JP5125233B2 - 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 that constitutes the capacitor or the switching element, and thereby there is also a variation in the pixel value 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 pixel value increases. Conversely, when the sensitivity of the detection element is low, or when dust or the like adheres to the detection element, the pixel value becomes small. A pixel having such a value is called a “missing 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). As described in Patent Documents 1 and 2, the defective pixel is detected before the defective pixel is interpolated. In order to detect a missing pixel, if the difference between the target pixel value and the surrounding pixel values is equal to or greater than a predetermined value (a predetermined value), the pixel having the pixel value is determined as a missing pixel. In addition, when an image is divided into small sections and the divided area is set as a sub-area, and the difference between the median value of the pixel in the sub-area and the target pixel value is equal to or greater than a specified value, the target pixel is determined as a defective pixel. The method of detecting as is also proposed (see, for example, Patent Document 3).
JP 2000-135210 A (page 4-9, FIGS. 3 and 4) JP 2003-219272 A (page 7) JP 2007-54527 A (page 1-9, FIGS. 2, 3 and 5)

  However, there are the following problems when detecting missing pixels. In other words, if the pixel surrounding the target pixel for detecting the defective pixel is a defective pixel and the defective pixel is connected by a plurality of pixels to form a defective pixel group, the difference in pixel values is compared. May not be detected as a defective pixel. In addition, when compared with the average value of the pixel values of all the pixels, the characteristics of the acquired dark image (image acquired at the time of non-irradiation) are ignored, so that a normal pixel may be detected as a defective pixel. is there.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a radiation imaging apparatus capable of accurately detecting a defective pixel in consideration of image characteristics.

In order to achieve such an object, the present invention has the following configuration.
That is, the invention described in claim 1 includes radiation detecting means for detecting radiation transmitted through the subject, and defective pixel detecting means for detecting defective pixels for pixels based on the detected radiation, wherein the radiation detecting means Is a radiation imaging apparatus that is composed of detection elements arranged in a two-dimensional matrix that partitions pixels, and that performs image processing based on detected radiation, thereby imaging a subject. Pixel value collecting means for collecting pixel values based on radiation detected in an irradiation state or a radiation irradiation state of constant intensity over a plurality of frames, and a pixel value for averaging the pixel values collected by the pixel value collecting means between frames and averaging means, among the averaged pixel values at the pixel value averaging means, takes out a plurality fraction to said detection elements arranged row or column Its plurality amount based on the pixel value of a statistical quantity computing means for calculating statistics for row or column direction of the pixel values, statistics and for the row or column direction of the pixel values obtained by the statistical quantity computing means The pixel values collected by the pixel value collecting unit are compared, and the missing pixel detecting unit detects a missing pixel based on the comparison result of the statistic and the pixel value.

[Operation / Effect] According to the first aspect of the present invention, in the case of including the radiation detection means composed of the detection elements arranged in a two-dimensional matrix that partitions the pixels, the pixel value collection means is not irradiated. The pixel values based on the radiation detected in the state or the irradiation state of the constant intensity are collected over a plurality of frames, and the pixel value averaging means averages the pixel values collected by the pixel value collecting means between the frames, and the pixels Of the pixel values averaged by the value averaging means, a plurality of the above-described detection elements are taken out in the row or column direction, and a statistic calculation means is based on the pixel values for the plurality of pixel values. Finds the statistic for the row or column direction of the pixel value. The characteristics of the image are caused by the radiation detection means and depend on the row or column direction which is the arrangement direction of the detection elements. Therefore, the statistic calculation means calculates the statistic in the row or column direction of the pixel value, and thereby calculates the statistic in consideration of the characteristics of the image. Then, the pixel value obtained by the statistic calculation means in the row or column direction is compared with the pixel value collected by the pixel value collection means, and the defective pixel is detected based on the comparison result between the statistic and the pixel value. When the means detects the defective pixel, the defective pixel is detected in consideration of the characteristics of the image. As a result of considering the characteristics of the image, the defective pixel detection means can accurately detect the defective pixel.

  In the above-described invention, in order to interpolate the defective pixel detected by the defective pixel detecting means, it is preferable to include a defective pixel interpolating means for interpolating the defective pixel detected by the defective pixel detecting means. Described invention). Based on the radiation detected by the radiation detecting means, the defective pixel is interpolated by the defective pixel interpolating means and image processing is performed, thereby imaging the subject.

  In one example of these inventions described above, the statistic in the row or column direction of the pixel value obtained by the statistic calculation means is the median value in the row or column direction of the pixel value, and the statistic calculation means is the median filter. In this case, the median value obtained by the median filter processing and the pixel value collected by the pixel value collecting unit are compared, and the missing pixel detecting unit detects the missing pixel based on the comparison result between the median and the pixel value. (Invention of claim 3) That is, when the statistic is a median value, the statistic calculation means is a median filter, and the median value can be obtained by the median filter processing. In the above-described invention, the missing pixel can be detected by using the median as an example of the statistic. Of course, the statistic is not limited to the median, and an average value may be used as the statistic.

  The radiation detection means is composed of the detection element as described above, but the elements other than the detection element are connected to the control line for controlling ON / OFF of the switching element of the detection element, and downstream of the switching element, The radiation detection means is composed of a readout line for reading out a radiation detection signal based on the detected radiation. The image characteristics depend significantly on the readout line of the radiation detection means. Therefore, in these inventions described above, the statistic calculating means extracts a plurality of statistics in the direction along the readout line, and calculates the statistics in the direction along the readout line based on the pixel values for the plurality of pixels. It is preferable to obtain (the invention according to claim 4).

According to the radiation imaging apparatus according to the present invention, in the case where the radiation detection means configured by the detection elements arranged in a two-dimensional matrix that partitions the pixels is provided, the pixel value collection means is in a non-irradiation state or a constant intensity. The pixel values based on the radiation detected in the radiation irradiation state are collected over a plurality of frames , the pixel values collected by the pixel value collecting means are averaged between frames, and the pixel value averaging means Among the averaged pixel values, a plurality of pixels are extracted in the row or column direction in which the above-described detection elements are arranged, and based on the pixel values for the plurality of pixel values, the statistic calculation unit calculates the pixel value rows. Alternatively, the statistics for the column direction are obtained. Then, the pixel value obtained by the statistic calculation means in the row or column direction is compared with the pixel value collected by the pixel value collection means, and the defective pixel is detected based on the comparison result between the statistic and the pixel value. When the means detects the defective pixel, the defective pixel can be accurately detected in consideration of the characteristics of the image.

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, an A / D converter 8 that digitizes and extracts an X-ray detection signal that is a charge signal from the FPD 3, and an A / D converter 8 In addition to performing various processes based on the X-ray detection signal, the image processing unit 9 performs pixel registration, pixel averaging, intermediary filtering, and median filter processing, which will be described later, and defect registration such as detection and interpolation of defective pixels, A controller 10 that controls each of the components, a memory unit 11 that stores processed images, an input unit 12 that allows an operator to make input settings, a monitor 13 that displays processed images, and the like.

  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 A / D converter 8 converts the charge signal output from the FPD 3 from analog to digital, and outputs a digitized X-ray detection signal. The controller 10 is configured by a central processing unit (CPU) and the like, and the memory unit 11 is configured by a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. Yes. The input unit 12 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 that have passed through the subject M, and the image processing unit 10 performs image processing based on the detected X-rays, thereby imaging the subject M.

  As shown in FIG. 2, the image processing unit 9 includes a pixel value collection unit 21 that collects pixel values based on an X-ray detection signal detected in a non-irradiation state, and a pixel value collected by the pixel value collection unit 21. An averaging unit 22 that averages between frames, and a row in which detection elements to be described later are arranged among the pixel values collected by the pixel value collecting unit 21 and averaged between the frames by the averaging unit 22. Alternatively, a median filter 23 that takes out a plurality of pixels in the direction along the data bus line 39 (see FIGS. 3 and 4) as a column direction and performs a median filter process on the pixel values of the plurality of pixels, The median and pixel value collecting unit 21 collects the median filter 23 in the direction along the data bus line 39 and the averaging unit 22 performs interframe averaging. The defective pixel detection unit 24 that compares the processed pixel values and detects the defective pixel based on the comparison result of the median value and the pixel value, and the defective pixel that interpolates the defective pixel detected by the defective pixel detection unit 24 And an interpolation unit 25. With these configurations, the image processing unit 9 performs defect registration, which is a series of operations for detecting and interpolating missing pixels. The pixel value collection unit 21 corresponds to the pixel value collection unit in the present invention, the median filter 23 corresponds to the statistic calculation unit in the present invention, and the missing pixel detection unit 24 corresponds to the missing pixel detection unit in the present invention. The missing pixel interpolation unit 25 corresponds to the missing pixel interpolation means in this invention. The median value corresponds to a statistic, and the direction along the data bus line 39 corresponds to the row or column direction in which the detection elements are arranged.

  The missing pixel detection unit 24 is configured by a separation circuit, a comparator, and the like. The pixel value based on the X-ray detection signal is spatially expanded for each detection element constituting the capacitor or the switching element 32 by the separation circuit, By comparing the developed pixel values, the pixel having the maximum value or the minimum value is detected as a defective pixel. The defective pixel detection unit 24 is not limited to the above-described configuration, and the defective pixel detection unit 24 is configured by a low-pass filter (LPF) and a subtracter, and a high-frequency component among the spatially expanded pixel signals. 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.

  Further, the defective pixel is not limited to the pixel having the maximum value or the minimum value described above, and as described in the paragraph “Problems to be solved by the invention”, the peripheral pixel is a defective pixel and a plurality of defective pixels. This includes a case where a defective pixel group is formed by connecting pixels. In this case, the pixel having the maximum value or the minimum value described above cannot be detected as a defective pixel. Therefore, in order to detect such a defective pixel group as a defective pixel, the pixel value collection unit 21, the averaging unit 22, and the median filter 23 described above are provided in the preceding stage of the defective pixel detection unit 24. The pixel value collection unit 21, the averaging unit 22, and the median filter 23 will be described later with reference to the flowchart of FIG.

  The missing pixel interpolation unit 25 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. The switching element 32 corresponds to the switching element in the present invention, the gate bus line 36 corresponds to the control line in the present invention, and the data bus line 39 corresponds to the read line in the present invention.

  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 32 is turned on, the charge signal is provisionally accumulated and stored by 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.

  In summary, the FPD 3 includes detection elements (capacitors, switching elements 32, etc.) arranged in a two-dimensional matrix that partitions pixels. In elements other than the detection element, a gate bus line 36 that controls ON / OFF of the switching element 32 of the detection element, and a data bus that is connected downstream of the switching element 32 and reads an X-ray detection signal based on the detected X-rays. The line 39 constitutes the FPD 3. The characteristics of the image remarkably depend on the data bus line 39 corresponding to the readout line of the FPD 3. That is, depending on the characteristic of the amplifier 38 connected downstream of the data bus line 39, the characteristic of the image changes depending on the variation of the amplifier 38 for each data bus line 39.

  Therefore, in this embodiment, the direction along the data bus line 39 is adopted as the row or column direction in which the detection elements are arranged. The median filter 23 (see FIG. 2) extracts a plurality of medians in the direction along the data bus line 39, and based on the pixel values for the plurality of pixels, the median filter 23 (see FIG. 2) We are looking for a value.

  Next, a series of image processing in the apparatus of the present embodiment will be described with reference to the flowchart in FIG. 5, the schematic diagram in FIG. 6, and the schematic diagram in FIG. FIG. 5 is a flowchart showing a series of image processing, FIG. 6 is a schematic diagram of an image for explaining the inter-frame averaging, and FIG. 7 is a schematic diagram of a pixel for explaining the median filter processing. .

(Step S1) Acquire images of a plurality of frames (Image A)
After being detected by the FPD 3 in a non-irradiated state where X-rays are not irradiated and digitized by the A / D converter 8, they are sent to the image processing unit 9 as pixels. In this non-irradiation state, the FPD 3 detects X-rays, and the pixel value collection unit 21 of the image processing unit 9 collects pixel values based on the detected X-rays. By collecting each pixel value, an image composed of each pixel is acquired. This image is assumed to be an image A as shown in FIG. In this embodiment, the FPD 3 detects non-irradiated X-rays at a predetermined imaging cycle (for example, 0.033 sec / F of the TV rate), and acquires a plurality of frames of images A.

(Step S2) Averaging between frames (image B)
A plurality of frames are sequentially designated as F ₁ , F ₂ ,..., F _i , ..., F _m−1 , F _m . The averaging unit 22 averages (averages) the pixel values collected by the pixel value collecting unit 21 between frames. Specifically, the pixel in the image A is (x, y) as shown in FIG. The pixel value at the pixel (x, y) in the frame F _i is defined as P _i (x, y) (where i = 1, 2,..., M−1, m). An average value of pixel values P _i (x, y) is obtained for each identical pixel (x, y) between frames (indicated as “Average” in FIG. 6). That is, the average value can be obtained by 1 / n × ΣP _i (x, y) (where Σ is the sum of P _i (x, y) from i = 1 to m). An image composed of pixels (x, y) having the averaged pixel value (that is, average value) is set as an image B as shown in FIG. By acquiring this image B, inter-frame averaging is performed. By performing the inter-frame averaging by the averaging unit 22, the following problems can be solved.

  In other words, there are pixels that are not always determined as defective pixels but are recognized as defective on the image, in addition to pixels that are always defective. That is, at a certain point in time, it is determined that the pixel value is not a defective pixel at the same level as the surrounding pixel values, and at a certain point in time, the pixel value is extremely large / smaller than the surrounding pixel value and is determined to be a defective pixel. Pixels exist. Therefore, there is a problem that a defective pixel is normally detected as a normal pixel due to temporal variations. Therefore, by performing inter-frame averaging by the averaging unit 22, a pixel that is not always determined to be a defective pixel but is recognized as a defective pixel on the image can be detected as a defective pixel in step S6 described later. Note that step S2 is not always necessary, and if there is little time variation, an image for one frame is collected in step S1, and steps S3 and S4 to be described later are performed using the image. Therefore, the averaging unit 22 that executes step S2 is not necessarily required.

(Step S3) Median filter processing of image B (image C)
The data bus lines 39 are sequentially designated as L ₁ , L ₂ ,..., L _j , ..., L _n−1 , L _n . Among the pixel values collected by the pixel value collecting unit 21 and averaged between the frames by the averaging unit 22, a plurality of pixel values are extracted in the direction along the data bus line 39, and the pixel values for the plurality of pixel values are obtained. On the other hand, the median filter 23 performs median filter processing. In the present embodiment, description will be made assuming that the data bus line 39 and the pixel column are in one-to-one correspondence. Specifically, the averaging image B between frames, as shown in FIG. 7, a pixel column along the data bus line _{39 L 1, L 2, ...} , L j, ..., L n-1, L Divide into _n . Then, take out the pixels of the plurality (in FIG. 7 8) from within the pixel row L _j. The number of pixels to be extracted is not particularly limited, and is determined in consideration of the size of the assumed defective pixel group and the calculation processing time. For example, it may be taken out all the pixels belonging in the pixel column L _j, may retrieve pixel half from all pixels belonging in the pixel column L _j. Median filter processing is performed on the pixel values of a plurality of extracted pixels belonging to the pixel column L _j (indicated as “median” in FIG. 7). That is, pixel values having a median value are extracted by arranging the pixel values of the extracted pixels. The pixel values of all the pixels belonging to the same pixel column L _j are respectively replaced with the pixel values (that is, the median value) of the extracted pixels. The same median filter process is performed for the other pixel columns, and an image composed of the pixel column L _j having the pixel value replaced with the median value is acquired. This image is referred to as an image C. By acquiring this image C, the median filter processing of the image B is performed.

(Step S4) Comparison between Image B and Image C The median value in the direction along the data bus line 39 obtained by the median filter 23 (that is, the image C obtained by the median filter processing in step S3), and the pixel value The missing pixel detection unit 24 compares the pixel values collected by the collection unit 21 and averaged between frames by the averaging unit 22 (that is, the image B averaged between frames in step S2). Specifically, in order to compare the image B and the image C for each same pixel, an offset value is added to the image B and the image C is subtracted. The offset value is added to make it easy to produce a difference. When the distribution of image values is biased, it is preferable to add the offset value. Of course, the difference between the image B and the image C may be simply obtained without adding the offset value.

(Step S5) Less than lower limit threshold? or upper threshold exceeded?
In step S4, an offset value is added to the image B, the image C is subtracted, and it is determined whether or not the obtained pixel value is less than the lower threshold or exceeds the upper threshold. If it is less than the lower threshold or exceeds the upper threshold, the process proceeds to the next step S6. If the threshold value is equal to or higher than the lower threshold value and equal to or lower than the upper threshold value, it is determined that the corresponding pixel is not a defective pixel but a normal pixel, and a series of image processing ends.

(Step S6) Detection of Missing Pixel When the pixel is less than the lower limit threshold or exceeds the upper limit threshold, the missing pixel detection unit 24 determines that the corresponding pixel is a missing pixel. That is, when the pixel value of the pixel in the image B is compared with the median value in the image C in consideration of the offset value, it is extremely large when exceeding the upper limit threshold, and extremely small when less than the lower limit threshold. The corresponding pixel is a defective pixel. As described above, steps S4 to S6 are performed on all the pixels, and the defective pixel is added to the defective map to register the defective data.

(Step S <b> 7) Missing Pixel Interpolation The missing pixel interpolation unit 25 performs the interpolation of the missing pixels detected by the missing pixel detection unit 24. The image processing unit 9 performs various processes other than steps S1 to S7 on the image including the defective pixel interpolated in this way. Then, a series of processing ends.

  According to the apparatus of the present embodiment configured as described above, when the flat panel X-ray detector (FPD) 3 composed of detection elements arranged in a two-dimensional matrix that partitions the pixels is provided, the pixels The value collection unit 21 collects pixel values based on the X-ray detection signal detected in the non-irradiation state, and among the pixel values collected by the pixel value collection unit 21 and averaged between the frames by the averaging unit 22 A plurality of detection elements are taken out in the direction along the data bus line 39 as the row or column direction in which the detection elements are arranged, and the median filter 23 performs median filter processing on the pixel values for the plurality of pixel values. The characteristics of the image are caused by the FPD 3 and depend on the row or column direction which is the arrangement direction of the detection elements. In particular, as described above, the characteristics of the image remarkably depend on the data bus line 39 of the FPD 3. Therefore, when the median filter 23 obtains the median value in the direction along the data bus line 39 (that is, the pixel column), the median value is obtained as a statistic in consideration of the characteristics of the image. Then, the median value in the direction along the data bus line 39 obtained by the median filter 23 and the pixel value collected by the pixel value collecting unit 21 and averaged between frames by the averaging unit 22 are compared. In addition, the defective pixel detection unit 24 detects the defective pixel based on the comparison result of the pixel values, thereby detecting the defective pixel in consideration of the characteristics of the image. As a result of considering the characteristics of the image, the missing pixel detector 24 can accurately detect the missing pixel.

  Then, in order to interpolate the defective pixel detected by the defective pixel detection unit 24, a defective pixel interpolation unit 25 that performs interpolation of the defective pixel detected by the defective pixel detection unit 24 is provided. Based on the X-rays detected by the FPD (flat panel X-ray detector) 3, the defective pixel interpolation unit 25 performs image processing by interpolating the defective pixels, thereby imaging the subject.

  In the present embodiment, the median value is taken as an example of the statistic, and the median filter 23 is taken as an example of the statistic calculation means in the present invention. That is, the median value obtained by the median filter processing and the pixel value collected by the pixel value collection unit 21 are compared, and the missing pixel detection unit 24 detects the missing pixel based on the comparison result of the median value and the pixel value. ing. As described above, in this embodiment, the missing pixel can be detected by using the median as an example of the statistic.

  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, pixel values based on X-rays detected in a non-irradiation state are collected, and the collected pixel values are used to obtain a statistic (median value in the embodiment) to obtain a defect. Pixels are detected, but pixel values based on radiation (X-rays in the example) detected in a state of irradiation with a certain intensity of radiation (X-rays in the example) are collected, and the collected pixel values are used. A missing pixel may be detected by obtaining a statistic (median value in the embodiment).

  (6) In the above-described embodiment, the median value of the pixel value in the row or column direction has been described as an example of the statistic for the row or column direction of the pixel value (in the embodiment, the direction along the data bus line). However, it is not limited to this. For example, the average value of the pixel group in the row or column direction of the pixel value may be adopted as a statistic for the row or column direction of the pixel value.

  (7) In the above-described embodiment, the direction along the data bus line 39 (that is, the direction of the pixel column) is described as an example of the row or column direction in which the detection elements are arranged. However, the present invention is not limited to this. A direction along the pixel row, that is, the gate bus line 36 may be adopted. In this case, a plurality of values are extracted with respect to the direction along the gate bus line 36, and a statistic (median value in the embodiment) for the direction along the gate bus line 36 based on the pixel values for the plurality of pixels. Will be asked. However, since the characteristics of the image remarkably depend on the direction along the data bus line 39 rather than the direction along the gate bus line 36, a plurality of the characteristics along the data bus line 39 as in the embodiment. It is preferable to take out a plurality of pieces and obtain a statistic for the direction along the data bus line 39 based on the plurality of pixel values.

  (8) In the embodiment described above, a difference is taken for comparison, and a defective pixel is detected by determining whether or not it is less than the lower threshold or exceeds the upper threshold. However, the absolute value of the difference may be taken. In this case, a defective pixel is detected by determining only when the upper limit threshold is exceeded.

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 schematic diagram of an image used for explanation of averaging between frames. It is a schematic diagram of the pixel used for description of a median filter process.

Explanation of symbols

3 ... Flat panel X-ray detector (FPD)
DESCRIPTION OF SYMBOLS 21 ... Pixel value collection part 23 ... Median filter 24 ... Missing pixel detection part 25 ... Missing pixel interpolation part 32 ... Switching element 36 ... Gate bus line 39 ... Data bus line M ... Subject

Claims (4)

Radiation detection means for detecting radiation that has passed through the subject, and defective pixel detection means for detecting defective pixels for pixels based on the detected radiation, wherein the radiation detection means is in the form of a two-dimensional matrix that partitions the pixels. A radiation imaging apparatus that is composed of arrayed detection elements and performs image processing based on detected radiation to image a subject, which is detected in a non-irradiation state or a constant-intensity radiation irradiation state Pixel value collecting means for collecting pixel values based on the emitted radiation over a plurality of frames, pixel value averaging means for averaging pixel values collected by the pixel value collecting means between frames, and pixel value averaging means image in among the averaged pixel values, retrieves a plurality min to the row or column direction in which the detecting elements are arranged, on the basis of the pixel values of the plurality min And a statistic calculation means for calculating a statistic for the row or column direction of the value, collected pixel values in statistics and the pixel value collection means for the row or column direction of the pixel values obtained by the statistical quantity computing means And the missing pixel detecting means detects the missing pixel based on the comparison result of the statistic and the pixel value.   The radiation imaging apparatus according to claim 1, further comprising a defective pixel interpolation unit that performs interpolation of a defective pixel detected by the defective pixel detection unit, and based on the radiation detected by the radiation detection unit. A radiation imaging apparatus characterized in that imaging of a subject is performed by performing image processing by interpolating a defective pixel.   The radiation imaging apparatus according to claim 1 or 2, wherein the statistic for the row or column direction of the pixel value obtained by the statistic calculation unit is a median value for the row or column direction of the pixel value, The statistic calculation means is a median filter, and compares the median value obtained by the median filter processing with the pixel value collected by the pixel value collection means, and based on the comparison result of the median value and the pixel value, the missing value A radiation imaging apparatus, wherein the pixel detection means detects a defective pixel.   4. The radiation imaging apparatus according to claim 1, wherein the radiation detection unit is connected to a control line that controls ON / OFF of a switching element of the detection element and a downstream of the switching element, and is detected. A plurality of readout lines for reading out radiation detection signals based on the emitted radiation, wherein the statistic calculation means extracts a plurality of pieces in a direction along the readout line and reads out the plurality of pixels based on the plurality of pixel values. A radiation imaging apparatus characterized by obtaining a statistic for a direction along a line.

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