Improved labelling of no-carrier-added 123I-MIBG and preliminary clinical evaluation in patients with ventricular arrhythmias.
Meta-[123I]iodobenzylguanidine (123I-MIBG) is currently used to assess myocardial sympathetic innervation by single photon emission tomography (SPET). In recent studies, an enhanced cardiac uptake of 123I-MIBG with high specific activity has been reported, suggesting the clinical potential of no-carrier-added (n.c.a.) 123I-MIBG in the assessment of abnormalities in cardiac sympathetic function. This paper describes the preparation of n.c.a. 123I-MIBG by non-isotopic Cu(I)-assisted [123I]iododebromination and by [123I]iododestannylation, both resulting in n.c.a. 123I-MIBG with radiochemical yields of 88 +/- 6% and high specific activity (> or = 6.3 TBq.mumol-1) in a total synthesis time of less than 50 min. The diagnostic potential of n.c.a. 123I-MIBG (> 6.3 TBq.mumol-1) was studied in 13 patients (nine patients with malignant ventricular arrhythmias and four patients suspected of phaeochromocytoma) and compared to commercial 123I-MIBG (approximately 75 MBq.mumol-1) using a dual-headed SPET camera (MULTISPECT II). High specific activity results in higher 123I-MIBG uptake in the heart and in the liver in all patients. The calculated heart-to-lung and heart-to-liver count ratios 4.5 h post-injection increased by 22 +/- 6% and 10 +/- 5% with n.c.a. 123I-MIBG compared to commercial 123I-MIBG respectively. In contrast, no significant correlation between the specific activity of 123I-MIBG and lung uptake could be established in this study. Analysis of radioactivity in blood after the intravenous injection of n.c.a. and commercially available 123I-MIBG showed an initial rapid clearance of radioactivity from blood, followed by a plateau from 60 min onwards. Within the first 24 h, more than 85% of the plasma activity was unchanged 123I-MIBG. The free 123I-iodide concentration determined 24 h post-injection was 2 +/- 1% with commercial 123I-MIBG and 3 +/- 2% with n.c.a. 123I-MIBG. In conclusion, the results of this investigation indicate that n.c.a. 123I-MIBG is a promising clinical tool for imaging myocardial sympathetic dysfunction by SPET. High specific activity n.c.a. 123I-MIBG can now be prepared by simple one-step methods giving high radiochemical yields and high purity suitable for clinical application. This encourages the further clinical validation of n.c.a. 123I-MIBG on a large scale.
Samnick
S
S
Department of Nuclear Medicine, University of Saarland, Homburg/Saar, Germany.
Bader
J B
JB
Müller
M
M
Chapot
C
C
Richter
S
S
Schaefer
A
A
Sax
B
B
Kirsch
C M
CM
D019797:3-Iodobenzylguanidine; D000368:Aged; D001145:Arrhythmias, Cardiac / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008099:Liver / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D019275:Radiopharmaceuticals; D015899:Tomography, Emission-Computed, Single-Photon
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine