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The accuracy of three-dimensional transverse section positron emission imaging for quantification of myocardial infarction size was validated and compared with the accuracy of two dimensional planar positron imaging. After induction of acute anterior myocardial infarction in anaesthetised dogs, gallium-68 albumin microspheres were injected into the left atrium. Planar and transverse section images of the thorax were obtained with a multicrystal positron camera. After staining with tetrazolium tetrachloride injected intravenously, the hearts were excised, sectioned manually, and planar imaging repeated. Each myocardial infarction was clearly delineated by transverse section imaging with high contrast ratios (mean 0.68 +/- 0.02 SEM); planar imaging identified seven of nine infarcts but with lower contrast ratios (0.24 +/- 0.04; P < 0.001). The volume of infarcted myocardium determined from transverse section images correlated well with true infarct volume (r = 0.94); whereas planar images poorly predicted infarct size (r = 0.63). Thus, computer-assisted transverse section positron imaging provides in vivo localisation of microsphere distribution for improved radioisotopic quantification of myocardial infarction.

We have tagged heptadecanoic acid with C-11 at the carboxyl group and have inserted a methyl radical in the beta position to inhibit beta oxidation of the fatty acid; we have then explored the tracer's potential as an indicator of myocardial metabolism for use with the positron tomograph. In this preliminary evaluation, biodistribution studies were made in rats and dogs, and imaging of normal and infarcted dogs was performed. At 30 min the tissue distribution studies in rats and dogs showed, respectively, 1.9% and 8.3% uptake in the heart. Sequential images of the canine heart exhibited a remarkable uptake, peaking at 16-18 min and retaining the same level of activity over the one-hour study period. Images of the heart after LAD ligation showed an area of diminished uptake corresponding to the region of infarction. Thus this agent has the basic properties required for potential use in the assessment and quantitation of free fatty-acid metabolism in the heart in a manner similar to the measurement of glucose metabolism in the brain with 2-[18F]fluoro-3-deoxy-D-glucose.