This is a non-invasive, outpatient test that is a more detailed ultrasound evaluation of the veins in your legs or arms. It can be done in the arms or legs for placement of an arterio-venous fistula for dialysis or in the legs before treatment for varicose veins. Vein mapping of the upper extremity also is done to evaluate superficial veins to determine if they can be used for creation of arterial grafts for use during coronary or peripheral bypass procedures.