Detection of the site of blockage that produces obstruction of the superior vena cava has usually been determined by venous angiography (1–3). The angiogram provides accurate information concerning alterations in circulation, but obstruction increases the risk of complications from the procedure. Also, passage of the contrast medium in high concentration through collaterals may produce a greater degree of discomfort than is usually encountered in angiographic studies. Not infrequently more than one injection has been required to produce the desired degree of visualization of the superior vena cava. An alternate method for evaluation of the superior vena cava is the technetium-99m pertechnetate (99mTc) superior vena cavogram. The use of stationary imaging devices for evaluation of vascular flow through major blood vessels has been documented by several investigators (4–8). The short half-life tracers used for these studies have produced no discomfort, morbidity, or mortality. Materials and Methods This rep...