Angiography is mainly an imaging technique, thus showing whether the lumen of a blood vessel is narrowed or occluded, whether there is plaque and whether the vessel is under pressure. Vascular imaging is usually divided into three types of examinations: 1) CT angiography: also called CTA, which is a CT scan with contrast enhancement to image blood vessels; 2) MRI angiography: also called MRA, which is a non-invasive examination that does not require the use of contrast; 3) DSA: the effect is better. DSA is the gold standard for all kinds of vascular examinations.