JP2006319529A - Imaging apparatus, imaging system employing it and imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an imaging apparatus in which both the addition of pixels and the switching of sensitivity can be carried out. <P>SOLUTION: The imaging apparatus arranged with a plurality of pixels two-dimensionally comprises a means for switching a resolution, a means for forming a combination unit from a plurality of pixels, a means for determining the required sensitivity of each combination unit, and a means for switching the sensitivity of each combination unit based on the determination result of required sensitivity. Furthermore, a means for outputting information about the determination result of the required sensitivity of each combination unit is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image pickup apparatus, an image pickup system using the same, and an image pickup method, and more particularly to a large still image pickup apparatus, a medical image pickup system using the same, and an image pickup method.

≪Application field technology≫
In recent years, digitization has progressed in various fields of medicine.

  Also in the field of X-ray diagnosis, in order to digitize an image, a two-dimensional X-ray imaging apparatus that converts incident X-rays into visible light by a scintillator (phosphor) and further captures the visible light image with an image sensor. It has been developed.

  In the field of X-ray still images, for example, large plate still image imaging using 17-inch size (43 cm × 43 cm) amorphous silicon (a-Si) as a two-dimensional X-ray imaging device for mammography and chest imaging. A device (hereinafter referred to as a flat panel detector) is made.

  In the field of X-ray animation, incident X-rays are converted into scintillators (phosphors) and I.D. I. A two-dimensional digital X-ray fluoroscopic apparatus that converts visible light with a TV camera using a CCD type image pickup device and a system that replaces the TV camera with a flat panel detector. Has been devised.

  Furthermore, application of a flat panel detector to an X-ray CT imaging apparatus is considered.

  In addition, a turntable is provided that can rotate the subject in an upright or sitting position for lung cancer screening for a normal healthy person. I. There has been proposed an apparatus that performs imaging while rotating with respect to a two-dimensional X-ray imaging apparatus such as a TV camera or a flat panel detector.

≪Flat panel detector and imaging device technology≫
The following is proposed by the present applicant as a flat panel detector usable in such an apparatus.

Patent Document 1
A flat panel detector is realized by tiling a plurality of imaging devices.

  Examples of pixel addition include the following.

Patent Document 2
A configuration that suppresses sensitivity reduction and noise generation during the addition operation is disclosed.

  There are the following techniques for improving the sensitivity and dynamic range characteristics of an imaging apparatus used in such a flat panel detector.

Patent Document 3
(1) A configuration is disclosed in which a dynamic range is expanded by performing non-destructive reading a plurality of times during one exposure time and electrically synthesizing these signals.

  (2) There is no description of resolution.

Patent Document 4
A structure in which a two-dimensional image sensor is employed as a detector of an X-ray CT imaging system and a plurality of capacitors, a sensitivity switching controller, and an output determination unit are provided in a pixel is disclosed.

  FIG. 16 shows this conventional technique.

  Reference numeral 100 denotes a photodiode, 101 denotes a data collection circuit, 102 denotes an output determination unit, 103 denotes a self-scanning FET, 104 denotes an A / D converter, 105 denotes a shift register, 106 denotes a data processing device, 107 denotes a capacitor switching controller, 108 Is a capacitance control FET, 109 is a capacitance expansion capacitor, and 110 is a reset FET.

  A configuration in which these circuits are formed on the same silicon wafer is also disclosed.

  (1) The sensitivity is switched for each pixel.

  (2) Each pixel has a plurality of capacitors (capacitance expansion capacitor 109) and a changeover switch (capacitance control FET 108).

  (3) The output determination unit 102 and the capacitor switching controller 107 may be arranged for each pixel, or may be arranged in different areas collectively.

  (4) The capacitor control information may be output to the outside.

(5) There is no description of resolution switching.
Patent Document 5
A structure is disclosed in which sensitivity is switched by switching a capacitor in a pixel portion between still image shooting and fluoroscopic shooting having different required sensitivities.

  FIG. 17 shows this conventional technique.

  Pd1 to Pd128 are photoelectric conversion elements, E is a power supply, Cd1 to Cd128, Ce1 to Ce128 are capacitors, Sc1 to Sc128 are switches, CK3 is a control signal, A1 to A128 are each preamplifier, and F is a shift register.

  (1) Each pixel has a plurality of capacitors (Cd1 to Cd128, Ce1 to Ce128) and a changeover switch (Sc1 to Sc128).

  (2) These capacitors are switched between still image shooting and fluoroscopic shooting, and the dynamic range is switched.

  (3) Change the dynamic range for all pixels at once.

(4) There is no description of resolution switching.
JP 2002-90462 A JP 2003-9003 A Japanese Patent Laid-Open No. 02-107076 JP 07-280945 A JP 61-244176 A

  Low speed (up to several frames per second), low sensitivity (dose is as large as about 10 mR), high resolution (pixel pitch of about 160 μm), and high speed (about 200 frames per second) in X-ray CT imaging ), High sensitivity (dose is 1/10 to 1/100 that of still images), and low resolution (pixel pitch of about 0.5 mm).

  The specifications required for imaging devices used in such fields are quite different.

  Furthermore, the dynamic range may be insufficient in the conventional imaging device at the time of each shooting.

  Since X-rays are reduced to about 1/100 due to absorption by the human body, X-ray irradiation is about 100 times larger in the X-ray subject nesting portion than in other portions.

  In the nest-extracted portion, the upper dynamic range is insufficient, and when the human body has metal or the like, the lower dynamic range tends to be insufficient in this portion.

  On the other hand, there is a need for an imaging system that can be used for different applications with different dynamic ranges, sensitivities, and resolutions. Further, there is a need for an imaging system that can change the dynamic range in real time in each area according to each resolution during each shooting. .

  As described above, the conventional imaging apparatus and method cannot cope with an application in which the speed, sensitivity, and resolution change depending on the shooting conditions and the dynamic range is insufficient during shooting.

  In Patent Document 5, one imaging device can be used in regions having different dynamic ranges, but the sensitivity cannot be changed for each pixel or for each combination unit of a plurality of pixels in each region.

  In Patent Document 4, the sensitivity can be switched during shooting, but the resolution cannot be changed.

  In Patent Document 3, the sensitivity can be switched during shooting, but the resolution cannot be changed, and high-speed reading with a moving image or continuous still images is difficult with non-destructive reading multiple times.

  I want to achieve both pixel addition and sensitivity switching. It cannot be realized only by combining conventional techniques.

  Accordingly, an object of the present invention is to make it possible to achieve both pixel addition and sensitivity switching.

  The present invention provides, as means for solving the above problems, in an imaging device in which a plurality of pixels are arranged two-dimensionally, means for switching resolution, means for forming a combination unit from the plurality of pixels, and the combination Means for performing necessary sensitivity determination for each unit, and means for switching the sensitivity for each combination unit based on the required sensitivity determination result.

  According to the present invention, in an imaging apparatus that forms a two-dimensional imaging region by arranging a plurality of imaging elements, each of the imaging elements includes a plurality of pixels arranged in a two-dimensional manner, means for switching resolution, Means for forming a combination unit from the plurality of pixels, means for performing a required sensitivity determination for each combination unit, and means for switching the sensitivity for each combination unit based on the required sensitivity determination result in the imaging region. It is characterized by that.

  In the imaging method of the imaging apparatus having a plurality of pixels arranged two-dimensionally, the present invention performs resolution switching, forms a combination unit from the plurality of pixels, performs a necessary sensitivity determination for each combination unit, The sensitivity for each combination unit is switched based on the required sensitivity determination result.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which can be shared by the use from which a dynamic range, sensitivity, and resolution differ can be provided.

  Furthermore, the dynamic range can be changed according to the resolution at the time of each photographing, and the imaging device can be provided.

  By using a flat panel detector having such an imaging device, it is possible to provide an imaging system that can be used for different applications ranging in dynamic range, sensitivity, and resolution, from still images (low speed, low sensitivity, high resolution) to CT imaging (high speed, high sensitivity, low resolution). .

  Furthermore, the dynamic range can be changed according to the resolution at the time of each photographing, and the imaging system can be provided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
≪Assuming a general imaging device≫
FIG. 1 is a configuration diagram of a circuit for one pixel and a circuit common to a plurality of pixels showing a first embodiment of the imaging apparatus of the present invention. FIG. 2 is a circuit configuration diagram for four pixels showing the first embodiment of the imaging apparatus of the present invention. FIG. 3 is a block diagram of the sensitivity switching circuit, the comparator, and the control circuit. FIG. 4 is a configuration diagram of an imaging device configured by arranging the blocks of FIG. 3 in a matrix.

<< Use the configuration disclosed in FIG. 1 of Patent Document 1 for the place where the signal of each pixel is added >>
As shown in FIG. 1, at least one photodiode PD, a reset switch SW3, a sensitivity switching switch SW2, a sensitivity switching capacitor CS, and the cathode side of the photodiode PD are connected to the gate, and one pixel stores a signal accumulated in the photodiode PD. An amplifier AMP1 (MOS transistor) for amplification and output, a current source I1 connected to the drain side of the amplifier AMP1 (the amplifier AMP1 and the current source I1 constitute amplification means), and a sampling source connected to the drain side of the amplifier AMP1 Sample switch SW4, a capacitor CH that holds the signal transferred through the sample switch SW4, an amplifier AMP2 (MOS transistor) that further amplifies and outputs the signal accumulated in the capacitor CH, and a source side of the amplifier AMP2 A pixel selection switch connected to the Ji SW5, consists current source I2 which is connected to the drain side of the amplifier AMP2, the drain side of the amplifier AMP2 is connected to the vertical output line VL.

  Pixels arranged adjacent to each other in the length direction of the vertical output line VL are connected between the pixel capacitance CH and the gate of the amplifier AMP2 via addition switches SW10 and SW12.

  Further, the pixels arranged adjacent to each other in the direction perpendicular to the length direction of the vertical output line are connected via the addition switch SW11 between the pixel capacitance CH and the gate of the amplifier AMP2.

  By setting the ADD signal to the high level, all the addition switches SW10, 11, and 12 are turned on, and the connection point (between the capacitor CH and the gate of the amplifier AMP2) connected by the addition switches SW10, 11, and 12 is common. Connected to.

  In this embodiment, when pixel addition is performed, the output signals of all the pixels constituting the addition unit are used, so the S / N is better than when the resolution is reduced by thinning-out reading.

  In particular, when considering use in medicine, it is preferable because exposure can be minimized and sensitivity can be increased.

  FIG. 2 shows a case where the combination unit is configured by 2 × 2 pixels. The circuit of each pixel is arranged in a symmetrical mirror arrangement.

  This facilitates the layout of wiring and the like. A control circuit is disposed between the pixels. The layout of these circuits is shown in FIG.

  The sensitivity switching circuit and the comparator corresponding to each pixel are arranged in each pixel region (pixel cell), but can be optimally arranged in the region between the pixels including the control circuit.

  In this embodiment, the sensitivity switching circuit is composed of an OR circuit, the comparator is composed of a circuit using an operational amplifier, and the control circuit is composed of an OR circuit.

  Since this imaging device uses a general CMOS process, these circuits can be easily formed in the imaging device integrally with a pixel circuit such as a photodiode or a MOS transistor switch.

  Peripheral circuits such as a vertical shift register, a multiplexer, and a readout amplifier are formed on the outer peripheral portion of the imaging device by the same process (not shown).

  In the present embodiment, before performing addition, the output is monitored at each pixel to detect the necessary sensitivity.

  For this purpose, each pixel has a sensitivity switching circuit and a comparator, and the comparator monitors the drain side output of AMP1.

  As a result, the required sensitivity can be detected independently of the pixel addition.

  The sensitivity switching circuit turns on the sensitivity switching switch according to the signal from the comparator, and connects the sensitivity switching capacitor CS to the photodiode PD.

  The sensitivity switching capacitor CS is set to 10 times the capacitance FD (not shown) formed at the connection portion between the photodiode PD and the AMP1, and the high sensitivity mode and the low sensitivity mode are switched.

  Basically, the sensitivity is switched to a high sensitivity mode that is advantageous in terms of noise when the amount of light is small, and to a low sensitivity mode when the amount of light increases.

  This can be done for each pixel.

Sensitivity switching operation during normal mode shooting In the normal mode, the ADD signal is always at a low level, and the addition switches SW10, SW11, and SW12 are turned off.

  First, the reset signal (RES) is set to a high level, the reset switch SW3 is turned on, and all pixels are reset at once.

  By setting the reset signal (RES) to the low level, signal accumulation in the photodiode PD starts.

  During this time, charges are accumulated in the photodiode PD by irradiating light.

  For example, when VRES = 3 V, the potential at the point P decreases due to light irradiation.

  FIG. 5 shows an outline of the relationship between the potential at the point P and the amount of light for a certain accumulation time.

  As the amount of light increases, the potential at point P decreases along L1.

  The reference voltage set by the comparator of each pixel is Vref.

  When the potential at point P falls below Vref (point R), the output from the comparator becomes high level.

  This signal A is input to the control circuit.

  The control circuit is an OR circuit, and similar signals are input from 4 pixels of 2 × 2.

  When even one of the inputs from the four pixels becomes high level, the control circuit outputs a high level signal B to the sensitivity switching circuit of each pixel (determines and outputs the sensitivity in units of combinations of four pixels).

  The sensitivity switching circuit is an OR circuit, and receives a signal from the comparator and a signal from the control circuit.

  Accordingly, when a high level signal is received from the control circuit or its own comparator, a high level signal is output, thereby turning on the sensitivity changeover switch SW2 and automatically switching the sensitivity.

  A dotted line in the figure indicates a case where sensitivity switching is not performed. At this time, the photodiode is saturated with the light amount F1.

  It can be seen that even a larger amount of light is not saturated by sensitivity switching.

  Even in the normal mode, the sensitivity is 2 × 2 as a combination unit.

  In general, the sensitivity switching during shooting is often required when strong light enters a certain area of the imaging region as shown in FIG.

  In this case, it is not necessary to switch the sensitivity for each pixel (there is rarely abrupt change for each pixel), and the switching may be performed in a certain region.

  Therefore, in this embodiment, even when the image resolution is 1 × 1, the sensitivity is switched in units of 2 × 2 combination.

  The output from the sensitivity switching circuit is output to the sensitivity information output line SL.

Read Operation FIG. 7A is a timing chart showing a read operation in the normal mode of the imaging apparatus.

  Here, the operation for two lines is shown.

  First, the sample hold signal S / H is set to the high level, and a signal (amplified signal) corresponding to the charge accumulated in the photodiode PD is sampled by the sample switch SW4 and held (held) in the capacitor CH.

  Here, the sample and hold operation is performed for all the pixels at once.

  Next, selection signals SEL1, SEL2, SEL3,... Output from a shift register (not shown) serving as a vertical scanning circuit sequentially become high level, and pixels arranged in the horizontal direction to which the selection signals are applied. The signal held in the capacitor CH is amplified and output from the group to the vertical output line VL.

  The signals output to the vertical output lines are sequentially selected by the horizontal scanning circuit (MUX) and output as an output signal (OUT) while each selection signal is at a high level.

  At the same time, the switch SW6 is turned on, and the output from the sensitivity switching circuit is output as sensitivity information to the sensitivity information output line SL.

  The sensitivity is switched at 2 × 2, but the output is read for each column.

  In this embodiment, the sensitivity information is output to a dedicated output line, but each signal can also be output by adjusting the output timing by sharing the vertical output line VL.

  Thereby, since the number of wirings (wiring length) can be reduced, manufacturing defects related to wiring can be reduced and yield can be improved.

In addition mode shooting Sensitivity switching operation First, the reset signal (RES) is set to high level, the reset switch SW3 is turned on, and all the pixels are reset at once.

  By setting the reset signal (RES) to the low level, signal accumulation in the photodiode PD starts.

  The addition in the present embodiment is performed after the signal is sampled and held as will be described later, so that signal accumulation is performed independently for each pixel.

  That is, the addition operation and the sensitivity switching operation can be performed as separate operations.

  According to the present embodiment, a combination for switching sensitivity can be selected separately from selection of resolution.

  The sensitivity switching operation in the addition mode is the same as in the normal mode.

  By irradiating light during the accumulation time, charges are accumulated in the photodiode PD.

  When the potential at the point P is lower than Vref, the output from the comparator becomes high level.

  This signal is input to the control circuit.

  The control circuit is an OR circuit, and similar signals are input from 4 pixels of 2 × 2.

  When one of the inputs from the four pixels becomes high level, the control circuit outputs a high level signal to the sensitivity switching circuit of each pixel (determines and outputs the sensitivity in units of combination of four pixels).

  The sensitivity switching circuit is an OR circuit, and receives a signal from the comparator and a signal from the control circuit.

  Therefore, when a high level signal is received from the control circuit or its own comparator, a high level signal is output, whereby the sensitivity changeover switch SW2 is turned on and the sensitivity in 2 × 2 combination units is automatically set. Switch.

  As for sensitivity, 2 × 2 is used as a combination unit.

  The required sensitivity is detected as a single-pixel comparator so that it can be correctly detected even if there is a variation in the comparator.

  The output from the sensitivity switching circuit is output to the sensitivity information output line SL.

Read Operation FIG. 7B is a timing chart showing a read operation in the addition mode of the imaging apparatus.

  First, the sample hold signal S / H is set to the high level, a signal (amplified signal) corresponding to the charge accumulated in the photodiode PD is sampled by the sample switch SW4, and held (held) in the capacitor CH.

  Here, the sample and hold operation is performed collectively for all pixels.

  Next, the ADD signal is set to a high level, and the addition switches SW10, SW11, and SW12 are turned on.

  Then, the potential of the capacitance CH of each pixel becomes an average potential of the potential of the capacitance CH of the four pixels before addition in units of four pixels.

  Next, the selection signals SEL1, SEL3, SEL5,. The signal held in the capacitor CH is amplified and output to the output line.

  At this time, since the potential of the capacitor CH is the same in units of four pixels, it is not necessary to set the selection signals SEL2, SEL4, SEL6,.

  The signal output to each vertical output line is selected by skipping one by the horizontal scanning circuit (MUX) while each selection signal is at a high level, and an average output of four pixels is output as an output signal (OUT). The

  In the normal mode shown in FIG. 7A, the horizontal scanning circuit (MUX) outputs the output of all pixels, whereas in the addition mode shown in FIG. 7B, the output corresponding to 1/4 of all the pixels. Only one quarter of the time is required.

  That is, the frame rate can be increased by about 4 times.

  Even if the capacitance CH is increased, the potential does not decrease because the amplifier AMP2 outputs a voltage.

  Furthermore, the potential does not decrease even if the addition switch or the wiring has a stray capacitance.

  In addition, since the capacitance CH can be increased, even if there is a leakage current in the addition switch or the wiring, the sensitivity is not lowered, and the noise is not increased.

  In this case, the effect is enhanced if the capacitance CH is larger than the capacitance of the photodiode PD.

  In the present embodiment, the amplifiers AMP1 and AMP2 and the current sources I1 and I2, which are amplification means, constitute a source follower circuit, and amplify the charge although the voltage is not amplified.

  Of course, a type that amplifies the voltage may be used.

  Sensitivity can be switched in real time corresponding to 1 × 1 normal mode and 2 × 2 addition mode.

  Sensitivity switching can be performed according to the normal mode and the addition mode by using a sensitivity switching circuit and a comparator corresponding to each pixel and a control circuit for controlling them.

  Even if one of the pixels constituting the combination unit exceeds the threshold value by the comparator, it operates on the sensitivity switching circuit of the other constituent pixels, and the sensitivities of all the constituent pixels are switched.

  Therefore, the sensitivity can be switched regardless of the detection variation of the comparator.

  Although the SW2 group that switches the sensitivity every 2 × 2 is shown, the combination unit is not limited to this.

  As described above, the sensitivity may be set in a larger combination unit than the resolution.

  In this embodiment, since the S / H (sample and hold) circuit is included in one pixel, the detection light can be accumulated at the same timing as all the pixels in any row of pixels in one imaging apparatus. An image is not distorted in one image pickup device, and an image is not discontinuous between adjacent image pickup devices in a large sensor panel in which a large number of image pickup devices are bonded together.

  Although the two-stage switching between the high sensitivity mode and the low sensitivity mode is shown, the level of sensitivity switching can be set as appropriate, and a sensitivity switching circuit, a comparator, and a control circuit corresponding to the switching can be prepared.

  In this embodiment, the simplest combination of 2 × 2 pixel addition and sensitivity is assumed, and the control circuit is one OR circuit. However, this control circuit is more general n × m (n and m are A circuit corresponding to a combination unit of 1 or more suitable integers) can be obtained.

(Second Embodiment)
FIG. 8 is a configuration diagram of a circuit for one pixel and a circuit common to a plurality of pixels, showing a second embodiment of the imaging apparatus of the present invention.

  In the present embodiment, the configuration of the control circuit is different from that of the first embodiment. Other circuits are common.

  An AND circuit is added to the control circuit of this embodiment, and an ADD signal and a signal from the OR circuit are input.

  With this AND circuit, the sensitivity can be switched for each pixel or for each 2 × 2 combination unit using the ADD signal.

Sensitivity switching operation during normal mode shooting In the normal mode, the ADD signal is always at a low level, and the addition switches SW10, SW11, and SW12 are turned off.

  As the amount of light increases, the potential at point P in a certain pixel decreases. The reference voltage set by the comparator of each pixel is Vref.

  When the potential at the point P is lower than Vref, the output from the comparator becomes high level.

  Although the signal A is input to the control circuit, the output signal from the control circuit is not input to the sensitivity switching circuit because the ADD signal is at a low level.

  On the other hand, the sensitivity switching circuit is an OR circuit, and receives a signal from the comparator and a signal from the control circuit.

  Therefore, when a high level signal is received from the comparator, a high level signal is output, whereby the sensitivity changeover switch SW2 is turned on, and the sensitivity of only that pixel is automatically switched.

  In the present embodiment, the sensitivity is changed for each pixel in the normal mode.

  The unit of resolution and the combination unit of sensitivity switching are the same.

  Also in this embodiment, the sensitivity information is output to the dedicated output line, but each signal can be output by adjusting the output timing by sharing the vertical output line VL.

  As a result, the number of wirings (wiring length) can be reduced, so that manufacturing defects related to wiring can be reduced and yield can be improved.

In addition mode photographing Sensitivity switching operation In the addition mode in this embodiment, the ADD signal is first set to the high level, and the addition switches SW10, SW11, and SW12 are turned on. At this time, a high-level ADD signal is also input to the AND circuit of the control circuit, and the output of the control circuit is supplied to all pixels.

  By irradiating light during a predetermined accumulation time, charges are accumulated in the photodiode PD.

  When the potential at the point P is lower than Vref, the output from the comparator becomes high level.

  This signal is input to the control circuit. The control circuit is an OR circuit, and similar signals are input from 4 pixels of 2 × 2.

  When one of the inputs from the four pixels becomes high level, the control circuit outputs a high level signal to the sensitivity switching circuit of each pixel (determines and outputs the sensitivity in units of combination of four pixels).

  The sensitivity switching circuit is an OR circuit, and receives a signal from the comparator and a signal from the control circuit.

  Therefore, when a high level signal is received from the control circuit or its own comparator, a high level signal is output, whereby the sensitivity changeover switch SW2 is turned on and the sensitivity in 2 × 2 combination units is automatically set. Switch.

  As for sensitivity, 2 × 2 is used as a combination unit.

  The required sensitivity is detected as a single-pixel comparator so that it can be correctly detected even if there is a variation in the comparator.

  The output from the sensitivity switching circuit is output to the sensitivity information output line SL.

  Sensitivity can be switched in real time corresponding to 1 × 1 normal mode and 2 × 2 addition mode.

  Sensitivity switching can be performed according to the normal mode and the addition mode by using a sensitivity switching circuit and a comparator corresponding to each pixel and a control circuit for controlling them.

  Even if one of the pixels constituting the combination unit exceeds the threshold value by the comparator, it operates on the sensitivity switching circuit of the other constituent pixels, and the sensitivities of all the constituent pixels are switched. Therefore, the sensitivity can be switched regardless of the detection variation of the comparator.

  The unit of resolution and the combination unit of sensitivity switching can be made the same.

  Although the SW2 group that switches the sensitivity every 2 × 2 is shown, the combination unit is not limited to this.

  Although the two-stage switching between the high sensitivity mode and the low sensitivity mode is shown, the level of sensitivity switching can be set as appropriate, and a sensitivity switching circuit, a comparator, and a control circuit corresponding to the switching can be prepared.

  In this embodiment, the simplest combination of 2 × 2 pixel addition and sensitivity is assumed, and the control circuit is one OR circuit. However, this control circuit is more general n × m (n and m are A circuit corresponding to a combination unit of 1 or more suitable integers) can be obtained.

(Third embodiment)
FIG. 9 shows a third embodiment of the imaging apparatus of the present invention.

  Among the circuits for one pixel, the photodiode PD, the all-pixel collective sensitivity changeover switch SWT, the sensitivity changeover switch SW2, the low sensitivity mode capacitor CSL, and the sensitivity changeover capacitor CS are shown.

  The sensitivity switching capacity CS is 10 times that of the photodiode PD in the high sensitivity mode, and the low sensitivity mode capacity CS is 100 times that of the photodiode PD.

  The other circuits are basically the same as those in the first and second embodiments, and will not be described.

  In this embodiment, the collective sensitivity switching signal SL applied from the outside of the imaging apparatus is set to a high level to turn on the all-pixel collective sensitivity switching switch SWT.

  The entire imaging apparatus is set to a low sensitivity mode, which can be used in an application with a large light amount level.

  When used in an application with a very small light amount level, the collective sensitivity switching signal SL is set to a low level to turn off the all-pixel collective sensitivity switch SWT.

  Thereby, the entire imaging apparatus is set to the high sensitivity mode.

  At this time, the comparator and sensitivity switching circuit for each pixel work, whereby the sensitivity switching capacitor CS is connected to the photodiode for each appropriate combination unit, and the sensitivity is switched.

  The sensitivity switching capacitor CS is in parallel with the low sensitivity mode capacitor CSL and has a capacity of 1/10, and the effect of sensitivity switching is small in the low sensitivity mode.

  Therefore, a second sensitivity switching capacitor and a second sensitivity switching switch having a capacity 1000 times the capacitance of the photodiode PD in the high sensitivity mode are added to the low sensitivity mode capacitor, and this is used as a sensitivity switching circuit. You may make it control by.

(Fourth embodiment)
FIG. 10 shows four pixels of the image pickup apparatus according to the fourth embodiment of the image pickup apparatus of the present invention. The basic pixel circuit is the same as that in the first embodiment.

  In the present embodiment, the required sensitivity is detected at the Q point where 2 × 2 4-pixel addition is performed.

  The control circuit is an OR circuit in which the output from the comparator and the collective sensitivity switching signal SL are input and the output is connected to the sensitivity switching switch of each pixel.

  The collective sensitivity switching signal SL is a signal applied from the outside of the imaging device.

  In normal mode, the sensitivity can be changed for all pixels at once.

  First, the ADD signal is always set to the low level.

  At this time, the comparator and the control circuit are reset (the reset circuit is not shown), and the output of the comparator is always at the low level.

  If the collective sensitivity switching signal SL is set to the low level, this signal is input to the control circuit, so that the output of the control circuit remains at the low level and all the pixels enter the high sensitivity mode.

  If the collective sensitivity switching signal SL is set to the high level, the output of the control circuit is set to the high level, and the sensitivity switching switches of all the pixels are turned on.

  Thus, the low sensitivity mode is set. Since the sensitivity for each pixel and each combination unit cannot be automatically changed in the normal mode, the normal mode of the present embodiment is a case where the sensitivity of the imaging device is totally changed in a scene where the light amount is totally different. Used for.

  In the addition mode, the low sensitivity mode is selected at once, or the high sensitivity mode automatically changes to the low sensitivity mode for each pixel addition unit (the sensitivity combination unit and the pixel addition unit are the same). .

  First, the ADD signal is always set to the high level. As a result, the outputs from the hold capacitors of the respective pixels are added at the Q point.

  When the collective sensitivity switching signal SL is set to a low level, this signal is input to the control circuit.

  The comparator is first reset (the reset circuit is not shown), and the output of the comparator becomes low level and is input to the control circuit.

  Therefore, the output of the control circuit is at a low level, and all the pixels are in the high sensitivity mode.

  By irradiating light during a predetermined accumulation time, charges are accumulated in the photodiode PD.

  At this time, the sample switch is turned on.

  As the potential at point P decreases, the potential at point Q also decreases. When the potential at point Q falls below Vref, the output from the comparator goes high.

  This signal is input to the control circuit, and its output becomes high level.

  As a result, the sensitivity changeover switch is turned on, and the four pixels are switched to the low sensitivity mode.

  During shooting in the high sensitivity mode, even if a high amount of light is incident, shooting can be performed without saturation.

  On the other hand, when the collective sensitivity switching signal SL is set to the high level, the output of the control circuit is always at the high level, and the sensitivity switching switches of all the pixels are turned on. Thus, the low sensitivity mode is set.

  Since a set of comparators and control circuits may be provided for each pixel addition unit, the entire circuit is simplified. The sensitivity switching circuit is integrated into the control circuit and simplified.

(Fifth embodiment)
≪Example applied to the flat panel detector of Patent Document 1 by the present applicant≫
<< As for the place where the signal of each pixel is added, the configuration disclosed in FIG.
FIG. 11 shows an image pickup apparatus according to a fifth embodiment of the image pickup apparatus of the present invention. FIG. 12 shows a case where a plurality of imaging devices are tiled to form a flat panel detector.

  Here, a scintillator is installed on a tiled image pickup device and is used for X-rays. FIG. 13 shows a cross section taken along the line A-A 'in FIG.

  In this embodiment, peripheral circuits (vertical shift register, horizontal shift register, multiplexer, output amplifier, etc.) of the imaging device, sensitivity switching circuit, comparator, and control circuit are arranged in the imaging region.

  Further, terminals and bumps for external connection are also arranged in the imaging area. As the sensitivity switching circuit, the comparator, and the control circuit, those shown in the first, second, third, and fourth embodiments can be used.

  By arranging peripheral circuits and functional circuits in the imaging region in this way, the entire surface of the imaging device can be made the imaging region.

  By tiling nine imaging devices, a high performance flat panel detector as shown in FIG. 12 (there is no defect due to connection of imaging devices and sensitivity switching can be set according to the application) can be realized. When one image pickup device is moved from an 8-inch wafer, a large flat panel detector of 40 cm × 40 cm can be realized.

(Sixth embodiment)
FIG. 14 shows a sixth embodiment of the present invention. This is a form in which a large flat panel detector according to the fifth embodiment is applied to a standing cone beam CT for still image shooting.

  Reference numeral 1 denotes an X-ray generator (X-ray source), 2 denotes an X-ray source power supply, X denotes irradiated continuous X-rays, 6 denotes a subject, 3 denotes an X-ray detection element, 4 denotes a rotating device (rotary base), 5 Is a rotary encoder, 7 is an X-ray flat panel detector, 8 is an imaging control device, and 9 is a display device.

  In the present embodiment, X-rays are used as radiation, but α rays, β rays, γ rays, and the like can also be used.

  The X-ray generator uses a general imaging device and is used in a continuous X-ray mode.

  The imaging control device only sets the tube voltage, tube current, and irradiation time and controls the start and stop of irradiation.

  The rotating device is a device that continuously rotates the rotating portion based on a rotation control signal from the imaging control device.

  A holding device (not shown) for holding the subject during rotation is installed in the rotating portion.

  Furthermore, a rotary encoder that measures the rotation angle of the rotation device and outputs the rotation angle to the imaging control device is provided.

  This is because a signal is generated every 0.36 degrees per projection when photographing 360 degrees per rotation with 1000 projections in full scan.

  The angle of rotation is measured and a signal for the angle is generated.

  If it is a rotation angle detection means, it will not be limited to the rotary encoder 5.

  With this signal, the accumulation time of the X-ray flat panel detector is controlled to acquire an image.

  FIG. 15 shows the system configuration of this embodiment.

  The imaging control device 8 includes a sensitivity information memory 14 that stores sensitivity information output from the flat panel detector 7 for X-rays, an image data memory 15 that stores projection image data, a correction data memory 16 that stores correction data, and an image processing unit. 17, an apparatus control unit 18, an accumulation time control unit 20, an accumulation time calculation counter 21, and a rotation device control unit 19. The X-ray flat panel detector 7 includes a sensitivity information reading unit 11, an A / D converter 12, and a driving unit 13.

  With this imaging system, shooting can be started quickly while the subject is in a standing position, replacement with the next subject can be completed in a short time, and the overall shooting time can be shortened.

  Furthermore, since imaging is performed at most by one rotation using cone beam X-rays, the system is suitable as a system suitable for examination such as reduction of subject exposure.

  In addition, since a gantry for rotating the X-ray source and the X-ray detector is not necessary, the positions of the X-ray source and the X-ray detector can be freely set, and the magnification rate and measurement site during measurement can be changed. be able to.

  Further, an X-ray source for general imaging can be used, and a gantry is not required, so that the cost of the system can be reduced.

  Furthermore, since the system configuration is simple, it is convenient for in-vehicle use.

  As a feature of the cone beam X-ray CT imaging apparatus, the detector only rotates on the rotation axis relative to the subject and does not move in the rotation axis direction.

  Thus, the entire region of interest of the subject can be captured, but using the large flat panel detector of the present invention, it is possible to acquire all projection image data for reconstructing all CT images with at most one rotation. it can.

  Furthermore, it is possible to perform still image shooting over a large area including the lung field as general imaging.

  The pixel pitch of the imaging device in this embodiment is set to 160 μm in consideration of still image shooting.

  At the time of still image shooting, the maximum is 6 images per second, and the X-ray dose is about 10 mR / image.

  On the other hand, at the time of X-ray CT imaging, the subject rotates once in 5 seconds and 1000 projection images are acquired, so the reading speed is 200 images per second.

  Further, the dose is about 1/100 of a still image per sheet, and is read at a pixel pitch of 0.64 mm by adding 4 × 4 pixels.

  By using the image pickup apparatus of the present invention, it is possible to perform shooting in the low sensitivity mode, high resolution, and low speed at the time of a still image, and to perform high sensitivity mode, low resolution, and high speed shooting at the time of CT imaging.

  Furthermore, the dynamic range may be insufficient during each shooting.

  Since X-rays are reduced to about 1/100 due to absorption by the human body, X-ray irradiation is about 100 times larger in the X-ray subject nesting portion than in other portions.

  The upper dynamic range is insufficient at the nest-extracted portion. If the human body has metal or the like, the lower dynamic range is insufficient in this portion.

  Even in such a case, since the sensitivity can be automatically changed according to the resolution, it is possible to prevent deterioration of image quality due to insufficient dynamic range.

  In particular, in the case of medical use, re-taking due to imaging failure is not preferable because of increased exposure. Therefore, the imaging system of this embodiment can prevent imaging failure due to sensitivity abnormality.

  Sensitivity information read from the flat panel detector 7 by the sensitivity information reading unit 11 is stored in the sensitivity information memory 14 and then used by the image processing unit 17 to correct the image data in accordance with the sensitivity.

  First, the output pixel data is corrected with sensitivity information.

  The ratio (capacity ratio) between the low sensitivity mode and the high sensitivity mode is k.

  When the output pixel value in the low sensitivity mode is n, correction is performed so that the actual pixel value is nxk.

  In the high sensitivity mode, the output pixel value is used as it is. This is performed for every correction unit by the sensitivity information map stored in the sensitivity information memory 14.

  Next, white correction data obtained in advance is corrected in the same manner to create white correction data. An image is formed by further correcting the pixel data after the sensitivity correction using the previously acquired FPN (fixed pattern noise) data and the white data after the sensitivity correction.

  Although FPN does not change with sensitivity, when it changes with sensitivity, sensitivity correction may be performed in the same manner as white correction data.

  According to the present embodiment, it is possible to realize an imaging system that is also used for different uses of dynamic range, sensitivity, and resolution.

  Furthermore, it is possible to realize an imaging system that can change the dynamic range in each area in real time according to the resolution at the time of each imaging.

  In this embodiment, a standing position is assumed, but a system that can also be used for fluoroscopic imaging can be realized by adopting a gantry method in which an X-ray and an imaging device rotate in a stand method or a C-arm method.

  The present invention can be used for an imaging system using an imaging device using radiation such as X-rays.

1 is a configuration diagram of a circuit for one pixel and a circuit common to a plurality of pixels showing a first embodiment of an imaging apparatus of the present invention. It is a circuit block diagram for 4 pixels which shows 1st Embodiment of the imaging device of this invention. It is a block diagram of a sensitivity switching circuit, a comparator, and a control circuit. It is a block diagram of the imaging device comprised by arranging the block of FIG. 3 in the matrix form. It is a graph which shows the outline of the relationship between the electric potential of P point, and the light quantity in a fixed accumulation time. It is a top view which shows the light irradiation state of an imaging region. 6 is a timing chart illustrating a reading operation in a normal mode and an addition mode of the imaging apparatus. FIG. 6 is a configuration diagram of a circuit for one pixel and a circuit common to a plurality of pixels showing a second embodiment of the imaging apparatus of the present invention. It is a circuit diagram which shows 3rd Embodiment of the imaging device of this invention. It is a circuit diagram which shows 4 pixels worth of the imaging device of 4th Embodiment of the imaging device of this invention. It is a top view which shows the imaging device of 5th Embodiment of the imaging device of this invention. FIG. 12 is a plan view showing a case where the imaging device of FIG. 11 is tiled to form a flat panel detector. It is sectional drawing which shows the cross section of A-A 'in FIG. It is a perspective view which shows the 6th Embodiment of this invention. It is a block diagram which shows the system configuration | structure of 6th Embodiment of this invention. It is a block diagram which shows the structure of a prior art. It is a circuit diagram which shows the circuit of a prior art.

Explanation of symbols

PD Photodiode CS Sensitivity switching capacitor VL Vertical output line CH Capacitance SW2 Sensitivity switching switch SW4 Sample switch for sampling SW5 Switch for pixel selection AMP1 Amplifier (MOS transistor)
AMP2 amplifier (MOS transistor)
I1 current source I2 current source

Claims (16)

In an imaging device in which a plurality of pixels are arranged two-dimensionally,
Means for switching the resolution;
Means for forming a combination unit from the plurality of pixels;
Means for determining the required sensitivity for each combination unit;
Based on the required sensitivity determination result, means for switching the sensitivity for each combination unit,
An imaging apparatus comprising: 2. The imaging apparatus according to claim 1, further comprising means for outputting necessary sensitivity determination result information for each combination unit. The means for switching the resolution, the means for forming a combination unit from the plurality of pixels, the means for determining the necessary sensitivity for each combination unit, and the means for switching the sensitivity for each combination unit are: an imaging region in which the pixels are arranged The image pickup apparatus according to claim 1, wherein the image pickup apparatus is disposed inside the image pickup apparatus. 4. The imaging according to claim 3, wherein the means for determining the required sensitivity for each combination unit performs sensitivity determination for each combination unit based on a required sensitivity determination result of at least one pixel in the combination unit. apparatus. The means for determining the required sensitivity for each combination unit performs the required sensitivity determination based on the output for each combination unit, and performs the required sensitivity determination for each combination unit based on the required sensitivity determination result for each combination unit. The imaging apparatus according to claim 3. 6. The image pickup apparatus according to claim 4, wherein means for determining a necessary sensitivity for each combination unit and means for performing sensitivity switching are provided for each combination unit. Each pixel has a photoelectric conversion unit,
Means for switching sensitivity for each combination unit, a plurality of signal storage capacitors connected to the photoelectric conversion unit corresponding to a plurality of sensitivity,
6. The imaging apparatus according to claim 4, further comprising: a switch that switches the signal storage means based on a required sensitivity determination result for each combination unit, and means for controlling the switch. In an imaging apparatus that forms a two-dimensional imaging region by arranging a plurality of imaging elements,
Each of the imaging elements includes a plurality of pixels arranged two-dimensionally,
Means for switching resolution;
Means for forming a combination unit from the plurality of pixels;
Means for determining the required sensitivity for each combination unit;
An imaging apparatus comprising: means for switching sensitivity for each combination unit based on the required sensitivity determination result in the imaging region. 9. The imaging apparatus according to claim 8, further comprising means for outputting necessary sensitivity determination result information for each combination unit. The imaging apparatus according to claim 8, further comprising a scintillator plate that converts radiation into light. An imaging device according to claim 10;
A radiation source for irradiating the subject with radiation;
Means for storing the necessary sensitivity determination result information;
Means for storing an image output signal from the imaging device;
An imaging system comprising: means for correcting the output signal based on necessary sensitivity information for each combination unit. In an imaging method of an imaging device having a plurality of pixels arranged two-dimensionally,
Change resolution,
Forming a combination unit from the plurality of pixels;
The necessary sensitivity is determined for each combination unit,
An imaging method, wherein the sensitivity for each combination unit is switched based on the required sensitivity determination result. Output an image signal according to the resolution,
13. The imaging method according to claim 12, wherein necessary sensitivity determination result information is output for each combination unit. 13. The imaging method according to claim 12, wherein the sensitivity for each combination unit is switched based on a required sensitivity determination result of at least one required sensitivity determination means in the combination unit. The imaging method according to claim 12, wherein necessary sensitivity determination is performed based on an output for each combination unit, and sensitivity for each combination unit is switched based on the required sensitivity determination result. The imaging method according to claim 12, wherein an image signal of the pixel is corrected based on necessary sensitivity determination result information for each combination unit.