Normalization of stress and delayed thallium-201 myocardial SPECT: where is the normal reference area?

We describe an unusual uptake pattern in a thallium SPECT study performed after dipyridamole infusion in a patient with a documented history of prior inferior infarction and recent typical chest pain. The stress study exhibited maximum uptake in the inferior wall. The delayed study showed an inferior defect more consistent with the notion of inferior necrosis, with a maximum uptake in the anterior wall. The authors propose a pathophysiologic interpretation consistent with coronary angiography findings, based on the assumption of coronary steal suggested by the occurrence of chest pain at the end of the dipyridamole infusion. The problem of selecting myocardial normal reference area(s) necessary to normalization prior to quantitative comparison stress and delayed studies is discussed.