No-carrier-added versus carrier-added123I-metaiodobenzylguanidine for the assessment of cardiac sympathetic nerve activity.
OBJECTIVE
No-carrier-added (nca) MIBG is primarily associated with specific uptake (i.e. uptake-1 mechanism). We evaluated the hypothesis that nca MIBG will be less influenced by changes in extra-neuronal uptake (i.e. uptake-2 mechanism) compared with carrier-added (ca) MIBG.


METHODS
No-carrier-added MIBG was compared with ca MIBG of two different manufacturers (ca MIBG-1 and ca MIBG-2, with a specific activity of 200 Mq/mumol and 40 MBq/mumol MIBG respectively) in rats (n=6 per group): controls, blocking uptake-1 (desipramine) and blocking uptake-2 (phenoxybenzamine hydrochloride). Dedicated pinhole SPECT was performed 2 h after injection of the radiotracer. After SPECT, biodistribution was assessed [% injected dose per gram tissue (%ID)].


RESULTS
No-carrier-added MIBG had the highest absolute cardiac uptake. Although a clear trend was observed, nca MIBG was not statistically significantly different from ca MIBG-1 (0.31+/-0.05 %ID vs 0.25+/-0.01 %ID,p=0.05). Blocking uptake-1 resulted in a significant decrease in absolute cardiac uptake only for nca MIBG (0.22+/-0.03 %ID,p=0.004). Blocking uptake-2 resulted in a significant reduction in ca MIBG-1 cardiac uptake (0.14+/-0.02 %ID,p=0.0001), but not in the cardiac uptake of nca MIBG or MIBG-2. SPECT showed the highest relative cardiac uptake for nca MIBG. Poor contrast between myocardium and surrounding tissue hampered assessment of relative cardiac uptake on SPECT of both ca MIBG-1 and ca MIBG-2.


CONCLUSIONS
No-carrier-added MIBG yields a higher myocardial uptake than ca MIBG and is associated with a higher specific as well as a lower non-neuronal uptake. We therefore conclude that for the scintigraphic assessment of the myocardial sympathetic nervous system, nca MIBG is to be preferred over ca MIBG.
Verberne
Hein J
HJ
Department of Nuclear Medicine, University of Amsterdam, F2-238, Academic Medical Center, PO Box 22700, 1100 DE, Amsterdam, The Netherlands. h.j.verberne@amc.uva.nl
de Bruin
Kora
K
Habraken
Jan B A
JB
Somsen
G Aernout
GA
Eersels
Jos L H
JL
Moet
Frits
F
Booij
Jan
J
van Eck-Smit
Berthe L F
BL
D019797:3-Iodobenzylguanidine / Q000737:chemistry / Q000493:pharmacokinetics*; D000818:Animals; D005240:Feasibility Studies; D006321:Heart / Q000000981:diagnostic imaging* / Q000294:innervation*; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D008657:Metabolic Clearance Rate; D009206:Myocardium / Q000378:metabolism*; D009928:Organ Specificity; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D051381:Rats; D017208:Rats, Wistar; D013564:Sympathetic Nervous System / Q000000981:diagnostic imaging* / Q000378:metabolism*; D014018:Tissue Distribution
D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine