Angiography, Digital Subtraction

A method of delineating Blood Vessels by subtracting a Tissue background image from an image of Tissue plus intravascular contrast material that attenuates the X-ray Photons. The background image is determined from a digitized image taken a few moments before injection of the contrast material. The resulting angiogram is a high-contrast image of the vessel. This Subtraction Technique allows extraction of a high-intensity signal from the superimposed background information. The image is thus the result of the differential Absorption of X-Rays by different Tissues.