Abstract
In oncologic PET, the SUV and standardized uptake ratio (SUR) of a viable tumor generally increase during the postinjection period. In contrast, the net influx rate (K(i) ), which is derived from dynamic PET data, should remain relatively constant. Uptake-time-corrected SUV (cSUV) and SUR (cSUR) have been proposed as uptake-time-independent, static alternatives to K(i) Our primary aim was to quantify the intrascan repeatability of K(i) , SUV, cSUV, SUR, and cSUR among malignant lesions on PET/CT. An exploratory aim was to assess the ability of cSUR to estimate K(i) Methods: This prospective, single-center study enrolled adults undergoing standard-of-care oncologic PET/CT. SUV and K(i) images were reconstructed from dynamic PET data obtained before (∼35-50 min after injection) and after (∼75-90 min after injection) standard-of-care imaging. Tumors were manually segmented. Quantitative metrics were extracted. cSUVs and cSURs were calculated for a 60-min postinjection reference uptake time. The magnitude of the intrascan test-retest percent change (test-retest |%Δ|) was calculated. Coefficients of determination (R (2)) and intraclass correlation coefficients (ICC) were also computed. Differences between metrics were assessed via the Wilcoxon signed-rank test (α, 0.05). Results: This study enrolled 78 subjects; 41 subjects (mean age, 63.8 y; 24 men) with 116 lesions were analyzed. For both tracers, SUV(max) and maximum SUR (SUR(max)) had large early-to-late increases (i.e., poor intrascan repeatability). Among [(18)F]FDG-avid lesions (n = 93), there were no differences in intrascan repeatability (median test-retest |%Δ|; ICC) between the maximum K(i) (K(i) (,max)) (13%; 0.97) and either the maximum cSUV (cSUV(max)) (12%, P = 0.90; 0.96) or the maximum cSUR (cSUR(max)) (13%, P = 0.67; 0.94). For DOTATATE-avid lesions (n = 23), there were no differences in intrascan repeatability between the K(i) (,max) (11%; 0.98) and either the cSUV(max) (13%, P = 0.41; 0.98) or the cSUR(max) (11%, P = 0.08; 0.94). The SUV(max), cSUV(max), SUR(max), and cSUR(max) were all strongly correlated with the K(i) (,max) for both [(18)F]FDG (R (2), 0.81-0.92) and DOTATATE (R (2), 0.88-0.96), but the cSUR(max) provided the best agreement with the K(i) (,max) across early-to-late time points for [(18)F]FDG (ICC, 0.69-0.75) and DOTATATE (ICC, 0.90-0.91). Conclusion: K(i) (,max), cSUV(max), and cSUR(max) had low uptake time dependence compared with SUV(max) and SUR(max) The K(i) (,max) can be predicted from cSUR(max).