JP4649874B2 - Radiation imaging device - Google Patents

Description

  The present invention relates to a radiation imaging apparatus including a flat panel detector for detecting radiation, and more particularly to a technique for reading pixel values from a plurality of readout lines with a switching matrix substrate.

  Conventionally, as this type of device, a flat panel detector having a switching matrix substrate for charge readout control is provided, and a line for reading out a pixel group of the same data line among the pixel group is divided into a plurality of parts. There is something.

  In the device configured as described above, the charge detected in the sensitive layer of the flat panel detector is stored in the storage capacitor, and the charge of each capacitor is read through each readout line as each pixel value at a predetermined timing. Has been issued. For example, when the readout line is configured in two directions up and down with the central portion as a boundary in a plan view, the pixel groups located on the same data line are respectively connected to the upper and lower sides with the central portion as a boundary via the readout line. It will be read out to the side.

  However, the conventional example having such a configuration has the following problems.

  That is, in the conventional device, charge leakage inherent to the switching matrix substrate occurs in the same readout line, and due to this, the charge of each pixel in the same readout line affects the pixel value of each other. Therefore, since the degree of influence is different for each readout line even on the same data line, an image constructed based on the pixel values of all pixels has artifacts that are false images at positions corresponding to the boundary of the readout line. There's a problem.

  In particular, if the radiation balance between the upper readout line and the lower readout line in the same data line is greatly different due to the placement balance on the flat panel detector such as the subject, the accumulated charge is also It is greatly different for each readout line. Then, the image of the subject or the like located so as to straddle the upper and lower readout lines should be continuously visible, but there is a difference in gradation due to the influence of each charge leakage. .

  This invention is made in view of such a situation, Comprising: The radiation imaging device which can suppress the artifact which generate | occur | produces in the position which hits the boundary of a read-out line by correct | amending the pixel value in the same read-out line The purpose is to provide.

  In order to achieve such an object, the present invention has the following configuration.

That is, the invention according to claim 1 is a flat panel detector for detecting radiation, having a pixel group arranged in a matrix, and when the vertical arrangement of the pixel group is a data line, the data line Each of which is composed of a plurality of readout lines and includes a switching matrix substrate that reads out each pixel value from the plurality of readout lines, and the pixel value of each pixel for a pixel group of a certain readout line is stored in the pixel group of the readout line. Correction means for correcting with a correction value based on the pixel value is corrected for each readout line, and the correction means multiplies the correction value by a coefficient based on an average value of the total pixel values of the readout line. It is a value obtained by the above.

  [Operation / Effect] According to the invention described in claim 1, the correction means corrects the pixel value of each pixel in the same readout line with a correction value corresponding to the number of pixels in the same readout line. Since the adverse effect on the pixel value due to the charge leakage occurring in the same readout line changes depending on the number of pixels in the same readout line, the pixel due to the charge leakage is corrected by correcting each pixel value with the correction value based on this. The adverse effect on the value can be suppressed. Therefore, in an image configured based on all pixel values, it is possible to suppress an artifact that occurs at a position corresponding to the boundary of the readout line.

In addition, the adverse effect due to charge leakage differs depending on the number of pixels in the same readout line, the total pixel value, individual differences between switching matrix substrates, and the like. Therefore, by multiplying the average value of the total pixel values by the coefficient to obtain a correction value, it is possible to correct with high accuracy in consideration of these.

  In the present invention, it is preferable that the coefficient is set in advance based on a leakage degree of accumulated charges in the switching matrix substrate. The degree of leakage of charge accumulation is unique to the switching matrix substrate, and varies depending on the type of substrate, manufacturing process, etc., and can be accurately corrected if these are taken into consideration in advance.

  Furthermore, the coefficient is preferably about ± 0.5%, for example. This is because empirically, this value can be corrected with high accuracy by using the value as a coefficient.

  According to the radiation imaging apparatus according to the present invention, by correcting each pixel value with a correction value based on the number of pixels in the same readout line, an adverse effect on the pixel value due to charge leakage can be suppressed. Therefore, an artifact generated at a position corresponding to the boundary of the readout line can be suppressed in an image configured based on all pixel values.

  Embodiment 1 of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram illustrating a schematic configuration of the radiation imaging apparatus according to the embodiment.

  The top plate 1 is for placing the subject M to be examined. The top plate 1 is made of an X-ray transmitting material. An X-ray tube 3 and a flat panel detector 5 sensitive to X-rays are disposed opposite each other at a position sandwiching the top plate 1.

  The imaging control unit 7 controls an irradiation control unit 9 that controls X-ray irradiation from the X-ray tube 3. The irradiation control unit 9 is controlled by a command signal output from the imaging control unit 11 in response to an instruction from the keyboard 11 or the mouse 13 operated by the photographer. Information on the X-ray irradiation intensity and irradiation time of the X-ray tube 3 and the amplification degree in the flat panel detector 5 are instructed from the keyboard 11 and the mouse 13.

  Signals corresponding to the transmitted X-rays detected by the flat panel detector 5 are collected by the signal collecting unit 15. The collected signal is processed in the data processing unit 17 and the constructed X-ray image is displayed on the monitor 19. Note that the data processing unit 17 corresponding to the correcting means in the present invention also performs correction processing related to pixel values described later.

  Now, the flat panel detector 5 will be described in detail with reference to FIG. FIG. 2 is a block diagram showing the configuration of the flat panel detector.

  The flat panel detector 5 according to this embodiment drives array amplifiers 21 and 23 that amplify charges detected according to transmitted X-rays and convert them into digital signals, and sensor pixels corresponding to the pixels of the present invention. A gate driver 25 and a control circuit 27 for controlling the array amplifiers 21 and 23 and the gate driver 25 are provided.

  In this embodiment, the flat panel detector 5 includes n × 2m switching matrix substrates 29 (for example, n = 2m and 3,072 × 3,072) sensor pixels in a matrix. It shall be. Specifically, n sensor pixels of sensor pixels 1-1 to 1-n are provided from left to right on the top (first row L1) in FIG. 2, and the second (second row L2). ) Is provided with n sensor pixels 2-1 to 2-n, and n sensor pixels m-1 to mn in the m-th (m-th row Lm). Is provided. Among these sensor pixels, the sensor pixels 1-1 to 1-n located in the first row L1 have their accumulated charges read from the read lines DU1 to DUn in accordance with the signal from the gate line GL1. The sensor pixels 1-2 to 2-n located in the second row L2 are read from the readout lines DU1 to DUn in response to a signal from the gate line GL2, and are located in the m-th row Lm. Each sensor pixel m-1 to mn is read from each readout line DU1 to DUn in accordance with a signal from the gate line GLm. These occupy a first area ar1 corresponding to the upper half of the flat panel detector 5. Note that the vertical arrangement of sensor pixel groups in the flat panel detector 5 is defined as data lines DL1, DL2, DL3,.

  A second region ar2 occupying the lower half of the flat panel detector 5 is located below the first region ar1. In the second area ar2, the sensor pixels are arranged so as to be symmetrical with respect to the first area ar1 described above.

  That is, n sensor pixels 1-1 to 1-n are provided from left to right at the bottom (first row L1) in the second region ar2, and the second (second row) from the bottom. L2) is provided with n sensor pixels 2-1 to 2-n,..., N (mth row Lm) from the bottom, n sensor pixels m-1 to mn. Sensor pixels are provided. Among each of these sensor pixels, each of the sensor pixels 1-1 to 1-n located in the first row L1 has its accumulated charge read out from each of the read lines DD1 to DUn in accordance with a signal from the gate line GL2m. The sensor pixels 2-1 to 2-n located in the second row L2 are read out from the readout lines DD1 to DDn in response to the signal from the gate line GL2m-1,... The sensor pixels m-1 to mn located are read from the read lines DD1 to DDn according to the signal from the gate line GLm + 1.

  As described above, the flat panel detector 5 includes the first region among the sensor pixels 1-1, 2-1,..., M−1 in the first region ar1 and the second region ar2 located in the data line DL1. The sensor pixels 1-1, 2-1,..., m-1 of ar1 are read from the upper readout lines DU1 to DUn, and the sensor pixels 1-1, 2-1,. -1 is read from the lower read lines DD1 to DDn. The same applies to the other data lines DL2, DL3, DLn, and separate reading is performed in the upper first area ar1 and the lower second area ar2 of the flat panel detector 5 (also referred to as 2ch reading). .

  Here, the sensor pixels 1-1 to mn described above will be described with reference to FIG. FIG. 3 is a circuit configuration diagram of the sensor pixel.

  Each of the sensor pixels 1-1 to mn described above is configured as shown in FIG.

  That is, corresponding to the sensor pixels 1-1 to mn (only four sensor pixels 1-1 to 2-2 are illustrated in FIG. 3), the detection element 30 and the capacitor that is a charge storage capacitor 31 and a thin film transistor 33 as a switching element that operates in response to signals of the gate lines GL1 to GLm and GLm + 1 to GL2m.

  The detailed structures of the flat panel detector 5 and the switching matrix substrate 29 are as shown in FIG. FIG. 4 is a longitudinal sectional view showing a part of the flat panel detector and the switching matrix substrate.

  The flat panel detector 5 includes a support substrate 5a that is transparent to radiation, a common electrode 5b for bias charge application formed on the lower surface thereof, and a hole injection blocking layer 5c on the lower surface of the common electrode 5b. And a detection layer 5d that generates electron-hole pair carriers in response to the incident radiation. The switching matrix substrate 29 provided on the lower surface of the flat panel detector 5 is provided on the upper surface of the insulating substrate 35 on the ground side electrode 31a of the capacitor 31 and on the gate electrode 33a of the thin film transistor 33 via the insulating film 37. The connection electrode 31b 31 and the source electrode 33b and drain electrode 33c of the thin film transistor 33 are stacked. Further, the upper surface is covered with a protective insulating film 39.

  Further, the connection-side electrode 31b of the capacitor 31 and the source electrode 33b of the thin film transistor 33 are formed simultaneously and are electrically connected. As the insulating film 37 and the protective insulating film 39, for example, a plasma SiN film can be employed. The flat panel detector 5 and the switching matrix substrate 29 are aligned and, for example, heated and pressurized bonded with an anisotropic conductive film (ACF) or anisotropic conductive paste interposed therebetween. to paste together. Thereby, the flat panel detector 5 and the switching matrix substrate 29 are bonded and integrated.

  Thus, the flat panel detector 5 and the switching matrix substrate 29 are configured. Therefore, the capacitor 31 of each sensor pixel has a common readout due to a certain amount of charge leakage due to the presence of leakage current inherent to the material and structure of the switching matrix substrate 29 even when the thin film transistor 33 is not in operation. It can be seen that charge amount mutual transfer can occur between adjacent capacitors 31 in the line (DUn or DDn).

  Here, with reference to FIG. 5, the reading of electric charges in the flat panel detector 5 will be described. FIG. 5 is a diagram for explaining reading in the flat panel detector.

  In the flat panel detector 5 having the above-described configuration, for example, when X-rays are incident on the sensor pixel P, the data processing unit 17 uses each of the sensor pixels 1-1 to m using the following correction formula. The pixel value corresponding to the charge amount of −n is corrected.

P (i, j) = P ′ (i, j) −K · Σ [P ′ (i, j)] / J
Here, the symbol i indicates the readout line (DU1, DU2 or DD1, DD2) to which the sensor pixel belongs, and the symbol j indicates the total number of sensor pixels included in the readout line (m in this embodiment). , P indicates a pixel value after correction, P ′ indicates a pixel value before correction, and K indicates in advance according to charge leakage based on materials and configurations of the flat panel detector 5 and the switching matrix substrate 29. Indicates the set coefficient. Further, Σ represents the total sum from j = 1 to J. The symbols j and i correspond to the symbols m and n of the sensor pixels 1-1 to mn described above, respectively. The coefficient K is preferably about ± 0.5% empirically. The influence on the pixel value due to the charge leakage varies depending on the number of pixels in the same readout line, the total pixel value, the type of substrate in the switching matrix substrate, the manufacturing process, individual differences, and the like. By multiplying, it is possible to correct with high accuracy in consideration of these.

  For example, as shown in FIG. 5, the sensor pixel P (sensor pixel 2-3 in FIG. 2) belongs to the first region ar1 and is positioned on the readout line DU3. Therefore, the pixel value P of the sensor pixel P is calculated from the collected pixel value P ′ as an average value of the total pixel values of all the sensor pixels 1-3 to m-3 (Σ [ A correction value obtained by multiplying P ′ (i, j)] / J) by a coefficient K is subtracted. As a result, it is possible to correct the charge fluctuation caused by the mutual influence of the accumulated charges of the sensor pixels belonging to the same readout line due to the common readout line.

  Next, the operation of the radiation imaging apparatus having the above-described configuration will be described with reference to FIG. FIG. 6 is a flowchart showing the operation.

Step S1
The imaging control unit 7 controls the irradiation control unit 9 and the flat panel detector 5 according to the imaging conditions instructed from the keyboard 11 or the like, thereby imaging the subject M.

Step S2
A signal collecting unit 15 collects signals based on transmitted X-rays via the flat panel detector 5.

Step S3
The data processing unit 17 captures a signal from the signal collecting unit 15 and obtains a correction value (second term of the correction formula) for each readout line using the correction formula described above.

Step S4
The data processing unit 17 applies the correction value obtained for each readout line to each sensor pixel to obtain each pixel value after correction.

Step S5
The data processing unit 17 constructs an image based on each corrected pixel value, and outputs it to the monitor 19 for display. The image at this time is of high quality with no artifacts at the position corresponding to the boundary in the reading direction.

  As described above, the data processing unit 17 corrects the pixel value of each pixel in the same readout line with a correction value corresponding to the number of pixels in the same readout line. The adverse effect on the pixel value due to charge leakage that occurs in the same readout line changes according to the number of pixels in the same readout line, the total pixel value, etc., so by correcting each pixel value with a correction value based on this, An adverse effect on pixel values due to leakage can be suppressed. Therefore, in an image configured based on all pixel values, it is possible to suppress an artifact that occurs at a position corresponding to the boundary of the readout line.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In each of the embodiments described above, the flat panel detector 5 having the same number of vertical and horizontal sensor pixels has been described as an example. However, the present invention is not limited to such a flat panel detector 5. The present invention can be applied even when the number of vertical and horizontal sensor pixels is different.

  (2) The present invention is not limited to the configuration of the flat panel detector 5 and the switching matrix substrate 29 in the above-described embodiment, and may be applied as long as the read line is read from two or more even locations. it can. For example, three-channel reading or four-channel reading that is read from three or four locations is also applicable.

  (3) In each of the embodiments described above, the readout line is divided with the central portion in the vertical direction as a boundary. However, the same operation and effect can be obtained even if the readout line is divided with the central portion in the horizontal direction as a boundary. Play.

It is a block diagram which shows schematic structure of the radiography apparatus which concerns on an Example. It is a block diagram which shows the structure of a flat panel detector. It is a circuit block diagram of a sensor pixel. It is a longitudinal cross-sectional view which shows a part of flat panel detector and a switching matrix board | substrate. It is a figure where it uses for description of the reading in a flat panel detector. It is a flowchart which shows operation | movement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Top plate 3 ... X-ray tube 5 ... Flat panel detector 17 ... Data processing part (correction means)
29 ... Switching matrix substrate 31 ... Capacitor 33 ... Thin film transistor 1-1 to mn ... Sensor pixel (pixel)
ar1 ... first area ar2 ... second area DU1 to DUn ... (upper) read line DD1 to DDn ... (lower) read line GL1 to GLm ... gate lines DL1 to DLn ... data lines

Claims (2)

A flat panel detector for detecting radiation,
A group of pixels arranged in a matrix;
When the vertical arrangement of pixel groups is a data line,
Each of the data lines is composed of a plurality of read lines,
A switching matrix substrate that reads out each pixel value from a plurality of readout lines,
Correction means for correcting the pixel value of each pixel for a pixel group of a certain readout line with a correction value based on the pixel group of the readout line;
Pixel value correction is performed for each readout line ,
The radiation imaging apparatus according to claim 1, wherein the correction unit sets the correction value to a value obtained by multiplying a value based on an average value of the total pixel values of the readout line by a coefficient . The radiation imaging apparatus according to claim 1 , wherein the coefficient is set in advance based on a degree of leakage of accumulated charges in the switching matrix substrate.

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