Three-Dimensional Heart Segmentation and Absolute Quantitation of Cardiac (123)I-metaiodobenzylguanidine Sympathetic Imaging Using SPECT/CT

Background: A three-dimensional (3D) approach to absolute quantitation of (123)I-metaiodobenzylguanidine (MIBG) sympathetic nerve imaging using single-photon emission tomography (SPECT) / computed tomography (CT) is not available. Therefore, we calculated absolute cardiac counts and standardized uptake values (SUVs) from images of 72 consecutive patients with cardiac and neurological diseases using (123)I-MIBG SPECT/CT and compared them with conventional planar quantitation. We aimed to develop new methods for 3D heart segmentation and the quantitation of these diseases. Methods: We manually segmented early and late SPECT/CT images of the heart in 3D, then calculated mean (SUV(mean)) and maximum (SUV(max)) SUVs. We analyzed correlations between SUVs and planar heart-to-mediastinum ratios (HMRs), and between washout rates (WRs) derived from the SUVs and planar data. We also categorized WRs as normal or abnormal using linear regression lines determined by the relationship between SPECT/CT and planar WRs, and assessed agreement between them. Results: We calculated SUV(mean) and SUV(max) from all early and late (123)I-MIBG SPECT/CT images. Planar HMRs correlated with early and late SUV(mean) (R(2)=0.59 and 0.73, respectively) and SUV(max) (R(2)=0.46 and 0.60, respectively; both p<0.0001). The SPECT/CT WRs determined based on SUV(mean) and SUV(max) (R(2)=0.79 and 0.45, p<0.0001) closely correlated with planar WRs. Agreement of high and low WRs between planar WRs and SPECT/CT WRs calculated using SUV(max) and SUV(mean) reached 88.1% and 94.4% respectively. Conclusions: We found that sympathetic nervous activity could be absolutely quantified in 3D from (123)I-MIBG SPECT/CT images. Therefore, we propose a new method for quantifying sympathetic innervation on SPECT/CT images.