JPH04252578A - X-ray subtraction system - Google Patents

Abstract

PURPOSE:To obtain a series of subtraction image with no archicraft without need of holding break of a patient by implementing subtraction between a live image and a mask image whose density is equal to each other. CONSTITUTION:Each picture element data in a concerned area is measured by a density measuring device 12, from which a density mean value or a representative value is outputted and a density representative value data measured for each mask image is written and stored in a mask image memory 14 corresponding to a picture data of each mask image. When a contrast agent fill image 16 picked up by injecting a contrast agent is inputted, the concerned area is measured and the operation of subtraction with respect to a mask image 14' having the same concerned area density in the mask image is implemented by a computing element 18.

Description

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

The present invention is utilized in the field of X-ray angiography. The present invention relates to an X-ray subtraction system,
More specifically, the present invention relates to an X-ray imaging system for blood vessels in areas affected by breathing, and in particular to improved removal of artifact images that are likely to be caused by breathing.

[Conventional technology]

[0002] Of the two digital X-ray images that show the same image of the same blood vessel site, one is an image taken without injection of a contrast medium (mask image), and the other is an image taken after injection of a contrast medium. X-ray digital angiosystems (angiography or DSA) are known which obtain (live images) and display a subtraction between the two images.

By the way, when taking X-ray images of blood vessels in areas affected by breathing, the image of the blood vessels fluctuates every breathing period, so two images of the same blood vessel area taken at the same breathing timing may appear the same. Collecting digital X-ray images is not easy. If different images of the same blood vessel site are subtracted, an image containing an artifact image (false image) will be displayed.

[0004] Conventionally, in order to avoid such artifacts caused by breathing, X-ray imaging is performed by asking the patient to stop breathing with the patient's cooperation, and capturing the point at which the patient stops breathing.

[Problem to be solved by the invention]

[0005] Conventional methods force patients to hold their breath for a long time, and in the case of unconscious patients, it may be impossible to hold their breath, making it difficult to always obtain artifact-free images. Ta.

An object of the present invention is to obtain an X-ray subtraction image of blood vessels and the like existing in areas affected by breathing without including artifacts in the image without forcing the patient or other subject to stop breathing. An object of the present invention is to provide an X-ray subtraction system capable of displaying images.

[Means to solve the problem]

[0007] The above-mentioned purpose is to set in advance a region of interest in which the image density changes significantly due to respiration in an X-ray imaging system for blood vessels existing in areas affected by respiration, and to calculate the representative concentration value within that region. and a plurality of mask images in which each image data of a plurality of images (mask images) captured without injecting a contrast agent and measured density information in the region of interest are written in correspondence for each image. Similarly, the representative density values within the region of interest are measured for the image captured after injecting the contrast agent (live image), and
This is achieved by comprising a computing unit that reads mask image image data whose measurement value matches the density representative value corresponding to the mask image from the memory and performs subtraction between the image data of the mask image and the live image. Ru.

[Effect]

For example, multiple images for one breathing period are recorded as mask images (imaging before contrast agent injection), and an area with an image part where the density changes due to breathing is set, and the density in that area is recorded in each image. DSA has the function of measuring the density in the same area for the live image (imaging after contrast agent injection) and performing subtraction between the live image and the mask image, which have the same density. Using the device, a series of artifact-free subtraction images can be obtained without the need to stop the patient's breathing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. 10 is an A/D converter that digitizes a video signal from a TV camera (not shown); 12 is a region-of-interest density measurement circuit; 14 is a mask image memory with region-of-interest density information; 18 is a computing unit; and 20 is a digital This is D/A conversion that converts image signals into analogs.

FIG. 2 is an explanatory diagram of how the same subject part appears as a slightly different image depending on breathing.

[0011] In this figure, body movements due to breathing are repeated with a cycle f of one breath as shown, and the images collected within that cycle are slightly shifted, the diaphragm A bulges and dents, and its back・Grand B is moving accordingly.

[0012] Therefore, in subtraction using a normal mask image, if breathing is not stopped, only a subtraction image that is very difficult to see due to background artifacts is obtained.

According to the embodiment of the present invention, a portion of the image whose density changes due to body movement is observed on the display image 22 on the CRT, and the portion is identified as an area of interest using a pointing device such as a track ball. 22a. This region of interest may be set at several locations.

Each pixel data within the region of interest set in this manner is measured by the density measuring device 12, and at the same time, the density average value or representative value within the region of interest is output, and each mask image is stored in the mask image memory 14. Density representative value data (density information) measured for each mask image is written and stored in correspondence with the image data. The number of mask images stored in this memory is, for example, one breathing period.

After that, when the contrast agent-filled image 16 captured by injecting the contrast agent is input, the concentration in the region of interest is measured in the same way as the mask image, and as shown in FIG. Mask images 14 with the same concentration in the region of interest
'The subtraction calculation is performed by the computing unit 18.

Normally, images with the same density in the region of interest have the same background shift due to the subject's body movement, so if subtraction is performed on images with the same density in the region of interest, a good result without artifacts can be obtained. You can get a good image.

Note that in FIG. 3, M represents a mask image, and L
represents a live image or a contrast agent-filled image. Further, the numbers shown below each image represent the density values within the region of interest of each image. Since the images with the same density in the region of interest are subtracted from both images, subtraction images = (L1-M1), (L2-M2)...
...(LK-MI) holds true.

[0018] Also, the image acquisition speed is, for example, 30, 60f.
The higher the speed of collection, such as the number of images per second (ps), the greater the range of selection of mask images.

Although the illustrated embodiment shows an example of application to an input video signal from a TV camera, it can also be applied as post-processing to images that have already been digitized and recorded on, for example, a hard disk. It is clear that it can be done.

【effect】

According to the present invention, it is possible to obtain a good subtraction image without forcing the subject to stop breathing, thereby reducing the burden on the patient and the like. In addition, since artifacts caused by breathing can be ignored, X-ray angiography examinations can proceed quickly.

[Brief explanation of the drawing]

[0021]

FIG. 1 is a block diagram illustrating an embodiment of the present invention.

FIG. 2 is an explanatory diagram of how images shift due to breathing.

FIG. 3 is an explanatory diagram of generation of a subtraction image according to the present invention.

[Explanation of symbols]

10 A/D converter 12 Concentration measurement device in the region of interest 14 Mask image memory with density information 18 Arithmetic unit 20 D/A converter 22 Screen 22a Area of interest

Claims (1)

[Claims] Claim 1: In an X-ray imaging system for blood vessels or the like existing in areas affected by breathing, a portion where the image density changes significantly due to breathing is set in advance as a region of interest, and a representative density value within that region is measured. a plurality of mask image memory in which each image data of a plurality of images (mask images) captured without injecting a contrast agent and measured density information in the region of interest are written correspondingly for each image; Similarly, the representative density value within the region of interest is measured for the image captured after injecting the contrast agent (live image), and the mask image image data whose measured value matches the representative density value corresponding to the mask image is selected. An X-ray subtraction system characterized by comprising a computing unit that reads data from a memory and performs subtraction between image data of a mask image and a live image.