JPH0351153B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a digital subtraction system that converts a radiation transmission image into a video signal, further digitizes it, and creates a difference image with a mask image in the form of a digital signal.

When drawing only a blood vessel image using this digital subtraction system, a contrast medium is generally injected from the venous system and flows from the heart to the examination site in the bloodstream. Therefore, as a difference image of the examined area,
First, large arteries close to the heart appear, followed by thin blood vessels in the periphery, but when peripheral blood vessels appear, the large blood vessels have almost disappeared, making it impossible to observe everything from large blood vessels to small blood vessels at the same time. Have difficulty.

In view of the above, the present invention provides an improved digital subtraction system that displays images that appear one after another during the movement of a contrast medium into a single image, allowing for simultaneous observation of images from large blood vessels to small blood vessels, for example. The purpose is to provide.

In order to achieve the above object, the digital subtraction system of the present invention is characterized by having an image storage means for difference images that stores a peak value (maximum value or minimum value) for each pixel of difference images sequentially obtained. do.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, X-rays are emitted from an X-ray tube 11 toward a subject 12, and the transmitted image of the X-rays that has passed through the subject 12 is amplified in brightness by an X-ray image intensifier 13 and turned into an optical image. converted. This optical image is converted into a video signal by an image pickup tube 14 and a camera control unit 15, processed in a video processor 20, and the resulting image is displayed by a monitor TV 16 and by a video disc recorder 17. The image data may be recorded or left as a hard copy on film by the multi-imager 18.

The video processor 20 includes a logarithmic converter 21;
AD converter 22, arithmetic unit 23, frame memory 24 for mask images, frame memory 25 for live images, and frame memory 26 for difference images.
, a comparator 27 , an enhancement circuit 28 , and a DA converter 29 . The video signal is first logarithmically converted by a logarithmic converter 21. This is to capture the ratio of the signal magnitude of the object to the background signal magnitude, regardless of the absolute value of the video signal magnitude. This makes it possible to obtain clear images of blood vessels, etc., regardless of whether bones or the like overlap or not. The video signal is further digitized by an AD converter 22.

The image before contrast agent injection is stored as a mask image in each pixel section of the frame memory 24 for each pixel. Next, when a contrast agent is injected, digital video signals of live images are sent one after another from the AD converter 22 and are stored in each pixel section of the frame memory 25 for each pixel. Both the mask image and the live image are integrated for several frames for each pixel by an arithmetic unit 23 and frame memories 24, 25 in order to minimize the influence of X-ray quantum noise. Next, when the arithmetic unit 23 subtracts the mask image from the live image for each corresponding pixel, only the image of the contrast agent remains as a difference image. For example, an image of a blood vessel containing a contrast agent is displayed. be exposed. The digital video signal of this differential image is compared with the digital video signal read out from the frame memory 26 for each corresponding pixel by a comparator 27. The frame memory 26 is reset by an operation such as pressing a button on a panel (not shown), which is performed before starting a contrast examination, and the storage classification of all pixels is set to the maximum or minimum value. . Here, it is assumed that the contrast agent portion takes a large value in the digital video signal and is set to the minimum value. As a comparison result, the larger one is selected for each pixel, and the digital video signal obtained from the comparator 27 is sent to the enhancement circuit 28 and stored again in the storage section corresponding to each pixel in the frame memory 26, and this process is repeated. It will be done. The digital video signal sent to the enhancement circuit 28 is contrast-enhanced, then converted back to an analog video signal by the DA converter 29, output from the video processor 20, and displayed on the monitor TV 16.

Therefore, monitor the contrast agent until it has flowed away from the examination area.
When observing the TV 16, the difference images that appear one after another will gradually accumulate on one screen. For example, a thick blood vessel image near the heart will appear first, and then thinner blood vessel images will gradually appear on top of this thick blood vessel image. When a highly stained image appears, it is also added to the same image, and a single image is created in which all the blood vessel images as difference images sequentially obtained by the flowing contrast medium are superimposed. An image is obtained in which the values at the highest contrast agent concentration are collected for each pixel.

Note that when the magnitude relationship of the obtained digital video signals is reversed, the frame memory 26 is set to the maximum value, and the comparator 27 selects the smaller one.

In the above example, the signal is processed in real time, but it is also possible to record the video signal before applying the differential image or any processing to the video disk recorder 17 or the like, and read this out later and process it as described above.

As described above with respect to the embodiments, the digital subtraction system according to the present invention includes a comparison means for comparing the digital video signals of two images pixel by pixel and extracting one of the signals of magnitude, and the comparison means including a difference image storage means for storing the extracted signal for each pixel;
The digital video signal stored in the image storage means for difference images is read out, and this signal is compared with the digital video signal of the difference images sequentially obtained by the comparison means pixel by pixel, and the comparison result is used as a difference image. Since the peak value image creation means for storing the image again in the image storage means for images is provided, a peak value image related to the difference image can be created in the image storage means for difference images with a simple configuration. As a result, it is possible to display, for example, all blood vessels from large to small on one image, or even a highly stained image due to a tumor or the like. Since a difference image with a large amount of information can be obtained in this way, it is particularly useful when examining areas such as the head and abdomen, lower limbs, etc., where organs have little movement.

[Brief explanation of drawings]

The figure is a block diagram of one embodiment of the present invention. 11...X-ray tube, 12...Subject, 13...X
Line image intensifier, 14... Image pickup tube, 15... Camera control unit, 16
... Monitor TV, 17 ... Video disk recorder, 18 ... Multi-imager, 20 ... Video processor, 21 ... Logarithmic converter, 22 ... AD converter, 23 ... Arithmetic unit, 24, 25, 26
... Frame memory, 27 ... Comparator, 2
8...Enhancement circuit, 29...DA converter.

Claims (1)

[Claims] 1. A radiation source that emits radiation to the subject, a means for converting the transmitted image of the radiation transmitted through the subject into a video signal, an AD conversion means for converting this video signal into a digital signal, and a A mask image image storage means for storing a digital video signal of the obtained mask image, and a mask image digital signal read out from the mask image image storage means from the digital video signal of live images sequentially obtained after contrast agent injection. A calculation means for subtracting, a comparison means for comparing the digital video signals of two images pixel by pixel and extracting a signal of one side of the magnitude, and a difference image storing means for storing the signal extracted by the comparison means for each pixel. The digital video signal stored in the differential image storage means is read out, and the comparison means compares this signal with the digital video signal obtained from the calculation means pixel by pixel. and a peak value image creation means for storing the comparison result in the difference image storage means again, and a DA for converting the digital video signal read from the difference image storage means of the peak value image creation means into an analog video signal. A digital subtraction system comprising a converting means and a means for displaying an image using this analog video signal.