F-18 meta-fluorobenzylguanidine PET imaging of myocardial sympathetic innervation

Background: I-123 meta-iodobenzylguanidine (MIBG) imaging has long been employed to noninvasively assess the integrity of human norepinephrine transporter-1 and, hence, myocardial sympathetic innervation. Positron-emitting F-18 meta-fluorobenzylguanidine (MFBG) has recently been developed for potentially superior quantitative characterization. We assessed the feasibility of MFBG imaging of myocardial sympathetic innervation. Methods: 16 patients were imaged with MFBG PET (30-minute dynamic imaging of chest, followed by 3 whole-body acquisitions between 30 minutes and 4-hour post-injection). Blood kinetics were assessed from multiple samples. Pharmacokinetic modeling with reversible 1- and 2-compartment models was performed. Kinetic rate constants were re-calculated from truncated datasets. All patients underwent concurrent MIBG SPECT. Results: MFBG myocardial uptake was rapid and sustained; the mean standardized uptake value (SUV (mean ± standard deviation)) was 5.1 ± 2.2 and 3.4 ± 1.9 at 1 hour and 3-4-hour post-injection, respectively. The mean K₁ and distribution volume (V_T) were 1.1 ± 0.6 mL/min/g and 34 ± 22 mL/cm³, respectively. Both were reproducible when re-calculated from truncated 1-hour datasets (Intraclass Correlation Coefficient of 0.99 and 0.91, respectively). Spearman’s ϱ = 0.86 between MFBG SUV and V_T and 0.80 between MFBG PET-derived V_T and MIBG SPECT-derived heart-to-mediastinum activity concentration ratio. Conclusion: MFBG is a promising PET radiotracer for the assessment of myocardial sympathetic innervation.