“Total cerebral angiography (DSA) is the “gold standard” for the diagnosis of carotid stenosis, which is classified according to the NASCET method (North American Symptomatic Carotid Endarterectomy Test) into four grades based on DSA findings.
(1) Mild stenosis is a reduction in the internal diameter of the artery of <30%.
(2) Moderate stenosis as a narrowing of the arterial internal diameter of 30% to 69%.
(3) Severe stenosis as a narrowing of the arterial internal diameter of 70%-99%.
(4) Complete occlusion is the pre-occlusive state with >99% stenosis”