JP5311995B2 - Imaging device and method - Google Patents

Description

  The present invention relates to an imaging device using a solid-state imaging device.

  In recent years, a system for taking an X-ray image of a subject using an image sensor having a large area has been developed. This system has the practical advantage of being able to record images over a very wide range of radiation exposure compared to conventional X-ray photography systems using silver halide photography. That is, an X-ray having a very wide dynamic range is photoelectrically converted using a phosphor, read as an electric signal, and this electric signal is further converted into a digital signal. By processing this digital signal and outputting the radiation image as a visible image to a recording material such as a photographic photosensitive material or a display device such as a CRT, a good radiation image can be obtained even if the radiation exposure varies to some extent. It is done.

As the image sensor, a CCD image sensor, a MOS image sensor, a CMOS image sensor, or the like is used. For example, Patent Document 1 discloses a technique of a radiation imaging system that uses a CMOS image sensor and can perform nondestructive readout.
JP-A-2005-143802

  In a sensor having a binning readout mode capable of setting a plurality of resolutions, pixel information is read out using a specific output line in accordance with the binning mode. For this reason, if there is an abnormality in the corresponding output line circuit unit, the pixel information cannot be read out, and the average target area in the binning mode becomes an output abnormality and is treated as a defective area.

  The present invention provides an X-ray imaging apparatus capable of discriminating whether there is a malfunction in an output circuit system or a sample hold capacitor system with respect to a readout abnormal pixel area and selecting an output line based on the discrimination result. With the goal.

The imaging apparatus according to the present invention that achieves the above object can set a plurality of resolutions by a binning output that outputs a signal of a new pixel based on a signal of a plurality of pixels that converts the amount of X-rays into an image signal. With a good shooting method,
And units of the plurality of pixels to be grouped as a signal of the one pixel based on the resolution as one unity, and the output characteristics of the output circuit corresponding to each pixel constituting the imaging means, intends row the binning output based on selection means for selecting the output circuit, characterized in that it comprises a.

  According to the present invention, it is possible to provide an imaging apparatus capable of determining whether an output circuit system problem or a sample hold capacitor system problem is associated with a readout abnormal pixel area and selecting an output line based on the determination result. Is possible.

  Thereby, when reading pixels in the binning mode, it is possible to display an imaging unit with a small number of abnormal areas as a whole or an imaging unit with a small number of abnormal areas in a region of interest.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and the technical scope of the present invention is determined by the scope of claims, and is limited by the following individual embodiments. is not.

  FIG. 1 is a block diagram showing a schematic configuration of an X-ray imaging apparatus according to an embodiment of the present invention. Reference numeral 104 denotes an X-ray room, and 105 denotes an X-ray control room. The X-ray chamber 104 is provided with an X-ray generator 117 that generates X-rays. The X-ray generator 117 includes an X-ray tube 119 that generates X-rays, and a high-voltage generation source 118 that generates a voltage for driving the X-ray tube 119. The X-ray irradiation operation is executed by controlling the X-ray generator 117 from the imaging control unit 107 via the control board 121 based on an instruction from the operator 116. Similarly, the X-ray image acquisition operation is executed by controlling the X-ray imaging apparatus 101 from the imaging control unit 107 via the control board 121. As described above, the imaging control unit 107 executes the X-ray imaging operation while synchronizing the X-ray generator 117 and the X-ray imaging apparatus 101 based on an instruction from the operator 116. The operating power of the X-ray imaging apparatus 101 is supplied from the power supply unit 120 in the external unit 103.

  The system control unit 106 stores the image data obtained from the X-ray imaging apparatus 101 in the internal RAM 111. The stored image data is displayed on the display 115 or stored in the hard disk 109 or the external storage device 110 at the request of the operator 116 after appropriate processing such as offset correction and gain correction. .

  Reference numeral 313 denotes an imaging unit capable of setting a plurality of resolutions by binning output that outputs a plurality of pixels as one unit and outputs one group of image data as a pixel average. X-rays generated by the X-ray generator 117 are applied to the subject 50. An X-ray image of the subject 50 is captured by the imaging unit 313. In order to set the resolution, the imaging control unit 107 can set a unit of pixels (2 pixels × 2 pixels,..., N pixels × N pixels (N is a natural number of 2 or more)). In addition, the imaging control unit 107 can detect the output of the output circuit corresponding to each pixel constituting the imaging unit, and specify a pixel that indicates an output abnormal value. Based on the set pixel unit and the previous specific result, it is possible to select an output circuit for performing binning output so as to exclude the output of the pixel indicating the output abnormal value.

  Next, the internal structure of the X-ray imaging apparatus 101 will be described with reference to FIG. The X-ray imaging apparatus 101 is configured by combining a phosphor 501 and a photoelectric conversion element 502 as shown in FIG. In the phosphor 501, the host material of the phosphor is excited (absorbed) by high-energy X-rays, and fluorescence in the visible region is generated by the recombination energy. That is, the phosphor 501 converts X-rays into visible light. The fluorescence may be due to the host itself such as CaWo4 or CdWo4, or due to the emission center substance added to the host body such as CsI: Tl or ZnS: Ag. The photoelectric conversion element 502 uses a CMOS type image pickup element, and charges accumulated from all the elements at a common time can be read out with a high signal-to-noise ratio (S / N). An equivalent circuit diagram of one pixel of the photoelectric conversion element 502 is shown in FIG. A portion surrounded by a dotted line corresponds to one pixel. An actual photographing apparatus has a high-resolution matrix structure such as 2688 pixels × 2688 pixels.

  The signal charge photoelectrically converted by the photodiode (PD) is converted to a signal voltage by an FD (Floating Diffusion) amplifier and amplified. A clamp circuit is built in the next stage of the FD amplifier, and a circuit for independently sampling and holding the PD signal voltage S and the clamp voltage N is built in the next stage of the clamp circuit, and the output signals are two systems independent of analog S and N. A sample hold circuit is provided for each pixel. All the pixels are reset simultaneously by a reset circuit (not shown), and after exposure, the output of the FD amplifier is sampled and held at the same time, thereby enabling a collective electronic shutter. ing.

  The readout matrix circuit unit is controlled by a vertical scanning circuit that sequentially selects horizontal lines in the vertical direction and control signals VSR, HSR, and HSR-8BLK that are output from a horizontal scanning circuit that selects pixels in the horizontal direction. Then, the signal charges of all the pixels are sequentially read out by the readout matrix circuit unit.

  Subsequently, a binning readout mode of the X-ray imaging apparatus will be described. FIG. 4 is a conceptual diagram of the binning readout mode. A switching transistor is directly connected to the sample and hold capacitor, and after sample and hold, the sample and hold capacitors of adjacent pixels are short-circuited. This is expressed as a binning readout mode (pixel average). Since the charge of the sample and hold capacitor is distributed to the sample and hold capacitor to be averaged, the output level is averaged. Here, pixel averaging is performed independently for each of the S circuit and the N circuit. The pixel averaging transistor is turned on when the pixel average control line is “High (H)”.

  Depending on the pixel area where the pixel averaging is performed, the average of 4 pixels (2 pixels × 2 pixels), the average of 16 pixels (4 pixels × 4 pixels), and the average of 64 pixels (8 pixels × 8 pixels) are obtained. Binning readout is executed by driving the horizontal scanning circuit and the vertical scanning circuit according to each average mode and performing readout.

  Binning readout mode settings such as 4-pixel average, 16-pixel average, and 64-pixel average are to detect signals from the image pickup unit with a group of adjacent pixels, and the resolution of the readout image is determined by the average number of pixels. Will change. For example, when the average number of pixels increases, the sensitivity increases due to the increase in area, but the resolution decreases. By sequentially reading in the direction of increasing the average number of pixels, the accumulated image is read out at a plurality of resolutions.

  The selection of the output circuit at the time of pixel average reading determines the normal / abnormal state of the output circuit by inspection, and determines the line to be used for reading based on the determination result. This determination method will be described with reference to FIG.

  First, in step S1, charge accumulation is performed for a certain period so that all pixels have a constant charge. Subsequently, in step S2, all the pixels are read out in a non-binning mode (setting not to perform binning output), and in step S3, a pixel showing an output abnormal value is specified. The imaging control unit 107 in FIG. 1 can identify a pixel indicating an abnormal output value based on the output result of the output circuit corresponding to each pixel when binning output is not performed.

  Subsequently, in step S4, the binning switch is turned on once. That is, the setting for not performing binning output is switched to the setting for performing binning output. In step S5, the binning switch is turned off again. That is, the setting for performing binning output is switched to the setting for not performing binning output. Subsequently, in step S6, all pixels are read again in the non-binning mode.

  In step S7, the read result is determined. Based on the set pixel unit, the imaging control unit 107 compares the output result of the output circuit when binning output is performed with the output result of the output circuit when binning output is not performed after performing binning output. On the basis of the above, it is possible to specify the defective part of the output circuit. That is, it is determined whether all pixels in the binning area are abnormal with respect to all pixels read in the non-binning mode in the previous step S6. The binning switch is turned on once and then turned off. Therefore, if there is an abnormality in the sample-and-hold capacitor system, the charges in the target binning region are averaged by the sample-and-hold capacitors, and as a result, the charges in the sample-and-hold capacitors in all the target regions become abnormal. Accordingly, when all the pixels in the binned area are determined to be abnormal as a result of reading again in the non-binning mode (S8-Yes), the process proceeds to step S8. In step S8, it is determined that the sample hold capacitor system is defective.

  On the other hand, if there is no problem in the sample-and-hold capacitor system and the output circuit system is defective, the charge of each sample-and-hold capacitor is a weighted average result even when the binning switch is turned on / off (S8-No). Therefore, as a result of reading it in the non-binning mode, only the defective pixel identified in step S3 is output as a defective pixel as it is. In this case, the process proceeds to step S9, and it is determined that the output circuit system is defective.

  As an example, FIG. 6 shows the state of the inspection result at the time of each defect described in FIG. When attention is paid to the defective pixel A, the binning switch is turned on once, and then the binning switch is turned off again to execute non-binning readout. As a result, when all the pixels become abnormal as a result 601, it can be determined that the sample-and-hold capacitor system is defective as described above. This determination result corresponds to step S8 in FIG. On the other hand, when only the defective pixel A results in 602 indicating abnormal output, it can be determined that the output circuit system is defective. This determination result corresponds to step S9 in FIG.

  Based on the malfunction information of the output circuit specified in this way, the output circuit is selected in the binning readout mode. The selection of the output circuit is performed by a sensor readout control circuit provided inside the X-ray imaging apparatus. The sensor readout control circuit is configured using an FPGA or ASIC, and executes a readout operation based on output circuit selection information set from the imaging control unit 107 that can control the X-ray imaging apparatus.

  The selection of the output circuit will be described with reference to FIG. FIG. 7 is a conceptual diagram of a pixel readout matrix of the photographing unit. In the non-binning mode, all readout lines are sequentially selected by driving the HSR and VSR, and all pixel information is read out. On the other hand, in each binning mode, reading is performed while skipping the output selection line according to the average area. The imaging control unit 107 selects an output line to be used for reading based on the defect information of the previous output circuit, and sets a necessary skip amount as output circuit selection information in the read control circuit unit. The sensor readout control circuit unit sequentially selects output lines based on the set skip amount. As a result, binning readout is performed using the normal output line except for the output line indicating the abnormal output value over the entire photographing unit.

  Note that this output circuit selection information may be stored in advance in a memory inside the photographing unit in accordance with each binning mode, or may be set from the photographing control unit 107 every time a photographing operation is performed.

  In addition, if there are defects in a plurality of output circuit units in the photographing unit, and any of the binning areas is output abnormally regardless of which line is selected, the number of normal output pixels in the attention area of the designated subject ( The output line may be selected so that the number of normal output pixels) is maximized. The attention area of the designated subject may be given a priority based on the position in advance, and may be set so that, for example, the priority at the center of the photographing unit is higher and the priority at the end of the photographing unit is lower. Further, for each photographing operation, the priority of the attention area may be determined to be higher based on the ROI information set at that time. In this case, the output circuit selection information is an operation set by the imaging control unit 107 for each imaging operation.

  FIG. 8 is a block diagram showing a specific configuration of the image processing unit 108 shown in FIG. Reference numeral 801 denotes a multiplexer for selecting a data path, reference numeral 802 denotes an X-ray image frame memory, reference numeral 803 denotes a dark image frame memory, and reference numeral 804 denotes an offset correction circuit. Reference numeral 805 denotes a gain correction data frame memory, 806 denotes a gain correction circuit, 807 denotes a defect correction circuit, and 808 denotes another image processing circuit.

  An X-ray image (FX) acquired by X-ray irradiation is stored in the X-ray image frame memory 802 via the multiplexer 801. Further, the corrected image (Fn) (dark image) acquired in the non-radiation state of X-rays is stored in the dark image frame memory 803 via the multiplexer 801. Offset correction (for example, X-ray image (FX) −corrected image (Fn)) is performed by the offset correction circuit 804. Subsequently, the gain correction circuit 806 performs gain correction (for example, (FX−Fn) / Fg) using the gain correction data Fg stored in the gain correction frame memory acquired in advance. Subsequently, the data transferred to the defect correction circuit 807 completes the sensor-dependent correction process derived from the X-ray imaging apparatus 101. Further, after other image processing circuits 808 perform general image processing, such as gradation processing, frequency processing, and enhancement processing, the captured image data that has undergone image processing is displayed in the display control unit 112. Is transferred. The display control unit 112 displays the transferred captured image data on the display 115.

  The gain correction data Fg is obtained from a gain correction image obtained by X-ray imaging without using a subject. The gain correction image acquisition process is performed in advance before normal imaging, but imaging is performed with a desired constant dose over the entire light receiving unit of the X-ray imaging apparatus 101. Further, in order to reduce the variation effect due to the granularity of X-ray quanta, a plurality of gain correction images (for example, 5 to 10 images) are acquired under the same imaging conditions, and gains are obtained by averaging them. Obtain correction data. Further, in the photographing unit having a plurality of binning readout modes, the gain correction image acquisition operation is repeated for each binning mode in consideration of the difference in image characteristics due to the difference in the binning mode.

  The flow of gain correction data acquisition will be described with reference to the flowchart of FIG.

  First, in step S91, X-ray irradiation is performed with a predetermined dose. Next, in step S92, the captured image data is read by unaverage reading without reading in the binning reading mode (pixel average). In step S93, the captured image data is read by binning reading with an average of four pixels. In step S94, the captured image data is read by binning reading with an average of 16 pixels, and the imaged image data is read by binning reading with an average of 64 pixels in step S95. In steps S93 to S95, image data is acquired while sequentially changing so as to increase the pixel average in the binning readout mode. At this time, the binning readout mode is changed in the direction in which the binning area is expanded so that non-destructive readout can be sequentially performed on the charges accumulated in one X-ray irradiation.

  In step S96, it is determined whether or not the repetition of a predetermined number of times of irradiation has been completed in order to acquire image data for the number of samples required to generate gain correction data. If the predetermined number of irradiations has not been repeated (S96-No), the process returns to step S91, and the same processes as those from step S91 to step S95 described above are repeated.

  In the processing from step S91 to step S95, gain correction images in a plurality of binning modes are acquired by one X-ray irradiation. Then, all necessary gain correction images are acquired by repeating the required number of sheets for averaging.

On the other hand, when it is determined that the repetition of the predetermined number of irradiations has been completed and the image data for the number of samples necessary for generating the gain correction data has been acquired (S96-Yes), the process proceeds to step S97. It is advanced. In step S97, the acquired gain correction image is averaged for each binning mode on the personal computer, and gain correction data Fg is generated. The imaging control unit 107 can acquire binning output image data with different resolutions and correct output characteristics of the output circuit based on the acquired image data.
In actual X-ray imaging, gain correction of the output circuit is performed using gain correction data acquired in the binning mode in accordance with the binning mode at the time of imaging.

  According to the present embodiment, an imaging apparatus capable of determining whether a malfunction of an output circuit system or a sample-hold capacitor system has occurred with respect to a readout abnormal pixel region and selecting an output line based on the determination result. Provision becomes possible.

  Thus, when reading pixels in the binning mode, it is possible to display an imaging unit with a small number of abnormal areas as a whole, or an imaging unit with a small number of abnormal areas in the attention area of a designated subject.

(Other embodiments)
Note that it is needless to say that the object of the present invention can also be achieved by supplying a computer-readable storage medium that records a software program for realizing the functions of the above-described embodiments to a system or apparatus. Needless to say, this can also be achieved by the computer (or CPU or MPU) of the system or apparatus reading and executing the program stored in the storage medium.

  In this case, the program itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program constitutes the present invention.

  As a storage medium for supplying the program, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a nonvolatile memory card, a ROM, or the like can be used.

  Further, the functions of the above-described embodiments are realized by executing the program read by the computer. In addition, it is also included that an OS (operating system) or the like running on a computer performs part or all of actual processing based on a program instruction, and the above-described embodiment is realized by the processing. Needless to say.

1 is a block diagram showing a schematic configuration of an X-ray imaging apparatus according to an embodiment of the present invention. 2 is a diagram for explaining an internal structure of an X-ray imaging apparatus 101. FIG. 6 is a diagram showing an equivalent circuit of one pixel of the photoelectric conversion element 502. FIG. It is a conceptual diagram of a binning read mode. It is a flowchart explaining the flow of the selection method of this output circuit, and the inspection method of an output circuit. It is a figure which illustrates the inspection result explained in FIG. It is a conceptual diagram of the pixel reading matrix of an imaging | photography part. It is a block diagram which shows the specific structure of the image process part 108 shown in FIG. It is a flowchart explaining the flow of the data for gain correction data acquisition.

Explanation of symbols

101: X-ray imaging apparatus 106: System control unit 107: Imaging control unit 114: Operation panel 115: Display 117: X-ray generator 120: Power supply unit

Claims (9)

An imaging unit capable of setting a plurality of resolutions by binning output that outputs a signal of a new pixel based on a signal of a plurality of pixels that converts the amount of X-rays into an image signal ;
And units of the plurality of pixels to be grouped as a signal of the one pixel based on the resolution as one unity, and the output characteristics of the output circuit corresponding to each pixel constituting the imaging means, intends row the binning output based on and selection means for selecting the output circuit,
An imaging apparatus comprising: Further comprising specifying means for specifying a pixel indicating an abnormal output value of the imaging means based on output characteristics of an output circuit corresponding to each pixel constituting the imaging means;
  The imaging apparatus according to claim 1, wherein the selection unit selects the output circuit except for a pixel indicating the output abnormal value. An imaging unit capable of setting a plurality of resolutions by binning output that outputs a signal of a new pixel based on a signal of a plurality of pixels that converts the amount of X-rays into an image signal;
A specifying means for detecting an output of an output circuit corresponding to each pixel constituting the photographing means and specifying a pixel showing an abnormal output value;
And designating means for accepting a designation of the area of interest of the subject,
An output circuit that obtains a normal output for performing the binning output, excluding the output of the pixel indicating the output abnormal value, based on a unit obtained by uniting a plurality of pixels and the specifying result by the specifying unit A selection means for selecting
With
It said selection means, so that the number of normal output pixel of interest of a specified said object by said designating means is maximum, you and selects the output circuit shooting device. An imaging unit capable of setting a plurality of resolutions by binning output that outputs a signal of a new pixel based on a signal of a plurality of pixels that converts the amount of X-rays into an image signal;
A specifying means for detecting an output of an output circuit corresponding to each pixel constituting the photographing means and specifying a pixel showing an abnormal output value;
An output circuit that obtains a normal output for performing the binning output, excluding the output of the pixel indicating the output abnormal value, based on a unit obtained by uniting a plurality of pixels and the specifying result by the specifying unit A selection means for selecting
With
The specifying means is:
Based on the output result of the output circuit corresponding to each pixel in the setting in which the binning output is not performed, the pixel indicating the output abnormal value is identified,
The output result of the output circuit after switching from the setting for not performing the binning output to the setting for performing the binning output, and the output circuit of the output circuit after switching from the setting for performing the binning output to the setting for not performing the binning output Comparing the output result, if the charge of all the sample and hold capacitors in the region to be binned output is abnormal, it is determined that there is a problem with the sample and hold capacitor,
The binning if subject to area charges of all of the sample-and-hold capacitor of the output is not abnormal, the shadow device shooting shall be the determining means determines that there is a malfunction in the output circuit. An imaging unit capable of setting a plurality of resolutions by binning output that outputs a signal of a new pixel based on a signal of a plurality of pixels that converts the amount of X-rays into an image signal;
A specifying means for detecting an output of an output circuit corresponding to each pixel constituting the photographing means and specifying a pixel showing an abnormal output value;
An output circuit that obtains a normal output for performing the binning output, excluding the output of the pixel indicating the output abnormal value, based on a unit obtained by uniting a plurality of pixels and the specifying result by the specifying unit A selection means for selecting
An acquisition means for switching the setting of a unit of the plurality of pixels as one unit for one X-ray irradiation, and acquiring image data of binning output of different resolutions;
Correction means for correcting output characteristics of the output circuit based on the image data acquired by the acquisition means;
It characterized in that it obtain Bei the shooting equipment. The abnormal output value means that charge is stored for a certain period of time so that each pixel has a constant charge by the specifying means, and the charge read out without setting binning output from each pixel is different from the constant charge. 6. The photographing apparatus according to claim 2, wherein the photographing apparatus outputs an output value in a case. The imaging apparatus according to claim 1, further comprising a setting unit that sets a unit of the plurality of pixels as one unit in order to set the resolution. The setting means, imaging apparatus according to claim 7, characterized in that to set the unit of pixels as one unity the plurality of pixels so as to increase the number of pixels the binning output. An imaging method for an imaging apparatus having an imaging means capable of setting a plurality of resolutions by binning output that is output as a new one-pixel signal based on a plurality of pixel signals for converting the amount of X-rays into an image signal. ,
  The selection unit of the imaging device has a unit of a plurality of pixels grouped as a signal of the one pixel based on the resolution, an output characteristic of an output circuit corresponding to each pixel constituting the imaging unit, A selection step of selecting an output circuit that performs the binning output based on
  A photographing method characterized by comprising:

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