The elimination rate of 123I-heptadecanoic acid after intracoronary and intravenous administration.

When calculating the elimination rate of radioactivity after the administration of radioiodinated heptadecanoic acid (123I-HDA), background correction is necessary due to the high level of background activity. In the present study, the subtraction method of Freundlieb et al. was investigated on validity. This was done by comparing the half-time values of the elimination rate after intravenous (i.v.) and intracoronary (i.c.) injection. In the latter case, no background correction was necessary. Six patients undergoing cardiac catheterization were studied. Scintigraphy was performed after the injection of 123I-HDA into the left coronary artery and after i.v. injection. Half-time values were calculated from regions of interest drawn over myocardium perfused by the left-anterior descending branch (LAD) and the left circumflex artery (LCX). In the LAD region, the mean half-time value in the i.c. study was 22 min, while in the corrected i.v. study, the mean value was 27 min. In the LCX region, the half-time values were 24 and 33 min, respectively. The background-subtraction procedure proposed by Freundlieb et al. for i.v.-injected 123I-HDA is incomplete, as it resulted in half-time values that were higher than those of the i.c. study.