JPH02202277A - Digital substruction angiography device - Google Patents

Abstract

PURPOSE:To form a subtraction picture in real time which is free from any motion artifact and has the high time resolution by subtracting the least value holding picture obtained before injection of a contrast medium from those obtained successively after injection of the contrast medium at every picture element. CONSTITUTION:A live picture is obtained by exposing X rays in a pulse form for at least one heart beat before injection of a contrast medium. Then a video signal A of the live image is inputted to a black peak holding circuit 1. Then the injection of the contrast medium is started and the X rays are exposed in a pulse form. Thus the signals A of the live picture are successively inputted to the circuit 1. The picture signals C which are successively obtained in such a manner are subtracted with the signals B read successively out of an picture memory 3 via a subtraction circuit 4. The background pictures of both pictures obtained at the subtracting side and the subtracted side are defined as pictures BZ. Thus it is possible to obtain in real time a subtraction picture of only blood vessel which is free from any motion artifact.

Description

[Detailed description of the invention] [Industrial application field]

The second invention relates to a digital subtraction angiography device, especially for organs that undergo periodic motion such as the heart.
The present invention also relates to an apparatus most suitable for performing digital subtraction angiography on areas of organs affected by periodic movements such as respiratory movements.

[Conventional technology]

Performing digital subtraction angiography on an organ region that undergoes periodic motion, such as the heart, requires special measures because the X-ray transmission image changes due to the motion. Conventionally, the following three methods have been proposed and implemented. As an example, an explanation will be given assuming that digital subtraction angiography is performed on a cardiac region. First, the
This is to perform subtraction between the image and the line-transparent image. The second one is for the multiple X-ray transmission images for about one heartbeat obtained before the contrast medium injection and the multiple X-ray transmission images for about one heartbeat obtained after the contrast medium injection. The process searches for those with the same cardiac phase and performs subtraction between them. In the third method, an X-ray transmission image is obtained in synchronization with an electrocardiographic waveform, and subtraction is performed between images of the same phase before and after contrast agent injection.

[Problem to be solved by the invention]

However, each of these conventional techniques has the following problems. In the first case, an obstruction shadow (hereinafter referred to as a motion artifact) due to the movement of the heart appears. With the second method, it is not possible to observe a subtraction image without motion artifacts in real time. In the third method, the number of images that can be collected per heartbeat is small, and the temporal resolution is poor. An object of the present invention is to provide a digital subtraction angiography apparatus that can obtain subtraction images in real time, without motion artifacts, and with high temporal resolution.

[Means to solve the problem]

In order to achieve the above object, the digital subtraction angiography apparatus according to the present invention performs a minimum value hold for each pixel on a plurality of X-ray transmission images for at least one motion cycle before contrast agent injection. A means for holding a contrast medium injection surface minimum value hold image, and a means for holding a minimum value hold image for each pixel between each X-ray transmission image sequentially obtained after contrast medium injection and the above contrast medium injection surface minimum value hold image. means for sequentially outputting the post-contrast medium injection minimum value held images, and means for performing pixel-by-pixel subtraction between the post-contrast medium injection minimum value held images and the above-mentioned contrast medium injection surface minimum value held image. Be prepared.

[For production]

The contrast agent injection plane minimum value hold image is an image in which the shapes that an X-ray absorbing tissue such as a bone or myocardium can take during one motion cycle are superimposed. On the other hand, the minimum value hold amount after contrast medium injection is calculated by sequentially performing minimum value hold images for each pixel between this minimum value hold image before contrast medium injection and the X-ray transmission images sequentially obtained after contrast medium injection. Since this is the obtained image, it is as if the image of the invading contrast agent was superimposed on the minimum value hold image of the contrast agent injection surface. Therefore, the minimum value hold image of the contrast agent injection surface is obtained from the minimum value hold image after contrast agent injection, which is sequentially obtained after contrast agent injection.
By subtracting pixel by pixel, the minimum value hold image of the contrast agent injection surface included in the minimum value hold image after contrast agent injection is removed, and only the image of the contrast agent, that is, only the image of the blood vessel portion is extracted. Post-contrast medium injection minimum value hold images obtained sequentially after contrast medium injection, except for the contrast medium image, are like superimposed shapes that X-ray absorbing tissues such as bones and myocardium can take during one motion cycle. Since it is an image, it does not differ depending on the phase of the periodic motion, and since this is removed, a subtraction image of only the blood vessels without motion artifacts can be obtained.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, a video signal A of a live image is sequentially input to a black peak hold circuit 1, and an image memory 3
Pixel by pixel is compared with the video signal B of the image read out, and the signal on the black level side of the two is output. Here, the video signal A of the live image is
In a X-ray TV system, X-rays are emitted in a pulsed manner (see Figure 2), and each time an X-ray transmission image is obtained, this is converted into a video signal via an image intensifier and a video camera, and is then converted into a video signal. It is assumed that the black level is obtained when the X-rays are blocked. The subtraction circuit 4 performs pixel-by-pixel subtraction between the output signal C of the black peak hold circuit 1 and the output signal B of the image memory 3, which are input when the switching circuit 2 is switched to the 21 side. be. To perform digital subtraction angiography of the cardiac region, first, at least one
A video signal A of a live image obtained by performing pulsed X-ray exposure for a period corresponding to a heartbeat (here, 1 second) is input to a black peak hold circuit 1. For example 30
When performing pulsed X-ray exposure at a rate of 30 times/second,
You can get two live images. The image of signal A at this time is an image of the heart and its vicinity, which expands and contracts during one heartbeat, as shown in FIG. During this period, the switching circuit 2 is switched to the 22 side, and the image memory 3 stores the whitest level of each pixel value as an initial value. Therefore, the original live image will be stored as is in the image memory 3 for the first live image, and the black peak bold movement will be performed between the second live image and the first live image. will be carried out. As a result, an image in which images of the X-ray absorbing tissue such as bone or myocardium before and after movement are superimposed, or an image when the X-ray absorbing tissue is expanded is stored in the image memory 3. Since such a black peak hold operation is performed one after another on the live images obtained one after another, the contents of the image memory 3, or the image represented by the signal B read out from the image memory 3, are as shown in FIG. Then, the images obtained before and after the movement of the X-ray absorbing tissue are sequentially superimposed, and then only the images when the X-ray absorbing tissue is expanded are sequentially obtained. When this black peak hold operation for the 30 live images is completed, the image obtained in the image memory 3 is the maximum of the bones and myocardium, like the image Bz of the images represented by the signal B in FIG. This is the image when expanded. This is because the outside of the myocardium is the lung field, which has little X-ray absorption and becomes a white-level pixel. Next, injection of the contrast medium is started, pulsed X-ray exposure is performed, and the video signal A of the live image is sequentially input to the black peak hold circuit 1. At this time, the switching circuit 2
It is knocked down to the 1st side. Therefore, the contents of the image memory 3 are fixed, and the image represented by the signal B read out sequentially in accordance with the input of the live image becomes the above-mentioned image Bz. Therefore, a black peak hold operation is performed between the live images and the image Bz that are sequentially input after the injection of the contrast medium. The live image at this time shows an image of the contrast agent that has entered the blood vessel, but other than that the image is the same as before the contrast agent was injected. Therefore, the image represented by the signal C obtained as a result of this black peak hold motion 1 will be like a contrast agent image superimposed on the above image Bz (second
(see figure). The images (represented by signal C) obtained sequentially in this way are:
The subtraction circuit 4 subtracts the image represented by the signal B sequentially read out from the image memory 3, but since the latter image is the above-mentioned image Bz, it is represented by the output signal of the subtraction circuit 4. As shown in FIG. 2, the image is a screen in which the background image C'ABz of both heads represented by the signal C is removed and only the contrast agent image is extracted, that is, images of blood vessels are sequentially displayed. And the background images of these images on the side to be subtracted and the side to be subtracted are both the image L? , B
Since it is Z and is not affected by periodic motion, a subtraction image of only blood vessels without motion artifacts can be obtained in real time. In the above example, a black peak hold operation is performed for 1 second before contrast medium injection, but this is only possible when the heart rate is 60 beats/min.
This is based on the assumption that the This can be done for a longer time than one heartbeat period, so it can be longer than this. In addition, the R wave is extracted from the electrocardiogram waveform, and the R wave-
This operation may be performed only during one heartbeat period between R waves. Furthermore, although digital subtraction angiography of the heart region has been described above, it is of course applicable to digital subtraction angiography of areas affected by periodic motion such as respiratory motion.

【Effect of the invention】

According to the digital subtraction angiography apparatus of the present invention, it is possible to perform digital subtraction angiography in real time on organ regions that undergo periodic motion, and it is possible to perform subtraction images without motion artifacts and with high temporal resolution. Obtainable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a time chart for explaining the operation. 1...Black peak hold circuit, 2...Switching circuit, 3
...Image memory, 4...Subtraction circuit.

Claims (1)

[Claims] (1) Means for holding a minimum value hold image before contrast agent injection obtained by holding a minimum value for each pixel for a plurality of X-ray transmission images for at least one motion cycle before contrast agent injection; Means for holding a minimum value for each pixel between each X-ray transmission image sequentially obtained after injection of a contrast medium and the above-mentioned minimum value hold image before injection of a contrast medium, and sequentially outputting a minimum value hold image after injection of a contrast medium; , means for performing pixel-by-pixel subtraction between the post-contrast medium injection minimum value hold image and the above-mentioned pre-contrast medium injection minimum value hold image.