Quantitative Analysis of Dynamic 123I-mIBG SPECT Imaging Data in Healthy Humans with a Population-Based Metabolite Correction Method

Conventional 2-dimensional planar imaging of (123)I-metaiodobenzylguanidine ((123)I-mIBG) is not fully quantitative. To develop a more accurate quantitative imaging approach, we investigated dynamic SPECT imaging with kinetic modeling in healthy humans to obtain the myocardial volume of distribution (VT) for (123)I-mIBG.

Methods: Twelve healthy humans underwent 5 serial 15-min SPECT scans at 0, 15, 90, 120, and 180 min after bolus injection of (123)I-mIBG on a hybrid cadmium zinc telluride SPECT/CT system. Serial venous blood samples were obtained for radioactivity measurement and radiometabolite analysis. List-mode data of all the scans were binned into frames and reconstructed with attenuation and scatter corrections. Myocardial and blood-pool volumes of interest were drawn on the reconstructed images to derive the myocardial time-activity curve and input function. A population-based blood-to-plasma ratio (BPR) curve was generated. Both the population-based metabolite correction (PBMC) and the individual metabolite correction (IMC) curves were generated for comparison. VT values were obtained from different compartment models, using different input functions with and without metabolite and BPR corrections.

Results: The BPR curve reached the peak value of 2.1 at 13 min after injection. Parent fraction was approximately 58% ± 13% at 15 min and stabilized at approximately 40% ± 5% by 180 min after injection. Two radiometabolite species were observed. When the reversible 2-tissue-compartment fit was used, the mean VT value was 29.0 ± 12.4 mL/cm(3) with BPR correction and PBMC, a 188% ± 32% increase compared with that without corrections. There was significant difference in VT with BPR correction (P = 2.3e-04) as well as with PBMC (P = 1.6e-05). The mean difference in VT between PBMC and IMC was -3% ± 8%, which was insignificant (P = 0.39). The intersubject coefficients of variation after PBMC (43%) and IMC (42%) were similar.

Conclusion: The myocardial VT of (123)I-mIBG was established in healthy humans for the first time. Accurate kinetic modeling of (123)I-mIBG requires both BPR and metabolite corrections. Population-based BPR correction and metabolite correction curves were developed, allowing more convenient absolute quantification of dynamic (123)I-mIBG SPECT images.