Comparing FDG quantification in tumors with the retention fraction and SUV in a dual scan examination after 60 and 90 minutes

2095 Objectives To determine and compare the time variability of the standard uptake value (SUV) and the retention fraction (RF) for FDG quantification between 60 and 90 minutes. Methods We analyzed 16 patients referred for staging or follow up of malignant disease. 60 minutes after injection of 350 MBq FDG using an automatic injector, partial body PET/CT images were acquired. Thirty minutes after imaging the PET acquisition of the tumor was repeated. The tumor RF was calculated for both scans by dividing the tumor uptake (kBq/cc) by the integral of a population based input curve. This input curve was calibrated with the measured blood pool activity in the aortic arch in scan 1. SUVmax and RFmax were determined in the same volume of interest (VOI) in both scans. Results The relative changes for SUVmax between scan two and one was 13.4±7.8% (-2.1 - 34.7%). In comparison the relative change for RFmax was significantly smaller with 0.5±6.5% (-13.5 - 17.4%) (p Conclusions FDG quantification using RF is significantly less time dependent between 60 and 90 minute, than SUV. Therefore RF may be a better quantifier for FDG uptake/metabolism more compatible with clinical reality where start times for the PET scan cannot always be tightly controlled. Research Support Non