Technetium 94m-labeled methoxyisobutyl isonitrile: dosimetry and resting cardiac imaging with positron emission tomography.

Abstract

Development of a positron-emitting form of technetium has allowed the imaging of technetium radiopharmaceuticals with positron emission tomography (PET). We used 94mTc to compare the distribution of the myocardial perfusion agent sestamibi at rest with the conventional PET perfusion tracer 13N-labeled ammonia (13N-ammonia). Dosimetry calculations were performed with the known whole-body distribution of 99mTc-labeled sestamibi. Dynamic PET imaging of 13N-ammonia and 94mTc-labeled sestamibi (94mTc-sestamibi) for 32 minutes was performed in eight patients with previous myocardial infarction. Initial myocardial and extramyocardial distribution of 94mTc-sestamibi was compared with that of 13N-ammonia by qualitative and quantitative analysis. Quantitative comparison of the two tracers was performed with region-of-interest analysis and circumferential profiles. Qualitatively, the cardiac distribution of the tracers was similar in normal and infarcted myocardium. A decrease in the definition of the epicardial and endocardial borders of the heart was seen with 94mTc-sestamibi, presumably because of the lower dose of radionuclide injected. Quantitatively, there was no difference in infarct size, defined prospectively as tracer activity less than 20% of maximum activity for the section, between the two tracers. Circumferential profile analysis with 12-degree radial sections similarly demonstrated no difference in regional cardiac distribution of the tracers. These results revealed no significant difference in myocardial uptake compared with 13N-ammonia suggesting that the myocardial uptake of sestamibi correlates with that of myocardial perfusion.