JP2020081664A - Radiation imaging device and method for controlling radiation imaging - Google Patents

Abstract

To provide an advantageous technique for reducing a fluctuation in time from start of radiation irradiation to sample hold of the signal.SOLUTION: Each of a plurality of pixels includes: a conversion element for converting the radiation into electrical signal; and a sample hold circuit which sample-holds the signal from the conversion element in a plurality of times according to a plurality of sample hold timing determined by a control part for determining the plurality of sample hold timing in each of the plurality of pixels every time a start of the irradiation of the radiation is detected in a radiation irradiation period. The sample hold circuit is reset during the period in which the conversion element is reset by a reset part before the start of radiation irradiation is detected.SELECTED DRAWING: Figure 6

Description

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

An energy subtraction method is an imaging method using a radiation imaging apparatus. The energy subtraction method is a method of obtaining a new image (for example, a bone image and a soft tissue image) by processing a plurality of images obtained by imaging a plurality of times by changing the energy of radiation applied to a subject. is there. The time interval for capturing a plurality of radiation images is, for example, several seconds or more in a radiation imaging apparatus for still image capturing, about 100 milliseconds in a normal radiation imaging apparatus for moving images, and even in a radiation imaging apparatus for high-speed moving images. It is about 10 milliseconds. When the subject moves during this time interval, artifacts due to the movement occur. Therefore, it has been difficult to obtain a radiation image of a subject such as a heart whose movement is fast by the energy subtraction method.

Patent Document 1 describes a system for performing dual energy imaging. In this system, the tube voltage of the X-ray source is set to the first kV value and then changed to the second kV value during imaging. Then, when the tube voltage has the first kV value, the first signal corresponding to the first sub-image is integrated, and after the integrated signal is transferred to the sample and hold node, the integration is reset. Then, when the tube voltage has the second kV value, the second signal corresponding to the second sub-image is integrated. As a result, reading of the integrated first signal and integration of the second signal are performed in parallel.

Japanese Patent Publication No. 2009-504221

When X-rays are radiated a plurality of times according to the method of Patent Document 1 to capture a moving image of a plurality of frames, the time from the exposure of the X-rays to the transfer of the signal to the sample and hold node is frame by frame. May be different. As a result, the energy and dose of the first sub-image are different from each other between frames, and the energy and dose of the second sub-image are different from each other between frames, which may reduce the accuracy of energy subtraction.

It is an object of the present invention to provide an advantageous technique for reducing the fluctuation in the time from the start of radiation irradiation to the sample and hold of signals.

One aspect of the present invention is a radiation imaging apparatus including a pixel array having a plurality of pixels and a readout circuit that reads out a signal from the pixel array, the radiation being emitted from a radiation source or provided from the radiation source. A detection unit that detects the start of radiation irradiation by the radiation source based on the information, a reset unit that resets the conversion element, and a plurality of times each time the detection unit detects the start of radiation irradiation. A control unit that determines the timing of a plurality of sample-and-holds in each pixel, and the timing of at least one sample-and-hold among the plurality of sample-and-holds is a timing in a radiation irradiation period. Each of the pixels includes a conversion element that converts radiation into an electric signal, and a sample hold circuit that samples and holds the signal from the conversion element a plurality of times in accordance with the plurality of sample and hold timings determined by the control unit. And the sample hold circuit is reset during a period in which the conversion unit is reset by the reset unit before detecting the start of irradiation of radiation.

According to the present invention, there is provided a technique capable of suitably controlling the sample-hold timing of a signal in radiographic image capturing by the energy subtraction method.

The figure which shows the structure of the radiation imaging device of 1st Embodiment of this invention. FIG. 3 is a diagram showing a configuration example of an imaging unit. The figure which shows the structural example of one pixel. The figure which shows operation|movement of the radiation imaging device in the expansion mode 1 (comparative example). The figure explaining the subject in expansion mode 1 (comparative example). The figure which shows operation|movement of the radiation imaging device in the expansion mode 2. The figure which shows the method 1 which a detection part detects the start of irradiation of the radiation from a radiation source. FIG. 6 is a diagram showing a method 2 in which the detection unit detects the start of irradiation of radiation from a radiation source. The figure which shows the structural example of the pixel of sample hold 3 system.

Hereinafter, the present invention will be described through exemplary embodiments thereof with reference to the accompanying drawings.

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

The radiation imaging apparatus 1 includes 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 (radiation source 400) and the imaging unit 100. sell. The control device 350 may include the signal processing unit 352 that processes the signal supplied from the imaging unit 100, as described above. All or part of the functions of the control device 350 may be incorporated in the imaging unit 100. Alternatively, some of the functions of the image capturing unit 100 may be incorporated in the control device 350. The control device 350 may be configured by a computer (processor) and a memory that stores a program provided to the computer. The signal processing unit 352 can be configured by a part of the program. Alternatively, the signal processing unit 352 may be configured by a computer (processor) and a memory that stores a program provided to the computer. All or part of the controller 350 may be configured by a digital signal processor (DSP) or a programmable logic array (PLA). The control device 350 and the signal processing unit 352 may be designed and manufactured by a logic synthesis tool based on a file describing the operation thereof.

The control device 350 transmits an exposure permission signal to the exposure control device 300 when permitting radiation (exposure) of radiation 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 multiple times. In this case, the control device 350 may transmit the exposure permission signal to the exposure control device 300 a plurality of times at a predetermined cycle, or every time the imaging unit 100 can image the next frame. The exposure permission signal may be transmitted to the exposure control device 300.

The radiation source 400 can emit radiation whose energy (wavelength) changes during continuous radiation periods (irradiation periods) of radiation. By using such radiation, a radiation image at each of a plurality of energies different from each other can be obtained, and these radiation images can be processed by the energy subtraction method to obtain one new radiation image.

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

Each of the plurality of pixels forming the pixel array 110 of the imaging unit 100 includes a conversion element that converts radiation into an electric signal (for example, electric charge), and a reset unit that resets the conversion element. Each pixel may be configured to directly convert radiation 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 for converting radiation into light can be used. The scintillator can be shared by a plurality of pixels forming the pixel array 110.

FIG. 2 shows a configuration example of the image pickup unit 100. The imaging unit 100 includes a pixel array 110 having a plurality of pixels 112 and a read circuit RC for reading signals from the plurality of pixels 112 of the pixel array 110. The plurality of pixels 112 may be arranged to form a plurality of rows and a plurality of columns. The read circuit RC may include a row selection circuit 120, a control unit 130, a buffer circuit 140, a column selection circuit 150, an amplification unit 160, an AD converter 170, and a detection unit 190.

The row selection circuit 120 selects a row of the pixel array 110. The row selection circuit 120 may be configured to select a row by driving the row control signal 122. The buffer circuit 140 buffers signals from the pixels 112 of the row selected by the row selection circuit 120 among the plurality of rows of the pixel array 110. The buffer circuit 140 buffers signals for a plurality of columns output to the plurality of column signal transmission lines 114 of the pixel array 110. The column signal transmission line 114 of each column includes a first signal line and a second column signal line that form a column signal line pair. A noise level of the pixel 112 (in a normal mode described later) or a radiation signal according to the radiation detected by the pixel 112 (in an expanded mode described later) can be output to the first column signal line. A radiation signal corresponding to the radiation detected by the pixel 112 may be output to the second column signal line 322. The buffer circuit 140 may include an amplifier circuit.

The column selection circuit 150 selects one row of signal pairs buffered by the buffer circuit 140 in a predetermined order. The amplification unit 160 amplifies the signal pair selected by the column selection circuit 150. Here, the amplification unit 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 amplification unit 160 and outputs a digital signal DOUT (radiation image signal).

The detection unit 190 detects the start of irradiation of radiation by the radiation source 400 based on the radiation emitted from the radiation source 400. The detection unit 190 detects the start of irradiation of radiation by the radiation source 400, for example, by detecting the radiation irradiated by the radiation source 400 onto the pixel array 110 based on the signal read from the pixel array 110 by the readout circuit RC. You can. When the detection unit 190 detects the start of radiation irradiation by the radiation source 400, the detection unit 190 generates a synchronization signal indicating the start and supplies the synchronization signal to the control unit 130.

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 unit), an amplification circuit 230, a sensitivity changing unit 240, a clamp circuit 260, sample hold circuits (holding units) 270 and 280, and an output circuit 310. The pixel 112 can have a normal mode and an extended mode as modes related to the imaging method. The extended mode is a mode for obtaining a radiation image by the energy subtraction method.

The conversion element 210 converts radiation into an electric 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 storage unit 211 that stores a converted electric signal (charge), that is, an electric signal according to radiation, and the charge storage unit 211 is connected to an input terminal of an amplifier circuit 230.

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

The charge storage unit 211 of the conversion element 210 and the gate of the MOS transistor 235 function as a charge-voltage conversion unit CVC that converts the charges stored in the charge storage unit 211 into a voltage. That is, the voltage V (=Q/C) determined by the charge Q accumulated in the charge accumulator 211 and the capacitance value C of the charge-voltage converter appears in the charge-voltage converter CVC. The charge-voltage converter CVC is connected to the reset potential VRES via the reset switch 220. When the reset signal PRES is activated, the reset switch 220 is turned on, and the potential of the charge-voltage converter is reset to the reset potential VRES. The reset switch 220 is a transistor having a first main electrode (drain) connected to the charge storage unit 211 of the conversion element 210, a second main electrode (source) to which a reset potential VRES is applied, and a control electrode (gate). Can be included. The transistor makes the first main electrode and the second main electrode conductive by applying an ON voltage to the control electrode and resets the charge storage unit 211 of the conversion element 210.

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

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

The output circuit 310 includes MOS transistors 311, 313 and row selection switches 312, 314. The MOS transistors 311 and 313 form a source follower circuit together with current sources (not shown) connected to the column signal lines 321 and 322, respectively.

The radiation signal, which is a signal output from the clamp circuit 260 according to the charge generated in the conversion element 210, can be sample-held (held) by the sample-hold circuit 280. The sample hold circuit 280 can include a switch 281 and a capacitor 282. The switch 281 is turned on when the row selection circuit 120 activates the sample hold signal TS. The radiation signal output from the clamp circuit 260 is written in the capacitor 282 via the switch 281 when the sample hold signal TS is activated.

In the normal mode, the reset switch 220 resets the potential of the charge-voltage converter CVC, and when the MOS transistor 262 is turned on, the clamp circuit 260 outputs the noise level (offset component) of the clamp circuit 260. The noise level of the clamp circuit 260 can be sampled and held (held) by the sample and hold circuit 270. The sample hold circuit 270 can include a switch 271 and a capacitor 272. The switch 271 is turned on when the row selection circuit 120 activates the sample hold signal TN. The noise level output from the clamp circuit 260 is written in the capacitor 272 via the switch 271 when the sample hold signal TN is activated. Further, in the extended mode, the sample hold circuit 270 can be used to hold the radiation signal which is the signal output from the clamp circuit 260 according 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 and hold circuits 270 and 280 are applied to the first column signal line 321 and the second column signal line 322 which form the column signal transmission path 114. Is output. Specifically, the 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. Further, the signal S corresponding to the signal held by the sample hold circuit 280 is output to the column signal line 322 via the MOS transistor 313 and the row selection switch 314.

The pixel 112 may include addition switches 301 and 302 for adding the signals of the plurality of pixels 112. In the addition mode, the addition mode signals ADDN and ADDS are activated. The activation of the addition mode signal ADDN connects the capacitors 272 of the plurality of pixels 112 to each other, and averages the signal (noise level or radiation signal). The activation of the addition mode signal ADDS connects the capacitors 282 of the plurality of pixels 112 to each other, and the radiation signals are averaged.

The pixel 112 may include the sensitivity changing unit 240. The sensitivity changing unit 240 can include switches 241, 242, capacitors 243, 244, and MOS transistors 245, 246. When the first change signal WIDE is activated, the switch 241 is turned on, and the capacitance value of the first additional capacitance 243 is added to the capacitance value of the charge-voltage converter CVC. This reduces the sensitivity of the pixel 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. The dynamic range can be expanded by adding a function of lowering the sensitivity of the pixel 112. When the first change signal WIDE is activated, the enable signal ENW may be activated. In this case, the MOS transistor 246 operates as a source follower. 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 may change due to charge redistribution. This can destroy some of the signal.

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

In the pixel 112 configured as shown in FIG. 3, signal destruction does not occur in the charge storage unit 211 or the like of the conversion element 210 during sample hold. That is, in the pixel 112 configured as shown in FIG. 3, the radiation signal can be read nondestructively. Such a configuration is advantageous for radiation imaging to which the energy subtraction method described below is applied.

The extended mode for obtaining a radiation image by the energy subtraction method will be described below. The extended mode may include the following four sub modes (extended modes 1 and 2). Here, extended mode 1 is a comparative example, and extended mode 2 is an improved example of comparative example 1.

FIG. 4 shows the operation of the radiation imaging apparatus 1 in the extended mode 1 (comparative example). In FIG. 4, the horizontal axis represents time. “Radiation energy” is energy of radiation emitted from the radiation source 400 and applied to the imaging unit 100. “PRES” is the reset signal RPES. “TS” is the sample hold signal TS. “DOUT” is the output of the AD converter 170. The synchronization of the radiation of the radiation from the radiation source 400 and the operation of the imaging unit 100 can be controlled by the control device 350 that generates the exposure permission signal. The operation control in the image pickup 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 the radiation 800 emitted from the radiation source 400 changes during the radiation emission period. This may be due to the rise and fall of the tube voltage of the radiation source 400 being dull. Therefore, it is considered that the radiation 800 includes radiation 801 in the rising period, radiation 802 in the stable period, and radiation 803 in the falling period. The energy E1 of the radiation 801, the energy E2 of the radiation 802, and the energy E3 of the radiation 803 may be different from each other. Utilizing this, a radiation image by the energy subtraction method can be obtained.

The control unit 130 sets the first period T1, the second period T2, and the second period T2 so that the following first period T1, second period T2, and third period T3 correspond to the rising period, the stable period, and the falling period, respectively. The third period T3 is defined. Each pixel 112 performs an operation of outputting a first signal according to the electric signal generated in the conversion element 210 in the first period T1. In addition, each pixel 112 performs an operation of outputting a second signal corresponding to the electric signal generated in the conversion element 210 in the first period T1 and the second period T2. In addition, each pixel 112 performs an operation of outputting a third signal according to an electric signal generated in 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 the first energy E1 is irradiated in the first period T1, radiation having the second energy E2 is irradiated in the second period T2, and radiation having the third energy E3 is irradiated in the third period T3. Is planned.

In the extended mode 1, the conversion element 210 of the pixel 112 is not reset (the reset signal PRES is not activated) in the irradiation period TT in which the radiation 800 is irradiated. Therefore, in the irradiation period TT in which the radiation 800 is irradiated, the electric signal (charge) according to the incident radiation continues to be accumulated in the conversion element 210. In the irradiation period TT in which the radiation 800 is irradiated, the conversion element 210 of the pixel 112 is not reset, so that the irradiation of the radiation that does not contribute to imaging can be reduced and a radiation image for the energy subtraction method can be obtained in a shorter time. It is advantageous.

Before the radiation 800 is emitted (irradiation to the imaging unit 100), the reset signal PRES is activated for a predetermined period, whereby the conversion element 210 is reset. 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 the radiation source 400 emits radiation in response to the exposure permission signal. It The sample hold signal TN is activated for a predetermined period after a predetermined period has elapsed since the reset signal PRES was activated for a predetermined period. As a result, the sample-hold circuit 270 samples and holds the signal (E1) corresponding to the electric signal generated by the conversion element 210 of the pixel 112 of the pixel array 110 in response to the irradiation of the radiation 801 of the energy E1.

The sample hold signal TS is activated for a predetermined period after a predetermined period has elapsed since the sample hold signal TN was activated for the predetermined period. As a result, the sample hold circuit 280 samples and holds 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 the irradiation of the radiation 801 of energy E1 and the radiation 802 of energy E2. It

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 read circuit RC as the first signal 805. In FIG. 4, “N” indicates a signal sample-held by the sample-hold circuit 270 and output to the first column signal line 321, and “S” is sample-held by the sample-hold circuit 280. The signals output to the column signal line 322 are shown.

Then, after a predetermined period has elapsed since the sample hold signal TS was activated for a predetermined period (after the irradiation of the radiation 803 with the energy E3 (irradiation of the radiation 800) is completed), the sample hold signal TS is again output for the predetermined period. Activated. As a result, the sample hold circuit 280 samples the signal (E1+E2+E3) corresponding to the electric signal generated by the conversion element 210 of the pixel 112 of the pixel array 110 in response to the irradiation of the radiations 801, 802, 803 of the energies E1, E2, E3. To be held.

Then, 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 read circuit RC as the second signal 806.

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

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

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 of energy E1, the dose e2 of the radiation 802 of energy E2, and the radiation 803 of energy E3. The 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) to obtain the irradiation amount e3 of the radiation 803 having the energy E3. Can be obtained. Further, the signal processing unit 352 calculates the difference ((E1+E2+E3)-(E2+E3)) between the second signal 806 (E2+E3) and the third signal (E1+E2+E3) to calculate the irradiation amount e1 of the radiation 801 having the energy E1. Obtainable. Further, the first signal 805 (E2) indicates the irradiation amount e2 of the radiation 802 having the 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 of the energy E1, the dose e2 of the radiation 802 of the energy E2, and the dose e3 of the radiation 803 of the energy E3. You can As the energy subtraction method, a method selected from various methods can be adopted. For example, the bone image and the soft tissue image can be obtained by calculating the difference between the radiation image of the first energy and the radiation image of the second energy. Further, the bone image and the soft tissue image may be generated by solving the non-linear simultaneous equations based on the radiation image of the first energy and the radiation image of the second energy. It is also possible to obtain a contrast agent image and a soft tissue image based on the first energy radiation image and the second energy radiation image. It is also possible to obtain an electron density image and an effective atomic number image based on the first energy radiation image and the second energy radiation image.

Problems in the extended mode 1 (comparative example) will be described with reference to FIG. As illustrated in FIG. 5, the time from when the control device 350 transmits the exposure permission signal to the exposure control device 300 to when the radiation source 400 starts emitting radiation (exposure) (this Is referred to as an “exposure delay”) can vary from frame to frame. In the example of FIG. 5, the exposure delay in the (n+1)th frame is larger than the exposure delay in the nth frame.

Explaining with reference to FIG. 4 that the exposure delay differs for each frame, the periods T1 and T2 from the start of the irradiation of the radiation 800 to the completion of the sample hold of the sample hold circuits 270 and 280 vary. Means Therefore, the energy and the irradiation amount (dose) of the radiation detected as the first signal 805, the second signal 806, and the third signal 807 may change between frames. This is because the energy of the radiation detected as the dose e1, the dose e2, and the dose e3 and the dose (dose) change from frame to frame, and the energy subtraction based on the dose e1, the dose e2, and the dose e3 It means that accuracy may be reduced. This can cause artifacts and/or flickering in the video.

FIG. 6 shows the operation of the radiation imaging apparatus 1 in the extended mode 2. Items that are not referred to as the extended mode 2 may be according to the extended mode 1. In order to solve the problem in the extended mode 1 (comparative example), the sample hold circuits 270 and 280 of the pixel 112 are sample-held in synchronization with the radiation actually emitted from the radiation source 400 instead of the exposure permission signal. Need to be done. Every time the synchronization signal 501 is supplied from the detection unit 190, the control unit 130 determines the timing of a plurality of sample-holds SH1, SH2, SH3 in each of the plurality of pixels 112 of the pixel array 110. In other words, the control unit 130 determines the timing of the sample-holds SH1, SH2, SH3 in each of the plurality of pixels 112 of the pixel array 110 each time the detection unit 190 detects the start of radiation irradiation. .. During the period between the first sample hold SH1 of the plurality of sample holds SH1, SH2, SH3 and the last sample hold SH3 of the plurality of sample holds SH1, SH2, SH3, the reset switch 220 causes the conversion element 210 to operate. Do not reset.

Here, in order to obtain a radiation image by the energy subtraction method, at least one sample-hold timing in the sample-hold timings SH1, SH2, and SH3 is a timing in the radiation irradiation period TT. In the first embodiment, the timings of the two sample-holds SH1, SH2 in the three sample-hold timings SH1, SH2, SH3 are the timings in the radiation irradiation period TT. The timings of the sample-and-holds SH1, SH2, SH3 can be determined in accordance with the elapsed times t1, t2, t3 from the synchronization signal, respectively. Therefore, the period from the start of radiation irradiation to the end of the sample hold SH1 is fixed between frames. In addition, the period from the start of irradiation of the radiation to the end of the sample hold SH2 is made constant between frames. In addition, the period from the start of radiation irradiation to the end of the sample hold SH3 is fixed between frames. As a result, it is possible to suppress a decrease in the accuracy of the energy subtraction, thereby reducing artifacts and/or blinking in the moving image.

A method of detecting the start of irradiation of radiation from the radiation source 400 in order to generate the synchronization signal 501 will be described. In order to detect the irradiation of the radiation, the control unit 130 performs reset RD at time t0 before the irradiation of the radiation 800 (irradiation to the imaging unit 100), and then performs the irradiation detection drive. In the present embodiment, the time at which the control unit 130 receives the exposure permission signal from the control device 350 is t0.

In the reset RD, the reset signal PRES is activated for a predetermined period in response to the reception of the exposure permission signal, whereby the conversion element 210 is reset. 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. Further, during this period, the sample hold signal TN and the sample hold signal TS are also activated for a predetermined period, so that the capacitance 272 of the sample hold circuit 270 and the capacitance 282 of the sample hold circuit 280 become reset levels. As a result, the sample hold circuit 270 and the sample hold circuit 280 are reset.

During the reset RD, if the first change signal WIDE and the second change signal WIDE2 of the sensitivity changing section 240 are activated for a predetermined period, the first additional capacitance 243 and the second additional capacitance 244 are also reset. Therefore, it is desirable to reset the additional capacitance as needed.

As described above, in the reset RD, the conversion element 210 is reset, the kTC noise of the clamp circuit 260 and the noise component due to the offset of the first amplification transistor are held in the clamp capacitor 261, and the capacitors 272 and 282 are It is initialized. In particular, the reset RD causes the capacitance 272 of the sample-hold circuit 270 and the capacitance 282 of the sample-hold circuit 280 to reach the reset level, so that it is possible to accurately detect a minute signal change in the exposure detection drive.

The exposure detection drive is performed after the reset RD. The exposure detection drive includes repetition of “sample and hold” by the sample and hold circuits 270 and 280 of the pixel 112 and “readout” of the signal from the pixel 112 by the read circuit RC. The exposure detection drive and the energy subtraction drive are controlled by the control unit 130. When the signal read from the pixel 112 by the read circuit RC exceeds the threshold value, the detection unit 190 determines that the radiation irradiation by the radiation source 400 has started, and generates the synchronization signal 501. In response to this, the control unit 130 starts the energy subtraction drive. The energy subtraction drive includes a drive in response to the synchronization signal 501 in FIG. 6, that is, a plurality of sample and hold circuits SH1, SH2, SH3 of the plurality of pixels 112 and a read operation by the read circuit RC. Here, the read operation by the read circuit RC includes an operation of outputting the first signal 805, the second signal 806, and the third signal 807.

It is preferable that the repetition of “sample hold” and “readout” in the exposure detection drive is performed at high speed (eg, μs order). This is because the timing at which the start of irradiation of radiation is detected is delayed by the time required for “sample hold” and “read”. For speeding up, the binning (addition number of pixels) at the time of reading may be changed during the exposure detection driving period. The read time can be shortened as the number of additions increases like binning 2×2, 4×4, 8×8,.... The image obtained by reading in the exposure detection drive is for determining the presence/absence of X-ray exposure for determining the start of radiation irradiation, and therefore it is not necessary to consider the resolution. Therefore, the resolution may be greatly reduced as in 32×32 binning to shorten the time required for reading. Further, the number of pixels 112 to be read may be limited.

When the number of pixels 112 to be read out is limited, the readout target for which the exposure detection drive is limited may be fixed or may be changed for each frame. For example, the read target for which the exposure detection drive is limited in the (n+1)th frame may be determined using the information of the nth frame (n is an integer of 1 or more). By using the information of the previous frame, it is possible to select a region where there is no subject or where the amount of transmitted radiation is expected to be large. As a result, it is possible to improve the detection accuracy of radiation irradiation start. In this case, the read target for which the exposure detection drive is limited in the first frame may be determined in advance before imaging, or there may be no subject or the amount of transmission of radiation based on the imaging information up to the previous time. Areas expected to be large may be selected.

In order to make it easier to detect a minute change in the signal, the sensitivity may be changed during the exposure detection drive period. For example, during the exposure detection drive period, the first change signal WIDE and the second change signal WIDE2 of the sensitivity changing section 240 may be deactivated to enter the high sensitivity mode.

When the detection unit 190 outputs the synchronization signal 501, the exposure detection operation shifts to the energy subtraction drive, so that the settings such as binning and gain are changed to the energy subtraction drive. At this time, since the radiation after the reset RD is sampled and held, there is no ineffective exposure.

FIG. 7 illustrates a method 1 in which the detection unit 190 detects the start of irradiation of radiation from the radiation source 400. When the control unit 130 receives the exposure permission signal from the control device 350, the control unit 130 resets RD, and the exposure detection drive is performed after the reset RD. When the radiation irradiation start is detected in the exposure detection drive, the control unit 130 is supplied with the synchronization signal 501 from the detection unit 190, and the energy subtraction drive is started.

As an example in which the start condition is different from the above-mentioned Method 1, Method 2 in which the detection unit 190 detects the start of irradiation of the radiation from the radiation source 400 is shown in FIG. When the control unit 130 receives from the control device 350 a signal indicating that the extended mode has been selected as the mode relating to the imaging method, the control unit 130 performs the reset RD, and the exposure detection drive is performed after the reset RD. When the radiation irradiation start is detected in the exposure detection drive, the control unit 130 is supplied with the synchronization signal 501 from the detection unit 190, and the energy subtraction drive is started. In the case of shooting a moving image, since the signal indicating that the extended mode has been selected as the mode relating to the imaging method cannot be used as the start condition in the second frame and thereafter, for example, reset RD is performed when the energy subtraction driving of the nth frame is completed. , The exposure detection drive of the (n+1)th frame is performed after the reset RD. When the start of radiation irradiation is detected in the exposure detection drive, the control unit 130 is supplied with the synchronization signal 501 of the (n+1)th frame from the detection unit 190, and the energy subtraction drive is performed. The operation after shifting to the exposure detection drive and the energy subtraction drive is the same as in the extended mode 2 described in FIG. 6 in both method 1 and method 2.

The start of the reset RD performed before the exposure detection driving is not limited to the method 1 and the method 2, and a signal that triggers the start of the reset RD may be separately provided. Further, the time from the end of the reset RD to the start of the exposure detection drive can be arbitrarily set.

It is considered that a dark current is accumulated in the conversion element 210 after the reset RD, but the influence of the signal due to the dark current is very small compared to the amount of signal actually detected from the emitted radiation, and can be ignored.

In the above description, the form in which three types of images having different energies are acquired has been described. However, the present invention is not limited to such a form. For example, as in the pixel configuration shown in FIG. 9, the number of sample and hold may be increased to three, and four types of images having different energies may be acquired. The sample hold circuit 290 in FIG. 9 can include a switch 291 and a capacitor 292. The switch 291 is turned on when the sample hold signal TS2 is activated by the row selection circuit 120. The radiation signal output from the clamp circuit 260 is written in the capacitor 292 via the switch 291 when the sample hold signal TS2 is activated. Then, the signal S2 corresponding to the signal held by the sample hold circuit 290 is output to the column signal line 323 via the MOS transistor 315 and the row selection switch 316. Alternatively, the number of times of sample hold may be reduced and two types of images having different energies may be acquired. Alternatively, two types of images having different energies may be obtained from three types of images having different energies.

In the above example, the rise and fall of the tube voltage of the radiation source 400 are blunted to obtain a plurality of images having different energies, and a new radiation image is formed based on the plurality of images. .. Images having different energies from each other can also be obtained by intentionally adjusting the waveform of the tube voltage of the radiation source 400. Alternatively, radiation having a wide energy band (wavelength band) may be emitted from the radiation source 400, and the energy of the radiation may be changed by switching a plurality of filters.

DESCRIPTION OF SYMBOLS 1 Radiation imaging device 110 Pixel array RC readout circuit 190 Detection part 130 Control part 210 Conversion element 270,280 Sample hold circuit

Claims (10)

A radiation imaging apparatus comprising: a pixel array having a plurality of pixels; and a readout circuit that reads out signals from the pixel array,
A detector that detects the start of irradiation of radiation by the radiation source based on the radiation emitted from the radiation source or information provided from the radiation source;
A reset unit for resetting the conversion element,
A control unit that determines the timing of a plurality of sample-and-holds in each of the plurality of pixels each time the start of radiation irradiation is detected by the detection unit;
The timing of at least one sample and hold among the plurality of sample and hold is a timing in a radiation irradiation period,
Each of the plurality of pixels includes a conversion element that converts radiation into an electrical signal, and a sample hold that samples and holds the signal from the conversion element a plurality of times in accordance with the plurality of sample hold timings determined by the control unit. And a circuit,
A radiation imaging apparatus, wherein a sample hold circuit is reset during a period in which the conversion element is reset by the reset unit before detecting the start of radiation irradiation. Further comprising a control device that transmits an exposure permission signal to an exposure control device that controls the radiation source,
The radiation source emits radiation according to the exposure permission signal,
The radiation imaging apparatus according to claim 1, wherein the control unit resets the sample hold circuit in response to reception of the exposure permission signal. As an imaging mode mode, there is an extended mode that is a mode for obtaining a radiation image by the energy subtraction method,
The radiation imaging apparatus according to claim 1, wherein the control unit resets the sample hold circuit in response to reception of a signal indicating that the extension mode is selected. The pixel is capable of detecting radiation with a first sensitivity or a second sensitivity higher than the first sensitivity,
The control unit sets the sensitivity of the pixel to the second sensitivity when the start of irradiation of radiation by the detection unit is detected. Radiation imaging device. In each of the plurality of pixels, the reset unit resets the conversion element during a period between the first sample hold of the plurality of sample and hold and the last sample hold of the plurality of sample and hold. do not do,
The radiation imaging apparatus according to any one of claims 1 to 4, wherein The control unit determines timings of the plurality of times of sample hold so that radiographic images at a plurality of different energies are obtained.
The radiation imaging apparatus according to claim 1, wherein the radiation imaging apparatus is a radiation imaging apparatus. The detection unit detects the start of irradiation of radiation by the radiation source based on an electric signal obtained from the pixel array,
The radiation imaging apparatus according to any one of claims 1 to 6, characterized in that. The control unit controls the plurality of pixels so that a period from the start of irradiation of radiation to the end of sample hold becomes constant.
The radiation imaging apparatus according to any one of claims 1 to 7, wherein the radiation imaging apparatus is a radiation imaging apparatus. In the plurality of frames, the control unit controls the plurality of pixels such that a period from the start of irradiation of the radiation to the end of sample hold is constant.
The radiation imaging apparatus according to claim 8, wherein the radiation imaging apparatus is a radiation imaging apparatus. A pixel array having a plurality of pixels, a readout circuit for reading a signal from the pixel array, and detection of start of irradiation of radiation by the radiation source based on radiation emitted from the radiation source or information provided from the radiation source. Detecting unit, a reset unit that resets the conversion element, and a control unit that determines the timing of a plurality of sample-holds in each of the plurality of pixels each time the start of irradiation of radiation is detected by the detecting unit. Each of the plurality of pixels includes a conversion element for converting radiation into an electric signal, and a signal from the conversion element for a plurality of times in accordance with the plurality of times of sample and hold determined by the control unit. A method of controlling a radiation imaging apparatus, comprising: a sample-hold circuit for sample-holding;
The timing of at least one sample and hold among the plurality of sample and hold is a timing in a radiation irradiation period,
A method of controlling a radiation imaging apparatus, wherein a sample hold circuit is reset during a period in which the conversion element is reset by the reset unit before detecting the start of radiation irradiation.

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