Multivariate analysis of various factors affecting background liver and mediastinal standardized uptake values

Standardized uptake value (SUV) is the most commonly used semi-quantitative PET parameter. Various response assessment criteria grade the tumor uptake relative to liver or mediastinal uptake. However various factors can affect the background SUV values. This prospective study was carried out to assess the variability of liver and mediastinal SUVs normalized to lean body mass (SUL-L, SUL-M), body surface area (SUB-L, SUB-M), and body weight (SUW-L, SUW-M) and their dependence on various factors which can affect SUV values.

Eighty-eight patients who underwent F-18 FDG PET/CT for various oncological indications were prospectively included in this study. SUVs of liver and mediastinum were calculated by ROIs drawn as suggested by Wahl, et al., in PERCIST 1.0 criteria. Multivariate linear regression analysis was done to assess for the various factors influencing the SUVs of liver and mediastinum. Factors assessed were age, sex, weight, blood glucose level, diabetic status, and uptake period. A P value less than 0.01 was considered significant.

SUL-L, SUL-M, SUB-L, SUB-M, SUW-L, SUW-M were not affected significantly by age, sex, blood glucose levels, diabetic status. The uptake period had a statistically significant effect on SUL-L (P = 0.007) and SUW-L (P = 0.008) with a progressive decrease with increasing uptake time. Body weight showed a statistically significant effect on SUW-L (P = 0.001) while SUL-L and SUB-L were not dependent on weight. SUB-L was least dependent on weight (P = 0.851) when compared with SUL-L (P = 0.425). However SUL-L was also not affected statistically significantly by variations in body weight (P = 0.425). Mediastinal SUVs were not significantly affected by any of the factors.

As mediastinal SUVs are not affected significantly by any of the factors, it can be considered as background when wide variations occur in uptake times or weight of the patient when comparing two PET/CT studies to evaluate response.