Significance of myocardial uptake of iodine 123-labeled beta-methyl iodophenyl pentadecanoic acid: comparison with kinetics of carbon 11-labeled palmitate in positron emission tomography.

BACKGROUND

A radioactively labeled beta-methyl branched fatty acid analog, 123I-15-(p-iodophenyl)-3-methyl pentadecanoic acid (BMIPP), has been developed to probe regional myocardial fatty acid metabolism. However, the significance of BMIPP uptake in the myocardium remains unclear.

METHODS AND RESULTS

To evaluate the significance of BMIPP uptake, single-photon emission computed tomography was performed 30 minutes after injection of BMIPP, and 201Tl-labeled single-photon emission computed tomography was taken on a separate day in 10 patients. Findings of BMIPP and 201Tl-labeled imaging were compared with the data obtained from positron emission tomography with 11C-labeled palmitate. The BMIPP uptake (percent of maximum) was significantly correlated with the early uptake (percent) and delayed uptake (percent) of 11C-labeled palmitate (r = 0.659 and r = 0.687, respectively) (p < 0.01 each), whereas it was not significantly correlated with the residual fraction (r = 0.205) or the clearance half-time of the early component (r = 0.138) of 11C-labeled palmitate as a marker of beta-oxidation of the fatty acid.

CONCLUSIONS

These data indicate that, although the myocardial uptake of BMIPP may not directly reflect beta-oxidation of fatty acids, its uptake may reflect both regional myocardial blood flow and fatty acid extraction.