JPS5939183A - Digital subtraction system - Google Patents

Abstract

PURPOSE:To obtain excellent picture with a few number of scanning lines, by subtracting a digital video signal of a mask image peak hold type picture memory from a digital video signal of live image peak hold type picture memory and displaying analogically the result. CONSTITUTION:The peak hold type picture memory is constituted of a comparator 24 and a frame memory 25 for a picture before injecting a contrast medium. In injecting the contrast medium, the peak hold type picture memory is formed with the comparator 24 and a frame memory 26 from the digital video signal of the live image. The peak value obtained finally at each period is read out from the memory 26 and given to a subtractor 27, where the value is subtracted with the mask image read out from the memory 25. The output is stored in a frame memory 28 and the difference image written is read out repeatedly by the number of frames required for a monitor TV16 until the next new difference image is written and displayed on the TV16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital subtraction system for a radiation imaging device.

Digital subtraction system is an X-ray imaging device.
It performs real-time image processing, mainly subtraction, on fluoroscopic images obtained from fluoroscopic images, and has received a lot of attention in recent years because of its remarkable improvements in angiography. In other words, since the video signal of the fluoroscopic image obtained from X-ray imaging @mounted tuna is digitized and ZABUTRAXILON is performed using a digital circuit, the contrast resolution is significantly improved compared to subtraction using conventional film, and as a result, the contrast agent can be Diagnosis using X-ray images obtained by intravenous injection has become easier, and JIII angiography can be easily performed, expanding the scope of application of MU angiography to the realm of screening. It has the advantage of

By the way, in the conventional digital subtraction system, in order to reduce the influence of X-ray quantum noise, the X#i! Although radiation doses are often used, this poses a problem because the patient's exposure to radiation becomes significantly large.

In view of the above, it is an object of the present invention to provide a digital subtraction system that is capable of obtaining images of excellent image quality with a small x-mm depth equivalent to that in X-ray fluoroscopy by improving the effects of X-ray quantum noise. purpose.

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, X# Sotachibana 11 to Subject 12
X-rays are emitted toward the subject 12, and the image transmitted by XmK is the X-ray image intensifier 1.
3, the image is amplified in brightness and converted into an optical image. This optical image is captured by the image pickup tube 14 and camera control unit).
15 into a video signal, which is converted into a video signal by a video processor 2
0, the resulting image is displayed on a monitor TV 5.

The video processor 20 includes a changeover switch 2], a logarithmic converter 22, an AIJ converter 23, a comparator 24, a frame memory 25 for the mask team, a frame memory 26 for live (8), and a 27, a frame memory 28 for differential images, an enhancement circuit 29, an IJAg converter 30, a sequence control circuit 31, and changeover switches 32, 33, and 34 controlled thereby.

The video signal is logarithmically converted by a logarithm converter 22 without being shuffled. This is to capture the ratio of the signal magnitude of the object to the background signal 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. In addition, if it is not desired to pass the logarithmic converter 22, the changeover switch 21 is switched in the direction opposite to that shown in the figure. The video signal is further digitized by an AD converter 23.

The image before contrast agent injection is stored in frame memory 2 as a mask image.
5, but in this case the ratio IN! The double unit 24 and the frame memory 25 constitute a peak-hold type image memory. That is, the digital video signals of both temperatures before injection of the contrast agent are sent from the AD converter 23 one frame at a time of +1I11 order, but the digital video signal for one frame of the previous one frame is stored in the frame memory 25. This is then read out and compared with the digital video signal for one frame that is currently being sent by the comparator 24 for each of all pixels. Then, the smaller (or larger) value is stored in the corresponding pixel section of the frame memory 25. When this operation is repeated for a certain period of time, for example, 1 second (30 frames), each pixel will have the smallest (or largest) appearance during that period.
A value (peak value) is stored in each pixel section of the frame memory 25. In this way, the mask 11 is memorized.

Next, when a contrast agent is injected, live digital video signals are sent one after another through the Al converter 23. In this case, a peak-hold type image memory is created by the 4 comparators 24 and the frame memory 26. configured. That is, by the same operation of 41Fl as above, the peak value between υ e.g., e.g., e.g., e.g. The contents of the frame memory 26 are cleared after the above-mentioned period has elapsed, and a new period of beak hole l' II+ operation is started.The beak fIC obtained by reading at the end of each of the above-mentioned periods is stored in the frame memory 26.t. The signal is sent to the subtracter 27, and the reduced snoring caused by the one masked image is output from the frame memory 25 as rJ.

That is, in this embodiment, a differential digital video signal is output from the subtracter 27 once every second, and this is stored in the frame memory 28 at the same time. The difference image written in this frame memory 28 is 1 until the next new difference image is written.
Number of frames required by monitor '1'V16 for seconds (
For example, 30 frames), IrDl is returned, the contrast is emphasized by the enhancement circuit 29, and then converted to analog by the LIA converter 30 and displayed on the monitor TV 16.
will be sent and displayed. Therefore, the monitor 1'V16 displays an image that rotates once per second, which is obtained as a result of digital subtraction in the video processor 20.

In this case, both the mask 2 and the live hoe, which are reduced by the power reducer 27, have the peak value stored in the peak hold type image memory. Therefore, the influence of X# quantum noise is reduced for both the mask image and the Leiber image. The reason for this will be explained based on FIG. If you look at just one frame, the video signal of the X# transmission image will be affected by X-ray Tsuko noise and will be random with respect to the true value shown by the solid line a in Figure 2. It increases and decreases finely, and the waveform resembles a dotted line with many small peaks and valleys. However, since this waveform of small peaks and troughs occurs completely randomly, if the peak value is selected for each pixel in a large number of frames in a fixed period, an envelope C on one side of the dotted line will be obtained. Since this envelope C can be viewed as a translation of the true value a, a video signal corresponding to the true value a from which the influence of noise has been removed can be obtained. Note that FIG. 2 shows one horizontal scanning period division of the video signal, and H indicates the horizontal synchronization norm ξ.

Therefore, in the past, it was necessary to emit a large dose of radiation to reduce the influence of X-ray quantum noise, but this can be improved by reducing the influence of X-ray quantum noise even when the influence of X-ray quantum noise is large. It is possible to reduce the exposure dose of the subject. In the above example, X-rays are continuously emitted at a dose as small as that during fluoroscopy, but the obtained difference image is, for example, 1 per second. Since the operation is intermittent, the operation mode is similar to the serial mode.

As described above, since a difference image of excellent image quality can be obtained with a small dose, it can be applied not only to subtraction using the intravenous injection method, but also to subtraction during selective contrast imaging from an artery. In the latter case, the patient's exposure dose can be reduced compared to film photography, and difference images with excellent image quality can be obtained. In the latter case, the contrast agent moves, but due to the peak hold effect of the contrast agent portion, a difference image with sufficiently deep shadows can be obtained even with a small amount of contrast agent. Therefore, the amount of contrast medium injected into the body can be reduced.

As described above with respect to the embodiments, according to the present invention, it is possible to obtain a Zabtraxian image of excellent image quality with a small dose of radiation, and the radiation dose to which a patient is exposed can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation. 11...X-ray device 12...Subject 13...
X-ray image intensifier 14... image pickup tube
15... Camera control unit 16... Monitor TV 20... Video controller 22... Logarithmic converter 23... AD converter 24... Comparator
25.26.28...Frame memory 29...
Enhancement circuit 30...L) A converter 31...Sequence control circuit Applicant Shimadzu Corporation tar 1st grade

Claims (1)

[Claims] (1) A radiation source that emits radiation toward the subject;
A means for converting the transmission (8) of the radiation transmitted through the object into a video signal, an AL converter for converting the video signal into a digital signal, and a digital video signal of the mask IW sequentially obtained before contrast agent injection. A peak-hold type RT memory for mask stop that compares the order of all pixels for a predetermined period and records only the peak value for each pixel, and a live RT memory that is used to obtain 111 images before contrast agent injection. A peak-hold type image memory for live images compares each pixel of the digital video signal in a predetermined period 47i and stores only the peak value for each pixel, and a peak-hold type image memory for live images stores the data every predetermined period. The digital video signal of the live image to be displayed is read out, and from the digital 4 video signal of this live image, 01 "Y' of the mask image read out from the peak hold type image memory for mask image.
A subtracter that subtracts 4 digital video signals, an IJA converter that converts the digital video signal obtained as a result of the subtraction into an analog video signal, and a display decoration that displays one image based on this analog video signal. A digital subtraction system.