Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T7/00—Details of radiation-measuring instruments
  • G01T7/005—Details of radiation-measuring instruments calibration techniques

Definitions

• the present invention relates to an X-ray diagnostic imaging apparatus including an X-ray flat panel detector (FPD), and more particularly to an improved technique for offset correction of FPD.
• FPD X-ray flat panel detector
• An X-ray image diagnostic apparatus converts and transmits transmitted X-rays of a subject to X-ray image data by FPD, and displays the output X-ray image data on a monitor.
• a plurality of detection elements are arranged in a matrix corresponding to each pixel of the X-ray image data, and a desired pixel can be read out via the switching element.
• This detector element is a scintillator (for example, cesium iodide) that generates light in response to the incidence of X-rays, a photodiode that converts the optical signal output from this scintillator, and charges, and stores the converted charges.
• a capacitor that is, each pixel of the X-ray image data corresponds to the electric charge accumulated in the capacitor of the respective detection element. Therefore, by driving the switching element and reading out the electric charge corresponding to the desired pixel, the X-ray image data is read out. obtain.
• Patent Document 1 JP 2002-159481 A
• the offset correction data of the FPD has a large temperature dependency. Specifically, the amount of current changes due to heat generation from the circuit portion itself and a temperature change around the detector. If the amount of change in the dark current amount is greater than a predetermined threshold, the conventional offset correction There was an unresolved problem that sometimes it could not be handled.
• An object of the present invention is to provide an X-ray diagnostic imaging apparatus capable of obtaining good image quality even when the amount of change in offset correction data in FPD is larger than a predetermined threshold.
• the X-ray image diagnostic apparatus of the present invention includes an X-ray generation unit that irradiates a subject with X-rays, and a transmission X-ray of the subject that is disposed so as to face the X-ray generation unit and converts the X-ray image data as X-ray image data.
• the offset correction data varies depending on the use environment of the X-ray flat panel detector based on the created offset correction data.
• Pixel detection means for detecting pixels outside the predetermined range, and predetermined data correction for the offset correction data of the detected pixels, and output to the offset correction means.
• a correction unit wherein the data corrected offset correction data is provided with an image display unit for displaying the image data that has been subtracted from by connexion the X-ray image data to said offset correction means.
• FIG. 1 is a functional block diagram showing a first embodiment of the present invention.
• FIG. 2 is a flowchart showing an operation procedure in FIG.
• FIG. 3 is a schematic explanatory diagram showing a region of 3 ⁇ 3 pixels in a photographed image, and a graph showing variations in luminance values of three pixels in the region.
• FIG. 4 is a functional block diagram showing Embodiment 2 of the present invention.
• FIG. 5 is a flowchart showing an operation procedure in FIG.
• FIG. 6 is a flowchart showing an operation procedure in the third embodiment. Explanation of symbols
• the X-ray diagnostic imaging apparatus includes an X-ray generating unit 1, an FPD 2 disposed opposite to the X-ray generating unit 1, and an operation of the X-ray diagnostic imaging apparatus.
• An operation panel 3 installed in the operator's operation room, an image processing device 4 connected to each component from the X-ray generation unit 1 to the operation panel unit 3, and an image connected to the image processing device 4
• a display unit 5 is provided.
• the X-ray generation unit 1 shields X-rays outside the irradiation range so that only the X-ray tube that generates X-rays and the irradiation range of the generated X-rays are irradiated. It has an X-ray aperture.
• the FPD 2 is arranged opposite to the X-ray generation means 1 and converts the incident X-rays as X-ray image data by the incidence of X-rays emitted from the X-ray generation unit 1.
• the subject ⁇ is located between the X-ray generator 1 and the FPD2, the X-rays emitted from the X-ray generator 1 pass through the subject ⁇ , and the transmitted X-ray enters the FPD2 X-ray images can be obtained.
• the shooting conditions (tube voltage, tube current time product, etc.) necessary for this shooting are input and set by the operator from the operation panel section 3.
• the X-ray image data converted and output from the FPD 2 is stored in the image data storage means 410 in the image processing apparatus 4.
• the storage means 410 stores not only a photographed image of the subject eye but also an offset image described later.
• Various image processing is performed by the image processing device 4 using the X-ray image data read from the storage means 410, and the X-ray image after the image processing is displayed on the image display unit 5 such as a display.
• the image processing device 4 uses the X-ray image data read from the storage means 410, and the X-ray image after the image processing is displayed on the image display unit
• the image processing apparatus 4 includes a correction data creation unit 411, a correction data storage unit 412 connected to the correction data creation unit 411, and an offset correction unit 413 connected to the correction data storage unit 412. I have.
• the correction data creation unit 411 creates correction data for offset correction of the dark current force of the FPD2. This dark current reading is performed in the absence of the subject eye and by irradiating X-rays. This is done by acquiring multiple images (offset images) in a shining state. This offset image is acquired in a timely manner during non-shooting. An average image of the plurality of offset images is used as correction data.
• the correction data storage unit 412 stores the correction data created by the correction data creation unit 411.
• the correction data in the correction data storage unit 412 is updated as appropriate to reflect changes in the operating environment of the device such as temperature.
• the offset correction unit 413 performs an offset correction process by subtracting correction data from the captured image of the subject P.
• the image processing apparatus 4 includes a variation pixel detection unit 414 connected to the image data storage unit 410, a position information storage unit 415 connected to the variation pixel detection unit 414, an offset correction unit 413, and a position A variable pixel correction unit 416 connected to the information storage unit 415 is also provided.
• the fluctuation pixel detection unit 414 detects a fluctuation pixel having a large fluctuation amount of the dark current amount.
• the variation pixel is detected by comparing each pixel value of the offset image immediately before photographing with each pixel value in the average image of a plurality of offset images acquired before that time. For example, if the pixel value of the offset image immediately before photographing has a difference of 10% or more with respect to the pixel value of the average image, the pixel is determined as a variable pixel.
• the position information storage unit 415 stores position information of pixels determined to be variable pixels. Since each pixel of the FPD2 is arranged in a plane coordinate form, the coordinates of each pixel may be stored as position information.
• the variable pixel correction unit 416 performs the following correction on the output of the variable pixel.
• correction is performed using the average pixel value of the non-varying pixels in the 3 ⁇ 3 pixel area centering on the varying pixels as the pixel value of the varying pixels.
• the image processing apparatus 4 is connected to the gain correction unit 417 connected to the variable pixel correction unit 416, the defective pixel correction unit 418 connected to the gain correction unit 417, and the defective pixel correction unit 418.
• the gain correction unit 417 corrects the relationship between the X-ray incident dose and the output value of each pixel of the FPD2 based on the sensitivity characteristic data defined in advance of the FPD2.
• the defective pixel correction unit 418 includes the position information of the defective pixels stored in the defective pixel information storage unit 419. Based on the information, the output of the defective pixel is corrected. For example, the image data after gain correction processing is corrected using the average pixel value of non-defective pixels in the 3 ⁇ 3 pixel region centered on the defective pixel as the pixel value of the defective pixel.
• the image processing apparatus 4 controls the entire X-ray image diagnostic apparatus.
• the image processing apparatus 4 acquires a plurality of offset images prior to imaging of the subject P, and stores the images in the image data storage unit 410. (Step S1)
• the variation pixel detection unit 414 detects the variation pixel using the offset image stored in the image data storage unit 410. Specifically, among the offset images, the pixel value of the offset image immediately before shooting is compared with the pixel value (threshold value) of an image obtained by averaging a plurality of offset images before that to detect a fluctuation pixel. To do. Here, if the pixel value of the offset image immediately before photographing is greater than 10% from the threshold value, it is determined that the pixel is a variable pixel. (Step S2).
• the image processing device 4 if it is detected the defective pixel and stores the position information of the pixel in the position information storage ⁇ 41 5. (Step S3)
• the image processing apparatus 4 captures the subject P based on the operation of the operator, acquires the captured image, and stores the captured image in the image data storage unit 410. (Step S4).
• the image processing device 4 reads the offset correction data from the correction data storage unit 412, and performs offset correction processing by subtracting the photographic image force correction data by the offset correction means 413 (step S5).
• the image processing device 4 causes the fluctuation pixel correction unit 416 to correct the pixel value of the fluctuation pixel of the dark current correction image subjected to the offset processing (step S6).
• the position information storage means 415 stores the position information of the variable pixels, and the average pixel value of the non-change pixels is changed in the 3 ⁇ 3 pixel area centered on the change pixels. Correction to the pixel value of the pixel is performed.
• the procedure of the variable pixel correction is as follows. First, the image processing apparatus 4 stores the position information. It is determined whether or not the position information of the variation pixel is stored in the unit 415. If the position information is present, variation pixel correction processing is performed on the output value of the pixel corresponding to the position information. Also, the image processing device 4 does not perform the variable pixel correction process if there is no position information! /.
• the image processing apparatus 4 After performing this variable pixel correction processing, the image processing apparatus 4 performs gain correction processing by the gain correction unit 417 (step S7). Further, the defective pixel correction unit 418 performs a defective pixel correction process on the gain correction image after the gain correction process (step S8). Then, the image processing device 4 displays the image subjected to these correction processes on the image display unit (step S9). Steps S7 and S8 can be performed as needed, or can be omitted if they are already performed in order, and step S9 (image display) after step S6 (fluctuating pixel correction processing) can also be performed. it can.
• a pixel with a large amount of variation in dark current is specified, and predetermined correction is performed by the variation pixel correction unit 416 on the pixel value of the pixel.
• predetermined correction is performed by the variation pixel correction unit 416 on the pixel value of the pixel.
• each pixel value of the offset image immediately before photographing is compared with each pixel value in the average image of a plurality of offset images acquired before that, and the variation pixel is detected.
• a pixel having a pixel value deviated by a certain width or more from an average pixel value in a predetermined area of the photographed image may be determined as a variation pixel.
• FIG. 3A shows an area indicated by 3 ⁇ 3 pixels in the photographed image.
• the pixel values of either vertical, horizontal, or diagonal pixel groups are shown in Fig. 3 (B).
• the output value is larger than other normal pixels. be able to.
• FPD pixels are about 0.15 mm square, for example, and even if there are high and low luminance values (pixel values) in the captured image, the pixel values of adjacent pixels differ greatly. This is rare, and it is possible to detect a fluctuating pixel by comparing the pixel values of adjacent pixels.
• FIG. 4 and FIG. 4 show an embodiment in which when a specific pixel is determined as a fluctuation pixel a predetermined number of times or more, the fluctuation pixel is determined as a defective pixel and a predetermined correction is performed on the output of the defective pixel. This will be explained based on 5.
• the main difference is that a counter means 420 and a defective pixel adding means 421 are added to the structure of the first embodiment, and the other structures are the same as in the first embodiment. It is the same.
• the counter means 420 is connected to the fluctuation pixel detection unit 414 and the position information storage unit 415
• the defective pixel addition unit 421 is connected to the position information storage unit 415 and the defective pixel information storage unit 419.
• the description will focus on the differences from the first embodiment.
• the counter unit 420 counts the number of times each pixel is determined to be a variable pixel by the variable pixel detection unit 414.
• the counter means 420 counts the cumulative number of times that the variation pixel detection unit 414 has determined that the pixel is a variation pixel from the start of use of the apparatus of the present invention.
• the number of times that the variation pixel detection unit 414 determines the variation pixel within a certain period may be counted.
• the counter unit 420 causes the position information storage unit 415 to store the count number. That is, the position information storage unit 415 of this embodiment also has a function of storing the count number of the counter unit 420.
• the defective pixel adding unit 421 determines that a pixel whose count number in the counter unit 420 exceeds a predetermined threshold value is a defective pixel, and determines the position information of the defective pixel as a defective pixel information storage unit 41 9.
• a pixel whose count number of the counter means 420 is 100 or more is determined as a defective pixel.
• the second embodiment is different from the first embodiment in the method of detecting a changing pixel by the changing pixel detection unit 414.
• the pixel value in the photographed image is compared with the average value of the pixel values in a specific area of the photographed image, and a pixel having a pixel value that deviates from the average value by a certain threshold is found.
• a pixel having a pixel value that is 20% or more out of the average pixel value in the 3 ⁇ 3 pixel region is determined as a variation pixel.
• the image processing device 4 acquires a captured image (step SI 1).
• the image processing apparatus 4 compares the pixel value in the photographed image with the average value of the pixel values in the specific region of the photographed image by the varying pixel detection means 414, and detects the varying pixel (step S12).
• the image processing device 4 stores, in the position information storage unit 415, the position information of the pixel determined to be a variation pixel and the number of times the pixel is determined to be a variation pixel (step S13).
• the image processing apparatus 4 determines whether or not the count number by the counter unit 420 is greater than or equal to a threshold value for the pixels that are determined to be the changing pixels and the pixels that are not determined to be the changing pixels (step S14). For example, the image processing apparatus 4 determines that a pixel having a count number of 100 or more in this determination is a defective pixel, adds its position information to the defective pixel adding unit 421, and adds the added information. It is stored in the defective pixel information storage unit 419 (step S15).
• the image processing apparatus 4 causes the offset correction unit 413 to perform offset correction on all pixels (step S16). Subsequently, in the image processing device 4, the variation pixel correction process is performed on the variation pixel by the variation pixel correction unit 416 (step S17). At that time, the image processing device 4 omits the variation pixel correction processing for the output value of the pixel determined to be the additional defective pixel among the variation pixels.
• the contents of this variable pixel correction process are the same as those in the first embodiment.
• gain correction processing is performed on the image data after the variation pixel correction processing (step S18). This processing content is also the same as the procedure in the first embodiment.
• the image processing device 4 performs defective pixel correction processing on the gain processed image.
• Step S19 Here, not only the pixels corresponding to the position information stored in the defective pixel information storage means in the initial stage, but also the defective pixel correction is applied not only to the output of the pixels that were later determined to be a variable pixel force defective pixel. Can be processed. This processing content is also the same as the procedure described in the first embodiment.
• the image processing device 4 displays the image-processed image on the display unit 5 (step S20).
• defective pixels that occur later are targeted by treating, as defective pixels, pixels that are frequently detected as varying pixels among the varying pixels. It can be detected accurately. Then, by performing a predetermined correction on the detected output value of the defective pixel, an appropriate image can be obtained even if there is a pixel with an unstable dark current amount.
• a third embodiment will be described in which the image processing apparatus 4 collects a certain number of offset images when the subject is not imaged, and detects these offset image force fluctuation pixels and defective pixels.
• the apparatus configuration of this embodiment is the same as that shown in FIG.
• the fluctuating pixel detection means 414 here compares the pixel value in the offset image with the average value of the pixel values in the specific area of the offset image, and the average value force of the pixel value that deviates beyond a certain threshold value.
• the fluctuating pixel is detected by finding the pixel. More specifically, a pixel indicating a pixel value having a difference of 20% or more of the average pixel value in the 3 ⁇ 3 pixel region is determined as a variation pixel.
• the image processing device 4 acquires an offset image during a time period when shooting is not performed at night or the like (step S31).
• the image processing apparatus 4 records the number of sheets and continues to acquire offset images until the total number reaches 100 (step S32).
• the image processing device 4 compares the pixel value of each offset image with the average pixel value in the 3 ⁇ 3 pixel region of the same image by the motion picture element detection unit 414, and 20% from the average pixel value.
• a pixel having a different pixel value as described above is determined to be a variable pixel (step S33).
• the image processing device 4 stores, in the position information storage unit 415, the position information of the pixel determined to be a varying pixel and the number of times the pixel has been determined to be a varying pixel (step S34).
• the image processing device 4 regards pixels that have changed as pixels in all 100 images as defective images for pixels that have been determined as changed pixels and pixels that have not been determined as changed pixels. Judgment is simple (step S35).
• the image processing device 4 stores the pixel determined as the defective pixel in the defective pixel position information storage unit 419 with its position information (step S36).
• the image processing apparatus 4 performs correction processing similar to that in the second embodiment on the variation pixels and defective pixels detected from the above operations (steps S16 to S16). S20) is applied.
• the offset correction target is not limited to the amount of dark current in the FPD2, but the FPD2 X-ray non-irradiation, such as the operating temperature of the FPD2, the heat distribution depending on the circuit configuration, the ambient temperature and humidity, and the installation of a cooler It includes all conditions and factors related to fluctuations in noise components over time.
• the offset image acquired in this embodiment may not be an offset image that is continuous in time series. For example, offset images collected every day may be used.
• the X-ray image diagnostic apparatus of the present invention can be suitably used for imaging X-ray images.
• the present invention can be used not only for X-ray apparatuses for general imaging but also for X-ray apparatuses for fluoroscopic imaging.

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• 2007
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