Suitability of radiopharmaceuticals for determining right-to-left shunting: concise communication.

Right-to-left shunting in noncyanotic patients was quantitated following the injection of either 99mTc-microspheres, 99mTc-macroaggregated albumin, or 113mIn-Fe(OH)3 particles. Shunting was determined by wholebody scanning followed by estimation of the nuclide fraction located in the systemic circulation. Both 99mTc-labeled radiopharmaceuticals yielded results consistent with normal pulmonary shunting in a noncyanotic patient, whereas 113mIn-Fe(OH)3 was less satisfactory. If the onset of scanning was delayed, however, the calculated shunt can be falsely elevated as the pulmonary particles fragment and pass onward or as the label is released. Consequently, proper choice of radiopharmaceutical and prompt scanning are crucial for accurate quantitation of right-to-left shunting.