JP2013012886A - Radiation imaging apparatus, method and radiation imaging system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation imaging apparatus for preventing a moving image photographing due to a frame rate request in which a desired number of nondestructive readings cannot be performed.
Radiation detection means for acquiring incident radiation by converting incident radiation into an electrical signal, acquisition means for acquiring a frame rate setting request when acquiring a radiation moving image by the radiation detection means, and Setting means for setting the number of non-destructive readings per unit frame by the radiation detection means, determination means for determining whether or not reading of the number of non-destructive readings is possible at the frame rate requested to be set, and the determination means Output means for outputting the determination result according to the above.
[Selection] Figure 7

Description

  The present invention relates to a radiation imaging apparatus that acquires a radiation imaging image from radiation transmitted through a subject.

  In recent years, in the field of digital radiographic imaging devices, instead of image intensifiers, large-area flats of equal-magnification optical systems using photoelectric conversion elements have been proposed to improve resolution, reduce volume, and suppress image distortion. Panel-type radiation sensors are widely used.

  Radiation imaging devices using photoelectric conversion elements include amorphous silicon type, CCD type, and CMOS type.

  An image sensor using an amorphous silicon semiconductor on a glass substrate is easy to create a large screen. However, on the other hand, amorphous silicon is difficult to finely process a semiconductor substrate on a glass substrate as compared with a single crystal silicon semiconductor substrate. As a result, the semiconductor characteristics are not sufficient for the operation such as an increase in the capacitance of the output signal line. The CCD image pickup device is completely depleted and has high sensitivity, but the number of transfer stages of charge transfer increases as a large screen image pickup device. In addition, the power consumption is 10 times larger than that of the CMOS type image sensor, which is not suitable for a large screen.

  Here, as a large-area flat panel sensor, a CMOS image sensor is used as a photoelectric conversion element, and a large size is obtained by tiling a rectangular semiconductor substrate obtained by cutting out a CMOS photoelectric conversion element from a silicon semiconductor wafer into a rectangular shape. A device realizing the area is disclosed in Patent Document 1.

  The CMOS type image pickup device can be read at higher speed than amorphous silicon by fine processing, and higher sensitivity can be obtained. Further, there is no problem in the number of transfer stages and power consumption of charge transfer as in a CCD type image sensor, and the area can be easily increased, and the advantage is high as a large area flat panel type sensor, particularly as a moving image imaging device. Are known.

JP 2002-344809

  A radiographic image captured by a radiographic apparatus generally includes random noise. However, in a radiation imaging apparatus using a CMOS image sensor, non-destructive readout can be performed multiple times by holding the charge of the CMOS image sensor after radiation imaging.

  Therefore, random noise in an image can be suppressed by performing non-destructive readout a plurality of times and obtaining an average value of a plurality of read radiographic images.

  In general, the greater the number of nondestructive readouts, the greater the effect of suppressing random noise. Therefore, the number of nondestructive readouts is determined according to the image quality of the radiation image to be obtained. However, when capturing a moving image, the time for performing non-destructive reading per unit frame is limited, and therefore, a desired number of non-destructive readings may not be performed. Therefore, the radiation imaging apparatus system must set various imaging parameters in consideration of the respective balances such as the frame rate and the number of nondestructive readouts.

  However, if the radiation imaging apparatus and the control apparatus are operating independently, a frame rate request that cannot perform a desired number of nondestructive readouts is made from the control apparatus to the radiation imaging apparatus. there is a possibility. In this case, a radiation moving image that does not satisfy the desired image quality is obtained, or frame dropping occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a radiation imaging apparatus that prevents moving image capturing in response to a frame rate request in which a desired number of non-destructive readouts cannot be performed.

  Radiation detection means for converting incident radiation into an electrical signal to acquire a radiation image, acquisition means for acquiring a frame rate setting request when acquiring a radiation moving image by the radiation detection means, and the radiation detection means Setting means for setting the number of non-destructive readings for each unit frame; determination means for determining whether or not the number of non-destructive readings can be read at the frame rate requested for setting; and a determination result by the determination means Output means for outputting.

  ADVANTAGE OF THE INVENTION According to this invention, the radiation imaging device which prevents the moving image imaging | photography by the frame rate request | requirement which cannot perform nondestructive reading of the desired frequency can be provided.

It is the figure which showed an example of the pixel circuit for 1 pixel. It is a figure which shows the timing chart which shows an example of the drive control at the time of video recording. It is a figure which shows typically an example of the internal structure of a CMOS rectangular semiconductor substrate. It is a typical block diagram which shows the whole large area flat panel type radiation moving image imaging device system. It is a figure which shows the time chart for reading the pixel data of the three tiled rectangular semiconductor substrates by one A / D. It is the circuit diagram and schematic block diagram of the pixel addition circuit in a CMOS type | mold rectangular semiconductor substrate. It is a processing flow which shows the process of the radiation imaging device 100 in this embodiment.

  Hereinafter, the configuration of the radiation imaging apparatus according to the present embodiment will be described with reference to the drawings.

  FIG. 1 shows an example of a pixel circuit for one pixel in a two-dimensional pixel circuit formed on a CMOS rectangular semiconductor substrate used for tiling.

  In FIG. 1, PD is a photodiode that performs photoelectric conversion. M2 is a reset MOS transistor (reset switch) for discharging charges accumulated in the floating diffusion, and Cfd is a capacitance of the floating diffusion (floating diffusion region) for accumulating charges.

  M1 is a sensitivity switching MOS transistor (sensitivity switching switch) for switching between the high dynamic range mode and the high sensitivity mode.

  C1 is a capacity for expanding the dynamic range. When the sensitivity changeover switch (M1) is turned on, charge can be accumulated. When the sensitivity changeover switch (M1) is turned on, the capacity of the floating node section is substantially increased and the sensitivity is lowered, but the dynamic range can be expanded. Therefore, for example, the sensitivity changeover switch (M1) is turned off during fluoroscopic photography that requires high sensitivity, and the sensitivity changeover switch (M1) is turned on during DSA photography that requires a high dynamic range. M4 is an amplification MOS transistor (pixel amplifier 1) that operates as a source follower. M3 is a selection MOS transistor (selection switch 1) for bringing the pixel amplifier 1 (M4) into an operating state.

  A clamp circuit that removes kTC noise generated in the photoelectric conversion unit is provided at the subsequent stage of the pixel amplifier (M4). Ccl is a clamp capacitor, and M5 is a clamp MOS transistor (clamp switch). M7 is an amplifying MOS transistor (pixel amplifier 2) that operates as a source follower. M6 is a selection MOS transistor (selection switch 2) for bringing the pixel amplifier (M7) into an operating state.

  Two sample and hold circuits are provided in the subsequent stage of the pixel amplifier 2 (M7). M8 is a sample and hold MOS transistor (sample and hold switch S) that constitutes a sample and hold circuit for storing optical signals. CS is an optical signal hold capacitor. M11 is a sample and hold MOS transistor (sample and hold switch N) that constitutes a sample and hold circuit for accumulating noise signals. CN is a noise signal hold capacitor. M10 is an optical signal amplification MOS transistor (pixel amplifier S) that operates as a source follower. M9 is an analog switch (transfer switch S) for outputting the optical signal amplified by the pixel amplifier S (M10) to the S signal output line. M13 is an amplifying MOS transistor (pixel amplifier N) for a noise signal that operates as a source follower. M12 is an analog switch (transfer switch N) for outputting the noise signal amplified by the pixel amplifier N (M13) to the N signal output line.

  The EN signal is a control signal that is connected to the gates of the selection switch 1 (M3) and the selection switch 2 (M6) and puts the pixel amplifier 1 (M4) and the pixel amplifier 2 (M7) into an operating state. When the EN signal is at a high level, the pixel amplifier 1 (M4) and the pixel amplifier 2 (M7) are simultaneously operated. The WIDE signal is connected to the gate of the sensitivity changeover switch (M1) and controls the changeover of sensitivity. When the WIDE signal is at a low level, the sensitivity selector switch is turned off and the high sensitivity mode is set. The PRES signal is a reset signal that turns on the reset switch (M2) to discharge the charge accumulated in the photodiode PD. The PCL signal controls the clamp switch (M5). When the PCL signal is at a high level, the clamp switch (M5) is turned on, and the clamp capacitor (Ccl) is set to the reference voltage VCL. The TS signal is an optical signal sample / hold control signal. When the TS signal is set to a high level and the sample / hold switch S (M8) is turned on, the optical signal is collectively transferred to the capacitor CS through the pixel amplifier 2 (M7). Next, the signal TS is set to the low level for all the images and the sample switch S (M8) is turned off, whereby the holding of the optical signal charge in the sample hold circuit is completed. The TN signal is a noise signal sample hold control signal. When the TN signal is set to a high level and the sample hold switch N (M11) is turned on, the noise signal is collectively transferred to the capacitor CN through the pixel amplifier 2 (M7). Next, the signal TN is set to the low level for all the images and the sample switch N (M11) is turned off, whereby the holding of the noise signal charge in the sample hold circuit is completed. After sample-holding the capacitors CS and CN, the sample-hold switch S (M8) and sample-hold switch N (M11) are turned off, and the capacitors CS and capacitor CN are disconnected from the previous storage circuit, so that they are sample-held again. It is possible to read out the optical signal accumulated up to 2 nondestructively.

  FIG. 2 is a timing chart showing an example of drive control during moving image shooting in the pixel circuit of FIG. The timing of the control signal until the charge is sampled and held in the optical signal hold capacitor CS and the noise signal hold capacitor CN in moving image shooting will be described below with reference to FIG.

  In the time chart of FIG. 2, when a shooting mode is set at (t50) and a shooting pulse is input, driving for shooting is started from (t51) using that as a trigger. From (t51) to (t56) is a reset drive R1 that performs reset and clamp.

  First, at (t51), the signal EN is set to a high level, and the pixel amplifier 1 (M4) and the pixel amplifier 2 (M7) are set in an operating state. Next, at (t52), the signal PRES is set to the high level, the photodiode PD is connected to the reference voltage, and resetting is performed. Thereafter, at (t54), the signal PRES is set to the low level to complete the reset, and the reset voltage is set on the pixel amplifier 1 (M4) side of the clamp capacitor (Ccl). Next, at (t53), the signal PCL is set to a high level to turn on the clamp switch (M5), and the reference voltage VCL is set on the pixel amplifier 2 (M7) side of the clamp capacitor (Ccl). Thereafter, the clamp switch (M5) is turned off at (t55), the electric charge according to the difference voltage between the reference voltage VCL and the reference voltage VRES is accumulated in the clamp capacitor (Ccl), and the clamping is finished. At (t56), the signal EN is set to the low level to end the reset driving R1, and from (t56), accumulation of the photoelectric conversion unit of the photodiode PD and the floating diffusion capacitor (Cfd) is started. In the time chart of FIG. 2, the accumulation time is controlled by performing this reset driving in a timely manner.

  The tiled CMOS image sensor collects all the pixels of each tiled image sensor at once in order to prevent image shift caused by temporal switching deviation between image sensors and scanning lines during moving image shooting. Thus, the accumulation start drive is performed at the same timing and the same period. Thereafter, the photoelectric charges generated in the photodiode PD are accumulated in the capacitor (Cfd).

  In the reset driving from (t51) to (t56), reset noise (kTC noise) is generated in the photoelectric conversion unit, but the reference voltage VCL is set on the pixel amplifier 2 (M7) side of the clamp capacitor (Ccl) of the clamp circuit. This eliminates the reset noise.

  Subsequently, when an imaging pulse is input, the sample driving S1 indicated by (t60) to (t70) is started using the imaging pulse as a trigger. At (t60), the signal EN is set to the high level and the selection switch 1 (M3) and the selection switch 2 (M6) are turned on, whereby the charge accumulated in the capacitor (Cfd) is subjected to charge / voltage conversion and operates as a source follower. The pixel amplifier 1 (M4) outputs a voltage to the clamp capacitor (Ccl). Although the output of the pixel amplifier 1 (M4) includes reset noise, since the pixel amplifier 2 (M7) side is set to the reference voltage VCL at the time of resetting by the clamp circuit, the pixel signal becomes an optical signal from which the reset noise has been removed. It is output to the amplifier 2 (M7). Next, the sample hold control signal TS is set to the high level at (t61), and the sample hold switch S (M8) is turned on, whereby the optical signal is transferred to the optical signal hold capacitor (CS) through the pixel amplifier 2 (M7). Is done. At (t63), the signal TS is set to the low level, and the sample hold switch S (M8) is turned off, whereby the photocharge signal is sampled and held in the optical signal hold capacitor (CS). Next, at (t64), the reset signal PRES is set to the high level, the reset switch (M2) is turned on, and the capacitor (Cfd) is reset to the reference voltage VRES. At (t66), the reset signal PRES is set to low level to complete the reset. At (t65), the signal PCL is set to the high level. In the clamp capacitor (Ccl), a charge in which reset noise is superimposed on the voltage difference between the voltage VCL and the voltage VRES is accumulated. Thereafter, the signal TN is set to the high level at (t67), and the sample hold switch N (M11) is turned on to transfer the noise signal when set to the reference voltage VCL to the noise signal hold capacitor (CN). Subsequently, at (t68), the signal TN is set to the low level and the sample hold switch N (M11) is turned off, whereby the noise signal is sampled and held in the noise signal hold capacitor (CN) of the noise signal. The signal EN and the signal PCL are set to low level at (t70) and (t69), and the sampling drive S1 is terminated. Sampling driving is performed for all pixels at once. Thereafter, the above operation is repeated according to the imaging pulse input timing.

  FIG. 3 is a diagram schematically showing an example of the internal structure of a CMOS rectangular semiconductor substrate.

  A rectangular semiconductor substrate 301 includes a chip select terminal CS, an optical signal output terminal S, a noise signal output terminal N, a vertical scanning circuit start signal VST, a vertical scanning circuit clock terminal CLKV, a horizontal scanning circuit start signal terminal HST, and a horizontal scanning circuit clock. A terminal CLKH is provided.

  Reference numeral 303 denotes a vertical scanning circuit that selects a horizontal pixel group and sequentially scans the pixel group in the vertical direction which is the sub-scanning direction in synchronization with the vertical scanning clock CLKV. Reference numeral 304 denotes a horizontal scanning circuit that sequentially selects the column signal lines of the horizontal pixel group that is the main scanning direction selected by the vertical scanning circuit one pixel at a time in synchronization with the horizontal scanning clock CLKH. Reference numeral 302 denotes the pixel circuit shown in FIG. 1. When the row signal line 305 which is the output line of the vertical and horizontal scanning circuit 303 is enabled, the optical signal voltage signal S sampled and held on the column signal lines 306 and 307, noise The voltage signal N is output. When the horizontal scanning circuit 304 sequentially selects the voltage signals output to the column signal lines 306 and 307, the voltage signals of the respective pixels are sequentially output to the analog output lines 308 and 309.

  As described above, in the rectangular semiconductor substrate, the pixel selection is performed by the switching operation by the XY address method using the vertical horizontal scanning circuit 303 and the horizontal scanning circuit 304, and the optical signal S and noise signal of each pixel amplified by the transistor are selected. The N voltage signal is output to the analog output terminals S and N through the column signal lines 306 and 307 and the analog voltage output lines 308 and 309.

  The terminal CS is a chip select signal input terminal. When the terminal CS is turned on, the optical voltage signal S and noise voltage signal N of the image sensor according to internal scanning are output from the analog output terminals S and N. The S signal output switching analog switch (transfer switch S), the N signal output switching analog switch (transfer switch N), the column signal lines 306 and 307, which are transmission paths for the optical voltage signal S and the noise voltage signal N, in the latter stage of the sample and hold circuit, Switching transistors that switch column signal lines according to the output of the horizontal scanning circuit 304 constitute a transmission circuit for readout scanning.

  Terminal CLKV is a clock for the vertical scanning circuit, and terminal VST is a start signal for the vertical scanning circuit. After the vertical scanning start signal VST is made high, the vertical scanning clock CLKV is inputted, so that V1, V2,... Vm and the row selection signal are sequentially switched to enable. When vertical scanning is started, the vertical scanning start signal VST is set to low. A terminal CLKH is a clock for the horizontal scanning circuit, and a terminal HST is a start signal for the horizontal scanning circuit. By making the horizontal scanning start signal HST high and inputting the horizontal scanning clock CLKH, H1, H2,... Hn and the column selection signal are sequentially enabled. When horizontal scanning is started, the horizontal scanning start signal HST is set to low.

  When the output of the row selection signal V1 of the vertical scanning circuit 303 is enabled, the pixel groups (1, 1) to (n, 1) in the horizontal row connected to the row selection signal V1 are selected, and each pixel in the horizontal row is respectively selected. S and N voltage signals are output to the column signal lines 306 and 307. By sequentially switching the column selection signal enable of the horizontal scanning circuit 304 to H1, H2,... Hn, the S and N voltage signals of the pixels in one horizontal row are sequentially analog via the analog signal output lines 308 and 309. Output to log output terminals S and N. By performing the same horizontal scanning up to the row selection signal Vm, pixel outputs of all pixels can be obtained.

  Next, the system of this embodiment will be described in detail with reference to the drawings.

  FIG. 4 is a schematic block diagram showing the entire large area flat panel radiation moving image capturing apparatus (X-ray moving image capturing apparatus) system (radiation image capturing system) in the present embodiment.

  Reference numeral 100 denotes a radiation imaging apparatus 100 that includes a radiation detection unit that detects radiation that has passed through a subject, and that converts incident radiation into an electrical signal to acquire a radiographic image. It is also possible to detect a radiation moving image by detecting radiation caused by continuous explosion.

  Reference numeral 101 denotes an image processing apparatus that performs predetermined image processing on an image acquired by the radiation imaging apparatus 100 and a system control apparatus 101 that controls radiation imaging.

  Reference numeral 102 denotes an image display apparatus 102 that displays an image acquired by the radiation imaging apparatus 100.

  Reference numeral 103 denotes an X-ray generator 103 that controls generation of X-rays.

  Reference numeral 104 denotes an X-ray tube 104 that irradiates the subject with X-rays.

  At the time of radiography, the radiation imaging apparatus 100 and the X-ray generation apparatus 103 are synchronously controlled by the image processing apparatus and system control apparatus 101. The radiation that has passed through the subject is converted into visible light by a scintillator (not shown), and is subjected to A / D conversion after photoelectric conversion in accordance with the amount of light. Then, frame image data corresponding to X-ray irradiation is transferred from the radiation imaging apparatus 100 to the image processing apparatus 101, and after image processing is performed, a radiation image is displayed on the image display apparatus 102 in real time.

  Reference numeral 109 denotes a photographing control unit 109. The imaging control unit 109 performs communication of control commands with the image processing apparatus 101, communication of synchronization signals, and transmission of image data to the image processing apparatus 101. The imaging control unit 109 also has a control function of a flat panel sensor, and is A / D converted from a plurality of A / D conversion devices in the radiation imaging apparatus 100, driving control of the flat panel sensor, imaging mode control, and radiation imaging apparatus 100. Digital image data for each block is combined with frame data and transferred to the image processing apparatus 101.

  Reference numeral 110 denotes a command control communication line 110. From the image processing apparatus 101, the setting of the imaging mode to the imaging control unit 109, the setting of various parameters, the imaging start setting, the imaging end setting, and the like are performed. Communicated.

  Reference numeral 111 denotes an image data interface 111. The captured image data is sent from the imaging control unit 109 to the image processing apparatus 101 via the data interface 111.

  Reference numeral 112 denotes a signal indicating from the imaging control unit 109 to the image processing apparatus 101 that the radiation imaging apparatus 100 is ready for imaging by a READY signal.

  Reference numeral 113 denotes an external synchronization signal, which is a signal that the image processing apparatus 101 receives the READY signal 112 of the imaging control unit 109 and notifies the imaging control unit 109 of the timing of X-ray exposure.

  An exposure permission signal 114 is transmitted from the image processing apparatus 101 to the X-ray generation apparatus 103 while the exposure permission signal 114 is enabled, and the X-rays received from the X-ray generation apparatus 104 are valid. X-rays are accumulated and X-ray images are formed.

  Reference numeral 105 denotes a flat panel sensor 105. The flat panel sensor 105 is configured by tiling a rectangular semiconductor substrate 106, which is a CMOS type image pickup element obtained by cutting a two-dimensional photoelectric conversion element into a strip shape from a silicon semiconductor wafer, in a matrix form of 12 columns × 2 rows. . A rectangular semiconductor substrate 106 cut into a strip shape having a width of about 20 mm and a length of about 140 mm is formed with 128 pixels in the horizontal direction and 896 pixels in the vertical direction at a pitch of 160 μm.

  The flat panel sensor 105 digitally converts the three tiled rectangular semiconductor substrates as a conversion area of one A / D converter 108. Here, the conversion clock of the A / D converter 108 for reading out the rectangular semiconductor substrate is set to 20 MHz. The A / D converter 108 performs one line A / D conversion on the rectangular semiconductor substrate in the horizontal direction while switching the chip select in one A / D conversion region composed of three rectangular semiconductor substrates. This conversion is sequentially repeated in the vertical direction from the outside toward the center.

  FIG. 5 is a diagram showing a time chart for reading pixel data of three tiled rectangular semiconductor substrates with one A / D.

  Signals CS0 to CS3 are chip select signals for controlling the output of analog signals from the rectangular semiconductor substrate. The numbers assigned to the analog output signals of the rectangular semiconductor substrate in FIG. 4 correspond one-to-one with the numbers of the chip select signal CS in the time chart. For example, while CS0 is “H”, the analog output of analog output signal number “0” on the rectangular semiconductor substrate is valid and is output to the amplifier 107 at the next stage. When CS1 is “H”, the analog output of the analog output signal number “1” becomes valid and is output to the amplifier 107 at the next stage. CS0 is connected to a rectangular semiconductor substrate with analog output signal number “0”, CS1 is connected to a rectangular semiconductor substrate with analog output signal number “1”, and CS2 is connected to a rectangular semiconductor substrate with analog output signal number “2”. , CS3 are connected to a rectangular semiconductor substrate of analog output signal number “3”.

  To read an image, first, the chip select C0 is selected.

  When the vertical scanning clock CLKV rises while the vertical scanning start signal VST is high, the row signal line V1 of the vertical scanning circuit of FIG. 3 is enabled, and the pixel group (1, 1) selected by the row signal V1 ( The output of (n, 1) becomes effective, and the pixel voltage signal of each pixel of (n, 1) is output from the pixel group (1, 1) to the column signal line.

  When the horizontal scanning clock CLKH rises while the horizontal scanning start signal HST is high, the column selection row signal H1 of the horizontal scanning circuit is enabled. In synchronization with the rising edge of CLKH, the column selection row signal of the horizontal scanning circuit is switched to H2,... Hn, pixels are sequentially selected from (1, 1) to (n, 1), and the chip select in the horizontal direction is selected. The scanning of the horizontal pixel group on the rectangular semiconductor substrate selected in C0 is completed. A / D conversion is performed in synchronization with CLKH. Next, the chip select is switched to C1, horizontal scanning is performed in the same manner, and C2 is also scanned in the same manner, thereby completing reading of the image group arranged in one horizontal line on the three rectangular semiconductor substrates.

  Thereafter, the horizontal scanning is similarly performed up to Vm while sequentially switching the row signal lines of the vertical scanning circuit according to CLKV, thereby completing the reading of all the pixels of the three rectangular semiconductor substrates.

  FIG. 6 is a circuit diagram and a schematic configuration diagram of a pixel addition circuit in a CMOS type rectangular semiconductor substrate. FIG. 6A is a circuit example in which a pixel addition circuit is inserted into a circuit obtained by simplifying the pixel circuit of FIG. 1 by two circuits. In the actual circuit, a pixel addition circuit is configured for each of the S signal and the N signal, but in FIG. 6, only one of the sample and hold circuits for the S signal and the N signal is shown for the sake of simplicity.

  Reference numerals 160 and 161 denote photodiodes of respective circuits. The photodiodes 160 and 161 correspond to the photodiode PD in FIG.

  Reference numerals 162, 163, 166, 167, 172, and 173 denote amplification MOS transistors (pixel amplifiers) that operate as source followers of the respective circuits. 162 and 163 correspond to the pixel amplifier 1 (M4) in FIG. 1, and 166 and 167 correspond to the pixel amplifier 2 (M7) in FIG. Reference numerals 172 and 173 correspond to the pixel amplifier S (M10) or the pixel amplifier N (M13) in FIG. Reference numerals 164 and 165 denote clamp capacitors of the respective circuits, which correspond to the clamp capacitors (Ccl) in FIG.

  Reference numerals 168 and 169 denote sample MOS transistors (sample switches) constituting a sample hold circuit for storing optical signals or noise signals of the respective circuits. Reference numerals 168 and 169 correspond to the sample hold switch S (M8) or the sample hold switch N (M11) in FIG.

  Reference numerals 170 and 171 denote optical signal or noise signal hold capacitors. The optical signal or noise signal hold capacitors 170 and 171 correspond to the optical signal hold capacitor (CS) or the noise signal hold capacitor (CN) of FIG. Reference numerals 150 and 151 denote addition MOS transistors (addition switches) constituting a pixel addition circuit.

  FIG. 6B shows a pixel addition circuit in which a pixel circuit for one pixel of a rectangular semiconductor substrate is represented by “□”.

  A portion surrounded by a dotted line in FIG. 6A and a portion surrounded by a dotted line in FIG. 6B indicate the same circuit portion. As shown in FIG. 6B, an optical signal or noise signal hold capacitor for each adjacent pixel is connected to perform pixel addition. As a result, the number of pixels to be scanned is reduced without discarding the pixel information, and signals can be read at a higher frame rate.

  In FIG. 6B, 2 × 2 pixel addition is performed when the signal ADD0 is at a high level and the signal ADD1 is at a low level. When the signal ADD0 is set to high level and the signal ADD1 is set to high level, 4 × 4 pixel addition is performed. This function is called an analog binning function because binning is performed in an analog manner.

  In addition, it has a function of digitally averaging the read images in the FPGA in the photographing unit. As the area of the addition average, for example, the addition average of 2 × 2 pixels and the addition average of 4 × 4 pixels are included. This function is called a digital binning function. In the digital binning function, it is known that the random noise amount is reduced to 1 / n by the averaging process of n × n pixels.

  In addition, since the CMOS sensor can perform nondestructive readout of pixels, it has a function of setting the number of nondestructive readouts according to an instruction from the system controller for the purpose of reducing random noise.

  The readout pixel value is added and averaged by the in-imaging unit FPGA, where the pixel value of the first non-destructive readout is PX1, and the pixel value of the n-th non-destructive readout is PXn. PX is

  It becomes. Theoretically, it is known that the amount of random noise is reduced to 1 / √n and the S / N ratio is improved by non-destructive reading n times. However, in reality, the occurrence of random noise is not completely random, and even if the number of nondestructive readings is increased more than a predetermined number, random noise may not be reduced. In particular, in the case of moving image shooting, it is often sufficient to perform non-destructive reading about 4 or 5 times within each unit frame. Therefore, in the case of moving image shooting, it is only necessary to provide an upper limit value for setting the number of nondestructive readouts and to set the number of nondestructive readouts within a range equal to or less than the upper limit value.

  It also has a function of reading a specific sensor area (area size setting) and outputting an image. For example, depending on the shooting target, there may be no problem even in a shooting area narrower than usual. Therefore, this function is used for the purpose of reducing the image size and shortening the image transfer time.

  FIG. 7 is a processing flow showing processing of the radiation imaging apparatus 100 in the present embodiment.

  (S1) In S1, the radiation imaging apparatus 100 is activated when the power is turned on.

  (S2) In S2, a command communication line is established between the radiation imaging apparatus 100 and the system control apparatus 101.

  The establishment of the communication line is performed according to the communication specification, and is, for example, a link establishment operation between the communication ICs. Further, in Ethernet (registered trademark) communication, a port link establishment operation is performed by designating an IP address.

  (S3) In S3, after the command communication line is established, the radiation imaging apparatus 100 receives an imaging unit state transition command from the system control apparatus 101.

  For the purpose of power saving, the radiation imaging apparatus 100 is in a sleep state in which the analog power supply is turned off, a ready state in which the analog power supply is turned on, and an exposure state in which imaging can be performed by repeated sensor reset driving. It has several photographing unit states such as a ready state. This is sequentially changed in accordance with a command from the system control apparatus 101.

  (S4) In S4, as in S3, the radiation imaging apparatus 100 receives an imaging mode setting command from the system control apparatus 101. The shooting mode setting parameter of the shooting mode setting command includes setting requests such as the number of non-destructive readings, analog binning setting, digital binning setting, gain setting, accumulation time setting, frame rate setting, and the like. The various settings may be changed according to the temperature in the radiation imaging apparatus 100. Note that the timing of the shooting mode setting command is an arbitrary or specified timing in the process of changing the shooting unit state.

  (S5) In S5, the radiation imaging apparatus 100 receives the imaging mode setting command and calculates the maximum frame rate (FPStmax) at which the image transfer system can operate.

  Specifically, the number of pixels in the horizontal direction of the photographing unit is n, the number of pixels in the vertical direction is m, the pixel transfer clock frequency is tk (MHz), and the analog binning setting is ab (ab = 2 for 2 × 2 binning, 4 × 4). Ab = 4) for binning, and digital binning setting db (db = 2 for 2 × 2 binning, ab = 4 for 4 × 4 binning),

  Calculate from In the image transfer operation, if there is an interval, FPStmax is calculated taking this into consideration. In addition, when an image processing system operation including memory access is affected, this is also taken into consideration.

  (S6) In S6, the maximum frame rate (FPSrmax) of the sensor readout system is calculated. First, the pixel readout time (rt) is calculated. The number of horizontal pixels of the sensor 1 chip is n1, the number of vertical pixels of the sensor 1 chip is m1, the number of non-destructive readings is ndr, and the analog binning setting is ab (ab = 2 for 2 × 2 binning, ab for 4 × 4 binning) = 4) When the sensor readout clock is sk (MHz)

  It becomes. Note that if there is an interval in the pixel readout time, rt is calculated by taking this into account.

  If the accumulation time setting is tt and the time for sampling driving is st, the maximum frame rate (FPSrmax) of the sensor readout system is

  It becomes. In the sensor readout system, if there is an interval, FPSrmax is calculated in consideration of the interval. In addition, when an image processing system operation including memory access is affected, this is also taken into consideration.

  (S7) In S7, the FPStmax calculated in S5 is compared with the FPSrmax calculated in S6. When FPStmax is larger, that is, when the frame rate is rate-determined by FPSrmax, the maximum frame rate FPSmax at which the photographing unit can operate is set to FPSrmax (S8). On the other hand, if FPSrmax is larger, the frame rate is rate-determined by FPStmax, so the maximum frame rate FPSmax at which the photographing unit can operate is set to FPStmax (S9).

  (S10) In S10, the calculated FPSmax is compared with the frame rate setting (FPSset) received from the shooting mode setting command. here,

  In other words, when the shooting operation is not possible with the frame rate setting specified by the control device (the desired number of non-destructive readouts cannot be performed within the readable time within the unit frame). Then, a determination NG notification is made (S12), and the process returns to receiving the shooting mode setting command.

  If the frame rate determination is OK (S11), since it is confirmed that the photographing at the designated frame rate is possible, the operation shifts to the photographing operation according to the photographing pulse input. An imaging operation is possible if the input period of the imaging pulse signal is equal to or less than the frame rate at which the determination is OK. The process of the above flow can be replaced with a general personal computer having a computer-readable recording medium in which various control programs (computers) are stored.

  With the above processing, it is possible to confirm in advance whether or not an imaging operation at a specified frame rate is possible, and it is possible to provide a highly reliable radiation imaging apparatus that does not cause a problem that a desired frame rate cannot be achieved.

  Further, in the operation determination, the parameters described in the embodiments are merely examples, and when there are other parameters that affect the frame rate, the determination notification can be performed in consideration of the parameters.

  Further, the imaging pulse signal at the time of the imaging operation may not be input from the control device but may be generated inside the imaging unit. In this case, after the determination is OK, a shooting operation is performed at the set frame rate by receiving a shooting start command. The determination result may be displayed on a display means (such as a monitor) by a display control means (not shown).

Claims (11)

Radiation detection means for converting incident radiation into an electrical signal and acquiring a radiation image;
An acquisition means for acquiring a frame rate setting request when acquiring a radiation moving image by the radiation detection means;
Setting means for setting the number of nondestructive readings per unit frame by the radiation detection means;
A determination means for determining whether or not reading of the number of nondestructive readings is possible at the setting requested frame rate;
A radiation imaging apparatus comprising: output means for outputting a determination result by the determination means.   The determination means includes at least a reading interval setting of the non-destructive reading, an analog binning setting, a digital binning setting, a gain setting, a reading area size setting, the accumulation time setting, and a temperature of the radiation detecting means. The radiation imaging apparatus according to claim 1, wherein it is determined whether reading of the number of nondestructive readings is possible based on any one of them.   The radiation imaging apparatus according to claim 1, wherein the setting unit acquires an upper limit value of the number of nondestructive readings, and sets the number of nondestructive readings below the upper limit value.   The radiation imaging apparatus according to claim 1, further comprising display control means for displaying a determination result by the determination means on a display means.   The acquisition unit acquires the frame rate setting request based on a maximum frame rate when the radiation moving image is transferred to the outside and a maximum frame rate of reading of the radiation detection unit. Item 2. The radiation imaging apparatus according to Item 1.   The radiation imaging apparatus according to claim 1, further comprising transfer means for transferring the radiation moving image to an external device. Radiation detection means for converting incident radiation into an electrical signal and acquiring a radiation image;
An acquisition means for acquiring a frame rate setting request when acquiring a radiation moving image by the radiation detection means;
Setting means for setting the number of nondestructive readings per unit frame by the radiation detection means;
Radiation imaging comprising: a determination unit that determines whether or not the number of nondestructive readings can be read at the frame rate requested to be set; and an output unit that outputs a determination result by the determination unit Equipment,
Transmission means for transmitting the frame rate setting request to the radiation imaging apparatus;
A radiation imaging system comprising: a control device having acquisition means for acquiring the radiation moving image from the radiation imaging device. A radiation detection step of causing the radiation detection means to convert the incident radiation into an electrical signal and acquiring a radiation image;
An acquisition step of acquiring a frame rate setting request when the acquisition unit acquires a radiation moving image by the radiation detection unit;
A setting step in which the setting means sets the number of non-destructive readouts per unit frame by the radiation detection means;
The output means comprises: a determination means for determining whether or not the nondestructive read count can be read at the frame rate requested for setting; and an output step for outputting a determination result by the determination means. A radiation imaging method. Computer
Radiation detection control means for converting incident radiation into an electrical signal and acquiring a radiation image by the radiation detection means;
An acquisition means for acquiring a frame rate setting request when acquiring a radiation moving image by the radiation detection means;
Setting means for setting the number of nondestructive readings per unit frame by the radiation detection means;
Radiation imaging comprising: a determination unit that determines whether or not the number of nondestructive readings can be read at the frame rate requested to be set; and an output unit that outputs a determination result by the determination unit A computer program for functioning as a device. Computer
Radiation detection control means for converting incident radiation into an electrical signal and acquiring a radiation image by the radiation detection means;
An acquisition means for acquiring a frame rate setting request when acquiring a radiation moving image by the radiation detection means;
Setting means for setting the number of nondestructive readings per unit frame by the radiation detection means;
Radiation imaging comprising: a determination unit that determines whether or not the number of nondestructive readings can be read at the frame rate requested to be set; and an output unit that outputs a determination result by the determination unit A computer-readable recording medium storing a computer program for functioning as a device. Radiation detection means for converting incident radiation into an electrical signal and acquiring a radiation image;
An acquisition means for acquiring a frame rate setting request when acquiring a radiation moving image by the radiation detection means;
An acquisition means for acquiring the number of nondestructive readings per unit frame by the radiation detection means determined by a request for an S / N ratio for the radiation moving image;
If the read time of the nondestructive read count is smaller than the readable time in the unit frame of the frame rate requested for the setting, it is determined that the read of the nondestructive read count is possible,
A determination unit that determines that reading of the nondestructive read count is not possible when the read time of the nondestructive read count is larger than a readable time in a unit frame of the frame rate requested to be set;
A radiation imaging apparatus comprising: output means for outputting a determination result by the determination means.

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