JP2022176882A - Radiation imaging device and radiation imaging system - Google Patents

Abstract

To provide a radiation imaging device and a radiation imaging system advantageous for obtaining an image with excellent quality in the radiation imaging device.SOLUTION: In a radiation imaging system RIS, a radiation imaging device 100 includes a pixel array 101 in which a plurality of pixels PIX that generate signals corresponding to incident radiation are arrayed and a reading circuit 103 that reads signals from the pixel array, and operates in a plurality of modes that include a first mode and a second mode in which the time between captures is longer than in the first mode. The reading circuit includes an integrating amplifier that amplifies the signals read from the pixel array, and a sample hold circuit that retains the signals amplified by the integrating amplifier. The integrating amplifier can switch current driving capability for driving input nodes of the sample hold circuit, and the current driving capability in the first mode is higher than the current driving capability in the second mode.SELECTED DRAWING: Figure 1

Description

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

2. Description of the Related Art Radiation imaging apparatuses using flat panel detectors (FPDs) made of semiconductor materials are widely used in medical image diagnosis and non-destructive inspection. As one of imaging methods using an FPD, a method of acquiring an energy subtraction image using radiation having different energy components is known. In Patent Document 1, in the first of two consecutive imaging, readout is performed in a low dose, small dynamic range, and low resolution mode, and in the second, a high dose, a large dynamic range, and resolution It has been shown that reading is performed in a mode with high . By reading out the first image in a mode with a small dynamic range and a low resolution, the time interval between the two images can be shortened, and motion artifacts in the energy subtraction image due to body movement of the subject can be reduced. Moreover, Patent Document 1 discloses that even in the case of acquiring a large number of frames at high speed as in tomosynthesis, a mode with a low dose, a small dynamic range, and a low resolution is used.

Japanese Patent Application Laid-Open No. 2003-284710

It is conceivable that the user uses two images acquired for energy subtraction images or one image out of a large number of continuously acquired images such as for moving images for diagnosis. However, an image read out in a mode with a small dynamic range and low resolution as in Patent Document 1 may have insufficient image quality for use in diagnosis.

SUMMARY OF THE INVENTION An object of the present invention is to provide an advantageous technique for obtaining an image of good image quality in a radiation imaging apparatus.

In view of the above problems, a radiation imaging apparatus according to an embodiment of the present invention includes: a pixel array in which a plurality of pixels that generate signals corresponding to incident radiation are arranged; a readout circuit that reads out signals from the pixel array; and operating in a plurality of modes including a first mode and a second mode having a longer time between imaging than the first mode, wherein the readout circuit is configured to read from the pixel array An integral amplifier that amplifies a read signal, and a sample-and-hold circuit that holds the signal amplified by the integral amplifier, wherein the integral amplifier is capable of switching a current driving capability for driving an input node of the sample-and-hold circuit. wherein the current driving capability in the first mode is higher than the current driving capability in the second mode.

The means described above provide an advantageous technique for obtaining an image of good image quality in a radiation imaging apparatus.

1 is a block diagram showing a configuration example of a radiation imaging system using a radiation imaging apparatus according to this embodiment; FIG. FIG. 2 is a diagram showing a configuration example of a pixel array of the radiation imaging apparatus in FIG. 1; FIG. 2 is a diagram showing a configuration example of a readout circuit of the radiation imaging apparatus of FIG. 1; FIG. 2 is a timing chart for explaining the operation of the radiation imaging apparatus in FIG. 1; 2A and 2B are diagrams for explaining the operation of the radiation imaging apparatus in FIG. 1; FIG. FIG. 2 is a flowchart for explaining the operation of the radiation imaging apparatus in FIG. 1; 2A and 2B are diagrams for explaining the operation of the radiation imaging apparatus in FIG. 1; FIG.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. In addition, 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.

The configuration and operation of the radiation imaging apparatus according to this embodiment will be described with reference to FIGS. FIG. 1 shows a configuration example of a radiation imaging system RIS (Radiology Information System) using a radiation imaging apparatus 100 according to this embodiment. The radiation imaging system RIS obtains a radiographic image of the subject by irradiating the subject with radiation and detecting the radiation that has passed through the subject. The radiation imaging system RIS includes, for example, a radiation imaging apparatus 100, a control device 111, a radiation source 112, and an exposure control device 113. The exposure control device 113 causes the radiation source 112 to emit radiation according to an exposure command such as a user pressing an exposure switch. The control device 111 controls the radiation imaging apparatus 100 according to imaging conditions set by the user. The control device 111 may also function as an image processing processor that acquires a radiographic image signal output from the radiographic imaging device 100 and generates and processes an image to be displayed on a display device (not shown). . Furthermore, the control device 111 controls the exposure control device 113 according to the imaging conditions set by the user.

The radiation imaging apparatus 100 includes an imaging unit 104 that captures a radiation image, a communication unit 107 that communicates with the control device 111, a control unit 106 that controls the imaging unit 104, and a power supply unit 108 that supplies power to the imaging unit 104. sell. The radiation imaging apparatus 100 can also include an analysis unit 109 that analyzes the image output from the imaging unit 104 and a processing unit 105 that performs arithmetic processing on the image. Some of the components of the radiation imaging apparatus 100 may be incorporated in the control device 111, or the radiation imaging device 100 and the control device 111 may be integrated. For example, in the configuration example shown in FIG. 1 , the analysis unit 109 and the processing unit 105 arranged in the radiation imaging apparatus 100 may be incorporated in the control device 111 .

The imaging unit 104 can include, for example, a pixel array 101, a scanning circuit 102, and a readout circuit 103. FIG. In the pixel array 101, a plurality of pixels PIX that generate signals according to incident radiation are arranged so as to form a plurality of rows and a plurality of columns. The scanning circuit 102 scans the pixel array 101 according to a mode selected from among a plurality of modes (imaging modes). A readout circuit 103 reads out signals from the pixel array 101 . More specifically, the readout circuit 103 reads out signals from the pixels PIX in a row selected by the scanning circuit 102 among the plurality of rows arranged in the pixel array 101 . Reading a signal from the pixel array 101 may mean that the readout circuit 103 processes the signal output from each pixel PIX of the pixel array 101 and outputs signal data corresponding to the output signal.

FIG. 2 shows a configuration example of the pixel array 101 of the radiation imaging apparatus 100. As shown in FIG. FIG. 3 shows a configuration example of the readout circuit 103 of the radiation imaging apparatus 100. As shown in FIG. Each of the plurality of pixels PIX includes a conversion element 201 that converts radiation or light into a signal (charge), and a switch element that outputs the generated signal to a readout circuit. In one example, the conversion element 201 is a photoelectric conversion element that converts light irradiated to the conversion element 201 into an electric charge. diode or MIS type photodiode. In this case, as the conversion element 201, a wavelength conversion body (scintillator) that converts radiation into light in a wavelength band detectable by the photoelectric conversion element can be further arranged. In this case, the conversion element 201 can be called an indirect conversion element. As the conversion element 201, a direct conversion element that directly converts radiation into electric charge may be used.

A transistor having a control terminal and two main terminals, such as a thin film transistor (TFT), can be used as the switch element 202 . One electrode of the conversion element 201 is electrically connected to one of the two main terminals of the switch element 202, and the other electrode of the conversion element 201 is electrically connected to the power supply section 108 via a common bias line Vs. connected to In FIG. 2, the conversion elements 201 are denoted by Sij (where i indicates the row number and j indicates the column number) in order to distinguish the conversion elements 201 from each other. In order to distinguish the switch elements 202 from each other, the switch elements 202 are denoted by Tij (where i indicates the row number and j indicates the column number).

The control terminals of the switching elements 202 of the plurality of pixels PIX forming one row are connected to the drive line Gi (i is the number of the row) of the row. For example, the control terminals of the switching elements 202 (T11 to T1n) of the pixels PIX forming the first row are electrically connected to the drive line G1 of the first row. Therefore, the minimum unit for driving the plurality of pixels PIX arranged in the pixel array 101 by the scanning circuit 102 is the pixel PIX forming one row.

The other main terminals of the switching elements 202 of the plurality of pixels PIX forming one column are connected to the signal line Sigj (j is the number of the column) of the column. For example, the main terminals of the switching elements 202 (T11 to Tm1) of the plurality of pixels PIX forming the first column are electrically connected to the signal line Sig1 of the first column. While the switch element 202 is in a conductive state, a signal corresponding to the charges generated by the conversion element 201 is output to the readout circuit 103 via the signal line Sig. Each of the plurality of signal lines Sig1-Sign is electrically connected to the readout circuit 103. FIG.

The readout circuit 103 includes a plurality of amplifier circuits 300 that respectively amplify a plurality of signals output in parallel from the pixel array 101 via the signal lines Sig1 to Sign. Each of the plurality of amplifier circuits 300 can be arranged corresponding to each of the plurality of signal lines Sig. The amplifier circuit 300 of the readout circuit 103 includes an integral amplifier 302 that amplifies the signal read out from the pixel array 101 and a sample and hold circuit 303 that holds the signal amplified by the integral amplifier 302 . Further, amplifier circuit 300 may include buffer amplifier 304 and buffer amplifier 305 . Buffer amplifier 304 and buffer amplifier 305 buffer the signal output from sample hold circuit 303 .

Integrating amplifier 302 may include, for example, operational amplifier 311 , feedback capacitor 312 , and reset switch 313 arranged in parallel between pixel array 101 and sample-and-hold circuit 303 . The operational amplifier 311 has an inverting input terminal that receives a signal supplied via the signal line Sig, a non-inverting input terminal that receives a reference voltage Vref from the reference power supply 110, and an output terminal. A feedback capacitor 312 and a reset switch 313 are arranged in parallel between the inverting input terminal and the output terminal of the operational amplifier 311 . Feedback capacitor 312 may have a variable capacitance value Cf. In other words, the feedback capacitor 312 is configured to switch the capacitance value Cf.

The sample and hold circuit 303 includes a CDS circuit 341 and a CDS circuit 342 that respectively perform correlated double sampling (CDS). The CDS circuit 341 includes a holding circuit 323 and a holding circuit 324, and performs CDS based on a signal supplied via the signal line Sig. The buffer amplifier 304 is configured by a differential amplifier, differentially amplifies the output from the holding circuit 323 and the output from the holding circuit 324, and outputs the result. The CDS circuit 342 includes a holding circuit 333 and a holding circuit 334, and performs CDS based on a signal supplied via the signal line Sig. The buffer amplifier 305 is composed of a differential amplifier, differentially amplifies the output from the holding circuit 333 and the output from the holding circuit 334, and outputs the result.

Holding circuit 323 may include switch 325 and capacitor 326 . The holding circuit 323 holds the signal supplied from the integrating amplifier 302 after processing it with a low-pass filter composed of the resistance element 322 and the capacitor 326 . Resistive element 322 can be selectively enabled or disabled by switch 321 . Holding circuit 324 may include switch 327 and capacitor 328 . The holding circuit 324 holds the signal supplied from the integrating amplifier 302 after processing it with a low-pass filter composed of a resistance element 322 and a capacitor 328 . Resistive element 322 can be selectively enabled or disabled by switch 321 .

Similarly, holding circuit 333 may include switch 335 and capacitor 336 . The holding circuit 333 holds the signal supplied from the integrating amplifier 302 after processing it with a low-pass filter composed of the resistance element 322 and the capacitor 336 . Resistive element 322 can be selectively enabled or disabled by switch 321 . Holding circuit 334 may include switch 337 and capacitor 338 . The holding circuit 334 holds the signal supplied from the integrating amplifier 302 after processing it with a low-pass filter composed of the resistance element 322 and the capacitor 338 . Resistive element 322 can be selectively enabled or disabled by switch 321 .

In the configuration shown in FIG. 3, the sample and hold circuit 303 is provided with two CDS circuits 341 and 342 . For example, the CDS circuit 341 may hold the signals of the pixels PIX arranged in the odd rows, and the CDS circuit 342 may hold the signals of the pixels PIX arranged in the even rows. The configuration of sample-and-hold circuit 303 is not limited to the configuration shown in FIG. 3, and may be a configuration in which only one CDS circuit is arranged. Also, three or more CDS circuits may be arranged in the sample-and-hold circuit 303 . Furthermore, if CDS is not implemented in readout circuit 103 , only one set of switch and capacitor may be arranged in sample and hold circuit 303 .

Readout circuitry 103 may further include multiplexer 306 , buffer amplifier 307 , and A/D converter 308 . A multiplexer 306 sequentially selects and outputs signals output in parallel from the plurality of amplifier circuits 300 . The buffer amplifier 307 impedance-converts the signal output from the multiplexer 306 and outputs it as signal data Vout of an analog electrical signal. The A/D converter 308 converts the signal data Vout output from the buffer amplifier 307 into signal data of a digital electrical signal, and supplies the signal data to the processing section 105 and the analysis section 109 .

The detection of the signal data described above is performed for each readout circuit 103 connected to each of the signal lines Sig1 to Sign, and image signals for one row are detected. By repeating this operation from the pixel PIX connected to the drive line G1 to the pixel PIX connected to the drive line Gm, signal data of a digital image of the entire surface of the pixel array 101 of the radiation imaging apparatus 100 is generated.

Next, the operation of the radiation imaging apparatus 100 will be described with reference to FIGS. 4(a) and 4(b). 4A and 4B are timing charts for explaining the imaging operation of the radiation imaging apparatus 100. FIG. In this embodiment, the radiation imaging apparatus 100 performs the output operation of the pixels PIX on a row-by-row basis. Here, one frame period includes an accumulation period and a readout period. The accumulation period is a period during which an accumulation operation is performed in which each of the plurality of pixels PIX accumulates signals (charges) corresponding to irradiated radiation. The readout period is a period in which the scanning circuit 102 sequentially scans a plurality of rows (driving lines G) and the readout circuit 103 performs a readout operation of reading signals for one frame from the pixel array 101 .

Further, the radiation imaging apparatus 100 repeats the pixel reset operation until the user presses the exposure switch and the radiation is emitted. The pixel reset operation is an operation of resetting each pixel PIX arranged in the pixel array 101 of the radiation imaging apparatus 100 by the scanning circuit 102 repeating scanning in row units, similarly to the readout operation performed in the readout period. be.

When the user presses the exposure switch, the pixel array 101 is irradiated with radiation, and charges corresponding to the irradiated radiation are generated in the conversion elements 201 (S11 to Smn). Next, the radiation imaging apparatus 100 starts a reset operation of the integrating amplifier 302 of the readout circuit 103 described below. Specifically, control signal RST is applied from control section 106 to reset switch 313, thereby resetting feedback capacitor 312 and resetting integration amplifier 302, which is a signal transmission path. The reset operation is then terminated by the reset switch 313 becoming non-conductive. Here, the reset operation of the integrating amplifier 302 is an operation while the reset switch 313 is maintained in a conducting state, and is an operation of returning the potential of the transmission path to a specified initial value.

Next, the radiation imaging apparatus 100 starts the noise component sample hold operation described below. A control signal ODDCDS1 is supplied from the control unit 106 to the sample hold circuit 303 . In response to supply of control signal ODDCDS1, switch 325 of holding circuit 323 of CDS circuit 341 is turned on, and the noise component of integrating amplifier 302 is transferred to capacitor 326 from reset integrating amplifier 302 . The noise component sample-and-hold operation is then completed by turning switch 325 into a non-conducting state. Here, the noise component sample-and-hold operation is an operation while switch 325 or switch 335 maintains a conductive state.

Next, the radiation imaging apparatus 100 starts the following output operation for the first row. Here, the start of the output operation of the first row is defined by the rise of the driving signal supplied from the scanning circuit 102 to the driving line G1 of the first row, and the switch element 202 (T11) of the pixel PIX arranged in the first row. ˜T1n) become conductive. By turning on the switch elements 202 (T11 to T1n), analog electric signals based on charges generated in the conversion elements (S11 to S1n) arranged in the first row are transferred from the respective pixels PIX to the signal lines Sig1 to Sign. output to the readout circuit 103 via the Next, due to the fall of the drive line G1, the switching elements 202 (T11 to T1n) of the pixels PIX arranged in the first row are brought into a non-conducting state, and the output operation from the pixels PIX is completed. In this embodiment, the output operation refers to the operation while the switch element 202 of the pixel PIX maintains the conducting state.

Next, the radiation imaging apparatus 100 starts a signal sample-and-hold operation described below. A control signal ODDCDS2 is supplied from the control unit 106 to the sample hold circuit 303, and the switch 327 of the holding circuit 324 of the CDS circuit 341 is turned on. By turning on the switch 327 , the read signal of the pixel PIX arranged in the first row is transferred to the capacitor 328 via the integrating amplifier 302 . At this time, the noise component of the integral amplifier 302 is added to the signal output from the pixel PIX. Next, the switch 327 is made non-conductive, and the signal added with the noise component is held in the capacitor 328 . The signal sample and hold operation is terminated by switch 327 becoming non-conductive. Here, the signal sample-and-hold operation is the state while switch 327 or switch 337 maintains the conductive state.

When signal sampling ends, the radiation imaging apparatus 100 starts signal processing operations described below. The noise component held in the capacitor 326 and the signal of the pixel PIX in the first column added with the noise component held in the capacitor 328 are input to the buffer amplifier 304, which is a differential amplifier. Then, the signal from which the noise component of integrating amplifier 302 has been removed is output from buffer amplifier 304 . After that, the noise component-removed signal selectively transferred by the multiplexer 306 is supplied to the A/D converter 308 via the buffer amplifier 307 . The A/D converter 308 converts the supplied signal of the pixel PIX in the first row and first column into digital data S(1,1), and sends the digitally converted signal data to the processing unit 105 for processing. Output. The signal output operation of the pixels PIX of the first row and second column is performed in parallel with the signal output operation of the first row and first column, and the A/D conversion of the first row and first column is performed. After that, the signal of the pixel PIX in the first row and second column is selectively transferred by the multiplexer 306 . The signal of the pixel PIX in the first row and second column is sent from the A/D converter 308 to the processing unit 105 as digital data S(1,2) in the same manner as the signal of the pixel PIX in the first row and first column. output. Thereafter, similarly, signal data output operations for the pixels PIX in the first row, third column to n-th column are sequentially performed. By this signal processing operation, the digital data S(1,3) to S(1,n) are respectively output as signal data to the processing unit 105, and the signal processing operation is completed. Here, this signal processing operation is performed from the start of the reset operation of a certain row to the start of the reset operation of the next row. In other words, the signal processing operation for the pixels PIX in a certain row is performed in parallel with the output operation for the pixels in the row next to the row.

Thereafter, reset operation, noise component sample-and-hold operation, output operation, signal sample-and-hold operation, and signal processing operation are performed in the second row in the same manner as in the first row. Similar processing is sequentially repeated for the third and subsequent rows, and signal data corresponding to all the pixels PIX of the pixel array 101 are output from the readout circuit 103 .

So far, the operation of acquiring a radiation image in the radiation imaging apparatus 100 has been described. Among these, if the time from the end of the output operation from the pixel PIX to the start of the signal sample-and-hold operation due to the fall of the drive signal applied to the drive line G is short, the switching noise of the switch element 202 is the cause. The image may contain noise. This is because the signal line voltage fluctuates when the drive signal applied to the drive line G falls through the parasitic capacitance between the drive line G and the signal line Sig, and while the signal line voltage fluctuates The cause is that the signal sample-and-hold operation is started.

FIG. 5 shows changes in the signal line voltage Vsig of the signal line Sig when the switch element 202 changes between the conducting state and the non-conducting state. The signal line voltage Vsig is fixed at the same potential as the reference voltage Vref by the integrating amplifier 302 . However, when the drive signal Vg rises and the switch element 202 becomes conductive, the voltage fluctuation of the drive line G is transmitted to the signal line Sig via the parasitic capacitance between the drive line G and the signal line Sig, and the signal line voltage Vsig momentarily becomes higher than the reference voltage Vref. After that, the signal line voltage Vsig returns to the same potential as the reference voltage Vref by the integration amplifier 302 .

Next, when the drive signal Vg falls and the switch element 202 becomes non-conductive, the voltage fluctuation of the drive line G is transmitted to the signal line Sig via the parasitic capacitance between the drive line G and the signal line Sig. The signal line voltage Vsig momentarily becomes lower than the reference voltage Vref. After that, the signal line voltage Vsig returns to the same potential as the reference voltage Vref by the integrating amplifier 302 .

At this time, as shown in FIG. 5, consider the case where the signal sample-and-hold operation is started before the signal line voltage Vsig returns to the reference voltage Vref. For example, when acquiring an energy subtraction image, in order to shorten the time interval between the first imaging and the second imaging in consideration of the influence of body movement, the signal sample and hold operation in the first imaging is performed as much as possible. This may be the case when starting early. Also, for example, it may correspond to a case where shooting is performed continuously, such as shooting a moving image. In this case, the switching noise component of the switching element 202 is sampled and held in addition to the signal output from each pixel PIX of the pixel array 101, and noise is added to the resulting image. According to experiments conducted by the inventor, the effect of switching noise is reduced by shortening the time from the fall of the drive signal Vg supplied to the drive line G and the end of the output operation to the start of the signal sample-and-hold operation. It has been confirmed that it is easy to add to images.

This can be improved by improving the current drivability of the integrating amplifier 302 for driving the input node of the sample-and-hold circuit 303 and speeding up the response to fluctuations in the signal line voltage Vsig. Experiments by the inventor have also confirmed that the effect of switching noise on images is reduced when the current drive capability of the integrating amplifier 302 is increased. Here, the current drive capability is defined as the capability of how much current the integrating amplifier 302 can pass through the output of the integrating amplifier 302 . In other words, the ability of the integrating amplifier 302 to output a larger amount of current to the input node of the sample-and-hold circuit 303 is called high current driving capability.

However, if the current drive capability of the integrating amplifier 302 is uniformly improved regardless of the imaging mode, the power consumption of the readout circuit 103 and, as a result, the power consumption of the radiation imaging apparatus 100 will increase. If power consumption increases in the radiation imaging apparatus 100, problems such as a decrease in the number of images that can be captured may occur, for example, when a battery with the same capacity is used. Further, for example, in the case of photographing one image at a time, especially a still image, signal sampling can be performed after the output operation is completed within a desired readout time per row without increasing the current driving capability of the integrating amplifier 302 . In some cases, it is possible to secure an appropriate amount of time until the start of the hold operation. In other words, it may not always be necessary to improve the current driving capability of the integrating amplifier 302 .

Therefore, in the present embodiment, the radiation imaging apparatus 100 has an imaging mode for performing a plurality of continuous imaging operations such as acquisition of an energy subtraction image, acquisition of a BMD (Bone Mineral Density) image, acquisition of a moving image, and a stationary mode. The current drive capability of the integrating amplifier 302 is switched between the imaging mode when acquiring one image such as an image. More specifically, the current drive capability of the integral amplifier 302 in a mode of performing a plurality of continuous imaging such as acquisition of an energy subtraction image, acquisition of a bone densitometry image, and imaging of a moving image is sufficient to produce a single image such as a still image. It is controlled so as to be higher than the current drive capability in the acquisition mode. As a result, when the same subject is photographed multiple times in succession, the readout time per line is shortened to reduce motion artifacts, etc., while each image can be used for diagnostic purposes with the effects of switching noise suppressed. high-quality images that can be used for Furthermore, in a shooting mode for acquiring a still image or the like, it is possible to set a mode in which power consumption is suppressed. Such switching of the current drive capability can be performed by the control unit 106, for example.

Here, acquisition of a bone densitometry image (BMD: Bone Mineral Density) is performed to quantitatively measure bone density. Therefore, compared to "energy subtraction imaging," which generates and renders an image in which only specific structures such as bones and lungs are emphasized from an image, more quantification is required. In common with bone densitometry images and energy subtraction images, it is necessary to shorten the readout time per row to reduce motion artifacts and the like. The reason for reducing motion artifacts in capturing bone densitometry images is that motion artifacts can degrade quantitative measurement accuracy. In two-shot imaging used to acquire energy subtraction images and bone densitometry images, more quantitative bone densitometry images require switching noise (changes in the amount of superimposed system noise due to differences in signal readout timing (differences )) is added to the image, it may not be possible to ensure the required measurement accuracy. Therefore, even with the same two-shot imaging, the acquisition of the bone densitometry image shortens the readout time per row to reduce motion artifacts and the like, compared to the acquisition of the energy subtraction image, while increasing the current drive capability. may be controlled to be higher than

In this embodiment, the readout circuit 103 can control the output impedance of the integrating amplifier 302 and can control the current driving capability of the integrating amplifier 302 . For example, by lowering the output impedance of the readout circuit 103, the current driving capability of the integrating amplifier 302 can be increased.

From here, the operation of the radiation imaging apparatus 100 for reducing the switching noise of the image according to the imaging mode will be described. The radiation imaging apparatus 100 has a first mode in which continuous imaging such as acquisition of an energy subtraction image and imaging of a moving image is performed, and a second mode in which a still image is captured with a longer interval between imaging than in the first mode. Works in multiple modes, including Here, the integral amplifier 302 of the radiation imaging apparatus 100 is configured to be able to switch the current drive capability for driving the input node of the sample-and-hold circuit 303 . That is, the drive capability of the integral amplifier 302 is switched according to the shooting mode. More specifically, the current drive capability of integrating amplifier 302 is switched such that the current drive capability in the first mode is higher than the current drive capability in the second mode.

This can switch the current drive capability of the integrating amplifier 302 by controlling the output impedance of the integrating amplifier 302, as described above. The output impedance of integrating amplifier 302 in the first mode is lower than the output impedance of integrating amplifier 302 in the second mode. As a result, in the first mode in which an energy subtraction image is obtained, a bone density measurement image is obtained, and a moving image is captured, the readout time per row is shortened to reduce motion artifacts, etc., while reducing the motion artifacts. It is possible to suppress deterioration of image quality. In addition, in the second mode in which still images are captured, it is possible to capture images with reduced power consumption.

For example, by switching the output impedance of the operational amplifier 311, the current driving capability of the integrating amplifier 302 can be switched. In this case, the output impedance of operational amplifier 311 in the first mode is lower than the output impedance of operational amplifier 311 in the second mode. This enables the control described above.

Further, for example, by switching the capacitance value Cf of the feedback capacitor 312, the current driving capability of the integrating amplifier 302 can be switched. In this case, the capacitance value Cf of the feedback capacitor 312 is switched so that the output impedance of the integrating amplifier 302 in the first mode becomes lower than the output impedance of the integrating amplifier 302 in the second mode. More specifically, the capacitance value Cf of feedback capacitor 312 in the first mode is smaller than the capacitance value Cf of feedback capacitor 312 in the second mode. This enables the control described above.

Only the output impedance of the operational amplifier 311 or only the capacitance value Cf of the feedback capacitor 312 may be switched according to the shooting mode. Also, the output impedance of the operational amplifier 311 and the capacitance value Cf of the feedback capacitor 312 may be switched according to the shooting mode. For example, consider a case where the radiation imaging apparatus 100 operates in three or more imaging modes. In this case, for example, the output impedance of the operational amplifier 311 and the capacitance value Cf of the feedback capacitor 312 may be switched in the mode operating at the highest speed (shortest time between shootings). On the other hand, in the medium speed mode, either the output impedance of operational amplifier 311 or the capacitance value of feedback capacitor 312 may be switched. The switching of the output impedance of the operational amplifier 311 and the switching of the capacitance value Cf of the feedback capacitor 312 may be appropriately combined according to each imaging mode.

Here, a method for shortening the time per frame, in other words, shortening the readout time per row in the radiation imaging apparatus 100 will be described. FIG. 4(b) shows four factors for shortening the readout time per row. A period 401 is a noise component sample-and-hold operation time for sampling the noise component of the integrating amplifier 302 . A period 402 is an output operation time during which the drive signal Vg rises to turn on the switch element 202 to transfer a signal from the pixel PIX to the readout circuit 103 . A period 403 is the time from when the driving signal Vg falls and the switch element 202 is brought into a non-conducting state to when the signal sample-and-hold operation is started. Period 404 is the time to sample the signal in the signal sample-and-hold operation.

In the radiographic imaging apparatus 100, in the imaging mode with short time intervals as described above, while shortening the period 403, the current drive capability of the integrating amplifier 302 is switched in order to suppress the influence of switching noise (still state). It will be higher than when shooting images etc.). However, the present invention is not limited to this, and in a mode of acquiring an energy subtraction image, acquiring a bone density measurement image, or capturing a moving image with a short time interval, the period 401, Period 402 and period 404 may be shortened. For example, by improving the current driving capability of the integrating amplifier 302 as described above, the time required for periods 401, 402, and 404 can be shortened.

On the other hand, when shooting a still image or the like, there is less need to shorten the periods 401 to 404 . Therefore, the radiation imaging apparatus 100 operates in a state where the current drive capability of the integrating amplifier 302 is low in order to suppress power consumption and increase the number of images that can be captured, for example. As a result, even when acquiring energy subtraction images, acquiring bone densitometry images, capturing moving images, and capturing still images, etc., high-resolution images with suppressed effects of switching noise can be obtained. High-quality radiographic images can be obtained. In addition, when capturing a still image or the like, the power consumption of the radiation imaging apparatus 100 can be reduced.

From here, a control method of the radiation imaging apparatus 100 for reducing switching noise of an image according to the imaging mode will be described. FIG. 6 shows an example of switching the current drive capability of the integral amplifier 302 according to the shooting mode. Here, in the radiation imaging apparatus 100, there are three types of imaging: still image imaging (still image imaging), two-shot imaging performed to acquire energy subtraction images and bone density measurement images, and moving image imaging (moving image imaging). A case is shown where the shooting mode is selectable. The current drive capability of the integrating amplifier 302 is in the order of current drive capability X<current drive capability Y<current drive capability Z, and the current drive capability Z has the highest ability to drive the input node of the sample-and-hold circuit 303 . In other words, the amount of current that can flow from the integrating amplifier 302 to the sample-and-hold circuit 303 is the largest at the current drive capability Z.

As shown in FIG. 6, in the radiation imaging apparatus 100, in order to reduce image switching noise, the current drive capability of the integrating amplifier 302 may be increased in the order of still image imaging, two-shot imaging, and moving image imaging. Also in two-shot imaging, as described above, the current drive capability of the integrating amplifier 302 may be increased in the order of acquisition of the energy subtraction image and acquisition of the bone density measurement image. As described above, the current drive capability of integrating amplifier 302 may be increased by, for example, switching the output impedance of operational amplifier 311 . Further, for example, the current driving capability of the integrating amplifier 302 may be increased by switching the capacitance value Cf of the feedback capacitor 312 . Further, for example, by switching the output impedance of the operational amplifier 311 and the capacitance value Cf of the feedback capacitor 312, the current driving capability of the integrating amplifier 302 may be increased.

Also, switching noise can be reduced by switching the time from the end of the output operation to the start of the sampling operation, which is the period 403 shown in FIG. 4B. That is, when the time between shootings such as still image shooting is long, the length of the period 403 can be lengthened. On the other hand, when obtaining an energy subtraction image, obtaining a bone density measurement image, or capturing a moving image, the shorter the length of the period 403, the shorter the time of one frame. Therefore, the length of the period 403 from when the switching element 202 is turned off in the period 403 to when the sampling operation is started can be set according to the maximum value of the current driving capability of the integrating amplifier 302 .

A method of controlling the readout time per row according to the driving capability of the integrating amplifier 302 will be described with reference to FIG. As shown in FIG. 7, the readout time for one row includes a period 701 during which the noise component of the integrating amplifier 302 is sampled, a period 702 during which the drive signal Vg rises and the switch element 202 is turned on to transfer the signal, and a period 702 during which the drive signal Vg falls. There are four elements: a period 703 from when the switch element 202 is turned off to the start of the sampling operation, and a period 704 for sampling the signal.

As described above, the radiation imaging apparatus 100 switches the output impedance of the operational amplifier 311 and the capacitance value Cf of the feedback capacitor 312, and switches the output impedance of the integrating amplifier 302, thereby controlling the current driving capability of the integrating amplifier 302. . At least one of operational amplifier 311 and feedback capacitor 312 may be controlled to variably lengthen or shorten period 703 shown in FIG. 7 depending on the resulting output impedance of integrating amplifier 302. can.

For example, the current drive capability of integrating amplifier 302 is increased. In other words, the output impedance of the integrating amplifier 302 is lowered by controlling at least one of lowering the output impedance of the operational amplifier 311 and lowering the feedback capacitance 312 of the integrating amplifier 302 . As a result, it is possible to shorten the length of period 403 from when the driving signal Vg turns switch element 202 into a non-conducting state to when the sampling operation is started, and a desired readout time per row can be obtained. can also For example, the time from when the switch element 202 transitions to the non-conducting state after being turned on to output a signal from the pixel PIX to the readout circuit 103 until the sample-and-hold circuit 303 samples the signal is the time required for a still image or the like. The mode for acquiring the energy subtraction image, the bone density measurement image, and the moving image shooting may be shorter than the mode for shooting. Also, in two-shot imaging used to acquire an energy subtraction image or a bone density measurement image, in the order of acquisition of the energy subtraction image and bone density measurement image, sample hold circuit 303 samples the signal. may be shorter.

In this case, increasing the current drive capability of the integrating amplifier 302 increases the power consumption of the readout circuit 103, resulting in an increase in the power consumption of the radiation imaging apparatus 100. FIG. Also, if the capacitance value Cf of the feedback capacitor 312 is too low, the desired image quality (for example, SNR) may not be obtained. In the balance between the two, that is, within the range in which the desired power consumption and desired image quality can be obtained, the switch element 202 is brought into a non-conducting state by falling the drive signal Vg, and the sampling is performed after the output operation is completed. It is also possible to control the length of the period 403 until the operation starts, or the readout time per row determined by the period 403 . Further, for example, the output impedance of the operational amplifier 311 or the capacitance value Cf of the feedback capacitor 312 is controlled according to the desired readout time per row or the desired length of the period 403, resulting in The output impedance of the resulting integrating amplifier 302 may be controlled. At this time, the scanning circuit 102 performs pixel addition in which a plurality of pixels PIX in a plurality of rows are driven at the same time, thereby shortening the readout time per frame. In such pixel addition as well, the output impedance of the operational amplifier 311 or the capacitance value Cf of the feedback capacitor 312 is controlled according to the desired readout time per row or the desired length of the period 403. . Thereby, the output impedance of the resulting integrating amplifier 302 may be controlled.

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, 101: pixel array, 103: readout circuit, 302: integral amplifier, 303: sample and hold circuit, PIX: pixel

Claims (16)

a pixel array in which a plurality of pixels that generate signals corresponding to incident radiation are arranged; and a readout circuit that reads out signals from the pixel array; A radiation imaging apparatus that operates in a plurality of modes including a second mode with a long interval between
The readout circuit includes an integral amplifier that amplifies the signal read out from the pixel array, and a sample-and-hold circuit that holds the signal amplified by the integral amplifier,
the integrating amplifier is configured to be able to switch current driving capability for driving an input node of the sample-and-hold circuit,
A radiation imaging apparatus, wherein the current drive capability in the first mode is higher than the current drive capability in the second mode. By switching the output impedance of the integrating amplifier, the current driving capability is switched,
2. The radiation imaging apparatus according to claim 1, wherein the output impedance of said integrating amplifier in said first mode is lower than the output impedance of said integrating amplifier in said second mode. the integrating amplifier includes an operational amplifier and a feedback capacitor arranged in parallel between the pixel array and the sample-and-hold circuit;
By switching the output impedance of the operational amplifier, the current driving capability is switched,
2. The radiation imaging apparatus according to claim 1, wherein the output impedance of said operational amplifier in said first mode is lower than the output impedance of said operational amplifier in said second mode. The feedback capacitor is configured to be able to switch a capacitance value,
4. The radiation imaging apparatus according to claim 3, wherein the capacitance value is switched such that the output impedance of the integrating amplifier in the first mode is lower than the output impedance of the integrating amplifier in the second mode. the integrating amplifier includes an operational amplifier and a feedback capacitor arranged in parallel between the pixel array and the sample-and-hold circuit;
By switching the capacitance value of the feedback capacitor, the current driving capability is switched,
2. The radiation imaging apparatus according to claim 1, wherein said capacitance value is switched such that the output impedance of said integrating amplifier in said first mode is lower than the output impedance of said integrating amplifier in said second mode. 6. The radiation imaging apparatus according to claim 4, wherein the capacitance value of said feedback capacitor in said first mode is smaller than the capacitance value of said feedback capacitor in said second mode. each of the plurality of pixels includes a switch element for outputting the signal generated by the plurality of pixels to the readout circuit;
The time from when the switching element transitions to the non-conducting state after being turned on to output a signal from the pixel to the readout circuit until the sample-and-hold circuit samples the signal is longer than that in the second mode. 7. The radiation imaging apparatus according to any one of claims 1 to 6, wherein the first mode is shorter. further comprising a control unit that controls the readout circuit to switch the current drive capability;
the first mode is at least one imaging mode of a moving image, an energy subtraction image, and a bone densitometry image;
8. The radiation imaging apparatus according to claim 1, wherein the second mode is a still image capturing mode. 9. The radiation imaging apparatus according to claim 1, wherein power consumption of said readout circuit in said first mode is greater than power consumption of said readout circuit in said second mode. wherein the plurality of modes further includes a third mode in which the time between shootings is shorter than that in the first mode;
10. The radiation imaging apparatus according to claim 1, wherein the current drive capability in the third mode is higher than the current drive capability in the first mode. the first mode is an energy subtraction image capturing mode,
11. The radiation imaging apparatus according to claim 10, wherein the third mode is a moving image capturing mode. the first mode is an energy subtraction image capturing mode,
11. The radiation imaging apparatus according to claim 10, wherein the third mode is a mode for capturing a bone density measurement image. the first mode is an imaging mode for bone densitometry images,
11. The radiation imaging apparatus according to claim 10, wherein the third mode is a moving image capturing mode. The plurality of modes further include a third mode in which the time between shootings is shorter than in the first mode, and a fourth mode in which the time between shootings is shorter than in the third mode. including
the current drivability in the third mode is higher than the current drivability in the first mode;
10. The radiation imaging apparatus according to claim 1, wherein the current drive capability in the fourth mode is higher than the current drive capability in the third mode. the first mode is an energy subtraction image capturing mode,
the third mode is an imaging mode for bone densitometry images,
15. The radiation imaging apparatus according to claim 14, wherein the fourth mode is a moving image capturing mode. a radiation imaging apparatus according to any one of claims 1 to 15;
a processor that processes signals output from the radiation imaging apparatus;
A radiation imaging system comprising:

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