Perfusion CT was introduced to help identify and quantify thepresence and extent of a perfusion deficit in patients presenting with acutestroke symptoms. The level of perfusion to the ischemic tissues may help todetermine the relative benefits and risks of a given therapy.Perfusion CT quickly monitors the contrast agent through the cerebralvasculature with any standard spiral CT scanner. Changes in tissueattenuation that occur in the brain are measured after the contrast injection.Post-processing of the perfusion CT data allows the generation of colorcodedmaps of various perfusion parameters, including cerebral blood flow(CBF), cerebral blood volume (CBV), mean transit time (MTT), and thetime-to-peak (TTP), the time from the start of contrast agent injection to thetime of maximum enhancement. Perfusion CT scan may become part of thescreening CT protocol in the future.