JPS6230493A - Digital subtraction device - Google Patents

Abstract

PURPOSE:To find out the speed of flow of blood by designating optional two points of upper stream and downstream of a blood vessel finding the difference in time at which a part of highest concentration of a contrast medium passed the points, and dividing the distance between the two points by the time difference. CONSTITUTION:The contents of a frame memory 7 are converted to analog signals by a D/A convertor 8 and sent to a picture display device 9, and accordingly, the locus of a contrast medium, i.e. the image of a blood vessel is displayed. One point P1 in the upperstream of the blood vessel and one point P2 in the downstream are pointed by a coordinate pointing device such as a light pen, etc. A processor 12 reads out time stored in a frame memory 11 at picture elements corresponding to points P1, P2 and determines the time difference. On the other hand, the processor 12 finds out the distance between points P1, P2, and divides the distance by above-mentioned time difference. Thus, the speed of moving of the peak of concentration of the contrast medium from the point P1 to point P2 is determined as the speed of blood flow, and displayed on a proper part of the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to medical radiological diagnostic equipment, and in particular to DSA
(Digital subtraction angiography)
This invention relates to a digital subtraction device for performing.

Conventional DSA technology extracts an image of only the contrast agent, that is, an image of only the blood vessel, by injecting a contrast agent into a blood vessel and performing subtraction on the obtained radiographic image.

Incidentally, in the field of DSA, in recent years, in addition to morphological analysis such as blood vessel stenosis, dynamic analysis such as blood flow rate and blood flow velocity has been promoted. This is due to the following reasons, for example: The cephalic vertebral artery branches from the carotid artery and is a blood vessel that supplies nutrients to the cerebellum.When there is insufficient blood sent to the cerebellum, movement disorders occur and people often complain of dizziness. However, these patients generally have small vertebral arteries, so it is necessary to measure blood flow in addition to morphological analysis such as measuring blood vessel diameter.

Conventionally, so-called time density curve processing, which graphs temporal changes in the concentration of a contrast medium in a blood vessel, has been proposed to determine blood flow velocity. As shown in Figure 2, a region of interest is set at each position of point PI and point P2 in the blood vessel image, the temporal change in contrast agent concentration in each of these regions is measured, and this is graphed. Obtain the time density curves C1 and C2 as shown in Figure 3, and divide the distance flliL between points P1 and P2 by the time T from the peak of these curves to obtain the blood flow velocity (L/T). It's about getting something.

Problems to be Solved by the Invention However, in the conventional time density curve processing as described above, density changes can only be captured in specific regions such as the set region of interest, points PI and P2 in the above example. Therefore, it is not possible to easily and quickly determine the blood flow velocity or blood flow volume at any location.

This invention provides a digital subtraction device that can easily and quickly determine the blood flow rate at any location, and furthermore, can easily and quickly determine the blood flow rate from the determined blood flow velocity. The purpose is to provide.

Means for Solving the Problems The digital subtraction device according to the present invention includes a comparing means for comparing video signals of a radiographic image obtained when a contrast medium flows into a blood vessel, pixel by pixel, between frames;
It has a frame memory means in which a signal with a higher contrast agent concentration selected as a comparison result is rewritten, a means for generating a time signal, and an address corresponding to each of the above-mentioned pixels. and memory means for writing a time signal at that time into an address corresponding to the pixel in response to a trigger signal generated when it is determined that the contrast agent concentration is higher in the old signal than in the old signal. Become.

For each pixel position, the time at which the signal with the highest contrast agent concentration was written is stored for that pixel. Each stored time represents the time at which the highest concentration of contrast agent passed through that pixel location, so later on, one point upstream and one point downstream in the blood vessel are stored. By reading out the times and finding the difference between them, the time required for the peak concentration portion of the contrast agent to pass between those two points can be found. By dividing the distance between the above two points by this time, the passing velocity at the peak concentration of the contrast agent, that is, the blood flow velocity can be obtained.

Embodiment In FIG. 1, a video signal representing an X-ray transmission image is sent to an A/D converter l from an image intensifier camera of an X-ray television fluoroscopy system (not shown). This video signal is converted into a digital signal by an A/D converter l and then sent to frame memories 2 and 3. first,
A signal before the contrast agent reaches the blood vessel at the imaging site is stored in the frame memory 2 as a mask image. After that, from the time the contrast agent reaches the blood vessel at the imaging site until it flows through the blood vessel and flows away, signals that are continuously sent frame by frame are stored in the frame memory 3 as a live image for each frame. Stored sequentially. The subtractor 4 subtracts the mask image from the live image for each pixel, and a live image of only the contrast agent portion in which the portion where no contrast agent is present is canceled is obtained for each frame. The live image showing only this contrast agent part is a
The signal is sent to the comparator 6 via the switch 5 which is tilted to the side.
The i-frame memory 7 is initially initialized to the maximum value, and a comparator 6 compares the contents of the frame memory 7 with the video signal sent via the switch 5 on a pixel-by-pixel basis. Here, the part where the contrast agent is present is
X from 1! ! It is assumed that the signal becomes low because a is blocked, and that the higher the concentration of the contrast agent, the lower the high scale signal becomes. This comparison by the comparator 6 shows that for a certain pixel, if a contrast agent is present in the image, the signal will be lower, so it will be lower than the signal read out first from the frame memory 7, and the comparator 6 will select the lower signal. The pixel is sent to the frame memory 7 and written to the address corresponding to that pixel. In this way, when the signal sent through the switch 5 is lower than the signal read out from the frame memory 7, a trigger signal is simultaneously generated and sent to the frame memory 11. In the frame memory 1, when a trigger signal is received in this way, the time signal generated from the time generator 10 at that time is written to the address of that pixel. That is, frame memory 1
1 has addresses corresponding to all pixels of one frame of image,
The storage capacity of each address is sufficient to store the time.

Such a comparison is made in the comparator 6, the lower signal is written to the frame memory 7, and the lower signal is written to the frame memory 1.
Writing of time to 1 is performed for each frame.

In a certain frame, if a signal lower than the signal stored in the frame memory 7 up to that time is sent,
The address of that pixel in the frame memory 7 is rewritten with this newly obtained lower signal, and since a trigger signal is generated from the comparator 6 at this time, the time is rewritten in the frame memory 11. If the signal stored in the frame memory 7 is lower than the newly obtained signal, the original stored signal is written again, and in this case, the trigger signal from the comparator 6 is Since this does not occur, the time is not rewritten in the frame memory 11.

Therefore, when such an operation is performed frame by frame and the contrast agent flows away from the imaging site, the address of each pixel in the frame memory 7 contains the highest contrast agent concentration until the contrast agent flows away. The signal in the frame where the contrast agent becomes high is retained, and an image representing the trajectory of the contrast agent is formed. The time of the frame where the contrast agent concentration becomes high will be recorded.

The contents of the frame memory 7 are converted into analog signals by the D/A converter 8 and sent to the image display device 9, so after the contrast agent has flowed away, the image display device 9 allows the contrast agent to flow through the blood vessels. The contrast agent trajectory, that is, the image of the blood vessel will be displayed. So, on this image, light pen 13
One point P1 upstream of the blood vessel and one point P2 downstream are specified using a coordinate indicating device such as the following. The processor 12 then determines this point P1. Frame memory 1 at the pixel corresponding to P2
Read the time stored in 1 and find the difference in time. On the other hand, the processor 12 calculates the distance between points P1 and 22, and divides this distance by the time of the above difference, thereby calculating the speed at which the peak concentration of the contrast agent moves from point P1 to point P2. The speed is calculated and displayed at an appropriate location on the screen.

Furthermore, points P3 and P4 corresponding to the edge of the blood vessel are specified using the light pen 13 or the like. Then, processor 12
Accordingly, the distance between this point P3.24 is determined as the diameter of the blood vessel, and the blood flow rate is determined by multiplying the cross-sectional area determined from this diameter value by the above-mentioned blood flow velocity. This blood flow rate is displayed at an appropriate location on the screen in line with the blood flow velocity described above.

In this way, since the time point at which the contrast medium concentration peak passes is recorded for each pixel, the blood flow velocity at any location can be easily and quickly determined, and the blood flow rate can also be determined easily and quickly. is required.

Note that in the above example, the switch 5 is turned to the a side, and the video signal after subtraction processing is handled, and the peak hold operation is performed by the comparator 6 and the frame memory 7, but the switch 5 is turned to the b side. , a similar peak hold operation may be performed on the raw video signal before subtraction processing; in this case,
The only difference is that since no subtraction processing is performed, background bones and other images appear in the resulting image.

Effects of the Invention According to this invention, the time at which the signal with the highest contrast agent concentration was written is stored for each pixel of a frame image. By specifying this, the time difference when the part with the highest contrast agent concentration passes can be immediately determined, and the blood flow velocity can be determined by dividing the distance between the two points by this time difference. In this way, the blood flow velocity can be determined easily and quickly. Furthermore, if the blood flow velocity is determined in this way, the blood flow rate can also be determined easily and quickly.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2 and 3 are for showing conventional examples, FIG. 2 is a diagram showing a blood vessel image, and FIG. 3 is a time density curve. It is a diagram. 1...A/D converter

Claims (1)

[Claims] (1) Comparison means for comparing video signals of radiographic images obtained when a contrast agent flows into blood vessels for each pixel between frames, and a signal with a higher contrast agent concentration selected as a result of the comparison. It has a frame memory means that is rewritten, a means for generating a time signal, and an address corresponding to each pixel, and the comparison means determines that the new signal has a higher contrast agent concentration than the old signal. A digital subtraction device comprising memory means in which a current time signal is written to an address corresponding to the pixel in accordance with a trigger signal generated when the determination is made.