JPH1147123A - Digital subtraction angiograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce quantum noises of X-rays and improve the guiding property of a catheter by suppressing the specific picture element value of a subtraction image and the positive or negative display gradation. SOLUTION: An X-ray high-voltage device 1 applies a high voltage to an X-ray tube display via the control signal from a CPU circuit 13 and irradiates X-rays to a subject 3. An optical image is formed by an image intensifier 4, it is photographed by a TV camera 5, and it is stored in a frame memory 11 as it is without being processed by an arithmetic unit 8. Gradation conversion and rewriting of the content of a lookup table 12 are made by the instruction of the CPU 13. The quantum noise of X-rays is normally distributed centering on 0 by subtraction, and the output is suppressed to 0 against the input in the fixed width centering on 0 to reduce the quantum noise. When the width for suppressing the output to 0 is changed and adjusted while the image is observed by the instruction of the CPU 13, the noise can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital subtraction angiography apparatus for subtracting and displaying images before and after injection of a contrast agent, and more particularly to a blood vessel image and a fluoroscopic image which are instantaneously imaged by injecting a small amount of a contrast agent. The present invention relates to a digital subtraction angiography apparatus suitable for creating a blood vessel road map image that subtracts and superimposes on a fluoroscopic image.

[0002]

2. Description of the Related Art In order to obtain an angiographic image of a target site,
Usually, it is necessary to insert a catheter into a blood vessel near a target site and inject a contrast medium. Since blood vessels are not shown in the X-ray fluoroscopic image, a doctor operates a guide wire or a catheter based on anatomical knowledge and inserts a blood vessel near a target site. At this time, there is a technique of operating a catheter by injecting a small amount of a contrast agent and remembering a blood vessel image (called a flash image) instantaneously in order to check the running state of the blood vessel.

However, since a flash image is displayed only for a moment, it is a difficult technique to remember and operate the flash image. In order to support this technology, a method of storing a flash image in an image memory and superposing the flash image on a perspective image has been adopted. It is only necessary to operate the guide wire etc. with reference to the flash image displayed superimposed,
This operation becomes easy.

In such a conventional apparatus, a perspective image (FIG. 3A) before and after a flash is used as a mask image, and the mask image and the flash image (FIG. 3A) are subtracted to shade a bone or the like. The erased blood vessel image (mapping mask image: FIG. 3 (c)) is superimposed on the perspective image and displayed (blood vessel roadmap image: FIG. 3 (d)), and the operation of a guide wire or the like is performed according to the blood vessel roadmap image. I was going.

[0005]

FIG. 3 shows a perspective image.
As shown in (a), there is X-ray quantum noise (noise caused by variations in X-ray photons). The mapping mask image (FIG. 3 (c)) obtained by only subtracting the fluoroscopic image and the flash image contains the quantum noise of the X-ray.

When this is superimposed on a fluoroscopic image to form a blood vessel road map image, the above-mentioned quantum noise of X-rays is mixed in,
As shown in FIG. 3D, the image becomes very difficult to see, and there is a problem in that the operation of the guide wire or the like with reference to this image is inconvenient.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image processing method for an X-ray image of a blood vessel road map.
An object of the present invention is to provide a digital subtraction angiography apparatus suitable for guiding a catheter, a guide wire, or the like by reducing quantum noise of a line.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to subtract an image before injection of a contrast agent (hereinafter referred to as a mask image) and an image after injection of a contrast agent (hereinafter referred to as a live image) and collect the subtraction image and the image in real time. In a digital subtraction angiography apparatus for displaying a superimposed image on the same screen as a superimposed image, a gradation processing means for suppressing near 0 and either positive or negative display gradation of the pixel value of the subtraction image This is achieved by providing

The gradation processing means includes a pixel value conversion table for cutting the pixel value of the subtraction image around 0 and either positive or negative, and refers to the conversion table to determine the pixel value of the subtraction image. Means for converting the density value of

With such a gradation processing means, the display gradation in the gradation region corresponding to the quantum noise of X-rays is suppressed with respect to the mapping mask image obtained from the subtraction image of the mask image and the live image. By superimposing the fluoroscopic image and the fluoroscopic image, it is possible to obtain a blood vessel roadmap image with less X-ray quantum noise and easy to see. Therefore, if the operation of the guide wire or the like is performed with reference to the blood vessel road map image, the operability is remarkably improved.

[0011]

FIG. 1 shows an embodiment of the present invention in which a mapping mask image obtained by subtracting a perspective image and a flash image is subjected to gradation processing, and this image is superimposed on the perspective image to obtain a blood vessel road map image. Is shown. 1 is an X-ray tube device 2
A high voltage (tube voltage) applied between the anode and the cathode of the X-ray tube 2 for generating a desired X-ray from the X-ray tube 2 and a current (tube current) flowing between the anode and the cathode of the X-ray tube 2 Occurs depending on the fluoroscopy and imaging conditions specified by the operation device (not shown),
An X-ray high-voltage device for control, 3 is an object, and 4 is an image intensifier (hereinafter abbreviated as II) for converting an X-ray intensity distribution image transmitted through the object into an optical image and amplifying it. , 5 is the I.D. I. A TV camera (hereinafter abbreviated as TV camera) for converting the optical image of the TV camera into an electric signal (video signal), and an analog / digital converter (hereinafter A / D converter) 6 for converting an analog signal from the TV camera into a digital value.
D converter). Numeral 7 is a logarithmic conversion table for performing logarithmic conversion on the digital image data converted by the A / D converter. This is an X-ray attenuating exponentially. An image is obtained by exponentially converting the amount of linear absorption. Therefore, when performing the subtraction, it is necessary that the image has a linearity with respect to the X-ray absorption amount. Therefore, the linearity is obtained by converting the logarithm, which is an inverse function of the exponential function. . An arithmetic unit 8 performs various operations such as subtraction of a live image (an image before the injection of the contrast agent) and a mask image (an image after the injection of the contrast agent) and superimposition of images. Video signal)
The A converter displays an analog image from the D / A converter on a television monitor (hereinafter abbreviated as TV monitor) 10. Reference numeral 11 denotes a frame memory for storing the image data calculated by the arithmetic unit 8, and reference numeral 12 denotes a data conversion (density conversion) lookup table for performing various gradation processes on the image data stored in the frame memory. The density value of each pixel is converted by referring to this table. Reference numeral 13 denotes a control circuit (hereinafter abbreviated as CPU circuit) using a microcomputer for controlling the entire system.

The embodiment of the present invention configured as shown in FIG. 1 operates as follows. When a start of fluoroscopy is instructed by an operating device (not shown), the X-ray high-voltage device 1 applies a high voltage to the X-ray tube device 2 by a control signal from the CPU circuit 12 to generate X-rays. This X-ray passes through the subject 3 and becomes an optical image by an image intensifier (II) 4.

This optical image is photographed by the TV camera 5,
The data is converted into digital image data by the A / D converter 6.
The logarithmic conversion table 7 performs logarithmic conversion on digital image data. This digital image data is sent to the arithmetic unit 8. Then, when performing normal fluoroscopy (not a blood vessel road map image), the arithmetic unit 8 does not perform any processing, and the digital image data is converted into a video signal by the D / A converter 9 and displayed on the TV monitor 10. Is done.

When a blood vessel roadmap image is created, first, the digital fluoroscopic image data before the injection of the contrast agent is stored in the frame memory 11 as a mask image without any processing in the computing unit 8. Next, the contrast agent is flashed, and the digital image data of the flash image obtained thereby and the mask image stored in the frame memory 11 are subtracted by the arithmetic unit 8. At this time, the mask image read from the frame memory 11 is output to the arithmetic unit 8 as it is without performing any conversion in the lookup table 12.

The subtraction image thus obtained is stored in the frame memory 11 as a mapping mask image. Next, the mapping mask image stored in the frame memory 11 is subjected to gradation conversion by the look-up table 12, and becomes an image in which X-ray quantum noise is suppressed. Then, the mapping mask image subjected to the gradation conversion by the arithmetic unit 8 is superimposed on the fluoroscopic image and displayed on the TV monitor as a blood vessel road map image.

Necessity of gradation conversion and look-up table 1
Rewriting of the contents of 2 is performed in accordance with an instruction from the CPU circuit 13. Next, image conversion in the lookup table 12 will be described with reference to FIG.

FIG. 2A shows the look-up table 12.
Here is the table contents when no conversion is performed. Data that is a straight line with a slope of 1 is written so that the input and output have the same value. Figure 2 (a), (c)
Is a gradation conversion table for suppressing quantum noise of X-rays. X-ray quantum noise is 0 due to subtraction
, The X-ray quantum noise can be reduced by suppressing the output to 0 for an input having a constant width around 0 as shown in the graph (a). Here, if the width of suppressing the output to 0 is increased, the amount of reduction of the X-ray quantum noise is also increased, but at the same time, a part of the blood vessel image is cut off, so that it cannot be increased unnecessarily.

Therefore, the CPU circuit 1 is operated by an operating device (not shown).
By giving an instruction to 3 and rewriting the contents of the look-up table by changing the range in which the output is suppressed to 0, it is possible to make adjustments while observing the image so as to make it most visible. In the graph of (c), not only is the output suppressed to 0 for an input having a constant width around 0, but all outputs are set to 0 if the input is 0 or less. This is because the blood vessel shadow of the flash image has a smaller pixel value than the non-contrast part, so when subtracting the flash image from the perspective image, the blood vessel shadow of the mapping mask image will have a positive value. . Therefore, a negative value area is not a blood vessel shadow, and this area is all 0
By doing so, noise components such as quantum noise of X-rays and artifacts due to body motion can be reduced. Of course, when subtracting the fluoroscopic image from the flash image to create a mapping mask image, the area of positive value is set to 0, contrary to (c). In the gradation processing based on the graph (c), noise can be further reduced.

As described above, the mapping mask image shown in FIG.
By performing the gradation processing of the conversion tables (a) and (c), the mapping mask image and the blood vessel roadmap image are easy-to-view images with reduced X-ray quantum noise as shown in FIGS. Can be As a result, it greatly contributes to the operation of the catheter, the guide wire, and the like.

[0020]

As described above, according to the present invention, the mapping mask image and the pixel value are subjected to gradation processing for suppressing any of the display gradations near 0 or positive or negative. Since the X-ray quantum noise of the blood vessel road map image on which the perspective image is superimposed can be reduced, these images can be easily viewed, and the operability of a catheter, a guide wire, and the like operated by referring to the images can be improved. .

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital subtraction angiography apparatus according to the present invention.

FIG. 2 is an explanatory diagram of a lookup table which is a main part of the present invention.

FIG. 3 is an explanatory diagram of a blood vessel road map image.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 X-ray high-voltage device 2 X-ray tube device 3 Subject 4 Image intensifier 5 TV camera 6 Analog / digital converter 7 Logarithmic conversion table 8 Operation unit 9 Digital / analog converter 10 TV monitor 11 Frame memory 12 Lookup Table 13 Control circuit (CPU circuit)

Claims (2)

[Claims] 1. An image before injection of a contrast agent (hereinafter referred to as a mask image) and an image after injection of a contrast agent (hereinafter referred to as a live image) are subtracted, and the subtraction image and an image acquired in real time are displayed on the same screen. A digital subtraction angiography apparatus for superimposing and displaying a digital image, comprising: a gradation processing means for suppressing a pixel value of the subtraction image in the vicinity of 0 and any one of positive and negative display gradations. Subtraction angiography device. 2. The image processing apparatus according to claim 1, wherein the gradation processing unit includes a conversion table of a pixel value that cuts a pixel value of the subtraction image near zero and either positive or negative, and refers to the conversion table to obtain the subtraction image. 2. The digital subtraction angiography apparatus according to claim 1, wherein the digital subtraction angiography apparatus converts the density value of each pixel.