JPH10216116A - X-ray image digital processing device - Google Patents

Abstract

(57) [Summary] [Problem] To perform gradation compression of a high luminance portion for suppressing halation without discomfort of an image. SOLUTION: A threshold value processing circuit 23 separates image data c having a pixel value smaller than the threshold value and image data d having a large value, and converts the image data d having a large pixel value into a two-dimensional spatial frequency processing circuit 24 and a gradation. After passing through the conversion circuit 25, the arithmetic circuit 26 adds the image data c having a small pixel value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for converting an X-ray image signal used in medical treatment and the like into digital image data for processing.

[0002]

2. Description of the Related Art It is widely used to take an X-ray fluoroscopic image of a subject (such as a patient's body) as an electric image signal using an X-ray TV system and display it on a monitor device for observation. I have. Further, it has become popular to convert this image signal into digital image data and perform various digital image processing.

[0003] By the way, in a portion where the X-ray directly enters the image pickup apparatus without passing through the body or the like, the brightness of the image becomes extremely high and halation occurs. Conventionally, in order to prevent the halation of the high luminance portion, a method of compressing a portion brighter than a fixed or fluctuating threshold value in a gradation direction,
Alternatively, a method is known in which a portion of an analog X-ray image signal that is brighter than a fixed threshold is slightly delayed in the time direction to perform subtraction processing from the original signal.

[0004]

However, as in the prior art, simply compressing a high-luminance portion in the gradation direction loses the information contained in that portion, and the image contrast is lost. Gives the observer a sense of discomfort. Further, in this case, even if the threshold value is changed based on the input signal, the function does not function sufficiently in single shot shooting, and appropriate gradation compression cannot be performed. Further, in the method of subtracting the delayed signal from the original signal, information that runs in the horizontal direction (scanning line direction) in the image of the subtracted portion occurs.

In view of the above, the present invention achieves both the suppression of halation in a high-brightness portion and the prevention of lack of contrast in the high-brightness portion, and has been improved so as not to cause information loss in the scanning line direction. It is an object to provide a line image digital processing device.

[0006]

In order to achieve the above object, in an X-ray image digital processing apparatus according to the present invention, A / D conversion means for A / D converting an input analog X-ray image signal; Threshold value processing means for performing threshold processing on the digitized image data to separate image data having a pixel value larger than the threshold value and image data having a small pixel value, and separated image data having a large pixel value Means for performing edge enhancement processing on the image data, means for performing tone compression on the image data on which the edge enhancement has been performed, and image data having a large pixel value which has been subjected to the edge enhancement and tone compression. Computing means for adding image data having a small pixel value.

Since image data having a pixel value larger than the threshold value is subjected to gradation compression, halation is suppressed, but information alone in a high-luminance portion is lost. Therefore, gradation compression is performed by performing edge enhancement processing on image data having a pixel value larger than the threshold value while preventing loss of information in a high luminance portion. This makes it possible to achieve both suppression of halation in a high-brightness portion and prevention of lack of contrast in the high-brightness portion. Since the delayed signal is not subtracted from the original signal, there is no loss of information traveling in the scanning line direction.

[0008]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, X-rays emitted from an X-ray tube 11 penetrate a subject 10 and enter an image intensifier 12, and an X-ray transmission image is converted into an optical image. A TV camera 14 is connected to the image intensifier 12 via an optical system 13, and an image signal of an output optical image of the image intensifier 12 is obtained. This image signal is sent to the TV monitor device 15 through the digital image processing device 20 to display an X-ray fluoroscopic image.

The digital image processing device 20 includes an A / D converter 21, a non-linear conversion circuit 22, and a threshold processing circuit 2.
3, a two-dimensional spatial frequency processing circuit 24, a gradation conversion circuit 25, an arithmetic circuit 26, a processing circuit 27, and a D / A converter 28. An analog X-ray image signal output from the TV camera 14 is first converted into digital data by an A / D converter 21 and sent to a nonlinear conversion circuit 22.

The intensity of X-rays transmitted through an object (X-ray absorber) 10 having an absorption coefficient μ and a thickness t is expressed by the following equation (1).

(Equation 1) Therefore, the conversion table set in the non-linear conversion circuit 22 is basically a LOG function or a function convex upward. Thus, in the case of the subject 10 having a stepwise shape that changes linearly, the image data (the output a of the A / D converter 21) as shown by A in FIG. (The output b of the nonlinear conversion circuit 22 is as shown in FIG. 2B). In FIGS. 2A to 2G, the horizontal axis indicates a position in a certain direction (for example, a scanning line direction), and the vertical axis indicates a pixel value.

The output image data b of the non-linear conversion circuit 22 is sent to a threshold value processing circuit 23 and separated into image data c having a pixel value smaller than a predetermined threshold value and image data d having a pixel value higher than the predetermined threshold value. (See C and D in FIG. 2). The image data d having a large pixel value is subjected to edge enhancement processing by the two-dimensional spatial frequency processing circuit 24. This allows E in FIG.
2 is obtained and then sent to the gradation conversion circuit 25 and compressed in the gradation direction.
The image data f as shown by is output.

The edge-enhanced and gradation-compressed image data f is added to the image data c having a small pixel value by the threshold value processing circuit 23 in the arithmetic circuit 26, and the result is shown in FIG. The image data g as indicated by G is output, and the image data g is sent to the processing circuit 27 and subjected to other processing, and then returned to the analog image signal by the D / A converter 28.

Therefore, before the gradation conversion circuit 25 compresses the gradation of the high luminance portion, the two-dimensional spatial frequency processing circuit 24
2D, the image data (shown in FIG. 2D) having a large pixel value is converted into image data (shown in FIG. 2E) in which the edge is enhanced. The original image information is not lost as shown in FIG. Therefore, as shown in FIG. 2G, the loss of image information in the high-brightness portion can be avoided while suppressing the halation by gradation-compressing the high-brightness portion.
Since image data having a pixel value smaller than the threshold value is not subjected to gradation compression and is left as it is, it is possible to maintain a dynamic range in a region of interest where X-ray absorption is large and to prevent deterioration in image quality.

In this case, since the edge emphasis processing is performed by the two-dimensional spatial frequency processing circuit 24, there is no loss of information traveling in a specific direction. Further, since the threshold value for determining the region to be subjected to gradation compression is fixed, the same effect is obtained not only when the image signals of each frame are sequentially obtained in a moving image style but also for a single-shot (still image-like) image signal. can get.

In the above description, the edge enhancement processing of image data having a large pixel value is performed by the two-dimensional spatial frequency processing circuit 24. However, the edge enhancement processing can be performed by other configurations. For example, smoothing is performed by a two-dimensional smoothing processing circuit, and then subtraction from the original image data is performed to obtain image data of only an edge portion. When this is added to the original image data, the edge is enhanced. Image data can be obtained. In addition, the specific configuration and the like can be variously changed without departing from the gist of the present invention.

[0016]

As described above, according to the X-ray image digital processing apparatus of the present invention, while maintaining the dynamic range in the region of interest where the X-ray absorption is large and preventing the image quality from deteriorating, the gradation compression is performed in the high luminance portion. To suppress halation,
Moreover, it is possible to obtain an image without a sense of discomfort in the high luminance portion.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing each data profile.

[Explanation of symbols]

 Reference Signs List 10 subject 11 X-ray tube 12 image intensifier 13 optical system 14 TV camera 15 TV monitor device 20 digital image processing device 21 A / D converter 22 nonlinear conversion circuit 23 threshold processing circuit 24 two-dimensional spatial frequency processing circuit 25 Gradation conversion circuit 26 Operation circuit 27 Processing circuit 28 D / A converter

Claims (1)

[Claims] 1. An analog X-ray image signal input to
A / D conversion means for performing D conversion, and threshold processing means for performing threshold processing on the digitized image data and separating the image data into image data having a pixel value larger than the threshold and image data having a smaller pixel value Means for performing edge enhancement processing on the separated image data having a large pixel value, means for performing gradation compression on the processed edge-enhanced image data, and processing for performing the edge enhancement and gradation-compressed large pixels. An X-ray image digital processing device comprising: arithmetic means for adding the image data of the value and the image data of the separated small pixel value.