Evaluationin Dogs of a New Double—DoseTechnique for ImagingChanges in Myocardial Perlusion

relevant situations in an experimental canine modelinorder (a) to compare the observedthallium distributions of the subtracted images with blood flows measured by micro spheres, and (b) to explore a number of technical considerations inherent in the method. Caninepreparation.Ten of myocardial perfusion with thallium immediately before and after an interventionthat altersbloodflow hasbeendifficultdueto presenceof residual activity from the first tracer dose at the time of the second imaging. In a canine model we investigateda techniqueusingtwo separate thalliuminjectionsduring an interventionand after its reversal. Imageswere obtainedafter each injection, and a difference image was obtained by subtractingthe first from the second imageto correctfortracer persistingfromthe firstinjection.Interventionsoncoro nary bloodflow included:transientocclusion,subcriticalstenosiswith dipyridam ole infusion,and permanentocclusion.The first images showed defects corre spondingto the occlusionor stenosis,while the “differenceâ€(cid:157)imagescorrelated with myocardialperfusionat the time of the secondinjection.This techniqueal lowsrapidevaluationofchangesinperfusioninresponseto interventions,andmay findapplicationin severalclinicalprocedures.