JP2012090032A - Line artifact detector and detection method - Google Patents

Abstract

A line artifact detector capable of accurately acquiring line artifact information even during an imaging period without partial shielding of radiation such as X-rays.
A radiation sensor, a gate driving circuit for sequentially applying a driving voltage to each of a plurality of gate lines in the radiation sensor, and a plurality of gate lines connected to the gate line to which the driving voltage is applied. A reading circuit 14 that reads image signal information via a signal read line connected to the pixel, and an effective image that displays image signal information from a pixel group that performs a photoelectric conversion action among the image signal information read by the reading circuit 14 A display area 16 and an inspection image display area 17 that displays image signal information from a pixel group that does not perform photoelectric conversion are provided.
[Selection] Figure 1

Description

  Embodiments described herein relate generally to a line artifact detector capable of detecting a line artifact and a detection method thereof.

  As a new generation X-ray diagnostic detector, a radiological image detector using an active matrix has attracted much attention. By irradiating the radiation image detector with X-rays, an X-ray image or a real-time X-ray image is output as a digital signal. In addition, since it is a flat solid detector, it is highly expected in terms of image quality and stability. For this reason, many universities and manufacturers are working on research and development.

  Radiation image detectors are roughly classified into two methods, a direct method and an indirect method.

  The direct method is a method in which X-rays are directly converted into a charge signal by a photoconductive film such as a-Se and led to a charge storage capacitor.

  One indirect method is a method in which X-rays are received by a phosphor layer and converted into visible light, and then the visible light is converted into signal charges by an a-Si photodiode or the like and led to a charge storage capacitor.

  Many of the radiation image detectors currently in practical use employ the indirect method.

  A conventional indirect radiation image detector includes a fluorescence conversion film that converts incident X-rays into fluorescence, and an image detection unit that converts the fluorescence into image information using an electrical signal.

  FIG. 9 shows an equivalent circuit diagram of an image detection unit in a conventional indirect radiation image detector.

  In this image detection unit, for each pixel 1 composed of a TFT switch 3, a photodiode 8, and a capacitor 9, a signal readout line 2 for vertical wiring and a gate line 4 for horizontal wiring pass through the TFT switch 3. Further, the signal readout line 2 is connected to the integrating amplifier 5. The signal readout line 2 reads out the signal of the pixel group in the column connected to the TFT switch 3, and the gate line 4 controls on / off of the TFT switch 3.

  In this radiation image detector, the electrical signal of the pixel 1 can be read out to the integrating amplifier 5 through the signal readout line 2 by selecting an arbitrary gate line 4 and turning on the TFT switch 3.

  However, in this radiation image detector, many line artifacts may occur in the specific signal readout line 2. This is due to the structure peculiar to the two-dimensional detector using the TFT switch 3.

  That is, in such a two-dimensional detector, a current leak occurs in the photodiode 8 or the like and excessive charge is accumulated in the capacitance of the pixel 1, so that charge leaks from the TFT switch 3 or TFT switch 3 There may be a case where a leak occurs due to a defect of itself. At this time, if even one pixel has a defect in which charge leaks from the TFT switch 3, it appears in the image as a line artifact.

  Depending on the degree of this line artifact, it may be difficult to distinguish it from a normal location.

  For example, when the subject is smaller than the area of the detector, the dose after the object is transmitted is low, but a very high dose is irradiated in the surrounding area. In this case, in the high dose area, the amount of charge accumulated in the pixel 1 is large, so that the amount of leakage current of the TFT also increases, and line artifacts are likely to appear due to defects in the TFT switch 3 and variations in characteristics.

  On the other hand, in an image output irradiated with a uniform dose, a leak at a specific portion is difficult to distinguish from a normal image.

  Conventionally, such line artifacts are detected by comprehensive judgment using an image signal in a state where radiation such as X-rays is not irradiated or an image signal which is irradiated with an arbitrary dose to block a part of the detection area. It had been.

JP 2009-128023 A

  However, in the conventional method for inspecting line artifacts, it is necessary to inspect before or at the end of imaging with an image detector, or to interrupt imaging for inspection. In addition, there are problems such as the necessity of adjusting the dose irradiated for inspection, problems such as omission of inspection, and inability to inspect during imaging.

  On the other hand, line artifact information is detected from the acquired effective pixel image by image processing, and line artifact correction is also performed based on this information. However, an accurate line artifact signal cannot be separated and is completely The current situation is that no correction has been made.

  The present invention has been made to solve the above problems, and a line artifact detector capable of accurately acquiring line artifact information even during an imaging period without partial shielding of radiation such as X-rays and a detection method thereof. The purpose is to provide.

  In order to achieve the above-described object, the present line artifact detector includes a plurality of pixels arranged two-dimensionally on a substrate, a plurality of gate lines extending in one of a row direction and a column direction, and the gate lines. A plurality of signal readout lines extending in a direction perpendicular to the extending direction of the plurality of pixels, wherein the plurality of pixels are divided into a pixel group that performs a photoelectric conversion action and a pixel group that does not perform a photoelectric conversion action, A pixel group that performs a photoelectric conversion action and a pixel group that does not perform the photoelectric conversion action are respectively connected to one of the plurality of gate lines and one of the plurality of signal readout lines. The drive voltage is applied to a radiation sensor including a detection unit, a gate drive circuit that sequentially applies a drive voltage to each of the plurality of gate lines, and a pixel group that performs the photoelectric conversion action. A pixel group that reads image signal information through the signal readout line connected to a plurality of pixels connected to a gate line, displays the image signal information as an effective pixel display area, and does not perform the photoelectric conversion function A reading circuit that reads image signal information through the signal readout line connected to a plurality of pixels connected to the gate line to which the drive voltage is applied, and at least temporarily displays the image signal information as an inspection image display region And.

  In order to achieve the above-described object, the detection method of the line artifact detector includes a plurality of pixels that perform a photoelectric conversion action on a substrate that are two-dimensionally arranged and extend in one of the row direction and the column direction. A plurality of gate lines, and a plurality of signal readout lines extending in a direction perpendicular to the extending direction of the gate lines, and the plurality of pixels are each of the plurality of gate lines. A line artifact detection method in a line artifact detector comprising a radiation sensor connected to one of the plurality of signal readout lines and one of the plurality of signal readout lines, wherein each of the plurality of gate lines is detected. Sequentially apply a driving voltage to the image signal through the signal readout line connected to a plurality of pixels connected to the gate line to which the driving voltage is applied. A reading period assuming a pixel group that does not perform photoelectric conversion is provided before and after the timing of reading the image signal information, and line artifacts are detected by reading the image signal information in the reading period. It is characterized by that.

The schematic diagram which shows the structure of the line artifact detector which concerns on 1st Embodiment. The perspective view which shows an example of the radiation sensor used for the line artifact detector of FIG. The elements on larger scale of the image detection part surface of FIG. FIG. 3 is an equivalent circuit diagram of the image detection unit in FIG. 2. FIG. 2 is a plan view illustrating an example of a gate driving circuit and a reading circuit in FIG. 1. The timing chart which shows the drive method of the line artifact detector which concerns on 1st Embodiment. It is an image display example containing a line artifact, (a) is an image display photograph by a prior art example, (b) is an image display photograph by 1st Embodiment. The timing chart which shows the drive method of the line artifact detector which concerns on 2nd Embodiment. The equivalent circuit diagram of the image detection part in the conventional indirect type radiographic image detector.

  Hereinafter, the present embodiment will be described with reference to the drawings.

[First Embodiment]
(Overall configuration of line artifact detector)
FIG. 1 shows a line artifact detector according to the first embodiment.

  The line artifact detector 10 is two-dimensionally arranged in a radiation sensor 11 having a phosphor layer that converts incident X-rays into light and an image detection unit that converts incident light into an electrical signal, and the image detection unit. A gate drive circuit 12 for sequentially applying a drive voltage for each scan line for each pixel, a drive control circuit 13 for generating a drive signal for determining a scan timing in the column direction for the gate drive circuit 12, and a selected one line A reading circuit 14 that reads an electric signal of the pixel, a reading control circuit 15 that generates a reading signal that determines a reading timing in the reading circuit 14, an effective pixel display region 16 that displays an effective pixel obtained by the reading circuit 14, And an inspection image display area 17 for displaying a line artifact signal.

(Radiation sensor 11)
FIG. 2 shows an example of a specific configuration of the radiation sensor 11.

  The radiation sensor 11 includes a fluorescence conversion film 23 that converts incident X-rays 21 into fluorescence, and an image detection unit 25 that converts the fluorescence into image information using an electrical signal.

  The image detection unit 25 is formed by providing a circuit layer 29 on which a large number of pixels 1 including photodiodes and thin film transistors (TFT switches 3) are arranged on a holding substrate 27 mainly composed of a glass substrate.

  FIG. 3 is a partial enlarged view of the surface of the image detection unit 25.

  On the surface of the image detection unit 25, the pixels 1 including the TFT switches 3 and the photodiodes 8 are arranged in a grid pattern. Each pixel 1 is connected to one of a plurality of gate lines 4 arranged in the row direction, and one of the signal readout lines 2 arranged in the column direction. Connected to one. Further, each photodiode 8 is connected to one of a plurality of bias lines 39 arranged in the column direction.

  Such an image detection unit 25 is manufactured by a TFT panel manufacturing process similar to the manufacturing process of the liquid crystal display device. That is, after forming the signal wiring (the signal readout line 2 and the gate line 4) and the TFT switch 3 on the holding substrate 27, the photodiode 8 is formed in a lattice shape on the TFT switch 3, and the output is disposed below the TFT. It is manufactured by electrically connecting to the switch 3 and further forming a bias line 39.

  FIG. 4 shows an equivalent circuit of the image detection unit 25.

  The pixel 1 includes a TFT switch 3, a photodiode 8, and a capacitor 9. The gate line 4 is connected to the gate of the TFT switch 3, the signal readout line 2 is connected to the source of the TFT switch 3, and the TFT switch 3 A photodiode 8 and a capacitor 9 are connected in parallel to the drain. The capacitor 9 is a capacitance between the electrodes of the photodiode 8.

  In this embodiment, a plurality of rows of dummy pixels 7 that do not convert X-rays or the like into electrical signals are provided outside the imaging effective area 6 that reads out images by converting X-rays or other radiation into electrical signals. Yes.

  For example, as shown in FIG. 4, the dummy pixel 7 can be configured by only the TFT switch 3 and the capacitor 9 without providing the photodiode 8. Further, when the photodiode 8 is provided, it may not be electrically connected to the TFT switch 3.

  The dummy pixel 7 is used for measuring the offset voltage of the amplifier IC that detects the signal charge. At this time, in order to improve the measurement accuracy of the offset voltage, it is possible to provide several to a dozen rows of dummy pixels 7.

  Further, the lower end of the signal readout line 2 is connected to the integrating amplifier 5 shown in FIG. 5, and the left end of the gate line 4 is connected to a specific signal line of the gate driver 31 shown in FIG.

(Gate driving circuit 12, reading circuit 14)
FIG. 5 shows an example of a specific configuration of the gate driving circuit 12 and the reading circuit 14 of FIG.

  The gate driving circuit 12 includes a gate driver 31 and a row selection circuit 33, and the reading circuit 14 includes an integrating amplifier 5, an A / D (analog / digital) converter 35, and a driver 37.

  The gate driver 31 has a function of sequentially changing the voltages of a large number of gate lines 4 connected to the radiation sensor 11 when receiving a signal from the outside. A row selection circuit 33 is connected to the gate driver 31.

  The row selection circuit 33 has a function of sending a signal to the corresponding gate driver 31 according to the scanning direction of the X-ray image, and is connected to the drive control circuit 13 of FIG.

  Further, the integrating amplifier 5 is connected to the signal readout line 2 in FIG. 4 on a one-to-one basis, and amplifies a charge signal transmitted through the signal readout line 2. The integrating amplifier 5 is connected to the driver 37 via the A / D converter 35.

  The driver 37 is connected to the reading control circuit 15 of FIG. 1, and reads a signal digitized by the A / D converter 35 by a reading signal from the reading control circuit 15.

(Driving method of line artifact detector 10)
FIG. 6 is a timing chart showing an example of a driving method of the line artifact detector 10.

  The “gate line 1” of the gate drive signal in FIG. 6 is a gate line connected to the pixel group in the uppermost row of the plurality of pixels 1 arranged in the matrix form of FIG. 4, and the “gate line 2” is the upper end. To the gate line connected to the pixel group in the second row. Similarly, the “gate line 3” is a gate line connected to the pixel group in the third row, and the gate line n is a gate line connected to the pixel group in the n th row. Further, “dummy line 1” is a gate line connected to the dummy pixel group in the top row in the next row of the gate line n, and “dummy line m” is connected to the dummy pixel group in the m-th row. Means the gate line.

  Based on the gate drive signals of the gate lines 1 to n shown in FIG. 6 generated by the drive control circuit 13 of FIG. 1, the gate drive circuit 12 applies a voltage to the gate lines 1 to n. Here, as shown in FIG. 6, a voltage (Lo state) for insulating the connected TFT switch 3 is applied to the gate lines 1 to n in most of the periods. Only a drive voltage (Hi state) is applied to bring the TFT switch 3 into a conductive state.

  Further, the period during which the gate drive circuit 12 applies the voltage for turning on the TFT switch 3 to each of the gate lines 1 to n is different, as shown in FIG. 6, from the gate line 1 to the gate line n. Voltage application is performed with the periods shifted in order. In this way, the charge signals from the pixels 1 belonging to different gate lines are input to the integrating amplifier 5 through the signal readout line 2 without crossing each other.

  Further, for each of the dummy lines 1 to m shown in FIG. 6, the gate drive circuit 12 from the dummy line 1 to the dummy line m is based on the gate drive signal generated by the drive control circuit 13 of FIG. Voltage application is performed with the periods shifted in order.

  Next, based on the read signal from the read control circuit 15, the charge accumulation operation is performed by the integrating amplifier 5 for all the pixels 1 connected to a predetermined gate line over a certain period, and the signal read line 2 is set by the read circuit 14. Read the flowing charge.

  While X-rays are being irradiated from the outside, reading operation is performed at each timing indicated by “signal 1” to “signal n” of each gate line pixel signal output in FIG. The integration switch 5 is operated only during the period when the charge signal of the pixel 1 flows through the signal readout line 2 by turning on the TFT switch 3, and the noise signal flowing through the signal readout line 2 is cut off during an unnecessary period. As a result, it is possible to output image information composed of digital signals to the effective pixel display area 16 shown in FIG.

  Here, if radiation such as X-rays is not irradiated, leak charges other than electrical signals to be converted as image information are accumulated in the capacitor 9.

  As described above, the dummy pixel 7 is composed of only the TFT switch 3 and the capacitor 9 without providing the photodiode 8, and therefore does not convert radiation such as X-rays into an electric signal. As in the case of not irradiating, leak charges other than the electric signal to be converted as image information are accumulated in the capacitor 9 of the dummy pixel 7.

  Accordingly, the “pixel 1” to “signal dummy m” of each gate line pixel signal output shown in FIG. 6 are output in the same manner as the outputs of “signal 1” to “signal n”, thereby providing the dummy pixel 7. The line artifact signal leaking through the TFT switch 3 can be read by the reading circuit 14.

  Therefore, by outputting the inspection image display area 17 in FIG. 1 to the outside, it is possible to determine the influence of line artifacts and defects based on the signal output from the dummy pixel 7 even while an image is acquired by irradiation with radiation such as X-rays. .

  FIG. 7 shows an example in which the effective pixel display area 16 and the inspection image display area 17 are actually displayed. For comparison, an example of only the conventional effective pixel display region 16 is also shown.

  In the effective pixel display area 16, it can be seen that the line artifact appears remarkably in the portion where the X-ray dose in the subject is small, but is difficult to detect in the portion where the X-ray dose around the subject is high.

  Accordingly, as shown in FIG. 7A, in the conventional display only in the effective pixel display region 16, it is difficult to confirm the line artifact in the portion where the X-ray dose is large, whereas as shown in FIG. When both the effective pixel display area 16 and the inspection image display area 17 are provided, the line artifact can be easily confirmed using the inspection image display area 17.

  Therefore, according to the present embodiment, it is possible to detect line artifacts even during the imaging period, and it is possible to accurately detect artifacts caused by circumstances such as the intensity of image signals such as radiation during image acquisition. Become.

  The inspection image display area 17 may be displayed continuously during imaging. However, after displaying the inspection image display area 17 once and confirming the site where the line artifact has occurred, the display is turned off and only the effective pixel display area 16 is displayed. You can also

[Second Embodiment]
Since the line artifact is caused by the electric charge leaking to the signal readout line 2, it is equivalent even if the integrating amplifier 5 is accumulated at a timing when the dummy pixel 7 is assumed without actually providing the dummy pixel 7. Output can be obtained.

  Therefore, as a second embodiment, in the line artifact detector configured in the same manner as in the first embodiment except that the dummy pixel 7 is not provided, the detector is driven by a gate drive signal as shown in FIG. did.

  That is, first, similarly to the first embodiment, the gate drive circuit 12 generates each gate line based on the gate drive signals of the gate lines 1 to n shown in FIG. 8 generated by the drive control circuit 13 shown in FIG. A voltage is applied to 1 to n. Here, as shown in FIG. 8, a voltage (Lo state) for insulating the connected TFT switch 3 is applied to the gate lines 1 to n in most of the periods. Only the voltage (Hi state) for making the TFT switch 3 conductive is applied.

  Further, the period during which the gate driving circuit 12 applies the voltage for turning on the TFT switch 3 to each of the gate lines 1 to n is different, as shown in FIG. 8, from the gate line 1 to the gate line n. Voltage application is performed with the periods shifted in order.

  Next, by performing a reading operation at each timing indicated by “signal 1” to “signal n” of each gate line pixel signal output in FIG. 8, the TFT switch 3 is turned on in each gate line 1 to n to thereby form a pixel. The integrating amplifier 5 is operated only during a period in which one charge signal flows through the signal readout line 2.

  Thereafter, “signal dummy 1” to “signal dummy m” of each gate line pixel signal output of FIG. 8 is further processed at the timing assuming dummy pixels 1 to n in the first embodiment. The same output as each output of “signal n” is performed.

  Information on the leakage current can be obtained by obtaining the charge information flowing through the signal readout line 2 in the readout period assuming the dummy pixels.

  Therefore, this method can also detect an artifact caused by a phenomenon peculiar to a TFT used in the radiation image detection apparatus.

[Third Embodiment]
In the first or second embodiment described above, an arbitrary specified value is provided for the output in the inspection image display area 17, and selective processing such as correction of line artifacts is performed when the specified value is exceeded. You can also.

  The line artifact can be determined by, for example, the following calculation.

When | Vout (n) −Vout_ave | ≧ Vout_th, n_ch is a defective line.

Here, Vout (n): output of the nth line, Vout_ave: average value of all lines, Vout_th: defect determination reference value The leak current of the TFT switch 3 is the signal output of the pixel at the leak location Depending on the condition of the subject, the dose of radiation such as X-rays, and the influence of the irradiation area will vary, but the pixel signal output in the signal dummies 1 to m is always determined and used as the correction data. It is possible to correct line artifacts even in the state of radiation such as a rough subject and X-rays.

  Furthermore, if it is within an arbitrary signal output that can ensure the necessary contrast, it can be corrected by image processing after digital signal conversion as a line artifact including an offset of the amplifier IC. As described above, defect correction can be performed in image processing after digital signal conversion.

[Other embodiments]
In the above embodiment, an example of the indirect system in which the photodiode 8 is provided as the radiation sensor 11 is shown. However, the X-ray is directly converted into a charge signal by a photoconductive film such as a-Se, and the charge accumulation is performed. The same method can be applied to a direct system that leads to a capacitor.

  In addition, when radiation such as X-rays is pulse-irradiated and then images are sequentially read out for each gate line, the influence of artifacts may be attenuated immediately after irradiation with radiation such as X-rays. By starting the reading from the row of dummy pixels, the influence of the artifact can also be detected.

  Further, in the detector provided with a dummy pixel or the like for canceling the injection to the signal readout line 2 by the ON / OFF voltage control of the TFT switch 3 of the gate line 4, the dummy pixel 7 in the first embodiment is not affected. Thus, it is impossible to read the signal by turning on the TFT switch 3 of the actual pixel, but it is possible to obtain the same effect by reading the signal by driving assuming the dummy pixel as in the second embodiment. it can.

1: Pixel 2: Signal readout line 3: TFT switch 4: Gate line 5: Integration amplifier 6: Imaging effective area 7: Dummy pixel 8: Photo diode 9: Capacitor 10: Line artifact detector 11: Radiation sensor 12: Gate drive Circuit 13: Drive control circuit 14: Reading circuit 15: Reading control circuit 16: Effective pixel display area 17: Inspection image display area 21: Incident X-ray 23: Fluorescence conversion film 25: Image detection unit 27: Holding substrate 29: Circuit layer 31: Gate driver 33: Row selection circuit 35: A / D converter 37: Driver 39: Bias line

Claims (4)

A plurality of pixels arranged two-dimensionally on the substrate, a plurality of gate lines extending in one of the row direction or the column direction, and a plurality of lines extending in a direction perpendicular to the extending direction of the gate lines The plurality of pixels are divided into a pixel group that performs a photoelectric conversion action and a pixel group that does not perform a photoelectric conversion action, and the pixel group that performs the photoelectric conversion action and the photoelectric conversion action are not performed. Each of the pixel groups includes a radiation sensor including an image detection unit connected to one of the plurality of gate lines and one of the plurality of signal readout lines;
A gate driving circuit for sequentially applying a driving voltage to each of the plurality of gate lines;
For the pixel group performing the photoelectric conversion action, image signal information is read through the signal readout line connected to a plurality of pixels connected to the gate line to which the drive voltage is applied, and the image signal information is converted into an effective pixel. Image signal information is read through the signal readout line connected to a plurality of pixels connected to the gate line to which the drive voltage is applied for the pixel group that is displayed as a display area and does not perform the photoelectric conversion function. A reading circuit that at least temporarily displays the image signal information as an inspection image display area;
A line artifact detector comprising:   A drive control circuit for generating a drive signal for determining the scanning timing in the column direction for the gate drive circuit; and a read control circuit for generating a read signal for determining the read timing for the reading circuit. The line artifact detector according to claim 1.   The pixel that performs the photoelectric conversion function includes a TFT switch and a photodiode, while the pixel that does not perform the photoelectric conversion function includes a TFT switch and converts the incident radiation to fluorescence on the image detection unit. The line artifact detector of claim 1, comprising a layer. A plurality of pixels that perform photoelectric conversion on the substrate are two-dimensionally arranged, a plurality of gate lines extending in one of the row direction and the column direction, and a direction orthogonal to the extending direction of the gate lines A plurality of signal readout lines extending to the plurality of pixels, and the plurality of pixels are respectively connected to one of the plurality of gate lines and one of the plurality of signal readout lines. A method for detecting line artifacts in a line artifact detector comprising a radiation sensor comprising:
A drive voltage is sequentially applied to each of the plurality of gate lines, and image signal information is obtained via the signal readout line connected to a plurality of pixels connected to the gate line to which the drive voltage is applied. In addition to reading, before and after the timing of reading the image signal information, a reading period assuming a pixel group that does not perform photoelectric conversion is provided, and line artifacts are detected by reading the image signal information in the reading period. Detection method of a characteristic line artifact detector.

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