JP2023077985A - Radiation imaging apparatus and radiation imaging method - Google Patents

Abstract

To provide a technique advantageous for reducing the variation in the noise accumulation time from resetting to exposure imaging in the time of consecutive imaging of a radiation image.SOLUTION: A radiation imaging apparatus comprises: a conversion element which converts the radiation into an electric signal; a sample hold circuit which sample-holds a signal from the conversion element plural times; a drive start detection unit which detects the imaging drive start from a radiation generation device; and a reset control unit which determines the timing of resetting in each of the plurality of conversion elements. The timing of at least one sample-holding in the plural times of sample-holding by the sample hold circuit is the timing in the irradiation period of the radiation. The reset control unit controls the reset timing so as to reset the conversion element every time the start of imaging driving is detected by the drive start detection unit.SELECTED DRAWING: Figure 6

Description

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

There is an energy subtraction method as an imaging method using a radiation imaging apparatus.

The energy subtraction method is a method of obtaining new images (e.g., images of bones and soft tissues) by processing multiple images obtained by imaging multiple times with different energies of radiation irradiated to the subject. be.

Patent Literature 1 describes a technique that is advantageous for reducing variations in the time from the start of radiation irradiation to signal sample-and-hold. This technique has a detection unit that detects irradiation of radiation, and is a technique of determining the timing of sampling and holding a plurality of times each time irradiation of radiation is detected. This technology has provided a technology capable of suitably controlling signal sample-and-hold timing in radiographic imaging by the energy subtraction method.

JP 2019-24926

However, even in the technique of Patent Document 1, there is room for improvement in terms of countermeasures against noise contained in image signals. An object of the present invention is to provide a radiation imaging apparatus that solves the above problems.

In view of the above problems, a radiation imaging apparatus of the present invention provides a pixel array having a plurality of pixels each provided with at least a conversion element that converts radiation into an electrical signal and a sample-and-hold circuit that samples and holds the signal from the conversion element a plurality of times. a readout circuit for reading signals from the pixel array; and radiation detection for detecting the start of radiation irradiation by the radiation generator based on radiation emitted from the radiation generator or information provided from the radiation generator. a timing control unit that determines the timing of sampling and holding a plurality of times in each of the plurality of pixels each time the radiation detection unit detects the start of radiation irradiation; and imaging from the radiation generation device. a drive start detection unit that detects the start of drive; and a reset control unit that determines reset timing for each of the plurality of conversion elements, wherein at least one sample is sampled out of a plurality of sample-holds by the sample-and-hold circuit. The hold timing is the timing in the radiation irradiation period, and the reset control section controls the reset timing so as to reset the conversion element each time the start of imaging driving is detected by the drive start detection section. It is characterized by

According to the present invention, it is possible to take measures against noise contained in image signals, and to provide better images.

1 is a diagram showing the configuration of a radiation imaging apparatus according to a first embodiment of the present invention; FIG. FIG. 4 is a diagram showing a configuration example of an imaging unit; 4A and 4B are diagrams showing configuration examples of one pixel; FIG. FIG. 5 is a diagram showing the operation of the radiation imaging apparatus in extended mode 1 (comparative example); FIG. 10 is a diagram for explaining a problem in extended mode 1 (comparative example); FIG. 8 is a diagram showing the operation of the radiation imaging apparatus in extended mode 2; FIG. 10 is a diagram for explaining improvement results of problems in extended mode 2; FIG. 10 is a diagram showing the operation of the radiation imaging apparatus in extended mode 3;

The invention will now be described through its exemplary embodiments with reference to the accompanying drawings.

FIG. 1 shows the configuration of a radiation imaging system 1 according to the first embodiment of the invention. The radiation imaging system 1 can include an imaging section 100 including a pixel array 110 having a plurality of pixels, and a signal processing section 352 that processes signals from the imaging section 100 . The imaging unit 100 can have, for example, a panel shape. The signal processing unit 352 may be configured as part of the control device 350 as illustrated in FIG. may be housed in a different housing. A radiation imaging system 1 is a system for obtaining a radiation image by an energy subtraction method. The energy subtraction method is a method of obtaining new radiographic images (e.g., bone images and soft tissue images) by processing multiple images obtained by imaging multiple times with different radiation energies applied to the subject. is. The term radiation can include, for example, X-rays as well as α-rays, β-rays, γ-rays, particle rays, and cosmic rays.

The radiation imaging system 1 can include a radiation source 400 that generates radiation, an exposure control device 300 that controls the radiation source 400 , and a control device 350 that controls the exposure control device 300 and the imaging unit 100 . The radiation source 400 and the exposure control device 300 constitute a radiation generator. The control device 350 can include the signal processing section 352 that processes the signal supplied from the imaging section 100, as described above. All or part of the functions of the control device 350 can be incorporated into the imaging section 100 . Alternatively, part of the functions of the imaging section 100 can be incorporated into the control device 350 . The control device 350 can be configured by a computer (processor) and a memory storing programs to be provided to the computer. The signal processing unit 352 can be configured by part of the program. Alternatively, the signal processing unit 352 may be configured by a computer (processor) and a memory storing programs to be provided to the computer. All or part of controller 350 may be implemented by a digital signal processor (DSP) or a programmable logic array (PLA). The controller 350 and signal processor 352 may be designed and manufactured by a logic synthesis tool based on a file describing their operation. Note that the imaging unit 100, the signal processing unit 352, and the control device 350 constitute a radiation imaging apparatus.

The control device 350 transmits an exposure permission signal to the exposure control device 300 when permitting radiation emission (exposure) by the radiation source 400 . Upon receiving the exposure permission signal from the control device 350, the exposure control device 300 causes the radiation source 400 to emit (exposure) radiation in response to the reception of the exposure permission signal. When capturing a moving image, the control device 350 transmits an exposure permission signal to the exposure control device 300 a plurality of times. In this case, the control device 350 may transmit the exposure permission signal to the exposure control device 300 a plurality of times in a predetermined cycle, and each time the imaging unit 100 becomes capable of imaging the next frame. , an exposure permission signal may be transmitted to the exposure control device 300 .

Radiation source 400 may emit radiation that varies in energy (wavelength) during successive emission periods (irradiation periods) of the radiation. Using such radiation, radiographic images are obtained at a plurality of energies different from each other, and one new radiographic image can be obtained by processing these radiographic images by the energy subtraction method.

Alternatively, the radiation source 400 may have the ability to change the energy (wavelength) of the radiation. The radiation source 400 can have the ability to change the energy of the radiation, for example, by changing the tube voltage (the voltage applied between the cathode and anode of the radiation source 400).

The pixel array 110 of the imaging unit 100 has a plurality of pixels, and each of the plurality of pixels is a conversion element that converts radiation into an electric signal (for example, electric charge) and a sample that samples and holds the signal from the conversion element. It includes a hold circuit and a reset section for resetting the conversion element. Each pixel may be configured to convert radiation directly into an electrical signal, or may be configured to convert radiation into light, such as visible light, and then convert the light into an electrical signal. In the latter, a scintillator can be used to convert radiation into light. A scintillator may be shared by multiple pixels that make up the pixel array 110 .

FIG. 2 shows a configuration example of the imaging unit 100. As shown in FIG. The imaging unit 100 includes a pixel array 110 having a plurality of pixels 112 and a readout circuit RC for reading out signals from the plurality of pixels 112 of the pixel array 110 . The plurality of pixels 112 may be arranged in rows and columns. The readout circuit RC can include a row selection circuit 120, a control section 130, a buffer circuit 140, a column selection circuit 150, an amplification section 160, an AD converter 170, and a detection section 190 that detects changes in AD-converted charge amount. The control unit 130 functions as a timing control unit that determines the sampling timing of the sampling circuit, which will be described later. Further, the detection unit 190 functions as an irradiation detection unit that detects the start of radiation irradiation by the radiation generator based on the signal output by the conversion element.

Row select circuit 120 selects a row of pixel array 110 . Row select circuit 120 may be configured to select a row by driving row control transmission line 122 . Buffer circuit 140 buffers signals from pixels 112 in a row selected by row selection circuit 120 among the plurality of rows of pixel array 110 . The buffer circuit 140 buffers the signals for multiple columns output to the multiple column signal transmission paths 114 of the pixel array 110 . Column signal transmission line 114 in each column includes a first signal line and a second column signal line forming a column signal line pair. A noise level of the pixels 112 (in the normal mode described later) or a radiation signal corresponding to radiation detected by the pixels 112 (in the extension mode described later) can be output to the first column signal line. A radiation signal corresponding to the radiation detected by the pixel 112 can be output to the second column signal line. Buffer circuit 140 may include an amplifier circuit.

Column selection circuit 150 selects signal pairs for one row buffered by buffer circuit 140 in a predetermined order. The amplifier section 160 amplifies the signal pair selected by the column selection circuit 150 . Here, the amplifier 160 may be configured as a differential amplifier that amplifies the difference between the signal pair (two signals). The AD converter 170 may include an AD converter 170 that AD-converts the signal OUT output from the amplifier 160 and outputs a digital signal DOUT (radiation image signal).

FIG. 3 shows a configuration example of one pixel 112 . The pixel 112 includes, for example, a conversion element 210, a reset switch 220 (reset section), an amplifier circuit 230, a sensitivity change section 240, a clamp circuit 260, sample hold circuits (holding sections) 270 and 280, and an output circuit 310. The pixel 112 can have a normal mode and an extended mode as modes related to imaging schemes. Extended mode is a mode for obtaining a radiographic image by the energy subtraction method.

Conversion element 210 converts the radiation into an electrical signal. The conversion element 210 can be composed of, for example, a scintillator that can be shared by a plurality of pixels and a photoelectric conversion element. The conversion element 210 has a charge accumulation section 211 that accumulates the converted electric signal (charge), that is, an electric signal corresponding to radiation.

The amplifier circuit 230 can include MOS transistors 235 and 236 and a current source 237 . MOS transistor 235 is connected to current source 237 via MOS transistor 236 . MOS transistor 235 and current source 237 form a source follower circuit. MOS transistor 236 is an enable switch that is turned on when enable signal EN is activated to activate the source follower circuit formed of MOS transistor 235 and current source 237 .

The charge storage portion of the conversion element 210 and the gate of the MOS transistor 235 function as a charge-voltage conversion portion CVC that converts the charge stored in the charge storage portion into a voltage. That is, a voltage V (=Q/C) determined by the charge Q accumulated in the charge storage unit and the capacitance value C of the charge-voltage conversion unit appears in the charge-voltage conversion unit CVC. The charge-voltage converter CVC is connected to the reset potential VRES through the reset switch 220 . When the reset signal PRES is activated, the reset switch 220 is turned on, resetting the potential of the charge-voltage converter to the reset potential VRES. The reset switch 220 is a transistor having a first main electrode (drain) connected to the charge storage portion of the conversion element 210, a second main electrode (source) to which a reset potential VRES is applied, and a control electrode (gate). can contain When the ON voltage is applied to the control electrode of the transistor, the first main electrode and the second main electrode of the transistor are electrically connected to reset the charge storage section 211 of the conversion element 210 .

The clamp circuit 260 clamps the reset noise level output from the amplifier circuit 230 by the clamp capacitor 261 according to the reset potential of the charge-voltage converter CVC. The clamp circuit 260 is a circuit for canceling the reset noise level from the signal (radiation signal) output from the amplifier circuit 230 according to the charge (electrical signal) converted by the conversion element 210 . The reset noise bell includes kTC noise at the time of resetting the charge-voltage converter CVC. The clamping operation is performed by turning on MOS transistor 262 by activating clamp signal PCL and then turning off MOS transistor 262 by deactivating clamp signal PCL.

The output side of clamp capacitor 261 is connected to the gate of MOS transistor 263 . The source of MOS transistor 263 is connected to current source 265 via MOS transistor 264 . MOS transistor 263 and current source 265 constitute a source follower circuit. MOS transistor 264 is an enable switch that is turned on when an enable signal EN0 supplied to its gate is activated to activate a source follower circuit formed by MOS transistor 263 and current source 265 .

Output circuit 310 includes MOS transistors 311 and 313 and row select switches 312 and 314 . MOS transistors 311 and 313 configure source follower circuits together with current sources (not shown) connected to column signal lines 321 and 322, respectively.

A radiation signal, which is a signal output from the clamp circuit 260 in response to charges generated by the conversion element 210 , can be sample-held (held) by the sample-and-hold circuit 280 . Sample-and-hold circuit 280 may have switch 281 and capacitor 282 . Switch 281 is turned on when sample hold signal TS is activated by row selection circuit 120 . The radiation signal output from the clamp circuit 260 is written to the capacitor 282 via the switch 281 by activating the sample-and-hold signal TS.

In the normal mode, the reset switch 220 resets the potential of the charge-voltage converter CVC, and the noise level (offset component) of the clamp circuit 260 is output from the clamp circuit 260 when the MOS transistor 262 is turned on. The noise level of clamp circuit 260 can be sampled and held by sample and hold circuit 270 . The sample and hold circuit 270 can have a switch 271 and a capacitor 272 . Switch 271 is turned on when sample hold signal TN is activated by row selection circuit 120 . The noise level output from the clamp circuit 260 is written into the capacitor 272 via the switch 271 by activating the sample hold signal TN. Also, in extended mode, the sample and hold circuit 270 can be used to hold the radiation signal, which is the signal output from the clamp circuit 260 in response to the charge generated in the conversion element 210 .

When the row selection signal VST is activated, signals corresponding to the signals held in the sample hold circuits 270 and 280 are applied to the first column signal line 321 and the second column signal line 322 forming the column signal transmission line 114. output. Specifically, a signal N corresponding to the signal (noise level or radiation signal) held by the sample hold circuit 270 is output to the column signal line 321 via the MOS transistor 311 and the row selection switch 312 . A signal S corresponding to the signal held by sample hold circuit 280 is output to column signal line 322 via MOS transistor 313 and row select switch 314 .

Pixel 112 may include summing switches 301 , 302 for summing the signals of multiple pixels 112 . In addition mode, addition mode signals ADDN and ADDS are activated. Activation of the addition mode signal ADDN connects the capacitors 272 of the plurality of pixels 112 to average the signal (noise level or radiation signal). Activation of the addition mode signal ADDS connects the capacitors 282 of the plurality of pixels 112 to average the radiation signal.

Pixel 112 may include sensitivity modifier 240 . The sensitivity changing unit 240 can include switches 241 and 242, capacitors 243 and 244, and MOS transistors 245 and 246. When the first change signal WIDE is activated, the switch 241 is turned on and the capacitance value of the first additional capacitor 243 is added to the capacitance value of the charge-voltage converter CVC. This reduces the sensitivity of the pixels 112 . Further, when the second change signal WIDE2 is also activated, the switch 242 is also turned on, and the capacitance value of the second additional capacitance 244 is added to the capacitance value of the charge-voltage converter CVC. This further reduces the sensitivity of the pixel 112 . By adding the ability to desensitize the pixels 112, the dynamic range can be increased. The enable signal ENW may be activated when the first change signal WIDE is activated. In this case, MOS transistor 246 performs a source follower operation. Note that when the switch 241 of the sensitivity changing unit 240 is turned on, the potential of the charge storage unit 211 of the conversion element 210 can change due to charge redistribution. This may corrupt part of the signal.

The reset signal PRES, enable signal EN, clamp signal PCL, enable signal EN0, sample hold signals TN and TS, and row selection signal VST are control signals controlled (driven) by the row selection circuit 120, and are shown in FIG. Corresponds to row control signal 122 . Also, the row selection circuit 120 generates a reset signal PRES, an enable signal EN, a clamp signal PCL, an enable signal EN0, sample hold signals TN and TS, and a row selection signal VST according to timing signals supplied from the control section 130 .

In the pixel 112 configured as shown in FIG. 3, signal destruction does not occur in the charge accumulation portion 211 of the conversion element 210 and the like during sample-and-hold. That is, the pixels 112 configured as shown in FIG. 3 can read radiation signals non-destructively. Such a configuration is advantageous for radiation imaging to which the energy subtraction method described below is applied.

An extension mode for obtaining a radiographic image by the energy subtraction method will be described below. Extended mode may include the following three sub-modes (extended modes 1, 2, 3). Here, extended mode 1 is a comparative example, and extended modes 2 and 3 are improved examples of comparative example 1. FIG.

FIG. 4 shows the operation of the radiation imaging system 1 in extended mode 1 (comparative example). In FIG. 4, the horizontal axis is time. “Radiation energy” is energy of radiation emitted from the radiation source 400 and applied to the imaging unit 100 . “PRES” is a reset signal RPES. "TS" is the sample and hold signal TS. “DOUT” is the output of AD converter 170 . Synchronization of radiation emission from the radiation source 400 and operation of the imaging unit 100 can be controlled by a controller 350 that generates an exposure enable signal. Operation control in the imaging unit 100 is performed by the control unit 130 . The clamp signal PCL is also activated for a predetermined period while the reset signal PRES is activated, and the noise level is clamped in the clamp circuit 260 .

As illustrated in FIG. 4, the energy (wavelength) of radiation 800 emitted from radiation source 400 varies during the emission period of the radiation. This can be attributed to the fact that the tube voltage of the radiation source 400 is controlled in two stages, low energy and high energy, and that the rise and fall of each tube voltage are dull. Now consider radiation 800 as consisting of radiation 801 during the low energy radiation period, radiation 802 during the high energy radiation period, and radiation 803 during the low energy radiation fall period. Energy E1 of radiation 801, energy E2 of radiation 802, and energy E3 of radiation 803 can be different from each other. Using this, a radiographic image can be obtained by the energy subtraction method.

The control unit 130 controls the first period T1, the second period T2, and the third period T3 to correspond to the low-energy radiation period, the high-energy radiation period, and the low-energy radiation fall period, respectively. T1, a second period T2 and a third period T3 are defined. Each pixel 112 performs an operation of outputting a first signal according to the electrical signal generated by the conversion element 210 in the first period T1. Also, each pixel 112 performs an operation of outputting a second signal according to the electrical signal generated by the conversion element 210 in the first period T1 and the second period T2. Also, each pixel 112 performs an operation of outputting a third signal according to the electrical signal generated by the conversion element 210 in the first period T1, the second period T2 and the third period T3. The first period T1, the second period T2 and the third period T3 are different periods. Radiation having a first energy E1 is emitted during the first period T1, radiation having a second energy E2 is emitted during the second period T2, and radiation having a third energy E3 is emitted during the third period T3. is scheduled.

In extension mode 1, the conversion element 210 of the pixel 112 is not reset (the reset signal PRES is not activated) during the irradiation period TT during which the radiation 800 is applied. Therefore, during the irradiation period TT during which the radiation 800 is irradiated, electric signals (charges) corresponding to the incident radiation continue to be accumulated in the conversion element 210 . In the irradiation period TT during which the radiation 800 is irradiated, the conversion elements 210 of the pixels 112 are not reset. Advantageous.

Before the radiation 800 is emitted (irradiating the imaging unit 100), the reset signal PRES is activated for a predetermined period of time, thereby resetting the conversion element 210. FIG. At this time, the clamp signal PCL is also activated for a predetermined period, and the reset level (noise level) is clamped in the clamp circuit 260 .

After the reset signal PRES is activated for a predetermined period, the exposure control device 300 transmits an exposure permission signal to the radiation source 400, and radiation is emitted from the radiation source 400 in response to this exposure permission signal. be.

The controller 350 samples and holds the sample-and-hold circuits 270 and 280 of the pixels 112 in synchronization with the radiation actually emitted from the radiation source 400 rather than with the exposure permission signal. The control unit 130 determines the timing of multiple sample-holds SH1, SH2, SH3, SH0 and resets RES1, RES2 in each of the plurality of pixels 112 of the pixel array 110 each time the synchronization signal is supplied from the detection unit 190. do. In other words, each time the detection unit 190 detects the start of irradiation of radiation, the control unit 130 performs a plurality of sample-holds SH1, SH2, SH3, SH0 and a reset RES1 in each of the plurality of pixels 112 of the pixel array 110. , RES2. During the period between the first sample hold SH1 among the multiple sample holds SH1, SH2, SH3 and SH0 and the sample hold SH3 among the multiple sample holds SH1, SH2 and SH3, the reset switch 220 is set to the conversion element 210. not reset.

After a predetermined period of time has elapsed since the sample-and-hold signal TN was activated for a predetermined period (SH1), the sample-and-hold signal TS is activated for a predetermined period (SH2). As a result, the signal (E1+E2) corresponding to the electric signal generated by the conversion element 210 of the pixel 112 of the pixel array 110 in response to irradiation of the radiation 801 of the energy E1 and the radiation 802 of the energy E2 is sampled and held by the sample and hold circuit 280. be.

Next, a signal corresponding to the difference between the signal (E1) sampled and held by the sample and hold circuit 270 and the signal (E1+E2) sampled and held by the sample and hold circuit 280 is output from the readout circuit RC as the first signal 805. In FIG. 4, "N" indicates a signal sampled and held by the sample hold circuit 270 and output to the first column signal line 321, and "S" indicates a signal sampled and held by the sample hold circuit 280 and sent to the second column signal line 321. Signals output to the column signal line 322 are shown.

Next, after a predetermined period of time has passed since the sample-and-hold signal TS was activated for a predetermined period (SH2) (after the irradiation of the radiation 803 with the energy E3 (irradiation of the radiation 800) is completed), the sample-and-hold signal TS is set to a predetermined value. It is activated again (SH3) for a period of time. As a result, the signal (E1+E2+E3) corresponding to the electrical signal generated by the conversion element 210 of the pixel 112 of the pixel array 110 upon irradiation with the radiation 801, 802, 803 of energy E1, E2, E3 is sampled by the sample-and-hold circuit 280. It is held.

Next, a signal corresponding to the difference between the signal (E1) sampled and held by the sample and hold circuit 270 and the signal (E1+E2+E3) sampled and held by the sample and hold circuit 280 is output from the readout circuit RC as the second signal 806.

Next, the reset signal PRES is activated for a predetermined period (RES1), and the sample and hold signal TN is activated for a predetermined period (SH0). As a result, the sample hold circuit 270 samples and holds the reset level (0). Next, a signal corresponding to the difference between the signal (0) sampled and held by the sample and hold circuit 270 and the signal (E1+E2+E3) sampled and held by the sample and hold circuit 280 is output from the readout circuit RC as the third signal 807.

For the next imaging, the reset signal PRES is activated for a predetermined period (RES2) before the radiation 800 is emitted (irradiation to the imaging unit 100), thereby resetting the conversion element 210. FIG. At this time, the clamp signal PCL is also activated for a predetermined period, and the reset level (noise level) is clamped in the clamp circuit 260 .

By repeating the operation described above a plurality of times, it is possible to obtain a plurality of frames of radiographic images (that is, moving images).

The signal processing unit 352 can obtain the first signal 805 (E2), the second signal 806 (E2+E3), and the third signal 807 (E1+E2+E3) as described above. Based on the first signal 805, the second signal 806, and the third signal 807, the signal processing unit 352 calculates the dose e1 of the radiation 801 with the energy E1, the dose e2 of the radiation 802 with the energy E2, and the dose e2 of the radiation 803 with the energy E3. An irradiation amount e3 can be obtained. Specifically, the signal processing unit 352 calculates the difference ((E2+E3)−E2) between the first signal 805 (E2) and the second signal (E2+E3), thereby obtaining the dose e3 of the radiation 803 of energy E3. can be obtained. Further, the signal processing unit 352 computes the difference ((E1+E2+E3)−(E2+E3)) between the second signal 806 (E2+E3) and the third signal (E1+E2+E3), thereby calculating the dose e1 of the radiation 801 with the energy E1. Obtainable. A first signal 805 (E2) indicates the dose e2 of the radiation 802 of energy E2.

Therefore, the signal processing unit 352 obtains a radiation image by the energy subtraction method based on the dose e1 of the radiation 801 with energy E1, the dose e2 of the radiation 802 with energy E2, and the dose e3 of the radiation 803 with energy E3. can be done. As the energy subtraction method, a method selected from various methods can be adopted. For example, a bone image and a soft tissue image can be obtained by calculating the difference between the radiographic image of the first energy and the radiographic image of the second energy. Alternatively, the bone image and the soft tissue image may be generated by solving nonlinear simultaneous equations based on the radiographic image of the first energy and the radiographic image of the second energy. It is also possible to obtain a contrast agent image and a soft tissue image based on the radiographic image of the first energy and the radiographic image of the second energy. Also, an electron density image and an effective atomic number image can be obtained based on the radiographic image of the first energy and the radiographic image of the second energy.

In order to obtain a radiographic image by the energy subtraction method, the timing of at least one sample hold in the multiple sample hold timings SH1, SH2, and SH3 is the timing in the radiation irradiation period TT. In the first embodiment, the timings of the two sample-holds SH1, SH2 in the timings SH1, SH2, SH3 of the three sample-holds are the timings in the radiation irradiation period TT.

The timings of the multiple sample holds SH1, SH2, SH3, SH0 and the resets RES1, RES2 can be determined according to the elapsed times t1, t2, t3, t4, t5 from the synchronization signal, respectively.

By performing sample-and-hold in synchronization with the radiation actually emitted from the radiation source 400, the period from the start of radiation irradiation to the end of sample-and-hold SH1 is made constant between frames. In addition, the period from the start of radiation irradiation to the end of sample hold SH2 is constant between frames. In addition, the period from the start of radiation irradiation to the end of sample hold SH3 is constant between frames. This suppresses the deterioration of the accuracy of energy subtraction, thereby reducing artifacts and flickering in moving images.

Problems in extended mode 1 (comparative example) will be described with reference to FIG. As illustrated in FIG. 5, the time between one frame is fixed by performing sampling and holding in synchronization with the actually emitted radiation. However, because resetting cannot be performed immediately before exposure, noise (dark current noise) accumulates between frames. Dark current noise accumulates in proportion to time, so if the accumulation time is constant, it can be removed by correction (offset correction). Since noise accumulates, the image quality deteriorates. In addition, in the case of extended mode 1 (comparative example) shown in FIG. 5, by synchronizing the timing of sampling and holding multiple times with the detection of radiation irradiation, the radiation that should be performed immediately before irradiation is converted into an electrical signal. The resetting of the conversion element is performed after the exposure photographing. In extended mode 1, after reset, the signal begins to accumulate ready for the next exposure at any time. Although no signal is basically accumulated in a state in which radiation is not exposed, dark current noise is generated that accumulates in proportion to time. If the time from resetting to the next shooting can be assumed to some extent, as in frame shooting of a moving image, it is possible to create an offset image in which dark current noise is accumulated in the same time period and perform correction in advance.

However, for example, in the case of 3D shooting with the C-arm, when shooting continuously by changing the frame rate during one shooting, or between movie shootings, the time from resetting to the next shooting may increase. Sometimes unknown. In such a case, unpredictable dark current noise is accumulated, and correction using an offset image cannot be performed. As a result, there is a problem that the image quality of the captured image deteriorates.

In addition, the first frame during X-ray video imaging may be discarded if the amount of accumulated dark current noise cannot be estimated. be.

FIG. 6 shows the operation of the radiation imaging system 1 in extended mode 2. As shown in FIG. Matters that are not referred to as extended mode 2 may follow extended mode 1. As one of the means for solving the problem in extended mode 1 (comparative example), in extended mode 2, driving is performed so that resetting can be performed immediately before exposure photography.

Specifically, the control device 350 detects that the exposure control device 300 generates an exposure permission signal for instructing exposure to the radiation source 400 (for example, pressing an exposure switch (not shown)), and Control is performed to reset the conversion element at this timing. In the example shown in FIG. 6, the control device 350 detects a synchronization signal, which is transmitted to the control device 350 when the exposure control device 300 generates an exposure permission signal, as the start of imaging driving, and receives this signal (at the rising edge of the synchronization signal). detection) as a trigger to instruct the reset of the conversion element. In other words, it can be said that the control device 350 includes a drive start detection section that detects the start of imaging drive from the radiation generating device, and a reset control section that determines reset timing in each of the conversion elements. It can be said that the reset control unit provided in the control device 350 controls the reset timing so as to reset the conversion element each time the drive start detection unit provided further in the control device 350 detects the start of the imaging drive. As a result, before the exposure permission signal is transmitted from the exposure control apparatus 300 to the radiation source 400 (in conjunction with the rise of the synchronization signal), the radiation imaging apparatus can start resetting the conversion elements.

The control device 350 determines the timing of reset RES0 in each of the plurality of pixels 112 of the pixel array 110 each time the rising edge of the synchronization signal is detected. In this manner, the conversion elements are reset during a predetermined period (T0) from when the exposure permission signal is transmitted from the exposure control apparatus 300 to the radiation source 400 until the radiation source 400 actually starts exposure. .

After that, the exposure control apparatus 300 causes the synchronization signal to fall when radiation is actually emitted from the radiation source 400 . Each time the controller 350 detects the falling edge of the synchronization signal, the timing of the multiple sample-and-hold SH1, SH2, SH3, SH0 and RES1 in each of the multiple pixels 112 of the pixel array 110 is determined. That is, the sample hold timing and the reset timing are determined based on the synchronization signal, which is information provided from the radiation generating apparatus and information relating to the start of imaging driving. The determination of the timings of the sample-and-hold SH1, SH2, SH3, and SH0 is not limited to this, and may be determined based on the signal output by the conversion element (signal change accompanying irradiation of radiation).

According to the extended mode 2 described above, the reset can be reliably performed immediately before exposure photography, and the influence of unpredictable dark current noise can be reduced even when the frame rate is variable.

FIG. 7 shows that the dark current noise accumulation time can be kept constant by resetting immediately before exposure in extended mode 2 even if the frame rate changes. Further, according to the present proposal, not only can the dark current noise accumulation time be kept constant, but also the dark current noise accumulation time can be reduced.

FIG. 8 shows the operation of the radiation imaging system 1 in extended mode 3. As shown in FIG. Matters not mentioned as extended mode 3 may follow extended mode 1. In extended mode 3, which solves the problem in extended mode 1, the exposure control device generates an exposure permission signal in synchronization with the reset timing determined by the control device 350 functioning as a reset control unit. Specifically, along with generation of a reset signal generated at reset timing determined by the control device 350, the control device 350 transmits a synchronization signal to the exposure control device 300, and the exposure control device 300 receives the synchronization signal. is triggered, an exposure permission signal is generated and transmitted to the radiation source 400 . In other words, in extension mode 3, the reset control unit of the control device 350 outputs information prompting the radiation generation device to start radiation irradiation in synchronization with the reset timing. The information prompting the start of radiation irradiation is a synchronization signal generated by the control device 350 .

As described above, in extended mode 3, after the exposure control device 300 detects the synchronization signal from the control device 350, the exposure control device 300 transmits an exposure permission signal to the radiation source 400, and the exposure permission signal Radiation is emitted from radiation source 400 in response to .

After that, when it is detected that radiation is actually emitted from the radiation source 400, the timing of a plurality of sample-and-hold SH1, SH2, SH3, SH0 and RES1, RES2 in each of the plurality of pixels 112 of the pixel array 110 is determined. do. A method similar to the extension mode 2 can be adopted for radiation detection.

Then, by raising the synchronization signal again at the timing when the RES2 is reset toward the next frame, the exposure permission signal rises again, and the next imaging is started. That is, t5, which is the timing of RES2, becomes the frame rate. If the frame rate is desired to be variable, changing t5 changes the frame rate. Also, by not raising the synchronization signal at the end of moving image shooting and raising the synchronization signal at the start of the next shooting, it is possible to start shooting at the timing of the staff.

As a result, resetting can be reliably performed immediately before exposure photography, and the influence of unpredictable dark current noise can be reduced even when the frame rate is variable.

According to the above-described present invention, it is possible to reset immediately before exposure photography, and it is possible to keep constant the time during which dark current noise is accumulated. As a result, offset correction can be performed even if the frame rate is variable, and deterioration of image quality due to dark current noise can be suppressed.

Also, the dark current noise accumulation time can be minimized. As a result, dark current noise can be reduced, and deterioration of image quality due to dark current noise can be suppressed.

Incidentally, in the above description, a form in which three types of images with mutually different energies are acquired has been described. However, the present invention is not limited to such forms. For example, the number of times of sample-and-hold may be increased to obtain four types of images with different energies. Alternatively, two types of images with different energies may be acquired by reducing the number of sample-holds. Alternatively, two types of images with mutually different energies may be obtained from three types of images with mutually different energies.

1 radiation imaging system 110 pixel array 112 pixel RC readout circuit 190 detector 130 controller 210 conversion element 270, 280 sample hold circuit 300 exposure controller 350 controller 400 radiation source

Claims (6)

a pixel array having a plurality of pixels including at least conversion elements for converting radiation into electric signals and sample-and-hold circuits for sampling and holding signals from the conversion elements a plurality of times;
a readout circuit for reading out signals from the pixel array;
an exposure detection unit that detects the start of radiation irradiation by the radiation generating device based on radiation emitted from the radiation generating device or information provided from the radiation generating device;
a timing control unit that determines a timing of sampling and holding a plurality of times in each of the plurality of pixels each time the radiation detection unit detects the start of radiation irradiation;
a drive start detection unit that detects the start of imaging drive from the radiation generator;
a reset control unit that determines reset timing in each of the plurality of conversion elements,
The timing of at least one sampling and holding out of the plurality of sampling and holding by the sample and hold circuit is the timing in the radiation irradiation period,
The radiation imaging apparatus, wherein the reset control unit controls reset timing so as to reset the conversion element each time the start of imaging driving is detected by the drive start detection unit. 2. The radiation imaging apparatus according to claim 1, wherein the timing control unit determines the timing of the multiple sample-and-holds so as to obtain radiation images at a plurality of energies different from each other. each of the plurality of pixels further has a reset unit that resets the conversion element;
2. The radiation imaging apparatus according to claim 1, wherein the reset unit resets the conversion element according to the timing determined by the reset control unit. The drive start detection unit detects the start of drive based on information provided from the radiation generator, and the provided information is information permitting irradiation or in synchronization with information permitting irradiation. 2. The radiation imaging apparatus according to claim 1, wherein the information is generated information. The reset control unit adjusts the reset timing so that the reset unit resets the conversion element between detection of start of imaging drive by the drive start detection unit and detection of start of radiation irradiation by the exposure detection unit. 4. The radiographic imaging apparatus according to claim 3, wherein the radiation imaging apparatus controls. a pixel array having a plurality of pixels including at least a conversion element that converts radiation into an electrical signal and a sample-and-hold circuit that samples and holds a signal from the conversion element a plurality of times;
a readout circuit for reading out signals from the pixel array;
an exposure detection unit that detects the start of radiation irradiation by the radiation generating device based on radiation emitted from the radiation generating device or information provided from the radiation generating device;
a timing control unit that determines a timing of sampling and holding a plurality of times in each of the plurality of pixels each time the radiation detection unit detects the start of radiation irradiation;
a reset control unit that determines reset timing for each of the plurality of conversion elements;
with
The timing of at least one sampling and holding out of the plurality of sampling and holding by the sample and hold circuit is the timing in the radiation irradiation period,
The radiation imaging apparatus, wherein the reset control unit outputs information prompting the radiation generator to start radiation irradiation in synchronization with the timing of the reset.

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