Subtraction angiography (DSA) is a computer-aided angiography method, which is a brand-new X-ray examination technique applied in clinic since 1970s. It is done by twice imaging with a computer program. Before the contrast agent is injected, the first imaging is performed, and the image is converted into a digital signal by the computer and stored. After injection of contrast agent, it is imaged again and converted into digital signal. Two times of digital subtraction, the same signal is eliminated, and a blood vessel image with only contrast agent is obtained. This kind of image is clearer and more intuitive than that displayed by conventional cerebral angiography, and it can also show some subtle vascular structures.

Extended data:

The basic principle of DSA imaging: the angiographic X-ray fluorescence images of the examination site without contrast agent and injected with contrast agent are obtained by the image intensifier respectively, and then scanned by the high-resolution television camera tube, and the images are divided into many small squares and made into a matrix to form a video image composed of pixels in the small squares, which is converted into numbers with different values through logarithmic amplification and A/D conversion to form digital images and stored separately.

Then it is input into an electronic computer for processing, and the digital information of the two images is subtracted to obtain differential signals with different values. After contrast enhancement and D/A conversion, it is converted into an ordinary analog signal, and a subtraction image with bones, muscles and other soft tissues removed is obtained, leaving only a simple blood vessel image to be displayed on the display.