The ability to directly measure velocity and volume flow rates adds a new dimension to the MR angiographic evaluation of patients with cerebrovascular disease. Reduced volume flow rates are associated with flow restrictive stenoses. Flow volumes begin to drop when the area of the vessel lumen is reduced by greater than 80%. Cerebrovascular flow reserve also can be determined by obtaining volume flow measurements before and after the administration of a vasodilator such as acetazolamide. Recent applications include the investigation of the flow dynamics associated with subclavian steal, aneurysms, and arteriovenous malformations.