrodes of the switch elements 123 arranged along the columns. Each sense line 110 is electrically connected to a readout circuit 222 . Drive lines 124 arranged for each row are connected to the control electrodes of the switch elements 123 . Gate control voltages Vd 1 to Vdn are applied to the drive lines 124 from the drive circuit 221 .

A plurality of pixels 121 including the detection element 122 may be arranged in the imaging region as shown in FIG. 2, or, for example, only one may be arranged. When a plurality of pixels 121 are arranged, the amount of incident radiation may be detected by only one of the detection elements 122 of the plurality of pixels 121 arranged, or by a plurality of detection elements 122 . may be broken. Further, by driving the drive line 104 during radiation irradiation without arranging the pixel 121, the pixel 101 may function as a detection element as described above, and the amount of incident radiation may be obtained.

In readout circuit 222 , signal line 106 and detection line 110 are each connected to the inverting input terminal of operational amplifier 150 . Also, the inverting input terminal of the operational amplifier 150 is connected to the output terminal via a feedback capacitor, and the non-inverting input terminal is connected to an arbitrary fixed potential. The operational amplifier 150 functions as a charge-voltage conversion circuit. After the operational amplifier 150 , an AD converter 153 is connected via a sample hold circuit 151 and a multiplexer 152 . The readout circuit 222 constitutes a digital conversion circuit that converts electric charges transferred from the conversion elements 102 and the detection elements 122 of the pixels 101 and 121 through the signal lines 106 and the detection lines 110 into digital electric signals. The readout circuit 222 may be integrated with each circuit, or may be arranged individually for each circuit.

Next, structures of the pixel 101 and the pixel 121 are described with reference to FIG. 3(a) is a plan view of the pixel 101, FIG. 3(b) is a plan view of the pixel 121, and FIG. 3(c) is a cross-sectional view of the pixel 121 between AA' in FIG. 3(b). respectively. In this embodiment, the pixels 101 and 121 use indirect conversion elements that use a scintillator that converts radiation into light and a photoelectric conversion element that converts the light converted by the scintillator into charges. As shown in FIG. 3A, a pixel 101 is provided with a conversion element 102 and a switch element 103 . Further, as shown in FIG. 3B, the pixel 121 is provided with the conversion element 102, the switch element 103, and the detection element 122 and the switch element 123. As shown in FIG. As shown in FIG. 3C, a PIN-type photodiode 134 may be used as the conversion element 102 . Also, the PIN-type photodiode 135 may be used for the detection element 122 as well as the conversion element 102 . The conversion element 102 can be stacked with an interlayer insulating layer 130 interposed on the switch element 103 using a TFT provided on an insulating support substrate 100 such as a glass substrate. Similarly, the detection element 122 can be laminated on the switching element 123 using a TFT provided on the supporting substrate 100 with the interlayer insulating layer 130 interposed therebetween.

The conversion element 102 and the detection element 122 are insulated so that the first electrode 131 of the conversion element 102 and the first electrode 132 of the detection element 122 adjacent to each other are not electrically connected. The insulation between the first electrodes 131 and 132 is enhanced by the inter-element insulating film 133 provided between the first electrodes 131 and 132 . PIN-type photodiodes 134 and 135 are laminated in the order of n-layer-i-layer-p-layer on the first electrodes 131 and 132 and the inter-element insulating film 133, respectively. Second electrodes 136, 137 are disposed on the photodiodes 134, 135, respectively. Furthermore, a protective film 138 , a second interlayer insulating layer 139 , a bias line 108 and a protective film 140 are arranged to cover the photodiodes 134 and 135 . A planarizing film (not shown) and a scintillator (not shown) are arranged on the protective film 140 . The second electrodes 136 , 137 are both connected to the bias line 108 . In this embodiment, the second electrodes 136 and 137 are made of light-transmissive electrodes such as indium tin oxide (ITO). The second electrodes 136 and 137 are configured so that light converted from radiation by a scintillator (not shown) on the protective film 140 can pass through the photodiodes 134 and 135 .

As shown in FIGS. 3A and 3B, the pixels 101 and 121 have different sizes of conversion elements 102 for generating radiation images. Therefore, even when the dose of radiation incident on the pixel 101 and the pixel 121 is the same, the amount of charge output from each conversion element 102 is different. When the electrical signal read out by the readout circuit 222 from the charge output from the conversion element 102 of the pixel 121 is used for the radiation image, necessary correction such as white correction (gain correction) may be performed as appropriate. Further, for example, only the detection element 122 may be arranged without arranging the conversion element 102 in the pixel 121 . In this case, some pixels do not output electrical signals for forming a radiographic image, but the electrical signals output from the pixels 101 arranged around the pixels 121 are used to interpolate (generate) the signals of the pixels 121 in the radiographic image. ). Also, in the detection element 122, the electrical signal used for detecting the amount of incident radiation may be used for forming a radiographic image.

Next, the operation flow of each component in radiographic imaging will be described with reference to FIG. 4(a). FIG. 4(a) is a flow chart of imaging in this embodiment. First, the user inputs imaging information on the user interface of the radiation control unit 229 (S401). The imaging information includes, for example, the tube voltage and tube current of the radiation source 227 for irradiating the radiation imaging apparatus 200 with radiation, the irradiation time of radiation, the target radiation dose, and the like. In addition, when a plurality of detection elements 122 are arranged in the pixel array 228, the detection element 122 for obtaining the incident radiation dose among the plurality of detection elements 122, in other words, the position for obtaining the incident radiation dose is included in the imaging information. Information may also be included, namely the location of the region of interest. The imaging information also includes information such as the tube voltage index of the radiation source 227, the grid exposure multiple, the radiation absorption rate of the additional filter, the distance between the radiation source 227 and the object, the thickness of the object, and the radiation transmittance of the object. good too. Further, for example, the imaging information includes the number of binnings when forming one pixel of a radiographic image using the outputs of the conversion elements 102 of the plurality of pixels 101 and pixels 121, the setting of the gain in the readout circuit 222, and the like. may be In addition, instead of the user inputting and setting the imaging information one by one, for example, the user may select a combination of preset imaging information from recipes stored in the radiation control unit 229 . Further, for example, the radiation control unit 229 may automatically determine the combination of imaging information by the user inputting the body part to be imaged and the age and physique of the subject. Further, a sensor or the like may be provided in each unit of the radiation imaging apparatus 200, the radiation control unit 229, and the radiation source 227 to automatically acquire any of the imaging information. For example, an infrared sensor attached to the radiation source 227 may measure the distance between the radiation source 227 and the subject. Further, for example, a camera connected to the radiation control unit 229 may estimate the thickness of the subject, or may specify the part of the subject that is the region of interest and estimate the radiation transmittance of the region of interest of the subject. Further, for example, the distance between the radiation source and the subject, the grid exposure factor, the radiation absorption rate of the additional filter, and the like may be obtained by pre-calibration. Further, for example, the radiation imaging apparatus 200 may have a user interface, through which the user may input imaging information.

The radiation control unit 229 supplies imaging information including radiation irradiation information such as tube voltage, tube current, irradiation time, and target radiation dose to the control unit 225 of the radiation imaging apparatus 200 . The radiation control unit 229 also supplies imaging information to the calculation unit 240 arranged in the control unit 225 of the radiation imaging apparatus 200 . In this embodiment, the arithmetic unit 240 is arranged in the control unit 225 and is shown as part of the functions of the control unit 225, but is not limited to this. The arithmetic unit 240 may be a processing circuit including an FPGA arranged independently of the control unit 225 . The calculation unit 240 measures the amount of incident radiation based on the signal output from the detection element 122 during radiation irradiation. Further, although the details will be described later, the calculation unit 240 is arranged to obtain an offset correction value according to imaging conditions when measuring the amount of incident radiation. The imaging information can be supplied to the control unit 225 and the calculation unit 240 each time the information input to the radiation control unit 229 changes. Also, the imaging information may be supplied at a certain time cycle, or may be supplied at the timing when the user presses an exposure switch for instructing irradiation of radiation.

Next, processing performed by the calculation unit 240 in order to obtain offset correction values according to imaging conditions will be described. First, the calculation unit 240 estimates the dose of radiation incident on the radiation imaging apparatus 200 from imaging information set by the user and supplied from the radiation control unit 229. A signal value S output by sampling is estimated (S421).

For example, the calculation unit 240 calculates the radiation dose estimated to be incident on the radiation imaging apparatus 200 per unit time from the radiation irradiation time and the target radiation dose in the imaging information supplied from the radiation control unit 229 . The amount of radiation incident per unit time is proportional to the signal value detected by the detection element 122 per unit time. Therefore, the calculation unit 240 estimates the signal value S output by one sampling from the amount of incident radiation per unit time estimated from the imaging information and the sampling period for detecting the radiation signal during radiation irradiation. may

ここで、Ｖ：管電圧、ｎ：管電圧指数、Ｉ：管電流、ＳＩＤ：被写体距離、Ｂ：グリット露出倍数、ｄ：被写体厚、μ：被写体関心領域の放射線透過率、Ａｌ（Ｖ）：付加フィルタの放射線吸収率、Ｅ（ｔ）：単位時間あたりに入射する放射線の推定される線量である。 Also, for example, the calculation unit 240 performs calculation using the following formula (1) based on the imaging information supplied from the radiation control unit 229, and estimates the radiation dose incident per unit time. Then, the signal value S output by the detection element 122 in one sampling may be estimated from the sampling period for detecting the signal from the detection element 122 during radiation irradiation.

Here, V: tube voltage, n: tube voltage index, I: tube current, SID: subject distance, B: grid exposure multiple, d: subject thickness, μ: radiation transmittance of subject region of interest, Al (V): Radiation Absorption Rate of Additional Filter, E(t): Estimated dose of incident radiation per unit time.

If all the imaging information shown in Equation (1) cannot be obtained, for example, standard values may be input for the parameters for which information was not obtained. By inputting at least one piece of imaging information, the estimated radiation dose approaches the actual radiation dose, making it possible to more accurately determine the incident radiation dose.

Also, for example, during continuous imaging or when switching from moving image imaging to still image imaging, the signal value obtained by one sampling of the current imaging based on the actual measurement value of the irradiation dose at the time of immediately preceding imaging. S may be estimated. That is, the radiation imaging apparatus 200 performs the first imaging and the second imaging after the first imaging. In this case, the calculation unit 240 acquires the signal value output by one sampling during irradiation of the radiation by the detection element 122 in the second imaging according to the measured value of the radiation dose incident in the first imaging. . At this time, as shown in FIG. 4A, the control unit 225 of the radiation imaging apparatus 200 may further include a memory 231 that stores the actual measurement value of the radiation dose obtained in the immediately preceding imaging. The memory 231 may be configured independently from the control unit 225, similar to the calculation unit 240. FIG. The calculation unit 240 stores, for example, the actual measurement value of the radiation dose when the image was captured in the previous frame in the case of continuous imaging, and the actual measurement value of the incident radiation during the imaging of the moving image in the case of switching from the moving image to the still image. 231 and used to estimate the signal value S in the next imaging. When the imaging conditions are the same between the previous imaging and the current imaging, it is possible to accurately calculate the signal value S per sampling from the radiation dose actually measured in the previous imaging. Also, if the imaging conditions differ between the previous imaging and the current imaging, each parameter may be corrected by substituting the radiation dose and imaging information actually measured during the previous imaging into Equation (1). By estimating the radiation dose from the current imaging information using the modified formula (1), it is possible to improve the estimation accuracy of the signal value S output from the detection element 122 in one sampling.

Subsequently, before radiation irradiation, the calculation unit 240 calculates the offset component of the detection element 122 according to the signal value S output by one sampling during radiation irradiation by the detection element 122 estimated from the imaging information. is determined (S422). The accuracy of the offset component required when obtaining the integrated dose of radiation depends on the signal value when the signal is sampled during radiation irradiation. For example, when the signal value is small, the accuracy of the offset component may be affected relatively more than when the signal value is large. In other words, under imaging conditions in which weak radiation is incident, the signal value S acquired by one sampling is small, so it is necessary to improve the accuracy of acquiring the offset component. Therefore, it is necessary to increase the number of times n of sampling the offset component. On the other hand, in the case of imaging conditions in which strong radiation is incident, the signal value S acquired by one sampling is large, so the accuracy of acquiring the offset component is relatively lower than in imaging conditions in which weak radiation is incident. good too. Therefore, the number of times n for sampling the offset component may be smaller than the imaging condition under which weak radiation is incident, and the delay from turning on an exposure switch described later to starting radiation exposure can be shortened.

For example, based on the signal value S and the noise value σ of the offset component caused by the dark current or the like output by the detection element 122, the calculation unit 240 determines the number of times n to sample the offset component. The number n of times the offset component is sampled is determined so that the effect of the acquisition accuracy of the offset component on the estimated signal value S output by one sampling is sufficiently small.

ここで、Ｔは、精度基準となるしきい値である。Ｔの値は、所望の放射線信号検出精度に合わせて任意に設定できる。オフセット成分のノイズσは、メモリ２３１内に事前に記憶されていてもよいし、オフセット成分をサンプリングする回数を決定する動作に入る前に、実測して取得してもよい。また、メモリ２３１内にオフセット成分のノイズσを記憶している場合、実測した値を元にノイズσの値を更新してもよい。 For example, the number of times n to sample the offset component may be determined by a criterion such as Equation (2) shown below.

Here, T is a threshold that serves as an accuracy standard. The value of T can be arbitrarily set according to the desired radiation signal detection accuracy. The noise σ of the offset component may be stored in the memory 231 in advance, or may be obtained by actual measurement before starting the operation of determining the number of times the offset component is sampled. Further, when the noise σ of the offset component is stored in the memory 231, the value of the noise σ may be updated based on the actually measured value.

The signal value S that the detection element 122 outputs in one sampling during radiation irradiation and the number of times n that the offset component of the detection element 122 is sampled are determined, for example, by an arithmetic element such as an FPGA mounted in the arithmetic unit 240. may be computed as Further, for example, a look indicating the relationship between the signal value S output by the detection element 122 during irradiation of radiation, which is estimated from the imaging information, by the radiation imaging apparatus 200 and the number of times the offset component is sampled. An up-table (LUT) may also be included. The LUT may be stored in memory 231, for example. The calculation unit 240 refers to the lookup table based on the relationship between the irradiation time and the target radiation dose supplied from the radiation control unit 229 and the noise σ of the offset component, and determines the number n of times the offset component is sampled. good too.

The calculation unit 240 calculates the offset component after the user sets the imaging information and before the user receives a signal instructing the user to start imaging a radiographic image, that is, until the user turns on the exposure switch. The number n of times to sample may be determined. The number of times n for sampling the offset component may be determined after the exposure switch is turned on. It becomes a shooting delay.

After the imaging information is set by the user, when the user turns on the exposure switch provided in the radiation control unit 229 (S402), the radiation control unit 229 instructs the radiation imaging apparatus 200 to start imaging a radiographic image. An instruction signal is transmitted (S403). The control unit 225 of the radiation imaging apparatus 200 samples the offset component from the detection element 122 for the number of times n of sampling determined in advance by the calculation unit 240 in response to the reception of the signal instructing the start of imaging from the radiation control unit 229. (S423). The calculation unit 240 acquires an offset correction value having an accuracy corresponding to the signal value S output from the detection element 122 in one sampling during radiation irradiation from the offset components sampled n times. When the calculation unit 240 acquires the offset correction value, the control unit 225 outputs a signal for permitting the radiation source 227 to irradiate the radiation imaging apparatus 200 with radiation. More specifically, the controller 225 transmits an irradiation permission signal to the radiation controller 229 . Acquisition of the offset correction value may be completed before the exposure switch is pressed. Also, the exposure switch may be a two-step switch, one for starting the idling of the radiation tube of the radiation source 227 and the other for irradiating the subject with radiation.

Upon receiving the irradiation permission signal from the radiation imaging apparatus 200, the radiation control unit 229 outputs an irradiation command to the radiation source 227 and the control unit 225 of the radiation imaging apparatus 200 (S404). The radiation source 227 starts emitting radiation according to the exposure command (S411). In addition, the control unit 225 operates the detection unit 223 according to the exposure command to start obtaining a radiographic image (S424). Specifically, the conversion elements 102 of the pixels 101 and 121 arranged in the pixel array 228 of the detection unit 223 accumulate electric charges according to the amount of incident radiation. At the same time, a detection operation for acquiring the amount of radiation incident on the detection element 122 of the pixel 121 is started.

When irradiation of radiation is started, the calculation unit 240 corrects the signal value output from the detection element 122 of the pixel 121 according to the offset correction value obtained from the offset component obtained before irradiation of radiation, based on the correction value. to measure the incident radiation dose (S425). The control unit 225 compares the radiation dose measured by the calculation unit 240 with the target radiation dose information among the imaging information supplied from the radiation control unit 229 . Specifically, the control unit 225 compares the cumulative value of the radiation dose obtained from the correction value obtained by correcting the signal value according to the offset correction value by the calculation unit 240 with the target radiation dose. Based on this comparison result, an irradiation stop determination is performed to determine whether to continue or stop radiation irradiation (S426). Here, it is assumed that the calculation unit 240 calculates the cumulative value of the radiation dose. good too. When the cumulative value of the radiation dose detected by the detection elements 122 of the pixels 121 has not reached the target radiation dose, the control unit 225 determines that radiation irradiation needs to be continued, and performs radiographic image acquisition and detection operations. Continue (NO in S426). When the cumulative value of the radiation dose detected by the detection elements 122 reaches the target radiation dose, or when it is predicted that the target radiation dose will be reached, the control unit 225 controls the radiation source that irradiates the radiation imaging apparatus 200 with radiation. 227 outputs a signal for stopping radiation irradiation. More specifically, the control unit 225 outputs an irradiation stop signal to the radiation control unit 229 to stop irradiation of radiation (YES in S426). The radiation control unit 229 outputs an irradiation stop command to the radiation source 227 based on the irradiation stop signal output from the control unit 225 (S405). In accordance with the irradiation stop command, the radiation source 227 stops radiation irradiation (S412). Radiation irradiation may be stopped by, for example, stopping the irradiation command output from the radiation control unit 229 to the radiation source 227 instead of outputting the irradiation stop command. Further, the detection unit 223 may stop the detection operation in response to the output of the irradiation stop command.

In the present embodiment, the irradiation stop determination is performed by the control unit 225 of the radiation imaging apparatus 200, but the present invention is not limited to this. For example, as shown in FIG. 4B, the calculation unit 240 outputs to the radiation control unit 229 a correction value obtained by correcting the signal value output from the detection element 122 according to the offset correction value. Based on this correction value, the radiation control unit 229 may make a stop determination and output an irradiation stop command (S406). In this case, the radiation control unit 229 does not need to send information on the target radiation dose to the control unit 225 before radiation irradiation. In addition, the operation of obtaining a radiographic image and detecting a radiation dose may be stopped in response to the radiation control unit 229 making a decision to stop the irradiation and outputting a command to stop the irradiation.

Further, the control unit 225 outputs an irradiation stop signal when the irradiation time of the subject with the radiation from the radiation source 227 reaches the upper limit of the irradiation time in the imaging information supplied from the radiation control unit 229 before irradiation with radiation. You may According to the irradiation stop signal, the radiation control unit 229 outputs an irradiation stop command to the radiation source 227, and the radiation source 227 stops irradiation of radiation. Radiation irradiation is stopped according to the upper limit of the irradiation time before the cumulative value of the radiation dose incident on the detection element 122 reaches the target radiation dose, or even before it is expected to reach the target radiation dose. As a result, for example, even if the amount of radiation incident on the detection elements 122 of the pixels 121 is not normally detected, it is possible to avoid excessive irradiation of the subject.

The control unit 225 of the radiation imaging apparatus 200 reads out signals corresponding to charges accumulated in the conversion elements 102 of the pixels 101 and 121 after irradiation with radiation. Thereby, a radiographic image can be acquired (S427).

Next, in this embodiment, operation timing of each component in radiographic imaging will be described with reference to FIGS. FIG. 5 is a timing chart showing operation timing of each component of the radiation imaging apparatus 200. As shown in FIG. A period T1 shown in FIGS. 4(a), 4(b), and 5 represents an idling period during standby. During this period T1, as shown in FIG. 5, the pixels 101 and 121 arranged in the pixel array 228 repeat the idling operation (reset operation) by the signal applied from the driving circuit 221. FIG. The idling operation may be performed, for example, after the detector 223 is powered on until sampling of the offset component is started. Also, as shown in FIGS. 4A and 4B, the period T1 is the time during which the user inputs the imaging information, the time until the user presses the exposure switch, and the radiation imaging apparatus 200. is the time for determining the number of times n that the calculation unit 240 samples the offset component.

During the period T1, in order to periodically remove (reset) offset components caused by dark current and the like generated in the conversion elements 102 of the pixels 101 and 121, a Hi signal is periodically applied to the gate control voltages Vg1 to Vgn. be done. Similarly, in order to remove an offset component caused by dark current or the like generated in the detection element 122 of the pixel 121, a high signal is always applied to the gate control voltages Vd1 to Vdn, and the switch element 123 of the pixel 121 is turned on. state. Here, the Hi signal is a voltage at which the switch elements 103 and 123 are turned on, and the Lo signal is a voltage (for example, 0 V) at which the switch elements 103 and 123 are turned off. Also, in the timing chart of this embodiment shown in FIG. 5, an example of detecting the amount of incident radiation using a plurality of detection elements 122 is shown. In this case, the respective detection elements 122 may be set with the same target radiation dose, or may be set with different target radiation doses. Further, the control unit 225 may output a stop determination signal when one of the detection elements 122 of the plurality of pixels 121 reaches the target radiation dose, or the average value of the plurality of detection elements 122 may be equal to the target radiation dose. A stop determination signal may be output when the Also, the control unit 225 may output a stop determination signal when all the detection elements 122 reach the target radiation dose. These settings may be appropriately set depending on the subject, imaging conditions, the position of the detection element 122 within the pixel array 228, and the like.

Next, when the exposure switch is pressed and the radiation imaging apparatus 200 receives a signal instructing the start of imaging of a radiation image from the radiation control unit 229, the radiation imaging system SYS shifts to period T2. A period T2 is a period for sampling an offset component from the detection element 122 and obtaining an offset correction value. In the period T2, a Hi signal is periodically applied to the gate control voltages Vd1 to Vdn while radiation is not applied, and the offset component is obtained from the detection element 122. FIG. The number of times the Hi signal is applied is based on the number n of times the offset component determined by the calculator 240 is sampled during the period T1. The period in which the Hi signal is applied to the gate control voltages Vd1 to Vdn may be the same as the period in which signals are detected from the detection elements 122 during radiation irradiation. That is, the control unit 225 performs sampling of the offset component and detection of the incident radiation dose from the detection element 122 at the same sampling period. By performing the same drive when sampling the offset component and when detecting the incident radiation dose, the offset signal amount when acquiring the offset correction value and the offset signal amount when detecting the incident radiation dose are obtained. , can be values close to each other. As a result, the calculation unit 240 can accurately acquire the offset correction value and perform highly reliable offset correction. The offset correction value may be an average value or mode value of a plurality of signal values of the sampled offset components. Also, for example, the offset correction value may be an average value excluding the maximum and minimum values of a plurality of sampled offset component signal values. The offset correction value can be obtained as appropriate based on statistics of multiple signal values of the sampled offset components.

Acquisition of the offset correction value may be completed in the period T1 as described above, but the accuracy can be improved immediately before the irradiation of radiation and the detection of radiation are started. By obtaining the offset correction value immediately before radiation irradiation, the effect of temporal changes in the offset component is reduced, and the amount of offset signal when obtaining the offset correction value and the amount of incident radiation when detecting the radiation dose are reduced. and the amount of offset signal can be made close to each other. In addition, the offset component is sampled immediately before the radiation is irradiated, and the same drive is continued to detect the amount of incident radiation. This suppresses signal fluctuations that occur when the drive is switched, improving detection accuracy. Decrease can be suppressed.

Next, when the radiation control unit 229 receives an irradiation permission signal from the radiation imaging apparatus 200, the radiation imaging system SYS shifts to period T3. A period T3 is a period for irradiating radiation and acquiring a radiographic image. FIG. 5 shows a timing chart when imaging is started when the radiation control unit 229 receives an irradiation permission signal from the radiation imaging apparatus 200 . In the period T3, Lo signals are applied to the gate control voltages Vg1 to Vgn that drive the switch elements 103, and each of the conversion elements 102 accumulates electric charge according to the amount of incident radiation. Also, a Hi signal is applied to the gate control voltages Vd1 to Vdn for driving the switch element 123 at a constant sampling period, and the charge detected by the detection element 122 is sent to the readout circuit 222 via the detection line 110. FIG. The readout circuit 222 supplies a signal based on the detected charges to the calculation section 240 of the control section 225 via the signal processing section 224 . The calculation unit 240 corrects the signal value output from the detection element 122 according to the offset correction value, and obtains the radiation dose incident on the detection element 122 for each sampling period. FIG. 5 shows a case where the dose of radiation that is always incident during the period T3 is acquired for each sampling cycle. It may terminate and accumulate charge. Also, during the period T2 to T3, the switch element 123 may continue to be driven at the same sampling period as described above. When the sampling period is changed or the sampling is temporarily stopped when the period T2 shifts to the period T3, the signal may fluctuate due to the switching of driving. This may affect the signal value for detecting the radiation dose at the beginning of the period T3 and reduce the detection accuracy.

Further, in FIG. 5, the gate control voltages Vd1 to Vdn applied to the control electrodes of the switch elements 123 simultaneously become Hi signals, but the operation during the period T2 is not limited to this. For example, as shown in FIG. 6, the timings of the Hi signals of the gate control voltages Vd1 to Vdn corresponding to the switch elements 123 for the detection elements 122 connected to the same detection line 110 may be separated. In this case, the spatial resolution of the detection area can be increased, although the amount of signal that can be read at one time is reduced. Also, sampling of the offset component of the detection element 122 is obtained at the same period as the drive period of each switch element 123 .

The charge sent from the detection element 122 to the readout circuit 222 is converted into voltage information by the operational amplifier 150 . Next, it is sampled by the sample hold circuit 151 based on the sampling period, and converted into an electric signal of digital data by the AD converter 153 via the multiplexer 152 .

The calculation unit 240 corrects the signal value indicating the radiation dose detected by the detection element 122 and converted from the charge to the electric signal using the offset correction value obtained in advance. After that, the control unit 225 calculates the cumulative value of the radiation dose obtained by the calculation unit 240 based on the correction value obtained by correcting the signal value output from the detection element 122, and the radiation dose transferred in advance from the radiation control unit 229 to the control unit 225. Radiation irradiation stop determination is performed based on the information on the target radiation dose obtained. When the cumulative value of the irradiated radiation reaches the target radiation dose, or when it is predicted that the target radiation dose will be reached, the control unit 225 outputs a stop determination signal for stopping radiation irradiation to the radiation control unit 229. . Accordingly, the radiation control unit 229 causes the radiation source 227 to stop emitting radiation. In addition, the length of the period T3 may be determined in advance for each imaging mode or irradiation time input in advance. For example, even if the target radiation dose is not reached as described above, radiation irradiation may be stopped when the upper limit of the irradiation time input as the irradiation information is reached. After the cumulative value of the radiation dose detected by the detection elements 122 reaches the target radiation dose, or after a predetermined time has passed, the radiation imaging system SYS shifts from period T3 to period T4.

A period T4 is a period for obtaining a captured radiographic image after radiation irradiation. During the period T4, the control section 225 outputs a control signal for reading the signal charge accumulated in the conversion element 102 to the driving circuit 221. FIG. The drive circuit 221 sequentially applies Hi signals to the gate control voltages Vg1 to Vgn according to the control signal, and sequentially scans the switch elements 103 of the pixels 101 and 121. FIG. The electric charge accumulated in the conversion element 102 is converted into voltage information by the operational amplifier 150 , sampled by the sample-and-hold circuit 151 , and converted into an electric signal of digital data by the AD converter 153 via the multiplexer 152 . A radiographic image is formed based on the electrical signals acquired and read out by the conversion elements 102 .

Here, the effect of this embodiment will be described. During the period T2 shown in FIG. 5, the offset component superimposed on the radiation detection signal is obtained. The offset component output from the detection element 122 can change depending on the operating conditions of the detection element 122 and the switch element 123 . For example, the dark current of the detection element 122 and the offset level of the switch element 123 may change depending on the sampling period, the temperature at the time of imaging, and the like. These effects can change the amount of offset signal output from the detection element 122 . Therefore, in the present embodiment, before irradiation of radiation, the control unit 225 acquires the offset component output by the detection element 122 immediately before irradiation of radiation at the same sampling period as when detecting radiation. Therefore, it is possible to acquire an offset component that matches the sampling period of the detection element 122 and the imaging environment. The number of times n to sample the offset component is determined by the calculation unit 240 based on imaging information set by the user, such as radiation irradiation information. This makes it possible to acquire the offset component with more suitable accuracy for each imaging condition. Also, for example, the offset component is sampled more than necessary in order to improve the accuracy of the offset component, and the possibility of an unnecessary delay occurring between the user's depression of the exposure switch and imaging can be suppressed. By using the offset correction value acquired from this offset component, it is possible to improve the accuracy of AEC for detecting the dose of radiation incident during irradiation of radiation during period T3.

Second Embodiment A radiation imaging apparatus according to some embodiments of the present invention will now be described with reference to FIGS. 1(b) and 7. FIG. FIG. 1B shows a configuration example of a radiation imaging apparatus 200a according to the second embodiment of the present invention. Compared to the radiation imaging apparatus 200 of the first embodiment shown in FIG. 1A, a radiation control unit 229 that controls the radiation source 227 connected to the radiation imaging apparatus 200a is connected to the database 230 (recording unit). be. Points other than this may be the same as the radiation imaging apparatus 200 shown in FIG.

The database 230 records (stores) past information, which is imaging information in past imaging, and actually measured values of incident radiation doses in the past information. In this embodiment, the calculation unit 240 uses the measured values of the radiation dose in the information similar to the current imaging information among the past information from the database 230 to estimate the detection element 122 to output in one sampling during radiation irradiation. get the value of the signal According to this signal value, the calculation unit 240 determines the number of times n to sample the offset component.

More specifically, as shown in the flowchart of FIG. 7, first, the radiation control unit 229 compares imaging information input by the user to the radiation control unit 229 with past information stored in the database 230 ( S701). For example, the user inputs imaging information related to the tube voltage and tube current of the radiation source 227 , irradiation time, imaging region, subject thickness, and the like to the radiation control unit 229 . The radiation control unit 229 searches the database 230 for past information having imaging information similar to the input imaging information, and investigates the measured radiation dose per unit time when radiation is actually applied. Next, the radiation control unit 229 transfers the measured value of the radiation dose per unit time to the calculation unit 240, and based on this measured value, the calculation unit 240 determines the number of times n to sample the offset component. Also, the database 230 may record the number n of times the offset component is sampled in the past information. The calculation unit 240 may determine the number of times n to sample the offset component in the current imaging based on the number of times n recorded in the database 230 .

In this embodiment, the radiation control unit 229 searches the database 230 for imaging conditions for imaging information input by the user, but the present invention is not limited to this. For example, the radiation control unit 229 may transfer information regarding irradiation of radiation among the imaging information input by the user to the calculation unit 240 , and the calculation unit 240 may search the database 230 for past information.

Also, the method of determining the number of times n to sample the offset component using the database 230 is not limited to the above method. For example, when the same patient and the same site are imaged for follow-up observation, the radiation control unit 229 inputs the patient name, patient identification ID, etc. to the radiation control unit 229, and the radiation at the time of past imaging from the database 230. Acquire imaging information such as the irradiation conditions of Based on this imaging information, the radiation control unit 229 transfers information about the dose of radiation applied to the radiation imaging apparatus 200 to the control unit 225 and the calculation unit 240 of the radiation imaging apparatus 200 . The calculation unit 240 may determine the number of times n to sample the offset component based on this information.

The imaging information (past information) related to past imaging conditions stored in the database 230 may be accumulated for each imaging of a subject that has actually been imaged. Further, for example, imaging information manually created at the time of factory shipment or maintenance of the database 230 may be recorded.

As described above, two embodiments according to the present invention have been shown, but each embodiment described above can be modified and combined as appropriate. For example, if the calculation unit 240 cannot determine the number of times n to sample the offset component for the imaging information, the radiation imaging apparatus 200 may not permit the radiation source 227 to emit radiation. More specifically, when the input imaging information greatly deviates from the approximate recommended value determined by the subject's imaging region, sex, age, etc., the calculation unit 240 samples the offset component using a mechanism such as an interlock. It may not be possible to determine the number of times n to perform. The control unit 225 does not have to permit the radiation control unit 229 or the radiation source 227 to start radiation irradiation when the calculation unit 240 cannot determine the number of times n to sample the offset component. Further, for example, even if the measured value of the radiation dose is not stored in the database 230, the control unit 225 does not have to permit the start of radiation irradiation.

A radiation imaging system in which the radiation imaging apparatuses 200 and 200a of the present invention are incorporated will be exemplified below with reference to FIG. X-rays 6060 generated by an X-ray tube 6050, which is a radiation source for irradiating a radiation imaging device 6040 (corresponding to the radiation imaging devices 200 and 200a described above), pass through a chest 6062 of a patient or subject 6061. , enter the radiation imaging device 6040 . The incident X-rays contain information about the inside of the patient's or subject's 6061 body. In the radiation imaging device 6040, the scintillator emits light in response to the incidence of the X-rays 6060, and the light is photoelectrically converted by the photoelectric conversion element to obtain electrical information. This information is converted into digital data, image-processed by an image processor 6070 as a signal processing unit, and can be observed on a display 6080 as a display unit in the control room.

This information can also be transferred to a remote location by a transmission processor such as telephone line 6090 . This allows the display 6081, which is a display unit in a doctor's room or the like, in another location to allow a doctor in a remote location to make a diagnosis. Also, this information can be recorded on a recording medium such as an optical disc, or can be recorded on a film 6110 as a recording medium by the film processor 6100 .

The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the claims are appended to make public the scope of the invention.

122: detection element, 200, 200a: radiation imaging device, 223: detection unit, 225: control unit

Claims (14)

a detection element arranged in a detection unit for acquiring a radiographic image and detecting incident radiation;
A radiation imaging apparatus comprising: a calculation unit for measuring the amount of incident radiation based on a signal output from the detection element during radiation irradiation,
The calculation unit is
Before irradiation,
determining the number of times the offset component of the detection element is sampled according to the signal value output by the detection element in one sampling during radiation irradiation, which is estimated from the set imaging information;
obtaining an offset correction value from the offset component of the detection element sampled over the number of times of sampling;
1. A radiation imaging apparatus that measures an incident radiation dose based on a correction value obtained by correcting a signal value output from said detection element according to said offset correction value during radiation irradiation. The calculation unit estimates a signal value output by the detection element in one sampling during radiation irradiation by calculating a radiation dose per unit time incident on the detection element estimated from the imaging information. 2. The radiation imaging apparatus according to claim 1, wherein: The radiation imaging device performs a first imaging and a second imaging after the first imaging,
The computing unit estimates a signal value output by one sampling during irradiation of radiation by the detection element in the second imaging according to the measured value of the radiation dose incident in the first imaging. 3. The radiation imaging apparatus according to claim 1 or 2, characterized by: The radiation imaging apparatus further includes a recording unit that records past information, which is the imaging information in past imaging, and actual measurement values of incident radiation dose in the past information,
The calculation unit calculates a signal value output by one sampling from the detection element during irradiation of radiation from an actual measurement value of a radiation dose in information similar to the current imaging information among the past information from the recording unit. 3. The radiation imaging apparatus according to claim 1, wherein the estimation is performed. The radiation imaging apparatus creates a lookup table indicating a relationship between a signal value output by one sampling from the detection element during radiation irradiation estimated from the imaging information and the number of times the offset component is sampled. further includes
2. The radiation imaging apparatus according to claim 1, wherein said calculation unit determines the number of times of offset component sampling from said lookup table. 6. The radiation imaging apparatus according to any one of claims 1 to 5, wherein the imaging information includes a radiation irradiation time and a target radiation dose. The imaging information includes tube voltage, tube voltage exponent, tube current, grid exposure multiple of a radiation source for irradiating radiation to the radiation imaging apparatus, radiation absorption rate of an additional filter, position of a region of interest, radiation source and subject. 7. The radiation imaging apparatus according to any one of claims 1 to 6, characterized in that at least one of a distance of .theta. 8. The calculation unit determines the number of times the offset component is sampled after setting the imaging information and before receiving a signal instructing start of radiographic imaging. The radiation imaging apparatus according to any one of . The radiation imaging device is
starting sampling of the offset component from the detection element in response to receiving a signal instructing start of imaging of a radiographic image;
10. A signal for permitting irradiation of radiation to a radiation source for irradiating said radiographic imaging device with radiation is output by said computing unit in response to acquisition of said offset correction value. The radiation imaging apparatus according to any one of . When the radiation dose measured by the calculation unit reaches the target radiation dose or is expected to reach the target radiation dose, the radiation imaging device irradiates the radiation imaging device with radiation, 10. The radiation imaging apparatus according to any one of claims 1 to 9, wherein a signal for stopping irradiation of radiation is output. 11. The radiation imaging apparatus according to any one of claims 1 to 10, wherein said radiation imaging apparatus performs sampling of said offset component and detection of an incident radiation dose at the same sampling period from said detection element. . The detection unit includes a pixel array in which a plurality of pixels for generating a radiographic image are arranged,
12. The radiation imaging apparatus according to claim 1, wherein said detection elements are arranged in said pixel array. The detection unit includes a pixel array in which a plurality of pixels for generating a radiographic image are arranged,
12. The radiation imaging apparatus according to any one of claims 1 to 11, wherein one of the plurality of pixels functions as the detection element. a radiation imaging apparatus according to any one of claims 1 to 13;
a signal processing unit that processes a signal from the radiation imaging device;
A radiation imaging system comprising:

Images