This ultrasound requires the patient to fast for eight hours prior to the test. This enables us to view the arteries as clearly as possible because overlying bowel gas would make them difficult to see. The main reason for this test is to check for narrowing or blockage in the renal arteries, mainly caused by high blood pressure or plaque build-up. The kidneys are evaluated and blood flow is recorded. Because of the location of the arteries, this test requires the patient to hold their breath frequently. This test may take up to one hour depending upon the difficulty.