Superior vena cava as the most optimal site for background correction in quantification of atherosclerosis

Objectives The aim of this study was to determine the optimal site for measuring blood pool activity (BPA) to calculate tissue to background ratio (TBR) in quantification of atherosclerosis.

Methods Ninety six PET/CT images of 32 subjects imaged at 1, 2, and 3 hours were included in this study. ROIs were placed around the left carotid wall in every slice (5 mm) of the registered images. FDG uptake in left carotid was quantified as weighted average SUVmean (wA-SUVmean) [∑ (SUVmean x surface area x thickness) / ∑volume]. FDG uptake in superior vena cava (SVC), inferior vena cava (IVC), jugular vein (JV) and right atrium (RA) were determined by placing ROI in the center of each vessel on every transverse slice and then mean BPA (V-SUVmean) was measured. Atherosclerosis (TBR) was calculated as wA-SUVmean divided by BPA (V-SUVmean) measured at different sites. Three investigators measured all studies separately for reproducibility of each site. Repeated measures ANOVA test was used to compare V-SUVmean and TBRs measured by 3 investigators and one-way ANOVA test was used to compare TBRs calculated based on V-SUVmean of different sites.

Results The mean of measurements at SVC, RA, JV, and IVC were 1.2, 1.4, 1.5, and 1.8 respectively (P=0.04). SVC measurements were the most reproducible site for calculating BPA (Pitman's ratio of variances for paired data; P=0.01); and the jugular vein was the least reproducible site.

Conclusions For accurate quantification of atherosclerosis, BPA should be measured. Based on these data, jugular vein, due to its small size, is suboptimal for this purpose. Spill-over from the hepatic uptake increases the measured activity in the IVC. SVC measurements have the lowest agree of inter-observer variation and also show the lowest SUV likely due to minimal spill-over from surrounding organs.