Clinical performance and radiation dosimetry of no-carrier-added vs carrier-added (123)I-metaiodobenzylguanidine (MIBG) for the assessment of cardiac sympathetic nerve activity

PURPOSE: We hypothesized that assessment of myocardial sympathetic activity with no-carrier-added (nca) (123)I-meta-iodobenzylguanidine (MIBG) compared to carrier-added (ca) (123)I-MIBG would lead to an improvement of clinical performance without major differences in radiation dosimetry. METHODS: In nine healthy volunteers, 15 min and 4 h planar thoracic scintigrams and conjugate whole-body scans were performed up to 48 h following intravenous injection of 185 MBq (123)I-MIBG. The subjects were given both nca and ca (123)I-MIBG. Early heart/mediastinal ratios (H/M), late H/M ratios and myocardial washout were calculated. The fraction of administered activity in ten source organs was quantified from the attenuation-corrected geometric mean counts in conjugate views. Radiation-absorbed doses were estimated with OLINDA/EXM software. RESULTS: Both early and late H/M were higher for nca (123)I-MIBG (ca (123)I-MIBG early H/M 2.46 ± 0.15 vs nca (123)I-MIBG 2.84 ± 0.15, p = 0.001 and ca (123)I-MIBG late H/M 2.69 ± 0.14 vs nca (123)I-MIBG 3.34 ± 0.18, p = 0.002). Myocardial washout showed a longer retention time for nca (123)I-MIBG (p < 0.001). The effective dose equivalent (adult male model) for nca (123)I-MIBG was similar to that for ca (123)I-MIBG (0.025 ± 0.002 mSv/MBq vs 0.026 ± 0.002 mSv/MBq, p = 0.055, respectively). CONCLUSION: No-carrier-added (123)I-MIBG yields a higher relative myocardial uptake and is associated with a higher myocardial retention. This difference between nca (123)I-MIBG and ca (123)I-MIBG in myocardial uptake did not result in major differences in estimated absorbed doses. Therefore, nca (123)I-MIBG is to be preferred over ca (123)I-MIBG for the assessment of cardiac sympathetic activity.