Quantitation of left-to-right cardiac shunts with radionuclide angiography.

A quantitative radionuclide angiogram technique using an intravenous injection of technetium99m (Tc-99m) pertechnetate is described for quantitation of left-to-right shunts in the central circulation. Data analysis assumes exponential indicator clearance from normal cardiac chambers by dilution. A late prolongation of tracer disappearance compared to the initial clearance rate indicates an abnormally early return of indicator to the cardiac chamber. Patients with left-to-right shunts demonstrate prolonged clearance of radioactivity from all cardiac chambers distal to the site of shunt. The magnitude of curve distortion is quantitatively related to the size of shunt, and counts recorded from the right lung are used for shunt quantitation. Quadratic regression analysis of data from 21 patients with left-to-right shunts and eight normal subjects demonstrated