JP4995193B2 - X-ray diagnostic imaging equipment - Google Patents

Description

  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 an FPD.

  The 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.

  In the FPD, 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 detection element includes a scintillator (eg, cesium iodide) that generates light upon incidence of X-rays, a photodiode that converts an optical signal output from the scintillator into electric charge, and a capacitor that accumulates the converted electric charge. It is equipped with. That is, each pixel of the X-ray image data corresponds to the electric charge accumulated in the capacitor of each detection element, so that the X-ray image data is read by driving the switching element and reading out the electric charge corresponding to the desired pixel. obtain.

  By the way, even when X-rays are not irradiated in the FPD, charges are accumulated in the capacitor by offset correction data including dark current flowing in the circuit portion of the detection element, and the accumulated charges are noise components, and the X-ray image This is one of the factors that degrade the image quality.

  As a countermeasure against the image quality deterioration, as described in Patent Document 1, the offset correction data is subtracted from the captured image data output from the FPD.

JP 2002-159481 A

  However, the offset correction data of FPD has a large temperature dependency, and specifically, the amount of current changes due to heat generation from the circuit portion itself and temperature change around the detector. When the amount of change in the dark current amount is larger than a predetermined threshold, there is an unsolved problem that conventional offset correction may not be able to cope with it.

  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 the FPD is larger than a predetermined threshold.

An X-ray diagnostic imaging apparatus according to the present invention includes an X-ray generation unit that irradiates a subject with X-rays, and an X-ray generation unit that converts the transmitted X-rays of the subject as X-ray image data. A line plane detector, correction data creating means for obtaining offset correction data using an output of the X-ray plane detector when X-rays are not irradiated by the X-ray generation means, and the offset correction from the X-ray image data An X-ray diagnostic imaging apparatus comprising an offset correction means for subtracting data, wherein the fluctuation of the offset correction data due to the use environment of the X-ray flat panel detector is outside a predetermined range based on the created offset correction data Pixel detection means for detecting pixels, pixel correction means for performing predetermined data correction on the offset correction data of the detected pixels and outputting to the offset correction means; and An image display unit that displays image data obtained by subtracting offset corrected data from the X-ray image data by the offset correcting unit;
It is provided with.

  According to the present invention, it is possible 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 the FPD is greater than a predetermined threshold.

FIG. 2 is a functional block diagram showing Embodiment 1 of the present invention. 2 is a flowchart showing an operation procedure in FIG. The model explanatory drawing which shows the area | region of 3x3 pixel in a picked-up image, and the graph which shows the dispersion | variation in the luminance value of three pixels in the area | region. FIG. 5 is a functional block diagram showing Embodiment 2 of the present invention. 5 is a flowchart showing an operation procedure in FIG. 10 is a flowchart showing an operation procedure in the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... X-ray generation part, 2 ... X-ray plane detector (FPD), 3 ... Operation panel part, 4 ... Image processing apparatus, 5 ... Image display part, P ... Subject.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
<Device configuration>
As shown in FIG. 1, the X-ray diagnostic imaging apparatus according to Embodiment 1 of the present invention operates an X-ray generating unit 1, an FPD 2 disposed opposite to the X-ray generating unit 1, and the operation of the X-ray diagnostic imaging apparatus. Control panel 3 installed in the operator's control room, an image processing device 4 connected to each component from the X-ray generation unit 1 to the control panel unit 3, and an image display unit connected to the image processing device 4 5 is provided.

  The X-ray generator 1 includes an X-ray tube that generates X-rays, and an X-ray diaphragm that blocks X-rays outside the irradiation range so that only the irradiation range of the generated X-rays is irradiated And have. The FPD 2 is disposed so as to face the X-ray generation unit 1 and converts the incident X-ray as X-ray image data by the incidence of the X-ray irradiated from the X-ray generation unit 1. At the time of imaging, the subject P is positioned between the X-ray generation unit 1 and the FPD 2, the X-ray irradiated from the X-ray generation unit 1 passes through the subject P, and the transmitted X-ray enters the FPD 2. An X-ray image can be obtained. The photographing conditions (tube voltage, tube current time product, etc.) necessary for this photographing are input and set by the operator from the operation panel unit 3. The X-ray image data converted and output from the FPD 2 is temporarily stored in the image data storage means 410 in the image processing device 4. The storage unit 410 stores not only a captured image of the subject P 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 unit 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 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.

  The correction data creation unit 411 creates correction data for offset correction from the dark current amount of the FPD2. The reading of the dark current amount is performed by acquiring a plurality of images (offset images) in the absence of the subject P and without irradiation with X-rays. Acquisition of this offset image is performed 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 usage environment of the apparatus such as temperature.

  The offset correction unit 413 performs offset correction processing by subtracting correction data from the captured image of the subject P.

  Further, 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 information storage unit. Also included is a variable pixel correction unit 416 connected to 415.

  The fluctuation pixel detection unit 414 detects a fluctuation pixel having a large fluctuation amount of the dark current amount. Here, the variation pixel is detected by comparing each pixel value of the offset image immediately before photographing with each pixel value in an average image of a plurality of offset images acquired before that time. For example, when 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 variation pixel.

  The position information storage unit 415 stores the position information of the pixels that are determined as the changing pixels. Since each pixel of 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. Here, in the dark current corrected image subjected to offset correction, correction is performed using the average pixel value of non-varying pixels in a 3 × 3 pixel area centering on the varying pixel as the pixel value of the varying pixel.

  In addition, the image processing apparatus 4 includes a gain correction unit 417 connected to the variable pixel correction unit 416, a defective pixel correction unit 418 connected to the gain correction unit 417, and defective pixel information connected to the defective pixel correction unit 418. And a storage unit 419.

  The gain correction unit 417 corrects the relationship between the incident dose of X-rays 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 corrects the output of the defective pixel based on the position information of the defective pixel stored in the defective pixel information storage unit 419. For example, the image data after the gain correction process is corrected using the average pixel value of the non-defective pixels in the 3 × 3 pixel region centered on the defective pixel as the pixel value of the defective pixel.

<Processing procedure>
In such an apparatus, a procedure for detecting a variable pixel and appropriately correcting the output value of the pixel will be described based on the flowchart of FIG. For each part of the apparatus, refer to FIG. Note that the image processing apparatus 4 performs overall control of the entire X-ray image diagnostic apparatus.

Prior to imaging of the subject P, the image processing apparatus 4 acquires a plurality of offset images and stores the images in the image data storage unit 410. (Step S1)
In the image processing device 4, 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 photographing is compared with the pixel value (threshold value) of an image obtained by averaging a plurality of offset images before that to detect a variation pixel. . Here, if the pixel value of the offset image immediately before photographing is larger than the threshold by 10% or more, it is determined that the pixel is a variable pixel. (Step S2).

When the variation pixel is detected, the image processing device 4 stores the position information of the pixel in the position information storage unit 415. (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 apparatus 4 reads the offset correction data from the correction data storage unit 412 and performs offset correction processing by subtracting the correction data from the captured image by the offset correction unit 413 (step S5).

The image processing device 4 causes the variation pixel correction unit 416 to correct the pixel value of the variation pixel of the dark current correction image that has been offset (step S6).
Specifically, the position information of the variation pixel stored in the position information storage unit 415 is read out, and the average pixel value of the non-variation pixels in the 3 × 3 pixel area centered on the variation pixel is calculated. Correction to pixel value is performed.

  The procedure of variable pixel correction is as follows. First, the image processing device 4 determines whether or not the position information of the variable pixel is stored in the position information storage unit 415, and if there is position information, the position information The variation pixel correction process is performed on the output value of the pixel corresponding to. Further, the image processing device 4 does not perform the variable pixel correction process if there is no position information.

  After performing this variation pixel correction process, the image processing apparatus 4 performs a gain correction process by the gain correction unit 417 (step S7). Further, the defective pixel correction unit 418 performs defective pixel correction processing on the gain corrected image after gain correction processing (step S8). Then, the image processing device 4 displays the image subjected to these correction processes on the image display unit (step S9). Note that steps S7 and S8 are performed as necessary, or can be omitted if they are already performed in order, and step S9 (image display) after step S6 (variable pixel correction processing) can also be performed. .

  As described above, according to the first embodiment, by specifying a pixel having a large amount of variation in dark current and performing a predetermined correction by the variation pixel correction unit 416 on the pixel value of the pixel, X Even when the amount of dark current in the line flat detector 2 varies greatly, good image quality can be obtained.

(Modification 1)
In Embodiment 1 described above, each pixel value of the offset image immediately before shooting is detected and the pixel variation in the average image of a plurality of offset images acquired before that is detected as a variable pixel. Instead, 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. FIG. 3B shows the pixel values of one of the vertical, horizontal, and diagonal pixel groups in this region. As shown in these figures, if some of the pixels are variable pixels (cross-hatched display in FIG. 3A), the output value is larger than that of other normal pixels. be able to. For example, it may be determined that a pixel having a difference of 20% or more from the average pixel value of three pixels arranged in a horizontal row is a variable pixel. FPD pixels are, for example, about 0.15 mm square, and even if there are high and low luminance values (pixel values) in the captured image, the pixel values of adjacent pixels are not significantly different. It is rare, and a variable pixel can be detected by comparing pixel values of adjacent pixels.

(Embodiment 2)
Next, when a specific pixel is determined as a variable pixel a predetermined number of times or more, an embodiment in which the variable pixel is determined as a defective pixel and predetermined correction is performed on the output of the defective pixel is illustrated in FIGS. Based on

<Device configuration>
In the present embodiment, as shown in FIG. 4, 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 other structures are the same as in the first embodiment. It is the same. The counter unit 420 is connected to the variation pixel detection unit 414 and the position information storage unit 415, and the defective pixel addition unit 421 is connected to the position information storage unit 415 and the defective pixel information storage unit 419. Hereinafter, the difference from the first embodiment will be mainly described.

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. Here, 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. In addition, the number of times that the variation pixel detection unit 414 determines the variation pixel within a certain period may be counted.
Then, 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.

  On the other hand, the defective pixel adding unit 421 determines a pixel whose count value in the counter unit 420 exceeds a predetermined threshold value as a defective pixel, and stores the position information of the defective pixel in the defective pixel information storage unit 419. Here, a pixel whose count number of the counter means 420 is 100 or more is determined as a defective pixel.

  In addition, in the second embodiment, the variation pixel detection method by the variation pixel detection unit 414 is different from that in the first embodiment. Here, the pixel value in the captured image is compared with the average value of the pixel values in a specific area of the captured image, and a pixel with a pixel value that deviates from the average value by a certain threshold or more is detected to detect a fluctuating pixel. To do. More specifically, a pixel having a pixel value that is 20% or more off the average pixel value in the 3 × 3 pixel region is determined as a variation pixel.

<Processing procedure>
In such an apparatus, a procedure for detecting a variable pixel and appropriately correcting the output value of the pixel will be described with reference to the flowchart of FIG. For each part of the apparatus, refer to FIG.

  First, the image processing device 4 acquires a captured image (step S11). Next, the image processing device 4 compares the pixel value in the photographed image with the average value of the pixel values in the specific area of the photographed image by the varying pixel detection means 414, and detects the varying pixel (step S12).

  At this time, 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 device 4 determines whether or not the count number by the counter unit 420 is greater than or equal to the 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 device 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 the added information is defective. It is stored in the pixel information storage unit 419 (step S15).

  Next, 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 as 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. Further, 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.

  Thereafter, the image processing apparatus 4 performs a defective pixel correction process on the gain processed image. (Step S19) Here, not only the pixel corresponding to the position information stored in the defective pixel information storage means in the initial stage but also the defective pixel correction for the output of the pixel that was later determined as the defective pixel from the variation pixel Can be processed. This processing content is also the same as the procedure described in the first embodiment.

  Then, the image processing device 4 displays the image processed image on the display unit 5 (step S20).

  As described above, according to the second embodiment, a defective pixel that occurs later can be accurately detected by treating, as a defective pixel, a pixel that is frequently determined as a variable pixel among the variable pixels. Can do. 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.

(Embodiment 3)
Embodiment 3 will be described in which a fixed number of offset images are collected when the image processing apparatus 4 does not image a subject, and detection of fluctuating pixels and defective pixels are detected from these offset images.

<Device configuration>
The apparatus configuration of this embodiment is the same as that shown in FIG. However, the fluctuation pixel detecting 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 pixel value that deviates from the average value by a certain threshold value or more. A variable pixel is detected by finding the pixel. More specifically, a pixel indicating a pixel value having a difference of 20% or more from an average pixel value in a 3 × 3 pixel region is determined as a variation pixel.

<Processing procedure>
A processing procedure in this apparatus will be described with reference to FIG.

  First, the image processing device 4 acquires an offset image during a time period when shooting is not performed, such as at night (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). Next, the image processing device 4 compares the pixel value of each offset image with the average pixel value in the 3 × 3 pixel area of the image by the variation pixel detection unit 414, and the difference is 20% or more from the average pixel value. A pixel having a certain pixel value is determined as a variation 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).

  Next, the image processing apparatus 4 determines that the pixels that have changed in all 100 images are defective pixels for the pixels that have been determined as changed pixels and the pixels that have not been determined as changed pixels (step S35). The image processing device 4 stores the position information of the pixel determined to be a defective pixel in the defective pixel position information storage unit 419 (step S36).

  When the subject is actually imaged, the image processing apparatus 4 performs the same correction process (steps S16 to S20) as that of the second embodiment on the fluctuating pixels and defective pixels detected from the above operations. Apply.

  According to this embodiment, by acquiring an offset image at the time of non-photographing, it is possible to efficiently detect a fluctuation pixel and a defective pixel.

  The target of offset correction is not limited to the amount of dark current of the FPD2, but the noise component when the FPD2 is not irradiated with X-rays, such as the operating temperature of the FPD2, the heat distribution due to the circuit configuration, the ambient temperature and humidity, and the installation of a cooler. It includes all conditions and factors related to fluctuations.

  Note that 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.

  In addition, the present invention may appropriately combine a part of the configurations described above, and various modifications can be made without departing from the spirit of the present invention.

  The X-ray image diagnostic apparatus of the present invention can be suitably used for taking X-ray images. In particular, the present invention can be used not only for X-ray apparatuses for general imaging but also for X-ray apparatuses for fluoroscopic imaging.

Claims (2)

X-ray generation means for irradiating the subject with X-rays, an X-ray flat panel detector disposed opposite to the X-ray generation means for converting and outputting the transmitted X-rays of the subject as X-ray image data, and the X-ray generation Correction data creating means for obtaining offset correction data using the output of the X-ray flat panel detector when X-rays are not irradiated by the means, and offset correction means for subtracting the offset correction data from the X-ray image data. In the X-ray diagnostic imaging device provided,
And change pixel detection means for variation of the offset correction data by using the environment of the X-ray flat panel detector based on the determined al offset correction data to detect pixels that are outside the predetermined range, the detected offset variations pixels Fluctuating pixel correction means for performing predetermined data correction on the correction data and outputting to the offset correction means, and image data obtained by subtracting the data-corrected offset correction data from the X-ray image data by the offset correction means an image display unit that displays, have,
In addition, the stability determination unit that determines whether or not the variation state of the offset correction data of the variation pixel is stable, and the position of the variation pixel when the stability determination unit determines that the variation is unstable. Defective pixel information adding means for adding information as defective pixel position information, and defective pixel correcting means for correcting the output of the defective pixel as a defective pixel based on the added position information,
The stability determination unit is a counter unit that measures and records the number of times that the variation pixel detection unit determines that the pixel is a variation pixel, or the number of times that the variation pixel correction unit corrects the variation pixel. The defective pixel information adding unit is characterized in that, when the number of times measured by the counter unit is equal to or greater than a predetermined value, the fluctuation pixel is determined as a defective pixel and the position information is stored in the defective pixel information storage unit. X-ray diagnostic imaging equipment. Correction data creation means for obtaining offset correction data using the dark current amount of the X-ray flat panel detector, variable pixel detection means for detecting a pixel in which the dark current amount of the X-ray flat panel detector fluctuates, and the detected Position information storage means for storing position information of the fluctuating pixels, X-rays are irradiated to the subject by the X-ray generation means, and the transmitted X-rays of the subject that are arranged opposite to the X-ray generation means are used as X-ray image data X-ray image data is acquired by conversion output by an X-ray flat panel detector, the image data storage means for storing the acquired X-ray image data, and the correction data creation means from the stored X-ray image data display offset correction means for subtracting the offset correction data created, and the defective pixel correction means for performing correction on the detected change pixel, the corrected change pixel as the X-ray image data by In X-ray image diagnostic apparatus having that an image display unit, a
Stability determination means for determining whether or not the variation state of the dark current amount of the variation pixel is stable;
When it is determined that the stability is unstable by the stability determination means, the defective pixel information adding means for adding the position information of the changed pixel as the position information of the defective pixel, and the output of the defective pixel based on the added position information Defective pixel correction means for correcting as defective pixels for,
The stability determination unit is a counter unit that measures and records the number of times that the variation pixel detection unit determines that the pixel is a variation pixel, or the number of times that the variation pixel correction unit corrects the variation pixel. The pixel information adding means, when the number of times measured by the counter means is equal to or greater than a predetermined value, determines that the fluctuation pixel is a defective pixel and stores the position information in the defective pixel information storage means. Line image diagnostic device.

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