JPS5980081A - Digital subtraction system - Google Patents

Abstract

PURPOSE:To obtain a differential image having an improved frame rate with a low cost, by carrying out simultaneously the odd field scan with an image pickup means of one side and the even field scan with an image pickup means of the other side respectively and storing a signal equivalent to a field to memory within a field period. CONSTITUTION:Image pickup tubes 16 and 17 are controlled by a camera controller 18. These tubes 16 and 17 perform interlaced scans along odd and even horizontal scanning lines respectively in each field period. Each output is selected by a switch circuit 33 via shift registers 29-32 after an A/D conversion and then allotted to a frame memory 35 or 36 by a switch circuit 34. This circuit 34 is connected to sides (a) and (b) in the odd and even field periods respectively. As a result, the signals equivalent to a frame are written to the memories 35 and 36 respectively within a field period. The signals photograhed in each 1/60sec are read out of the memories 35 and 36. These signals are added together to obtain a signal having a frame rate of 60 frames/sec.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in digitized subtraction systems.

A digital subtraction system converts a radiation transmission image into a video signal, further digitizes it, subtracts a mask image in the form of a digital signal, and creates a difference image on the mask image. Normally, from an economic point of view, a standard TV system (NTSC system) video camera is used to obtain the video signal, which limits the maximum frame rate of differential images to 30 frames/second. However, when photographing fast-moving parts such as the heart, a frame rate of 30 frames/second or more is often required. Of course, in such a case, it would be better to stop using the standard TV system, but this would require a special system 10, which would be expensive.

This invention is based on the premise of using a standard TV-type video camera, and has been improved to obtain differential images of up to 60 frames per second at a low cost by making minimal changes to the camera. The purpose is to provide a digital subtraction system with

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a high voltage is applied from an X-ray high voltage device 11, and X-rays are emitted from an X-ray tube 12 toward a subject 13.

The X-rays that have passed through the subject 13 are incident on the X-ray image intensifier 14, and the Xft5 transmitted image is converted into an optical image. This optical image is distributed in two directions by a distributor 15 such as a half mirror that distributes light in a 1:1 ratio, and one of the distributed images is photographed by an image pickup tube 16 and the other by an image pickup tube 17, and the image is videotaped. I get a signal. The image tubes 16, 17 are controlled by a camera controller 18, and one image tube 16 always has a standard T.
Scanning that should be performed during the odd field period of the V system, that is, interlaced scanning along the odd horizontal scanning lines as shown by the dotted line in FIG. Even during the period of
Scanning that should be performed during even-numbered fields in the standard TV system, ie, interlaced scanning along even-numbered horizontal scanning lines as shown by solid lines in FIG. 2, is performed.

Therefore, in just one field period, the video signal for one field that should be obtained in an odd field is transmitted from the image pickup tube 16, and the video signal for one field that should be obtained in an even field is simultaneously transmitted from the image pickup tube 17. What can be obtained is that if these signals are combined, the image information for one frame is obtained, so one frame of information can be obtained in 1/60 seconds.

The respective outputs of the image pickup tubes 16 and 17 are sent to the video processor 56, passed through the switching circuits 19 and 20 and the switching circuits 21 and 22, respectively, and the AD converter 2 via the logarithmic conversion circuits 23 and 24.
5.26 and converted into digital signals.

The switching circuits 21 and 22 are used to select whether or not to pass through the logarithmic conversion circuits 23 and 24. The digital signal output from the AD converter 252.26 is switched by the switching circuit 27.28 and sent to the shift registers 29 to 32.
It is divided into each category. These shift registers 29~
32 each has a capacity sufficient to accommodate eight pieces of data for each pixel, and is input in series and read out in parallel. Each output of these shift registers 29-32 is selected by a switching circuit 33, and further directed to one of the frame memories 35 and 36 by a switching circuit 34. That is, if one scanning line is divided into 512 trout as shown in FIG. 2, the operation will be as shown in FIG. 3. First, during the period in which signals for the first eight pixels are output from the AD converters 25 and 26, the switching circuits 27 and 2
8 is connected to the a side, and the signals for these 8 pixels are written to the shift registers 29 and 31, respectively. next 8
During the period when the signal for pixels is output, it is connected to the b side and written into the shift register 30.32, and during this period the shift register 29.31 retains its contents.
During this period, while the a side of the switching circuit 33 is connected, the contents of the shift register 29 are sent to, for example, the frame memory 35 via the switching circuits 33 and 34, and are stored therein. The contents of the shift register 31 are transferred to the switching circuit 33 while the a side of the
It is then sent to the frame memo IJ3'5 via the switching circuit 34 and stored therein. This operation is repeated until the odd numbered (
For example, the signals of each pixel on the scanning line of the 2n-1th) and the even numbered (for example, the 2nth month) are sequentially sent to one frame memory, for example, the frame memory 35, 8 pixels at a time, and are connected to the period a side of the odd field, Since it is connected to the side during the even field, all the signals of each pixel on the odd and even scanning lines, that is, the signals for one frame, are stored in the frame memory 35 during one field period of the odd field. In one field period of an even field, the signal for one frame is written as a frame)! Tongue 36
will be written in. In this way, the write operation of one frame's worth of signals is performed in one field period, but the read operation of these frame memories 35 and 36 is performed according to the normal standard TV system.
A signal for one frame is read out by interlaced scanning over a period of one frame (two fields). That is, signals for one frame are read out from these frame memories 35 and 36 every 1/30 seconds, but one signal from both of these
Since the signals for one frame are each taken alternately over a period of 1/60 seconds, a signal with a frame rate of 60 frames/second is obtained by combining both of these signals.

First, a mask image is photographed and the frame memory 35.36
Frame memo of one frame worth of signal obtained from! 74
1.42 respectively. Next, at 40, frame memories 41, 42 . The signal of the mask image outputted by lU is subtracted to obtain the signal of the difference image. These differential image signals pass through enhancement circuits 43, 44 and DA converters 45, 46, and are sent in the form of analog signals to TV monitors 47, 48 for display, and are then displayed on video tape recorders 49, 50 and video disc recorders 51. It is sent to a recording device such as .52 and recorded.

Therefore, these recording devices record subtraction image information at 60 frames/second. When this recorded information is reproduced and displayed via the switching circuit 53.54, the switching circuit 19.20 and the switching circuit 37.3
8 is connected to the b side, and switching circuits 27 and 28 are connected to the a side.

The control circuit 55 receives a synchronization signal from the camera controller 18 and controls the AD converters 25, 26, shift registers 29 to 32, and frame memo 1J35°36.41.4.
2, DA converter 45, 46, switching circuit 27.28.33
．． 34, 53, 54, etc., and control the switching circuits 19, 20, 21, 22, 37, 38 and the X-ray high voltage device 11.

FIG. 5 shows a case in which low current two-directional imaging is performed using two sets of the above-mentioned digital subtractor system, including two X-ray tubes 12A.

12B, X-rays are irradiated alternately every other field as shown in FIG. and video processor 56A
, 56B, only one frame memory 35 is used. Then, as shown in FIG.
Signal capture for one frame is performed alternately, and the difference images thus captured are each displayed on the TV monitor 47A.

47B, it is displayed over one frame wJ.

Therefore, in this case, the TV monitor 47A.

47B can each display differential images at a frame rate of 30 frames/second, and is suitable for observing fast-moving organs such as the heart from two sides. By the way, in the past, such 2
When performing directional photography, the frame rate of the image pickup tube is 30
Due to the frame rate per second, only a differential image of 15 frames per second could be obtained in one direction, making it impossible to observe the heart and the like.

In addition, in the configuration of the above embodiment, the control circuit 55 is configured to drive only one of the image pickup tubes 16 and 17 in a normal standard TV system to perform the same operation as a conventional normal digital subtraction system. If it is possible to control the frame rate, it is possible to use it properly for increasing the frame rate and for normal cases, which widens the range of applications, which is desirable.

As described above regarding the embodiments, according to the present invention,
One radiographic image is distributed so that video signals are obtained by two imaging means, and one imaging means always performs standard TV odd field scanning and the other even field scanning at the same time. Since the signal for one frame is stored in one frame memory during the process, it is possible to produce difference images with improved frame rate at low cost and with a simple configuration without much modification to the standard TV system. Obtainable.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a schematic diagram showing scanning lines, Figs. 3 and 4 are time charts for explaining the operation, and Fig. 5 is a diagram for showing an example of use. The block diagram and FIG. 6 are time charts for explaining the operation of FIG. 5. 12...X-ray tube 13...Subject 14...
X-ray image intensifier 15...distributor
16.17...Image tube u,"a-...Logarithmic transformation L
? r25, 26...AD converters 29-32...
Shift register 35.36...Frame memory 39.40...Arithmetic circuit 41.42...Mask image frame memory 43.44
...Enhancement circuit 45.46-DA converter 4
7.48 ・TV4=ri Applicant Shimadzu Corporation

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 an optical image, a distributor that distributes this optical image in two directions, and each distributed There are two imaging means that take images and obtain video signals, and one of these two imaging means always scans only the odd fields and the other scans only the odd fields during both the odd and even fields that make up each frame. A control circuit that controls scanning of only even fields, an AD converter that converts video signals obtained from each imaging means into digital signals, and a control circuit that scans both of the above two imaging means during one field period of an odd field. One frame worth of data obtained from the above AD converter. - A first frame memory that stores a digital video signal, and a digital video signal for one frame obtained from both of the two imaging means via the AD converter during one field period of an even field. a second frame memory for storing the digital video signal of the mask image; a mask image frame memory for storing the digital video signal of the mask image; and a mask image frame memory for storing the digital video signal of the mask image; a first arithmetic circuit that reads the signal on the field scanning line and subtracts the digital video signal of the mask image read from the mask image frame memory; A digital subtraction system 0 having a second arithmetic circuit that reads the signal on the line ' and subtracts the digital video signal of the mask image from the mask image frame memory by reading the signal on the even field scanning line in the even field period.