Evaluation of myocardial distribution of iodine-123 labeled metaiodobenzylguanidine (123I-MIBG) in normal subjects

The normal pattern of the myocardial sympathetic innervation was studied in 15 subjects using gamma camera scintigraphy with iodine-123 labeled metaiodobenzylguanidine (123I-MIBG). Seven younger subjects (mean age 24.6±3.6) and eight older patients (mean age 60.9±8.4) with normal cardiac function were studied. Planar imaging was obtained at 15 minutes and 3 hours, and SPECT was also performed 3 hours after injection of 111 MBq (3 mCi) of MIBG. The younger subjects showed higher the heart to mediastinum count ratio (2.91±0.25 vs. 2.67±0.34; p<0.05) and higher inferior to anterior count ratio (1.19±0.15 vs. 0.97±0.13; p<0.05) on the late scan. The bull's-eye polar map also differences in counts in the mid-inferior (p<0.005), basal-inferior (p<0.005) and mid-lateral sectors (p<0.01). But there was no significant difference in MIBG washout rate from myocardium between two groups. These data suggest that there is a difference of the cardiac sympathetic innervation, with older subjects having fewer sympathetic nerve terminals, especially in inferior than younger subjects. We conclude that the age difference in sympathetic nerve function should be considered in the interpretation of MIBG scan. (author)