Radioiodinated
fatty acid analogues modified by methyl-substitution are used for single photon emission tomography (SPET) imaging of the heart. The effect of mono- and dimethyl-substitution on heart-to-organ ratios was investigated in humans to evaluate their relative merits for SPET image quality. Planar total body scans were performed in fasting patients with
coronary artery disease, but without
heart failure, 1 h after administration of 111 MBq 15-(p-[I-123]-iodophenyl)-3-(R,S)-methylpentadecanoic
acid (
BMIPP, n = 7) or 111 MBq 15-(p-[I-123]-iodophenyl)-3,3-dimethylpentadecanoic
acid (
DMIPP, n = 4). Because these branched
fatty acids are used for cardiac imaging, we focused on heart-to-organ (heart/organ) ratios by comparing small regions of interest in heart, liver, lung, muscle and bladder. Both tracers showed good visualization of the heart.
DMIPP showed a relatively high liver uptake: the heart/liver ratios for
DMIPP and
BMIPP were 0.39 +/- 0.05 and 1.00 +/- 0.12, respectively (P < 0.0001). Increased lung activity was found for
BMIPP, with a heart/lung ratio of 1.63 +/- 0.17 versus 2.32 +/- 0.28 for
DMIPP (P < 0.001). In contrast to
DMIPP,
BMIPP also showed increased activity in the bladder. In conclusion,
BMIPP and
DMIPP show different distribution patterns. Despite the more favourable heart/lung ratios for
DMIPP, the high liver uptake affects cardiac SPET image quality and therefore
BMIPP appears to provide superior cardiac SPET image quality in humans.