Uptake of (18)F-fluoro-2-deoxyglucose in the Healthy Testes of Young Men as Assessed by Positron Emission Tomography/Computed Tomography; Including the Inter- and Intra-observer Variation

Knowledge of the physiological testicular accumulation of (18)F-fluoro-2-deoxyglucose (FDG) is essential in order to discriminate between normal and pathological findings. In this study, the (18)F-FDG-uptake in healthy testes of young men was assessed using positron emission tomography/computed tomography (PET/CT)-scans. A total of 40 testes of 20 men with a mean age of 26.5 ± 3.9 years were evaluated. (18)F-FDG-uptake was expressed as the standardized uptake value (SUV). Testicular volume was measured on CT and PET. All scans were assessed by three researchers, one of whom assessed every scan twice. Laterality indices and inter- and intra-observer variation were evaluated. Correlation between the SUVmax and SUVpeak, between SUVmean and SUVpeak and between age and SUVpeak were assessed. Testes showed an average SUVmax of 3.42 ± 0.61, SUVpeak of 3.06 ± 0.54 and SUVmean of 2.44 ± 0.44. The average testicular volume on CT was 23.0 ± 6.4 ml, whereas on PET it was 18.0 ± 5.1 ml. Laterality indices were calculated of 0.077 ± 0.065 (SUVmax), 0.074 ± 0.066 (SUVpeak), 0.072 ± 0.063 (SUVmean), 0.245 ± 0.259 (CT), and 0.200 ± 0.188 (PET), respectively. Inter- and intra-observer reliability were found to be perfect for the SUVs (intraclass correlation coefficient [ICC] 0.992-1.0), but poor for testicular volumes (ICC 0.854-0.902). Testicular (18)F-FDG uptake in young men can be measured accurately on PET/CT and shows high symmetry. Consequently, (18)F-FDG PET/CT has the potential to become a useful instrument in the evaluation of the functioning of the individual testis.