Myocardial perfusion with [¹¹C]metbyl triphenyl phosphonium: Measurements of the extraction fraction and myocardial uptake

The present study describes extraction fraction and uptake measurements of the [¹¹C]methyl triphenyl phosphonium (¹¹C-MTP), a promising positron emission tomography (PET) agent for cardiac imaging. PET imaging was Performed in mongrel dogs. Under physiological flow conditions ¹¹C-MTP uptake reached a maximum within the first 10 minutes after injection and remained constant during the entire observation period of 80 minutes. Over the same time period, the heartlblood ratio was 46 - 106:1, and the heart/lung ratio 14:1. following permanent occlusion of the left anterior descending coronary artery, ¹¹C-MTP uptake in the normally perfused myocardium also reached a maximum at 10 minutes after injection, whereas in the infarcted area there was no significant accumulation of ¹¹C-MTP. For a time period of 80 minutes the noninfarcted/infarcted myocardium ratio was 12:1. Extraction was measured in anesthetized dogs with a double isotope method using ^99mTc-HSA as the reference tracer. The extraction fraction was 91% at a flow of 69 mL/min/100g. As flow increased to five-fold (342 mL/min/100g) following administration of adenosine, extraction fell to 61%. Following coronary artery occlusion, the ¹¹C-MTP content in the myocardium was highly correlated (r = 0.93, p < 0.01; y = 10.46 + 0.92x) with the microsphere determined regional myocardial blood flow.