JP4501489B2 - Radiation imaging device - Google Patents

Description

  The present invention relates to a radiation imaging apparatus used in the medical field, industrial fields such as non-destructive inspection, RI (Radio isotope) inspection, optical inspection, and nuclear power field, and more particularly to a technique for detecting a defective pixel.

  Taking X-rays as an example, image processing in a radiation imaging apparatus is performed based on radiation detected by radiation detection means typified by a flat panel radiation detector (FPD). The FPD described above is configured by stacking a sensitive film on a substrate, detecting radiation incident on the sensitive film, converting the detected radiation into electric charges, and arranging the two-dimensional array. Charge is stored in the capacitor. The accumulated charge is read by turning on the switching element and sent to the image processing unit as an electrical signal for image processing. Therefore, there is a variation in the amount of charge accumulated for each detection element constituting the capacitor or the switching element, and accordingly, there is also a variation for pixels based on the electrical signal for each detection element.

  In particular, when it does not function as a detection element, the pixel value becomes extremely large and appears white on the image, or the pixel value becomes extremely small and becomes black on the image. When the sensitivity of the detection element is high, dark current is generated even when no radiation is incident, and the value of the pixel increases. Conversely, when the sensitivity of the detection element is low, or when dust or the like adheres to the detection element, the value of the pixel decreases. Such a pixel is called a “defective pixel”.

As a method of interpolating a defective pixel, there are a median filter process that replaces a defective pixel with a median pixel from a plurality of pixels adjacent to the defective pixel, an interpolation process that interpolates a pixel based on the adjacent pixel, and the like (for example, , See Patent Document 1 and Patent Document 2). In addition, a series of operations for detecting and interpolating missing pixels (this operation is hereinafter also referred to as “missing registration”) is performed every predetermined period (for example, one month).
JP 2000-284059 A (page 2-4, FIG. 2-4) JP 2000-135210 A (page 4-9, FIGS. 3 and 4)

  However, there are cases where the number of missing pixels increases or decreases even during the predetermined period described above, and image processing is performed without performing the missing registration accurately. Thus, it is conceivable to perform defect registration accurately by performing defect registration every period shorter than a predetermined period (for example, one day), but it is difficult to perform defect registration itself in a short period in terms of operation of the apparatus.

  The present invention has been made in view of such circumstances, and a radiation imaging apparatus capable of accurately performing a series of operations for detecting and interpolating a defective pixel without impairing the operation of the apparatus. The purpose is to provide.

  As a result of intensive studies to solve the above problems, the inventors have obtained the following knowledge.

  In other words, we focused on using pixel data that is routinely performed in a shorter period than missing registration. Calibration (calibration) is performed in a shorter period (for example, one day) than the defect registration.

  In order to reduce the variation in pixels for each detection element described above, there is calibration other than missing registration. In the calibration, in order to eliminate variations, for example, the gain of an amplifier (amplifier) for each detection element is adjusted to align the output side. Thus, for example, the inventors have found that defect registration is performed in a short period for each calibration by detecting defective pixels using the data of the calibrated pixels.

  The present invention based on such knowledge has the following configuration.

That is, the radiation imaging apparatus according to the present invention detects a defective pixel due to a variation of a detection element of the radiation detection unit with respect to a pixel based on the detected radiation and a radiation detection unit that detects the radiation transmitted through the subject. Image processing is performed by providing defective pixel detection means and defective pixel interpolation means for performing interpolation of defective pixels detected by the defective pixel detection means, and performing defective pixel interpolation by the defective pixel interpolation means based on the detected radiation. A radiation imaging apparatus that performs imaging of a subject, and includes a pixel calibration unit that performs calibration for each detection element that constitutes the radiation detection unit, and the defective pixel detection unit outputs the pixel calibration unit. The defective pixel is detected using the first calibration information, and the first calibration information is acquired in a state where the radiation detection means is not yet irradiated with radiation. Orazu radiation detection signal detecting means is outputted by detecting the radiation based on, defective pixel detecting means, in operation, further using a second calibration information for outputting the pixel calibration unit, a second calibration information Is characterized in that it is based on a radiation detection signal that is output when the radiation detection means detects radiation that has passed through the subject.

  [Operation / Effect] According to the invention described in claim 1, the defective pixel detecting means detects the defective pixel for the pixel based on the detected radiation. This detection is performed using calibration information relating to pixel calibration means. Therefore, it is possible to simultaneously detect and interpolate a defective pixel in accordance with the timing of calibration by the pixel calibration unit. Since the calibration by the pixel calibration means is performed in a predetermined period shorter than the period for detecting and interpolating the defective pixel, the detection and interpolation of the defective pixel are also performed in a shorter period than before. As a result, it is possible to accurately perform a series of operations (deletion registration) for detecting and interpolating a defective pixel without impairing the operation of the apparatus.

  Here, the calibration information related to the pixel calibration unit may be a pixel for which calibration has been performed, or may be the gain of the amplifier for each detection element.

In the above-described invention, a defect is obtained by combining each calibration information after calibration by the pixel calibration means obtained in each of the radiation irradiation state, the non-irradiation state before the radiation irradiation, and the non-irradiation state immediately after the radiation irradiation. pixel detection means have preferably that detects the defective pixel. By using the calibration information in each state in combination, the series of operations described above can be performed more accurately.

(Delete)

  In addition, the above-described defective pixel detection means further uses the third calibration information output from the pixel calibration means during operation, and the third calibration information is obtained after the radiation detection signal of the radiation that has passed through the subject is read out. It is more desirable if it is acquired in the state of (1) and is not based on the radiation detection signal output by the radiation detection means.

  According to the radiation imaging apparatus of the present invention, since the defective pixel is detected by using the pixel that has been calibrated by the pixel calibration unit, detection of the defective pixel and the calibration timing by the pixel calibration unit are performed. Interpolation can be performed simultaneously. As a result, it is possible to accurately perform a series of operations (deletion registration) for detecting and interpolating a defective pixel without impairing the operation of the apparatus.

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

  FIG. 1 is a block diagram of an X-ray diagnostic apparatus according to the embodiment, FIG. 2 is a block diagram showing a specific configuration of an image processing unit used in the X-ray diagnostic apparatus, and FIG. FIG. 4 is an equivalent circuit of a flat panel X-ray detector used in the X-ray diagnostic apparatus as viewed from the side, and FIG. 4 is an equivalent circuit of the flat panel X-ray detector as viewed from above. In this embodiment, a flat panel X-ray detector (hereinafter referred to as “FPD” as appropriate) is taken as an example of radiation detection means, and an X-ray diagnostic apparatus is taken as an example of a radiation imaging apparatus.

  As shown in FIG. 1, the X-ray diagnostic apparatus according to the present embodiment includes a top plate 1 on which a subject M is placed, an X-ray tube 2 that irradiates the subject M with X-rays, and a subject. FPD3 which detects the X-ray which permeate | transmitted M is provided. The FPD 3 corresponds to radiation detection means.

  In addition, the X-ray diagnostic apparatus further includes the top panel control unit 4 that controls the elevation and horizontal movement of the top panel 1, the FPD control unit 5 that controls the scanning of the FPD 3, and the tube voltage and tube current of the X-ray tube 2. An X-ray tube control unit 7 having a high voltage generation unit 6 to be generated, a calibration unit 8 for calibrating an X-ray detection signal that is a charge signal from the FPD 3, and digitizing the calibrated X-ray detection signal An A / D converter 9 to be taken out, and an image processing unit 10 that performs defect registration such as detection / interpolation of a defective pixel, which will be described later, in addition to performing various processes based on the X-ray detection signal output from the A / D converter 9. A controller 11 that controls these components, a memory unit 12 that stores processed images, an input unit 13 in which an operator performs input settings, and a mode that displays processed images. It has a such data 14. The calibration unit 8 corresponds to the pixel calibration means in this invention.

  The top board control unit 4 horizontally moves the top board 1 to accommodate the subject M up to the imaging position, moves up and down and horizontally moves the subject M to a desired position, or performs imaging while horizontally moving the subject M. Or performing horizontal control after the completion of imaging and retreating from the imaging position. The FPD control unit 5 performs control related to scanning by moving the FPD 3 horizontally or rotating around the body axis of the subject M. The high voltage generation unit 6 generates a tube voltage and a tube current for irradiating X-rays and applies them to the X-ray tube 2. The X-ray tube control unit 7 moves the X-ray tube 2 horizontally, Control relating to scanning by rotating around the axis of the body axis of M, control of the setting of the irradiation field of the collimator (not shown) on the X-ray tube 3 side, and the like are performed. When scanning the X-ray tube 2 or the FPD 3, the X-ray tube 2 and the FPD 3 move while facing each other so that the FPD 3 can detect the X-rays emitted from the X-ray tube 2.

  The calibration unit 8 calibrates the charge signal output from the FPD 3, that is, the pixel. In this embodiment, the gain of an amplifier (amplifier) 38 (see FIG. 4) for each switching element 32 to be described later is set. Adjust to align the output side. The A / D converter 9 converts the calibrated charge signal from analog to digital, and outputs a digitized X-ray detection signal. The controller 11 is configured by a central processing unit (CPU) and the like, and the memory unit 12 is configured by a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. Yes. The input unit 13 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. In the X-ray diagnostic apparatus, the FPD 3 detects X-rays transmitted through the subject M, performs calibration by the calibration unit 8 based on the detected X-rays, and performs image processing by the image processing unit 10. The subject M is imaged.

  As shown in FIG. 2, the image processing unit 10 includes a defective pixel detection unit 21 that detects a defective pixel and a defective pixel interpolation unit 22 that performs interpolation of the defective pixel detected by the defective pixel detection unit 21. Has been. With these configurations, the image processing unit 9 performs defect registration, which is a series of operations for detecting and interpolating missing pixels. The missing pixel detection unit 21 corresponds to the missing pixel detection unit in the present invention, and the missing pixel interpolation unit 22 corresponds to the missing pixel interpolation unit in the present invention.

  The missing pixel detection unit 21 is configured by a separation circuit, a comparator, and the like. The pixel based on the charge signal is spatially expanded and expanded for each detection element constituting the capacitor and the switching element 32 by the separation circuit. By comparing these pixels, the pixel having the maximum value or the minimum value is detected as a defective pixel. Note that the pixels are spatially developed in a state where the gain of the amplifier 38 is adjusted by the calibration unit 8, that is, in a state where the calibration is performed. Note that the missing pixel detection unit 21 is not limited to the above-described configuration, and the low-pass filter (LPF) and the subtractor constitute the missing pixel detection unit 21, and the high-frequency component in the spatially expanded pixel signal By passing only low-frequency components other than the steep pixel signal that is a low-pass filter and subtracting the low-frequency component and the entire signal with a subtractor to detect the steep pixels, that is, steep pixels, The pixel having the maximum value or the minimum value may be detected.

  In addition, the defective pixel is not limited to the pixel having the maximum value or the minimum value described above, a pixel having a constant value regardless of whether the X-ray is irradiated or not, or a constant value regardless of the X-ray incident dose. In addition, a pixel having a constant value up to an incident dose of X-rays, a pixel whose behavior is indefinite when exceeding a predetermined incident dose of X-rays, and a pixel that cannot detect X-rays are included. The missing pixel detector 21 is configured according to the characteristics of these pixels.

  The missing pixel interpolation unit 22 is configured by a median filter, for example, and detects a median pixel from a plurality of pixels by a median filter and replaces the missing pixel with the detected median pixel. Interpolate missing pixels.

  As shown in FIG. 3, the FPD 3 includes a glass substrate 31 and a thin film transistor TFT formed on the glass substrate 31. As shown in FIGS. 3 and 4, the thin film transistor TFT has a large number of switching elements 32 (for example, 1024 × 1024) formed in a vertical / horizontal two-dimensional matrix arrangement. The switching elements 32 are formed separately from each other. That is, the FPD 3 is also a two-dimensional array radiation detector.

  As shown in FIG. 3, an X-ray sensitive semiconductor 34 is stacked on the carrier collection electrode 33, and the carrier collection electrode 33 is connected to the source S of the switching element 32 as shown in FIGS. 3 and 4. Has been. A plurality of gate bus lines 36 are connected from the gate driver 35, and each gate bus line 36 is connected to the gate G of the switching element 32. On the other hand, as shown in FIG. 4, a multiplexer 37 that collects charge signals and outputs them to one is connected with a plurality of data bus lines 39 via amplifiers 38, and also shown in FIGS. Thus, each data bus line 39 is connected to the drain D of the switching element 32.

  With the bias voltage applied to the common electrode (not shown), the gate of the switching element 32 is turned on by applying the voltage of the gate bus line 36 (or 0 V), and the carrier collection electrode 33 is on the detection surface side. The charge signal (carrier) converted from the incident X-ray through the X-ray sensitive semiconductor 34 is read out to the data bus line 39 via the source S and drain D of the switching element 32. Until the switching element is turned on, the charge signal is temporarily accumulated and stored in a capacitor (not shown). The charge signals read to the respective data bus lines 39 are amplified by the amplifiers 38 and are collectively output as one charge signal by the multiplexer 37. The output charge signal is digitized by the A / D converter 8 and output as an X-ray detection signal.

  Next, a series of image processing in the apparatus of the present embodiment will be described with reference to the flowchart of FIG. 5 and FIGS. 6 and 7.

(Step S1) Calibration before X-ray Irradiation FPD 3 is detected in a non-irradiated state where X-rays are not irradiated and digitized by A / D converter 9 and then sent to image processing unit 10 as pixels. Then, the gain of the amplifier 38 is adjusted according to the pixel sent to the image processing unit 9. That is, the gain is adjusted and adjusted so that the pixels for each switching element 32 on the output side are the same. Thus, as shown in the timing chart of FIG. 6, the first calibration is executed by the calibration unit 8.

  Even if calibration is performed and the gain is adjusted to align the output side, these missing pixels usually have unique values. Therefore, as shown in FIG. 7B, these pixels remain as defective pixels even after calibration, and the values of other pixels other than the defective pixels are the same. FIG. 7A is a schematic diagram showing each pixel before calibration, and FIG. 7B is a schematic diagram showing each pixel after calibration. “X” in FIG. 7 represents a defective pixel for convenience.

(Step S <b> 2) Missing Registration The calibrated pixel is sent to the image processing unit 10 again. The missing pixel detection unit 21 in the image processing unit 10 detects a missing pixel using a pixel after calibration, that is, a pixel on the output side. The pixel after the calibration corresponds to the calibration information in the present invention. After detecting the defective pixel, the defective pixel interpolation unit 22 interpolates the defective pixel with a median filter. By performing a series of operations for detecting and interpolating the missing pixels, the missing registration is executed as shown in the timing chart of FIG.

(Step S3) Calibration of X-ray irradiation X-ray is irradiated from the X-ray tube 2 to the subject M (irradiation state). X-rays transmitted through the subject M are detected by the FPD 3 and digitized by the A / D converter 8 and then sent to the image processing unit 10 as pixels. As in step S1, calibration is performed according to the sent pixels (see the timing chart in FIG. 6). In this way, the second calibration is executed.

(Step S4) Missing Registration Similarly to step S2, the missing registration is executed by detecting and interpolating the missing pixel using the calibrated pixel (see the timing chart in FIG. 6).

(Step S5) Calibration Immediately after X-ray Irradiation The FPD 3 detects in the non-irradiation state immediately after X-ray irradiation and is digitized by the A / D converter 8, and then sent to the image processing unit 10 as pixels. As in steps S1 and S3, calibration is performed according to the sent pixels (see the timing chart in FIG. 6). In this way, the third calibration is executed.

(Step S6) Missing Registration Similar to steps S2 and S4, the missing registration is executed by detecting and interpolating the missing pixels using the calibrated pixels (see the timing chart in FIG. 6).

  According to the apparatus of the present embodiment configured as described above, the defective pixel detection unit 21 detects a defective pixel for a pixel based on the detected radiation. In this detection, calibration information relating to the calibration unit 8 (pixels after calibration in this embodiment) is used. Therefore, it is possible to simultaneously detect and interpolate missing pixels in accordance with the timing of calibration (calibration) by the calibration unit 8. Since the calibration by the calibration unit 8 is performed in a predetermined period (for example, one day) shorter than the period for detecting and interpolating the defective pixel, the detection and interpolation of the defective pixel are also performed in a shorter period than before. As a result, it is possible to accurately perform a series of operations (deletion registration) for detecting and interpolating a defective pixel without impairing the operation of the apparatus.

  In this embodiment, a defective pixel is obtained by combining each pixel after calibration obtained in each of the X-ray irradiation state, the non-irradiation state before the X-ray irradiation, and the non-irradiation state immediately after the X-ray irradiation. Detected. By using a combination of pixels after calibration in each state, the above-described defect registration can be performed more accurately. Specifically, there are defective pixels that can be found only in the X-ray irradiation state, those that can be found only in the non-irradiation state, and those that can be found according to the X-ray incident dose. By combining these states, more defective pixels can be detected.

  In this embodiment, the defective pixel is interpolated by replacing the defective pixel as in the median filter processing. However, as exemplified by the interpolation processing for interpolating the pixel based on the adjacent pixel, There is no particular limitation. In addition, when interpolating pixels based on adjacent pixels, measurement is performed in advance while performing calibration on pixels in a non-irradiated state in which X-rays are not irradiated, and pixel weighting is performed based on the correction data. do it.

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

  (1) In the above-described embodiment, the X-ray diagnostic apparatus as shown in FIG. 1 has been described as an example. However, the present invention is also applied to an X-ray diagnostic apparatus disposed on a C-type arm, for example. Also good. The present invention may also be applied to an X-ray CT apparatus.

  (2) In the above-described embodiment, the flat panel X-ray detector (FPD) 3 has been described as an example. However, X-ray detection configured by detection elements arranged in a two-dimensional matrix that partitions pixels. The present invention can be applied to any container.

  (3) In the above-described embodiments, the X-ray detector for detecting X-rays has been described as an example. However, in the present invention, a radioisotope (RI) is administered like an ECT (Emission Computed Tomography) apparatus. The radiation detector is not particularly limited as long as it is a radiation detector that detects radiation, as exemplified by a γ-ray detector that detects γ-rays emitted from a subject. Similarly, the present invention is not particularly limited as long as it is an apparatus that performs imaging by detecting radiation, as exemplified by the ECT apparatus described above.

  (4) In the above-described embodiment, the FPD 3 includes a radiation (in the embodiment, X-ray) sensitive semiconductor and directly converts the incident radiation into a charge signal by the radiation sensitive semiconductor. However, instead of the radiation-sensitive type, it is equipped with a light-sensitive semiconductor and a scintillator, and the incident radiation is converted into light by the scintillator, and the converted light is converted into a charge signal by the light-sensitive semiconductor. It may be an indirect conversion type detector.

  (5) In the above-described embodiment, the defective pixel detection unit 21 illustrated in FIG. 2 detects the defective pixel using the pixel after calibration, that is, the pixel on the output side, but as illustrated in FIG. In addition, by performing calibration, the output side may be even up to the defective pixel, and the defective pixel may disappear at first glance after calibration. FIG. 8A is a schematic diagram showing each pixel before calibration, and FIG. 8B is a schematic diagram showing each pixel after calibration. “X” in FIG. 8A represents a defective pixel for convenience. That is, in FIG. 8A, although there is a missing pixel, “x” representing the missing pixel disappears in a portion corresponding to the missing pixel in FIG. 8B.

  In this case, since the gain value of the detection element relating to the defective pixel is different from the gain value of the detection element relating to other pixels, the calibration unit 8 (see FIG. 1) sets the gain value, for example, the memory unit 12 (see FIG. 1). 1), and each gain is supplied to the defective pixel detection unit 21 of the image processing unit 10 (see FIG. 1) via the controller 11, and the defective pixel is detected using each gain.

  Thus, the calibration information may be a pixel that has been calibrated as in the above-described embodiment, or may be a gain.

  (6) The timing for performing calibration is not particularly limited. For example, it may be performed twice a day or once every three days.

  (7) If it is possible to detect a defective pixel only with the calibration data of the irradiation state or the non-irradiation state, the non-irradiation state before irradiation, the irradiation state, and the non-irradiation immediately after irradiation as in the above-described embodiment It is not always necessary to combine the states.

It is a block diagram of the X-ray diagnostic apparatus which concerns on an Example. It is the block diagram which showed the specific structure of the image process part used for the X-ray diagnostic apparatus. It is the equivalent circuit of the flat panel type X-ray detector used for the X-ray diagnostic apparatus viewed from the side. 2 is an equivalent circuit of a flat panel X-ray detector in plan view. It is a flowchart which shows a series of image processing. It is a timing chart of a series of calibration and defect registration. (A) is a schematic diagram showing each pixel before calibration, and (b) is a schematic diagram showing each pixel after calibration. (A) is a schematic diagram showing each pixel before calibration, and (b) is a schematic diagram showing each pixel after calibration.

3 ... Flat panel X-ray detector (FPD)
8 ... Calibration unit 21 ... Deficient pixel detection unit 22 ... Deficient pixel interpolation unit M ... Subject

Claims (2)

A radiation detection means for detecting radiation that has passed through the subject, a defective pixel detection means for detecting a defective pixel due to a variation of a detection element of the radiation detection means for a pixel based on the detected radiation, and a defective pixel detection means And a defective pixel interpolating unit that interpolates the detected defective pixel, and based on the detected radiation, the defective pixel is interpolated by the defective pixel interpolating unit to perform image processing, thereby imaging the subject. A radiation imaging device comprising:
Pixel calibration means for performing calibration for each detection element constituting the radiation detection means,
The defective pixel detection means detects the defective pixel using the first calibration information output from the pixel calibration means,
Orazu the first calibration information, which still radiation is acquired in a state of not being irradiated to the radiation detecting means, based on the radiation detection signals said radiation detecting means is outputted by detecting the radiation ,
The defective pixel detection means further uses second calibration information output by the pixel calibration means during operation,
2. The radiation imaging apparatus according to claim 1, wherein the second calibration information is based on a radiation detection signal output when the radiation detection means detects radiation that has passed through the subject.   The radiation imaging apparatus according to claim 1,
  The defective pixel detection means further uses third calibration information output by the pixel calibration means during operation,
  The third calibration information is acquired after the radiation detection signal of the radiation that has passed through the subject is read out, and is not based on the radiation detection signal output by the radiation detection means. A radiation imaging apparatus.

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