Effect of specific activity on cardiac uptake of iodine-123-MIBG.
Radioiodinated meta-iodobenzylguanidine (MIBG), an analog of norepinephrine, has been used to assess myocardial sympathetic innervation. Recent in vivo studies predict enhanced cardiac uptake of this radiopharmaceutical with high specific activity.


METHODS
To clarify the effect of specific activity on cardiac uptake of radioiodinated MIBG, the distribution and kinetics of no-carrier-added [123I]MIBG (> or = 7.4 TBq/mumol) were compared with those of commercial [123I]MIBG (approximately 74 MBq/mumol) in three healthy volunteers by serial imaging and blood sampling.


RESULTS
Higher specific activity result in higher uptake of radioiodinated MIBG in all volunteers in the heart (p < 0.05) and liver (p < 0.05) but not in the lung (p = 0.26). Due to rapid deiodination, a more pronounced accumulation of radioactivity was present in plasma after no-carrier-added MIBG than commercial [123I]MIBG, resulting in higher background and thyroid activity after administration of the former. Calculated heart-to-liver (p = 0.96) and heart-to-lung (p = 0.42) count ratios in all volunteers revealed no significant improvement in cardiac imaging with no-carrier-added [123I]MIBG compared to commercial [123I]MIBG.


CONCLUSIONS
This study highlights the appreciably higher in vivo deiodination of no-carrier-added [123I]MIBG compared to commercial preparation of [123I]MIBG in humans. Cardiac images acquired with no-carrier-added [123I]MIBG do not seem to be superior to those obtained with commercial MIBG.
Farahati
J
J
Department of Nuclear Medicine, University of Würzburg, Germany.
Bier
D
D
Scheubeck
M
M
Lassmann
M
M
Schelper
L F
LF
Grelle
I
I
Hanscheid
H
H
Biko
J
J
Graefe
K H
KH
Reiners
C
C
D019797:3-Iodobenzylguanidine; D000328:Adult; D004337:Drug Carriers; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D007462:Iodobenzenes / Q000493:pharmacokinetics*; D008099:Liver / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D011829:Radiation Dosage; D012016:Reference Values; D013961:Thyroid Gland / Q000378:metabolism; D014018:Tissue Distribution; D014915:Whole-Body Counting
D004337:Drug Carriers; D007457:Iodine Radioisotopes; D007462:Iodobenzenes; D019797:3-Iodobenzylguanidine