Concept: Digital subtraction angiography (DSA) is an angiographic method with the aid of electronic computer for imaging, which is a new X-ray examination technique applied in clinical practice since the 70s. It is done by applying computer program for two imaging sessions. Before injecting the contrast agent, the first imaging is performed and the images are converted into digital signals and stored by computer. After the contrast is injected, the image is imaged again and converted to a digital signal. The two digital times are subtracted to eliminate the same signal and a contrast-only image of the blood vessels is obtained. This image is clearer and more intuitive than the conventional cerebral angiography used in the past, and some fine vascular structures can be displayed. Clinical significance: Because DSA can not only clearly display the vascular images of the internal carotid artery, vertebrobasilar artery, intracranial great vessels and cerebral hemispheres, but also determine the blood flow of arteries, it has been applied to cerebrovascular disease examination, especially for the qualitative localization of aneurysms and arteriovenous malformations, which is the best diagnostic tool. It not only provides the exact location of the lesion, but also gives a clear understanding of the extent and severity of the lesion, which provides a more reliable objective basis for surgery. DSA can clearly show the narrowing and occlusion of arterial lumen and the establishment of collateral circulation, etc. For cerebral hemorrhage and subarachnoid hemorrhage, it can further identify the causes of hemorrhage, such as aneurysm, vascular malformation and cavernous hemangioma. Indications: ①Intracranial vascular diseases, such as atherosclerosis, embolism, stenosis, occlusive disease, arteriopathy, arteriovenous malformation, arteriovenous fistula, etc. ②Intracranial occupying lesions, such as intracranial tumors, abscesses, cysts, hematomas, etc. (③) Various extracerebral hematomas due to cranial trauma. ④Observation of cerebrovascular circulation status after surgery. Contraindications: ①Allergic to contrast agent. ②Severe hypertension with diastolic blood pressure greater than 110 mmHg (14.66 kPa). ③Severe hepatic and renal impairment. ④Patients with recent myocardial infarction and serious cardiac disorders, heart failure and arrhythmia. ⑤ Those with uncontrolled hyperthyroidism and diabetes mellitus