JP7190913B2 - 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. Japanese Patent Laid-Open No. 2002-200001 discloses that by detecting the radiation dose in real time, the integrated dose of incident radiation during irradiation is grasped and automatic exposure control (AEC) is performed.

JP-A-7-201490

Japanese Patent Application Laid-Open No. 2002-200003 discloses reading out signals from X-ray exposure amount detection pixels at predetermined time intervals and comparing them with preset predetermined values. However, in the case of conditions where strong radiation is incident (the amount of radiation per unit time is large), the signal value per signal readout becomes large, and when the accumulated signal value exceeds a predetermined value, appropriate exposure is not possible. It is possible to exceed the quantity. On the other hand, under the condition that weak radiation is incident (the radiation dose per unit time is small), the signal value per readout is small, but the number of readouts until the accumulated signal value reaches a predetermined value is large. The increase increases the number of times the readout circuit noise is superimposed on the signal value. Due to superimposition of noise, the accumulated signal value may contain a large error with respect to the target dose.

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique that is advantageous for improving the accuracy of AEC.

In view of the above problems, a radiation imaging apparatus according to an embodiment of the present invention is a radiation imaging apparatus that is arranged in an imaging unit for acquiring a radiation image and includes a plurality of detection elements for detecting incident radiation. The radiation imaging apparatus further includes a dose acquisition unit, and the dose acquisition unit performs different sampling cycles in parallel from the first detection element and the second detection element among the plurality of detection elements during the exposure control period. and detecting the amount of incident radiation based on the first signal obtained from the first detection element and the second signal obtained from the second detection element.

The above means provide a technique that is advantageous for improving the accuracy of AEC.

1 is a diagram showing a configuration example of a radiation imaging system using a radiation imaging apparatus according to an embodiment of the present invention; FIG. FIG. 2 is an equivalent circuit diagram showing a configuration example of an imaging unit of the radiation imaging apparatus of FIG. 1; FIG. 2 is an equivalent circuit diagram showing a configuration example of an imaging unit of the radiation imaging apparatus of FIG. 1; FIG. 2 is a flowchart showing an operation example of the radiation imaging apparatus in FIG. 1; FIG. 2 is a timing chart showing an operation example of the radiation imaging apparatus in FIG. 1; FIG. 2 is a timing chart showing an operation example of the radiation imaging apparatus in FIG. 1; FIG. 4 is a timing chart showing an operation example of a radiation imaging apparatus of a comparative example;

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.

A radiation imaging apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a configuration example of a radiation imaging system SYS using a radiation imaging apparatus 100 according to an embodiment of the present invention. In this embodiment, the radiation imaging system SYS includes a radiation imaging device 100 , a control computer 200 , a radiation control device 300 and a radiation generation device 400 .

The radiation imaging apparatus 100 is arranged in an imaging unit 120 for acquiring radiation images and includes a plurality of detection elements for detecting incident radiation. The imaging unit 120 further includes a pixel array in which a plurality of pixels for generating a radiographic image are arranged, and outputs image information, although the details of the configuration of the imaging unit 120 will be described later. The radiation imaging apparatus 100 acquires signals from the detection elements arranged in the imaging unit 120, and has a dose acquisition unit 140 that detects the amount of incident radiation to perform exposure control. Further includes a control unit 160 . The dose acquisition unit 140 calculates the signals output from the detection elements during radiation irradiation, and outputs exposure information including the amount of incident radiation and temporal fluctuations in radiation intensity. A digital signal processing circuit such as an FPGA (Field-Programmable Gate Array), a DSP (Digital Signal Processor), or a processor may be used for the dose acquisition unit 140 . Also, the dose acquisition unit 140 may use an analog circuit such as a sample-and-hold circuit or an operational amplifier. 1, the dose acquisition unit 140 is arranged in the radiation imaging apparatus 100, but part or all of the functions of the dose acquisition unit 140 may be included in the control computer 200. . In this case, the radiation imaging apparatus 100 and the functions of the dose acquisition unit 140 of the control computer 200 can be collectively referred to as the "radiation imaging apparatus" of the present invention.

The control computer 200 controls the radiation imaging system SYS as a whole, controls irradiation of radiation, and acquires radiation images. Also, the control computer 200 can function as a user interface when a user (for example, a doctor or a radiological technologist) uses the radiation imaging system SYS. The radiation control apparatus 300 operates the radiation generating apparatus 400 according to a signal regarding radiation irradiation control received from the control computer 200 . The radiation generation device 400 irradiates the radiation imaging device 100 with radiation according to the radiation control device 300 .

FIG. 2 is an equivalent circuit diagram showing a configuration example of the imaging unit 120 in this embodiment. The imaging unit 120 includes a pixel array 112 , a readout circuit 113 , a drive circuit 114 and an A/D converter 110 . FIG. 2 shows a pixel array 112 in which 5 rows×5 columns of pixels PIX are arranged for simplification of explanation. However, the actual pixel array 112 may have more pixels PIX arranged, for example, about 2800 rows by about 2800 columns of pixels PIX for a 17 inch imager.

The pixel array 112 has a plurality of pixels PIX arranged in a matrix. The pixel PIX includes a conversion element 102 that converts radiation into charge, and a switch element 101 that outputs an electrical signal corresponding to the charge. In this embodiment, as the conversion element 102, a wavelength conversion body (for example, a scintillator) that converts radiation into light that can be detected by the conversion element, a photoelectric conversion element that converts the light converted by the wavelength conversion body into an electric charge, is used. The photoelectric conversion element may be an MIS photodiode that is arranged on an insulating substrate such as a glass substrate and that is mainly made of amorphous silicon. A PIN photodiode arranged on a semiconductor substrate such as silicon may be used as the photoelectric conversion element. Further, the conversion element 102 is not limited to an indirect type conversion element provided with a wavelength converter that converts the above-described radiation into light in a wavelength band that can be sensed by the photoelectric conversion element, and directly converts radiation into electric charge. A direct type conversion element may be used. In this case, amorphous selenium or the like may be used as the main material of the conversion element. A transistor having a control terminal and two main terminals may be used as the switch element 101 . In this embodiment, a thin film transistor (TFT) is used as the switch element 101 .

One electrode of the conversion element 102 is electrically connected to one of the two main terminals of the switch element 101, and the other electrode is electrically connected to a bias power supply 103 via a common bias wiring Bs. The switch elements 101 arranged in the row direction (horizontal direction in FIG. 2), such as switches T11 to T15, have their control terminals electrically connected in common to the drive wiring Vg1. The switches T11 to T15 are supplied with driving signals for controlling the conductive states of the switches T11 to T15 from the driving circuit 114 on a row-by-row basis via the driving wiring Vg1. The switch elements 101 arranged in the column direction (the vertical direction in FIG. 2), such as the switches T11 to T51, have the other main terminals electrically connected to the signal wiring Sig1. While the switches T11 to T51 are in a conductive state, a signal corresponding to the charges accumulated in the conversion element 102 is output to the readout circuit 113 via the signal wiring Sig1. The signal wirings Sig1 to Sig5 arranged in the column direction transmit the signals output from the pixels PIX connected to the same driving wiring Vg to the readout circuit 113 in parallel.

In the present embodiment, the pixels PIX including the switches T23 and T43 are individually operated as detection elements for detecting the amount of incident radiation during exposure control, that is, during radiation irradiation. It is connected to the. Here, in FIG. 2, among the pixels PIX arranged in the pixel array 112, pixels functioning as detection elements are denoted as detection elements PIXD. Further, when indicating a specific detecting element among the respective detecting elements PIXD, a number is added to the reference symbol, such as detecting element PIXD1. In the configuration shown in FIG. 2, the detection element including the switch T23 is called the detection element PIXD1, and the detection element including the switch T43 is called the detection element PIXD2.

A plurality of detector elements PIXD for detecting the incident radiation dose are arranged in the pixel array 112, as shown in FIG. The detector elements PIXD may be arranged in close proximity such that a plurality of detector elements PIXD are arranged in one region of interest. For example, the detection elements PIXD may be arranged at intervals of 10 pitches or less in the pitch at which the plurality of pixels PIX are arranged. However, when the detector elements PIXD are arranged at one pitch, that is, adjacent to each other, when interpolating the image data at the position of the detector elements PIXD, the intervals between the pixels PIX for generating the radiographic image are widened. Interpolation accuracy may decrease. Therefore, for example, by arranging the detection elements PIXD at intervals of two or more pitches, it is possible to complement the image data at the position of the detection element PIXD using the pixel values of the surrounding pixels PIX adjacent to the detection element PIXD. Become. In the configuration shown in FIG. 2, the detection element PIXD1 and the detection element PIXD2 are arranged with an interval corresponding to the pixel PIX2 pitch.

In this embodiment, one detection element PIXD is connected to each of the drive wirings Vgd1 and Vgd2, but a plurality of detection elements PIXD may be connected to each of the drive wirings Vgd1 and Vgd2. Also, three or more detection elements PIXD may be arranged in one region of interest, and separate drive wiring Vgd may be connected to each of them. In addition, in the configuration shown in FIG. 2, the detection element PIXD outputs signals to the same signal wiring Sig3, but is not limited to this. good. In other words, the detector elements PIXD may be arranged in different columns. In addition, in the configuration shown in FIG. 2, the detection element PIXD1 and the detection element PIXD2 are arranged in different rows, but it is not limited to this. Detecting elements PIXD connected to different drive wirings Vgd may be arranged in the same row.

The readout circuit 113 is provided with an amplifier circuit 106 that amplifies signals output in parallel from the pixels PIX arranged in the pixel array 112 for each signal line Sig. Amplifier circuit 106 includes integrating amplifier 105 , variable amplifier 104 , and sample-and-hold circuit 107 .

The integral amplifier 105 amplifies the signals output from the pixel PIX and the detection element PIXD. More specifically, the integral amplifier 105 includes an operational amplifier that amplifies and outputs an electrical signal read from the pixel PIX and the detection element PIXD, an integral capacitor, and a reset switch. Integrating amplifier 105 can change the amplification factor by changing the value of the integrating capacitor. A signal output from the pixel PIX and the detection element PIXD is input to the inverting input terminal of the operational amplifier, and a reference voltage Vref is input from the reference power supply 111 to the non-inverting input terminal. Also, an amplified signal is output from the output terminal of the operational amplifier. Also, an integration capacitor is arranged between the inverting input terminal and the output terminal of the operational amplifier. Variable amplifier 104 amplifies the signal output from integrating amplifier 105 . A sample hold circuit 107 samples and holds the signal amplified by the integrating amplifier 105 and the variable amplifier 104 . The sample hold circuit 107 includes sampling switches and sampling capacitors.

The reading circuit 113 includes a multiplexer 108 that sequentially outputs the signals read out in parallel from the amplifier circuit 106 and outputs them as serial image signals, and a buffer amplifier 109 that impedance-converts and outputs the image signals. include. The image signal Vout which is an analog electrical signal output from the buffer amplifier 109 is converted into digital data by the A/D converter 110 . Digital data output from the detection element PIXD through the A/D converter 110 during radiation irradiation is supplied to the dose acquisition unit 140 described above. After radiation irradiation, signals converted into digital data output from the respective pixels PIX via the A/D converter 110 are supplied to the control computer 200 as image information. The control computer 200 may function as a signal processing unit that processes signals supplied from the pixels PIX of the radiation imaging apparatus 100 and displays them as radiographic images on the display unit of the control computer 200 or an external display.

The imaging unit 120 also includes a reference power supply 111 and a bias power supply 103 for the amplifier circuit as power supply units that supply various power supplies. A reference power supply 111 supplies a reference voltage Vref to the non-inverting input terminal of the operational amplifier of the integrating amplifier 105 . A bias power supply 103 supplies a common bias voltage Vs to the conversion element 102 of each pixel PIX via a bias wiring Bs.

The drive circuit 114 includes a conducting voltage Vcom for making the switch element 101 conductive and a non-conducting voltage Vss for making the switch element 101 non-conductive in accordance with the control signals D-CLK, OE, and DIO supplied from the drive control unit 160. Drive signals are output to the respective drive wirings Vg and Vgd. Thereby, the drive circuit 114 controls the conducting state and the non-conducting state of the switch element 101 to drive the pixel array 112 . A control signal D-CLK is a shift clock for a shift register used as the drive circuit 114 . The control signal DIO is a pulse transferred by the shift register. A control signal OE is a signal that controls the output terminal of the shift register. The time required for driving and the scanning direction are set as described above.

The drive control unit 160 also controls the operation of each component of the readout circuit 113 by supplying control signals RC, SH, and CLK to the readout circuit 113 . A control signal RC is a signal for controlling the operation of the reset switch of the integrating amplifier 105 . A control signal SH is a signal for controlling the operation of the sample hold circuit 107 . Control signal CLK is a signal for controlling the operation of multiplexer 108 .

In this embodiment, as shown in FIG. 2, the drive wirings Vg and Vgd connecting the detection element PIXD and the pixel PIX for generating the radiographic image are separated so that the switch elements 101 can be operated at different timings. is configured to In other words, the detection elements PIXD are provided independently of the pixels PIX for acquiring radiographic images. However, the arrangement of the detection elements is not limited to this configuration. For example, as shown in FIG. 3, some of the pixels PIX for acquiring the radiographic image are used as detecting elements without arranging the detecting elements PIXD independent of the pixels PIX for acquiring the radiographic image. It may work. In this case, the pixels PIX connected to the drive wiring Vg of a specific row within the region of interest are used as detection elements. At this time, although details will be described later, pixels PIX arranged in a plurality of rows within the region of interest among the pixels PIX are used as detection elements in order to acquire signals in parallel at different constant sampling cycles.

Next, the operation of the radiation imaging apparatus 100 according to this embodiment will be described with reference to FIGS. FIG. 4 is a flow chart showing an operation example of the radiation imaging apparatus 100, and FIG. 5 is a timing chart showing an operation example of the radiation imaging apparatus 100. As shown in FIG.

First, imaging preparation for acquiring a radiation image using the radiation imaging apparatus 100 is performed (S401). In the imaging preparation process, the subject (for example, a patient), the radiation imaging apparatus 100, and the radiation generating apparatus 400 are arranged. In addition, in the imaging preparation process, the irradiation conditions of radiation, the position of the region of interest for which automatic exposure control (AEC) is performed, the target dose, and the like are set. The setting of the target dose is set by the maximum value or average value of the radiation dose of one or more regions of interest, the difference or ratio between the maximum value and the minimum value of the radiation dose, and is converted into the threshold value of the radiation dose by the control computer 200. and supplied to the dose acquisition unit 140 of the radiation imaging apparatus 100 . The conversion of the radiation dose to the threshold value may be performed by the dose acquisition unit 140 . The dose acquisition unit 140 determines whether or not the incident radiation dose detected by the detection element PIXD of the radiation imaging apparatus 100 has reached the target dose, based on the radiation dose threshold.

When the imaging preparation is completed, the drive control unit 160 performs reset driving (idle reading driving) until radiation irradiation is started (S402). In the reset driving, as shown in FIG. 5, a voltage (conducting voltage Vcom) that makes the switching element 101 conductive is sequentially applied from the driving circuit 114 to the driving wiring Vg, and the dark generated in the conversion element 102 of each pixel PIX is reduced. This is an operation for resetting electric charges and the like. In reset driving, signals obtained from each pixel PIX may be used for offset correction when generating a radiographic image. In this reset drive, the conduction voltage Vcom is sequentially applied from the drive circuit 114 to the drive wiring Vgd, and the detection element PIXD also performs a reset operation at the same time.

The reset driving is repeated until the radiation exposure switch is pressed by the user. (NO in S403). When the user presses the exposure switch (YES in S403), the dose acquisition unit 140 acquires the offset signal of the detection element PIXD used for exposure control before radiation is emitted (S404). The drive control unit 160 controls the switch elements 101 of the detection elements PIXD so that they are sequentially turned on while radiation is not applied, so that the dose acquisition section 140 can acquire the offset signal. In order to suppress noise in the offset signal, the dose acquisition unit 140 may acquire the offset signal from each detection element PIXD multiple times and add and average the multiple offset signals. At this time, the dose acquisition unit 140 acquires the offset signal at the same sampling cycle as the signal sampling cycle during the exposure control period of each detection element PIXD. As shown in FIG. 5, the dose acquisition unit 140 acquires the offset signal of the detection element PIXD1 from the detection element PIXD1 at the same sampling period SR1 as the period during which exposure control is performed. Similarly, the dose acquisition unit 140 acquires the offset signal of the detection element PIXD2 from the detection element PIXD2 at the same sampling period SR2 as the period during which the exposure control is performed. As a result, when performing exposure control, it is possible to perform appropriate offset correction according to the sampling period for the signal output from each detection element PIXD.

After acquiring the offset signal of the detection element PIXD, irradiation of radiation is started (S405). For example, the dose acquisition unit 140 transmits to the control computer 200 a signal indicating that preparations for radiation irradiation have been completed in response to acquiring the offset signal of the detection element PIXD used during the exposure control period. . In response to this signal, the control computer 200 may cause the radiation generator 400 to start irradiating the radiation imaging apparatus 100 with radiation via the radiation control apparatus 300 . Further, for example, the dose acquisition unit 140 may directly transmit a signal indicating that preparations for radiation irradiation have been completed to the radiation control apparatus 300 . In response to this signal, the radiation control apparatus 300 causes the radiation generator 400 to start irradiating the radiation imaging apparatus 100 with radiation.

During radiation irradiation, the drive control unit 160 controls so that the switch elements 101 of the detection elements PIXD are sequentially turned on, whereby the dose acquisition unit 140 acquires signals for performing exposure control from the detection elements PIXD ( S406). At this time, the dose acquisition unit 140 acquires signals from the detection elements PIXD1 and PIXD2 arranged in the same region of interest in parallel at different constant sampling periods. As shown in FIG. 5, the conduction voltage Vcom is applied to the drive wiring Vgd1, and the sampling period SR1 for sampling the signal from the detection element PIXD1, and the conduction voltage Vcom is applied to the drive wiring Vgd2, and the signal is sampled from the detection element PIXD2. is different from the sampling period SR2. This allows the dose acquisition unit 140 to acquire signals with different sampling cycles for radiation incident on the same region of interest.

The combination of sampling periods may be predetermined values such as when the radiation imaging apparatus 100 is shipped from the factory. Also, the combination of sampling periods may be determined based on the imaging region, imaging conditions, and the like input to the control computer 200 by the user. In this case, a combination of sampling periods may be read out from the storage unit of the control computer 200 according to the imaging region, imaging conditions, or the like, or may be selected by the user as appropriate. For example, when the irradiation time of radiation is 1 ms to 1000 ms and the detection element PIXD is operated with two kinds of sampling periods in one region of interest, the ratio of the two sampling periods may be about 1:10. For example, as shown in FIG. 5, the short sampling period SR1 may be 1/3 or less and 1/20 or more of the long sampling period SR2.

Further, for example, during the period of exposure control, the dose acquisition unit 140 selects from two or more detection elements PIXD arranged in a region different from the region of interest where the detection elements PIXD1 and 2 are arranged, the detection element PIXD1 , 2 may be acquired in parallel. Here, the detector elements arranged in the regions of interest different from the detector elements PIXD1 and PIXD2 are referred to as detector elements PIXD3 and PIXD4, respectively. The dose acquisition unit 140 acquires signals from the detection elements PIXD3 and PIXD4 at different constant sampling periods, similar to the relationship between the detection elements PIXD1 and PIXD2. At this time, the sampling period for acquiring the signal from the detecting element PIXD1 or PIXD2 and the sampling period for acquiring the signal from the detecting element PIXD3 or PIXD4 may be the same sampling period. Also, the sampling periods for acquiring signals from all the detection elements PIXD1 to PIXD4 may be different.

That is, when there are a plurality of regions of interest when performing exposure control, the combination of sampling cycles may be the same or different for each region of interest. A region of interest, which is expected to receive a relatively large dose from the conditions of the imaging region, should be combined with a relatively short sampling period. Conversely, a region of interest in which the dose is expected to be relatively low may be combined with a longer sampling period.

FIG. 6 shows a timing diagram when some of the pixels PIX shown in FIG. 3 are made to function as detection elements. FIG. 6 is a timing chart showing a case where the pixels PIX connected to the drive wirings Vg2 and Vg4 are driven as detection elements. When the user presses the exposure switch, the conduction voltage Vcom is sequentially applied from the drive circuit 114 to the drive wires Vg2 and Vg4 before radiation is emitted, and the dose acquisition unit 140 functions as a detection element. Acquire the offset signal of the pixel PIX to be used. Next, during radiation irradiation, the drive circuit 114 applies the conduction voltage Vcom to the drive wirings Vg2 and Vg4, and the dose acquisition unit 140 receives signals for exposure control from the pixels PIX connected to the drive wirings Vg2 and Vg4. get. At this time, by differentiating the period in which the conduction voltage Vcom is applied to the driving wiring Vg2 and the driving wiring Vg4, the dose acquisition unit 140 outputs signals at different sampling periods from the plurality of pixels PIX functioning as detection elements. can be obtained.

The dose acquisition unit 140 detects the incident radiation dose based on signals acquired in parallel from the detection elements PIXD1 and PIXD2 at different sampling periods. More specifically, it is determined whether or not the incident radiation dose has reached the target dose using the cumulative value of the signal acquired from the detection element PIXD (S407). At this time, the dose acquisition unit 140 corrects the signal acquired from the detection element PIXD1 during irradiation of radiation according to the offset signal acquired from the detection element PIXD1 in S404, and obtains the corrected signal acquired from the detection element PIXD1. may be used to detect the amount of incident radiation. Similarly, the dose acquisition unit 140 corrects the signal acquired from the detection element PIXD2 during radiation irradiation according to the offset signal acquired from the detection element PIXD2 in S404, and converts the corrected signal acquired from the detection element PIXD2. may be used to detect the amount of incident radiation. Appropriate offset correction can be performed by applying the offset signal acquired by the dose acquiring unit 140 in the same sampling cycle as the acquisition of each signal to the signals acquired in mutually different sampling cycles.

When the dose acquisition unit 140 determines that the incident radiation dose has not reached the target dose (NO in S407), the drive control unit 160 continuously controls the pixels so that the dose acquisition unit 140 acquires signals from the detection elements PIXD. The array 112 is operated (S406). Also, the dose acquisition unit 140 determines whether or not the dose of incident radiation has reached the target dose (S407).

When the dose acquisition unit 140 determines that the incident radiation dose has reached the target dose (YES in S407), the dose acquisition unit 140 transmits a signal to the control computer 200 to stop radiation irradiation. In response to this signal, the control computer 200 stops radiation irradiation from the radiation generator 400 via the radiation control device 300 (S408). The dose acquisition unit 140 directly transmits a signal for stopping radiation irradiation to the radiation control device 300, and the radiation control device 300 causes the radiation generation device 400 to stop radiation irradiation in response to this. good. The dose acquisition unit 140 determines whether or not the incident radiation dose has reached the target dose, and outputs a signal for stopping the radiation irradiation when the target dose is reached. can have AEC functionality.

When the irradiation of radiation stops, the drive control unit 160 performs main reading driving to read out signals for generating a radiographic image accumulated in each pixel PIX (S409). The main read drive is an operation in which the conduction voltage Vcom is sequentially applied from the drive circuit 114 to the drive wirings Vg, and charges accumulated in the conversion elements 102 connected to the respective drive wirings Vg are read out. The signal read by the readout circuit 113 is converted into digital data by the A/D converter 110 and transferred to the control computer 200 as image information.

The pixel value at the position where the detection element PIXD is arranged in the image information becomes zero because it is read out during radiation irradiation, and the pixel value is missing. Therefore, as described above, the pixel values of the pixels PIX arranged around the detection element PIXD may be used to interpolate the pixel value at the position where the detection element PIXD is arranged. Also, the cumulative value of the signal read from the detection element PIXD during radiation irradiation can be the same amount as the charge accumulated in the detection element PIXD during radiation irradiation. That is, the accumulated value of the signals read from the detection element PIXD may be used as the pixel value at the position where the detection pixel PIXD is arranged.

Next, a method for calculating the signal acquired from the detection element PIXD by the dose acquisition unit 140 in order to perform exposure control will be described. FIG. 7 is a timing chart showing an operation example of the radiation imaging apparatus of the comparative example. In the comparative example shown in FIG. 7, acquisition of signals from the detector elements PIXD during radiation irradiation is all performed at the same sampling period.

The inventors have found the following problems as a result of performing AEC by sampling drive with a constant period shown in FIG.
1. For strong and short radiation, the signal value of the signal read out per time becomes large, and when the sampled signal becomes larger than the target value of the signal value set as the target dose, it is an appropriate exposure. There is a high probability that a certain target dose will be greatly exceeded. Therefore, a large error can occur with respect to the target dose.
2. For weak and long radiation, the signal value of the signal read out per time becomes small, but the number of times of sampling until the sampled signal reaches the target value of the signal value set as the target dose increases. Random noise of the readout circuit 113, an error between an offset signal obtained in advance before radiation exposure and an offset amount during exposure control, and the like are integrated as the number of sampling times increases, resulting in a large error with respect to the target dose. can live

Therefore, as shown in FIG. 5, signals are acquired in parallel at a plurality of different sampling periods from a plurality of detection elements PIXD arranged in one region of interest. It was found that the error with respect to the target dose can be reduced by suppressing . From the above-mentioned problems, shortening the period of sampling the signal from the detection element PIXD for strong and short radiation and lengthening the period of sampling the signal from the detection element PIXD for weak and long radiation are effective for the target dose. can be a method to reduce the error.

Using a plurality of detector elements PIXD, signals are acquired at a plurality of different sampling periods, strong and short radiation uses signals acquired with a short sampling period SR1, and weak and long radiation uses signals acquired with a long sampling period SR2. take advantage of Specifically, the dose acquisition unit 140 accumulates signals acquired in a short sampling period SR1 and signals acquired in a long sampling period SR2. The dose acquisition unit 140 uses the cumulative value of the signal acquired in the short sampling period SR1 until the number of times the signal is sampled in the short sampling period SR1 is preset, and determines whether or not the target dose has been reached. I do. On the other hand, when the number of times the signal is sampled in the short sampling period SR1 exceeds the preset number, the dose acquisition unit 140 determines whether the target dose has been reached using the cumulative value of the signal acquired in the long sampling period SR2. make a judgment as to whether

For example, when the irradiation time of radiation is 1 ms to 1000 ms, the short sampling period SR1 is 100 μs, and the long sampling period SR2 is 1000 μs, the preset number of times may be 10 times or more and 100 times or less. For example, according to the target dose, the dose acquisition unit 140 changes the timing of switching between the cumulative value of the signal with the short sampling cycle SR1 and the cumulative value of the signal with the long sampling cycle SR2, from 10 times to 100 times. good too. The switching timing may be changed by storing data indicating the relationship between the target dose and the switching timing in a storage unit in the dose acquisition unit 140, and reading the data from the storage unit by the dose acquisition unit 140. Also, the control computer 200 may supply the dose acquisition unit 140 with a signal that instructs the switching timing according to the target dose.

Further, for example, a signal to be used for exposure control may be determined among the signals acquired in a plurality of sampling cycles according to the incident radiation dose per unit time. For example, when strong radiation is incident, a signal obtained with a long sampling period SR2 may have a larger signal error than a signal obtained with a short sampling period SR1. Therefore, when the signal value of the signal acquired in the short sampling period SR1 exceeds a preset value (when strong radiation is incident), the dose acquisition unit 140 uses the cumulative value of the signal acquired in the short sampling period SR1. It is determined whether or not the target dose has been reached. On the other hand, the dose acquisition unit 140 uses the cumulative value of the signal acquired in the long sampling cycle SR2 until the signal value of the signal acquired in the short sampling cycle SR1 reaches a preset value (when weak radiation is incident). A determination is made as to whether or not the dose has been reached. A threshold value (preset value) for determining which sampling period the signal acquired in the exposure control is to be used for exposure control is, for example, stored in a memory provided in the radiation imaging apparatus 100 when the radiation imaging apparatus 100 is shipped. It may be stored in a section or the like. The dose acquisition unit 140 detects the incident radiation dose by referring to the threshold value stored in the storage unit and using the signal acquired in the short sampling period SR1 or the long sampling period SR2. Further, for example, the threshold value for determining in which sampling period the signal acquired is used for exposure control is determined by the control computer 200 based on the imaging region, imaging conditions, and the like input to the control computer 200 by the user. , may be supplied to the dose acquisition unit 140 .

In this way, the dose acquisition unit 140 acquires signals with different sampling periods in parallel from two or more detection elements PIXD arranged in one region of interest. As a result, it is possible to provide the radiation imaging apparatus 100 and the radiation imaging system SYS that achieve highly accurate automatic exposure amount control with respect to the target dose without depending on radiation irradiation conditions.

In the above-described embodiment, it has been described that the dose acquisition unit 140 performs exposure control using either the cumulative value of signals acquired in the short sampling period SR1 or the cumulative value of signals acquired in the long sampling period SR2. However, it is not limited to this. For example, the dose acquisition unit 140 may correct the cumulative value of the signal acquired in the short sampling period SR1 according to the cumulative value of the signal acquired in the long sampling period SR2. The dose acquisition unit 140 determines whether or not the target dose has been reached using the corrected cumulative value of the signal acquired in the short sampling period SR1.

As described above, the detection element PIXD1 whose signal is obtained by the dose acquisition unit 140 in the short sampling period SR1 and the detection element PIXD2 whose signal is obtained in the long sampling period SR2 by the dose acquisition unit 140 are close to the same region of interest. and distributed. Therefore, after a certain period of time has elapsed from the start of radiation irradiation, the cumulative values of the signals obtained by the detection elements PIXD1 and PIXD2 should be approximately the same. However, as described above, since the cumulative value of the signal acquired in the short sampling period SR1 has a large number of sampling times, the cumulative value of the signal acquired in the long sampling period SR2 has a larger error due to the influence of random noise and the like. .

Therefore, when updating the cumulative value of the signal acquired in the long sampling cycle SR2 every sampling cycle SR2, the dose acquiring unit 140 acquires the cumulative value of the signal acquired in the short sampling cycle SR1 in the long sampling cycle SR2. is replaced by the cumulative value of the signal obtained. As a result, in the short sampling period SR1, it is possible to suppress the influence of random noise and the like that accompanies an increase in the number of sampling times. Further, after replacing the signals acquired in the sampling period SR2 with the cumulative values, the dose acquisition unit 140 acquires the signals in the short sampling period SR1, thereby determining whether or not the target dose has been reached with high accuracy. be able to. The replacement of the cumulative value may be performed every sampling period SR2 as described above, or may be performed every sampling in a long sampling period SR2, for example, about 2 to 5 times. Correction may be performed at an appropriate frequency according to the ratio between the short sampling period SR1 and the long sampling period SR2.

Further, for example, the dose acquisition unit 140 calculates the ratio of change in signal value per unit time of each signal from the cumulative value of the signal acquired in the short sampling period SR1 and the cumulative value of the signal acquired in the long sampling period SR2. may be obtained. Acquisition of the signal value ratio may be performed by the dose acquisition unit 140 at the timing of acquiring the signal in the long sampling period SR2, for example.

For example, when the dose acquisition unit 140 updates the cumulative value of the signal acquired in the long sampling cycle SR2 every sampling cycle SR2, the dose acquisition unit 140 acquires the cumulative value of the signal acquired in the short sampling cycle SR1 in the long sampling cycle SR2. is replaced by the cumulative value of the signal obtained. Next, when accumulating the signals acquired in the short sampling period SR1, the dose acquisition unit 140 applies the above-described ratio of the signal values to the signal values of the signals acquired in the short sampling period SR1. Get the cumulative value of the acquired signal.

In this way, by using the corrected cumulative value of the signal acquired in the short sampling period SR1 for exposure control, the error with respect to the target dose is made equivalent to the cumulative value of the signal acquired in the long sampling period SR2. be able to. Furthermore, it becomes possible to determine whether or not the incident radiation dose has reached the target dose in the short sampling period SR1, and the accuracy of the AEC of the radiation imaging apparatus 100 is improved.

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.

100: radiation imaging apparatus, 120: imaging unit, 140: dose acquisition unit, PIXD: detection element

Claims (17)

A radiation imaging apparatus arranged in an imaging unit for acquiring a radiation image and including a plurality of detection elements for detecting incident radiation,
The radiation imaging device further includes a dose acquisition unit,
In the period during which the dose acquisition unit performs exposure control,
Obtaining signals in parallel from a first detection element and a second detection element among the plurality of detection elements at sampling periods different from each other;
1. A radiation imaging apparatus, comprising: detecting a dose of incident radiation based on a first signal obtained from the first detection element and a second signal obtained from the second detection element. The dose acquisition unit acquires the first signal obtained from the first detection element in a first sampling period and the second signal obtained from the second detection element in a second sampling period longer than the first sampling period. 2. The radiation imaging apparatus according to claim 1, wherein the amount of incident radiation is detected based on . The dose acquisition unit is
Determining whether or not the target dose has been reached using the cumulative value of the first signal until the number of times the first signal is sampled is a preset number,
3. The method according to claim 2, wherein when the number of times the first signal is sampled exceeds a preset number of times, it is determined whether or not the target dose has been reached using the cumulative value of the second signal. A radiation imaging device as described. 4. The radiation imaging apparatus according to claim 3, wherein the preset number of times is 10 times or more and 100 times or less. The dose acquisition unit is
When the signal value of the first signal exceeds a preset value, determining whether or not the target dose has been reached using the cumulative value of the first signal,
3. Radiation according to claim 2, wherein until the signal value of the first signal reaches a preset value, whether or not the target dose is reached is determined using the cumulative value of the second signal. Imaging device. The dose acquisition unit is
correcting the cumulative value of the first signal according to the cumulative value of the second signal;
3. The radiation imaging apparatus according to claim 2, wherein a determination is made as to whether or not the target dose has been reached using the corrected cumulative value of the first signal. The dose acquisition unit replaces the cumulative value of the first signal with the acquired cumulative value of the second signal when updating the cumulative value of the second signal every second sampling period. 7. The radiation imaging apparatus according to claim 6. The dose acquisition unit is
obtaining a ratio of changes in signal values per unit time of the first signal and the second signal;
8. The radiation imaging apparatus according to claim 6, wherein when accumulating the first signal, the ratio is applied to the signal value of the first signal to obtain the accumulated value of the first signal. . 9. The radiation imaging apparatus according to claim 2, wherein the first sampling period is 1/3 or less and 1/20 or more of the second sampling period. The dose acquisition unit is
obtaining a first offset signal in the first sampling period from the first detection element and a second offset signal in the second sampling period from the second detection element before radiation is applied;
During a period of performing exposure control, the first signal is corrected according to the first offset signal and the second signal is corrected according to the second offset signal, and the corrected first signal and the 10. The radiation imaging apparatus according to claim 2, wherein the amount of incident radiation is detected based on the second signal. In the period during which the dose acquisition unit performs exposure control,
from a third detection element and a fourth detection element arranged in a region of interest different from the region of interest in which the first detection element and the second detection element are arranged among the plurality of detection elements, the first detection element and the Acquiring a signal at a constant sampling period in parallel with the second detection element;
the first signal, the second signal, a third signal obtained from the third detection element in a third sampling period, and a third signal obtained from the fourth detection element in a fourth sampling period different from the third sampling period 11. The radiation imaging apparatus according to any one of claims 2 to 10, wherein the dose of incident radiation is detected based on the fourth signal. The imaging 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 the plurality of detection elements are arranged in the pixel array. The imaging 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 some of said plurality of pixels function as said plurality of detection elements. 14. The radiation imaging according to claim 12, wherein the first detection element and the second detection element are arranged at intervals of 10 pitches or less in the pitch at which the plurality of pixels are arranged. Device. 15. The first detection element and the second detection element are arranged at an interval of two pitches or more in the pitch at which the plurality of pixels are arranged. The radiation imaging apparatus according to . 16. The radiation imaging apparatus according to any one of claims 1 to 15, wherein the first detection element and the second detection element are arranged in the same region of interest. a radiation imaging apparatus according to any one of claims 1 to 16;
a signal processing unit that processes a signal from the radiation imaging device;
A radiation imaging system comprising:

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