JP2005176918A - Radiographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic apparatus capable of appropriately executing the image processing. <P>SOLUTION: An auto window control part (AWC) for automatically controlling a window executes the scaling (50 times scaling in this case) for fixing the range of all the remaining pixels from the maximum to the minimum values so that the pixels coincide with the pixels of the maximum value 500. Accordingly, as the scaling is executed with the pixels left as they are even if the pixels of the maximum value are defective pixels, an image with excellent contrast can be obtained. As a result, the appropriate image processing can be executed because of the scaling. Furthermore, as the pixels are left as they are even if the pixels of the maximum value are not defective ones but normal ones, the image processing can be appropriately executed without the pixels being complemented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radiation imaging apparatus used in the medical field, industrial fields such as nondestructive inspection, RI (Radio isotope) inspection, and optical inspection, and in the nuclear power field, and in particular, an image based on detected radiation. The present invention relates to processing technology.

  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 for interpolating the defective pixel, there are a median filter process for replacing the defective pixel with a median pixel from a plurality of pixels adjacent to the defective pixel, an interpolation process for interpolating a pixel based on the adjacent pixel, and the like. These processes are performed based only on pixel information regardless of the pattern of pixels adjacent to the defective pixel. For example, in the case of a pattern in which adjacent pixels also have a defective pixel, there is a risk of interpolation or replacement based on the information of the defective pixel. Therefore, in order to consider the pixel pattern, there is an interpolation processing method that classifies the defective pixel pattern and interpolates the defective pixel in accordance with the classification result (see, for example, Patent Document 1).
JP-A-10-51693 (page 4-7, FIG. 2, FIG. 4, FIG. 6-9)

  However, in the case of these methods including Patent Document 1 described above, pixels having extremely different values are regarded as defective pixels. Therefore, there is a possibility that interpolation or replacement may be performed as a defective pixel if the value is extremely different in spite of normal pixels. As a result, there is a risk that image processing cannot be performed properly.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the radiation imaging device which can perform an image process appropriately.

As a result of intensive studies to solve the above problems, the inventors have obtained the following knowledge.
In other words, the idea of appropriately performing image processing by interpolating the missing pixels was changed, and attention was paid to leaving the missing pixels as they are, or performing image processing by interpolation only when necessary.

  However, even if a missing pixel or a pixel that may be a missing pixel is left as it is, an image with a missing pixel is only obtained. Therefore, the inventors came up with the idea of appropriately performing image processing by combining different methods. By the way, in the field of video typified by television and personal computer monitors, a method called “Window Control” is used. In this method, for example, as shown in FIG. 6A, if there is a pixel having an extremely large value in a part of the monitor and the contrast is bad, a pixel having a large value (ie, as shown in FIG. 6B) Scaling is performed to determine the range from the maximum value to the minimum value for all the remaining pixels so as to match the pixel of the maximum value. The automatic window control is defined as “AWC (Auto Window Control)” in this specification. The inventor has considered replacing the pixel having the maximum value with a pixel that is a defective pixel or a pixel that may be a defective pixel. In this case, even if the defective pixel is left as it is, since the contrast is improved by performing the scaling, the image processing can be appropriately performed. The same can be said for the minimum value pixel.

The present invention based on such knowledge has the following configuration.
The invention according to claim 1 is a radiation imaging apparatus that includes radiation detection means for detecting radiation that has passed through a subject, and that performs image processing based on the detected radiation, thereby imaging the subject. Pixel scaling means for performing scaling to determine the range from the maximum value to the minimum value for all the remaining pixels so as to match the pixels of the maximum value or the minimum value among the pixels based on the detected radiation, Image processing is performed by scaling of the scaling means.

  [Operation / Effect] According to the invention described in claim 1, the pixel scaling means determines the range from the maximum value to the minimum value for all the remaining pixels so as to match the pixel of the maximum value or the minimum value. Perform scaling. Therefore, even if the pixel having the maximum value or the minimum value is a defective pixel, scaling is performed while leaving the pixel as it is, so that an image with good contrast can be obtained. As a result, it is possible to appropriately perform image processing by performing scaling. Even if the pixel having the maximum value or the minimum value is not a defective pixel but a normal pixel, the pixel is left as it is, so that image processing can be appropriately performed without the pixel being interpolated.

  In a case where the pixel having the maximum value or the minimum value can be determined as a defective pixel, in the above-described invention, the defective pixel detection unit that detects the defective pixel and the defective pixel interpolation that performs interpolation of the defective pixel detected by the defective pixel detection unit And image processing is performed by scaling of the pixel scaling means and interpolation of the missing pixel interpolation means (the invention according to claim 2). In this case, an image with good contrast can be obtained with the pixels interpolated, and image processing can be performed more appropriately.

  According to an example of the invention described in claim 2 described above, the above-described missing pixel detection unit detects a pixel having the maximum value or the minimum value used in the scaling of the pixel scaling unit as a missing pixel. Described invention). By detecting the pixel having the maximum value or the minimum value used for scaling as a defective pixel, it is possible to save the trouble of detecting the defective pixel.

  In another example of the invention described in claim 2, the above-described missing pixel interpolation means interpolates the missing pixel using a median pixel from a plurality of pixels around the missing pixel. Item 4). That is, interpolation is performed by replacing the missing pixel with the median pixel in the median filter processing.

  According to the radiation imaging apparatus of the present invention, the pixel scaling means performs scaling for determining the range from the maximum value to the minimum value for all the remaining pixels so as to match the pixel of the maximum value or the minimum value. The image processing can be appropriately performed by performing the scaling while leaving the pixels having the maximum value or the minimum value as they are.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of a flat panel X-ray detector and an X-ray diagnostic apparatus according to an embodiment. FIG. 2 is a block diagram showing a specific configuration of an image processing unit used in the X-ray diagnostic apparatus. FIG. 3 is an equivalent circuit of a flat panel X-ray detector viewed from the side, and FIG. 4 is an equivalent circuit of the flat panel X-ray detector 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, an image processing unit 9 that performs scaling and interpolation processing described later, a controller 10 that controls these components, and a memory unit that stores processed images and the like 11, an input unit 12 in which an operator makes input settings, a monitor 13 for displaying 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 the top and bottom up and horizontally to set 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 setting of the irradiation field of a 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 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 9 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 maximum value pixel detection unit 21 that detects a maximum value pixel, an AWC (Auto Window Control) unit 22 that automatically performs window control, and a maximum value pixel detection unit 21. A missing pixel determination unit 23 that determines whether or not a pixel having the maximum value detected by the value pixel detection unit 21 is a defective pixel, and a defective pixel interpolation unit 24 that performs interpolation of the defective pixel are configured. . With these configurations, the image processing unit 9 performs scaling and interpolation processing.

  The maximum value pixel detection unit 21 includes a separation circuit, a comparator, and the like. The pixel based on the charge signal is spatially expanded for each detection element constituting the capacitor and the switching element 32 in the separation circuit. By comparing the obtained pixels, the pixel having the maximum value is detected. When the pixel with the maximum value detected by the maximum value pixel detection unit 21 is determined as a defective pixel by the defective pixel determination unit 23, the maximum value pixel detection unit 21 has a function of detecting a defective pixel. This corresponds to the missing pixel detection means in this invention. The maximum value pixel detection unit 21 is not limited to the above-described configuration, and the maximum value pixel detection unit 21 is configured by a low-pass filter (LPF) and a subtractor as in Patent Document 1 described above, and spatially. Among the expanded pixel signals, only low-frequency components other than the steep pixel signal that is a high-frequency component are passed through a low-pass filter, and the low-frequency component and the entire signal are subtracted by a subtractor so that the steep pixel By detecting this, a steep pixel, that is, a pixel having the maximum value may be detected.

  The AWC unit 22 includes a multiplier or an adder, and performs scaling on all remaining pixels other than the maximum value pixel by the multiplier or the adder. The AWC unit 22 corresponds to the pixel scaling means in this invention.

  The missing pixel determination unit 23 is configured by a storage medium represented by a RAM or the like, a comparator, etc., and reads out the pixels performed in the past in the same detection element from the storage medium such as the RAM and compares them with a comparator. Whether or not the pixel is a defective pixel is determined.

  The missing pixel interpolation unit 24 is composed of a median filter or the like, detects a median pixel from a plurality of pixels by a median filter, and replaces the missing pixel with the detected median pixel. Interpolate pixels. The missing pixel interpolation unit 24 corresponds to the missing pixel interpolation means in this invention.

  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) X-ray irradiation The subject M is irradiated with X-rays from the X-ray tube 2. 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 maximum value pixel detection unit 21 of the image processing unit 9 as pixels.

(Step S <b> 2) Maximum Value Pixel Detection The maximum value pixel detection unit 21 spatially expands the pixels for each detection element constituting the capacitor and the switching element 32 as shown in FIG. 6A. For the convenience of illustration, the one-dimensional representation is shown in FIG. 6, but the two-dimensional expansion is performed corresponding to the arrangement of the switching elements 32. In the present embodiment, the signal is combined into one signal by the multiplexer 37 and then spatially expanded again. However, in the state of being spatially expanded without providing the multiplexer 37, the maximum value pixel detection unit 21 of the image processing unit 9 You may send it. In this case, since the data sent on the same data bus line 39 is superimposed on the charge signal connected to the gate bus line 36 at each ON / OFF switching time of each switching element 32, each gate is also switched at each switching time. Development is performed in a time-sharing manner by a separation circuit or the like so as to be every pixel of the bus line 36.

  When each pixel is developed for each detection element, each pixel is compared by a comparator to detect the maximum value pixel. For example, as shown in FIG. 7A, when the maximum value pixel is “500” and the remaining pixels are distributed around “10”, the maximum possible pixel value “500” is included. In comparison, the maximum pixel value “500” is detected. Then, steps S3 and S4 are performed in parallel.

(Step S3) Scaling The AWC unit 22 performs scaling for determining the range from the maximum value to the minimum value for all the remaining pixels so that the maximum value pixel matches “500”. For example, when the pixel having the value “10” among the remaining pixels is set to “500”, as shown in FIG. 7B, scaling is performed at 50 times 500/10 (FIG. 6, In FIG. 7, “× 50” represents 50 times scaling). The remaining pixels are also scaled by 50 times. This scaling is performed by a multiplier. The result after scaling is as shown in FIG.

  It should be noted that a pixel having a value other than “10” (for example, a pixel having a value of “12”) n is set to “500” and is multiplied by 500 / n (500/12 times for a pixel having a value of “12”) Scaling may be performed. Further, scaling may be performed by an adder. In this case, when the pixel having the value “10” is set to “500”, scaling is performed by adding 500−10 = 490 to the remaining pixels. And it jumps to step S6.

(Step S4) Is it a defective pixel?
The missing pixel determination unit 23 determines whether or not the maximum value pixel is a defective pixel. As an example of a technique for determining a defective pixel, previously performed pixels in the same detection element are stored in advance in a storage medium such as a RAM, and a detection element having a defective pixel and the maximum detected this time are detected. When the detection element of the value pixel is compared with the comparator and the two match, the maximum value pixel is determined as a defective pixel.

  As another example, a dark current that flows without irradiation without X-ray irradiation is stored in advance in a storage medium as a defective pixel, and a detection element in which the dark current flows and a detection element of the maximum value pixel detected this time Are compared with each other by a comparator, and the pixel having the maximum value is determined as a defective pixel. When the defective pixel determining unit 23 determines that the maximum value pixel is a defective pixel, the process proceeds to the next step S5, and when it is determined that the maximum value pixel is not a defective pixel, the process jumps to step S6.

(Step S5) Median Filter Processing The missing pixel interpolating unit 24 detects a median pixel from a plurality of pixels by a median filter, and replaces the missing pixel with the detected median pixel. Interpolate. For example, in the case of distribution as shown in FIG. 7A, pixels having a value of “11”, which is the median value, from the remaining pixels are excluded, as shown in FIG. 7C. Then, as shown in FIG. 7D, the pixel having the maximum value of “500”, that is, the defective pixel is replaced with the pixel “11”. In FIG. 7C and FIG. 7D, pixels to be replaced are distinguished by being surrounded by “◯”.

(Step S6) Compositing Each pixel scaled in step S3 is combined with the defective pixel subjected to the median filter processing in step S5 when the maximum value pixel is a defective pixel. In the case shown in FIG. 7, the value of the missing pixel subjected to the median filter processing is replaced from “500” to “11”. Therefore, the pixel replaced with “11” is also scaled by 50 times, and the scaling is performed. When combined with the remaining pixels already performed, the result is as shown in FIG.

  According to the apparatus of the present embodiment configured as described above, the AWC unit 22 performs scaling for determining the range from the maximum value to the minimum value for all the remaining pixels so as to match the maximum value pixel. . Therefore, even if the maximum value pixel is a missing pixel, scaling is performed while leaving the pixel as it is, so that an image with good contrast can be obtained. As a result, it is possible to appropriately perform image processing by performing scaling. Further, even if the maximum value pixel is not a defective pixel but a normal pixel, the pixel is left as it is, so that image processing can be appropriately performed without interpolation of the pixel.

  In the present embodiment, a maximum value pixel detection unit 21 that detects a defective pixel and a defective pixel interpolation unit 24 that performs interpolation of the defective pixel detected by the maximum value pixel detection unit 21 are provided. Image processing is performed by interpolation of the pixel interpolation unit 24. In this case, an image with good contrast can be obtained with the pixels interpolated, and image processing can be performed more appropriately.

  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, the pixels may be measured in advance without irradiation with X-rays, and the pixels may be weighted based on the correction data.

  In this embodiment, when the defective pixel determination unit 23 determines that the pixel is a defective pixel, the maximum value pixel detection unit 21 detects the maximum value pixel used in the scaling of the AWC unit 22 as the defective pixel. By detecting this pixel as a defective pixel, it is possible to save the trouble of detecting the defective pixel.

  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 scaling is performed so as to match the pixel of the maximum value. However, the scaling is not limited to the pixel of the maximum value, and from the maximum value to the minimum value so as to match the pixel of the minimum value. Scaling to determine the range may be performed.

  (6) In the above-described embodiment, the interpolation process represented by the median filter or the like is performed on the defective pixel. However, only the scaling may be performed without interpolating the defective pixel.

  (7) In the above-described embodiment, the maximum value pixel detection unit 21 detects the maximum value pixel used in the scaling of the AWC unit 22 as a defective pixel. However, the maximum value pixel detection unit 21 is defective other than the maximum value pixel used in the scaling. If there is a pixel that can be obtained, the pixel may be detected as a defective pixel. That is, the means for detecting the pixel with the maximum value and the means for detecting the defective pixel as in the maximum value pixel detection unit 21 may be separately provided. In the case of scaling, it is performed so as to coincide with the pixel detected by the means for detecting the maximum value pixel, and in the case of interpolation, the detection is performed on the pixel detected by the means for detecting the defective pixel. Such a modification can also be applied to the minimum value pixel.

1 is a block diagram of a flat panel X-ray detector and an X-ray diagnostic apparatus according to an embodiment. 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 the figure which expanded the pixel spatially, Comprising: (a) is each figure before scaling, (b) is each figure after scaling. (A)-(e) is the figure which showed the change of each pixel in a series of image processing.

Explanation of symbols

3 ... Flat panel X-ray detector (FPD)
DESCRIPTION OF SYMBOLS 9 ... Image processing part 21 ... Maximum value pixel detection part 22 ... AWC (Auto Window Control) part 24 ... Missing pixel interpolation part M ... Subject

Claims (4)

  A radiation imaging apparatus that includes radiation detection means for detecting radiation that has passed through a subject and that performs image processing based on the detected radiation, and that performs imaging of the subject, and includes a pixel based on the detected radiation. A pixel scaling unit that performs scaling to determine the range from the maximum value to the minimum value for all the remaining pixels so as to match the pixel of the maximum value or the minimum value, and performs image processing by scaling of the pixel scaling unit A radiation imaging apparatus.   2. The radiation imaging apparatus according to claim 1, comprising: a defective pixel detection unit that detects a defective pixel; and a defective pixel interpolation unit that performs interpolation of the defective pixel detected by the defective pixel detection unit, and the scaling of the pixel scaling unit And a radiation imaging apparatus that performs image processing by interpolation of a defective pixel interpolation unit.   3. The radiation imaging apparatus according to claim 2, wherein the missing pixel detection unit detects a pixel having a maximum value or a minimum value used for scaling of the pixel scaling unit as a missing pixel. 4. The radiation imaging apparatus according to claim 2, wherein the missing pixel interpolation means interpolates the missing pixel using a median pixel from a plurality of pixels around the missing pixel. Imaging device.

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