Evaluation in dogs of a new double-dose technique for imaging changes in myocardial perfusion

Assessment of myocardial perfusion with thallium immediately before and after an intervention that alters blood flow has been difficult due to presence of residual activity from the first tracer dose at the time of the second imaging. In a canine model we investigated a technique using two separate thallium injections during an intervention and after its reversal. Images were obtained after each injection, and a difference image was obtained by subtracting the first from the second image to correct for tracer persisting from the first injection. Interventions on coronary blood flow included: transient occlusion, subcritical stenosis with dipyridamole infusion, and permanent occlusion. The first images showed defects corresponding to the occlusion or stenosis, while the "difference" images correlated with myocardial perfusion at the time of the second injection. This technique allows rapid evaluation of changes in perfusion in response to interventions, and may find application in several clinical procedures.