Typically a catheter is inserted into a large artery (such as the femoral artery) and threaded through the circulatory system to the carotid artery, where a contrast agent is injected. A series of radiographs are taken as the contrast agent spreads through the brain's arterial system, then a second series as it reaches the venous system.
For some applications this method may yield better images than less invasive methods such as computed tomography angiography and magnetic resonance angiography. In addition, cerebral angiography allows certain treatments to be performed immediately, based on its findings. If, for example, the images reveal an aneurysm, metal coils may be introduced through the catheter already in place and maneuvered to the site of aneurysm; over time these coils encourage formation of connective tissue at the site, strengthening the vessel walls.