Simplified Quantification and Acquisition Protocol of ¹²³I-mIBG Dynamic SPECT

Abstract

Objectives: Previous studies have demonstrated the feasibility of absolute quantification of dynamic ¹²³I-metaiodobenzylguanidine (¹²³I-mIBG) single photon emission computed tomography (SPECT) imaging in human. This work reports on simplified quantification of dynamic ¹²³I-mIBG SPECT using practical protocols with shortened acquisition time and voxel-by-voxel parametric imaging. Methods: Twelve healthy human volunteers underwent five 15-min dynamic SPECT scans at 0, 15, 90, 120 and 180 min after ¹²³I-mIBG injection using a Discovery NM/CT 570c scanner. List-mode SPECT data were binned into 29 frames and reconstructed with corrections for attenuation, scatter and decay. Population-based blood-to-plasma correction and metabolite correction were applied to the image-derived input function. The likelihood estimation in graphical analysis (LEGA) technique was used as a simplified model to obtain volume of distribution (VT) values, which were compared to those obtained with the reversible two-tissue (2T) compartment model. Three simplified protocols were evaluated with 2T and LEGA, using a 30-min scan started with tracer injection plus a 15-min scan at 90, 120 or 180 min post-injection. Voxel-by-voxel LEGA fitting was applied to the aligned dynamic images using both the full dataset and the simplified protocols. Results: Correlation (y=0.955x+0.547, R2=0.997) and Bland-Altman plot (mean difference=-0.8 mL/cm³, 95% limits of agreement=[-2.5, 1.0] mL/cm³, normal VT range: 29.0 ± 12.4 mL/cm³) showed that LEGA can be used as a simplified model of 2T for ¹²³I-mIBG. High quality VT parametric images can be obtained with LEGA. Region of interest (ROI) modeling and parametric imaging results were in excellent agreement in terms of correlation (y=0.999x-1.026, R2=0.982) and Bland-Altman plot (mean difference=-1.0 mL/cm³, 95% limits of agreement=[-4.2, 2.1] mL/cm³). Reasonable correlations of VT values between all the simplified protocols and the full protocol (five 15-min scans) could be obtained with LEGA but not 2T. VT results were more reliable with a longer interval between the two acquisitions of simplified protocols for ROI-based modeling and parametric imaging. Conclusion: It is feasible to achieve reliable quantification of dynamic ¹²³I-mIBG SPECT with LEGA using a simplified protocol of a 30-min scan starting with tracer injection plus a 15-min scan no earlier than 180 min for ROI-based kinetic modeling and parametric imaging.