See Contrast Agents.

(DSA) Digital subtraction angiography is a radiographic imaging technique to visualize the blood vessels in the human body. DSA images are produced by the (computer) subtraction of pre-contrast images (the mask) from images after introduction of a contrast medium. Subtracting background structures and enhancing the contrast provides the visualization of blood vessels in a bony or dense soft tissue environment. The images are produced in real time, as the contrast agent is injected into the blood vessels.