Physiological testicular 18F-FDG uptake in boys: age-related patterns and association with body mass index.

PURPOSE: To characterize age-related patterns of testicular 18F-Fluorodeoxyglucose (FDG) uptake in boys and evaluate association with body mass index (BMI). MATERIALS AND METHODS: Testicular SUVmax, SUVmean and testicle-to-liver ratio (TLR) of boys aged 0-18 years selected by stratified random sampling were measured and compared across age groups. Age-stratified reference values were established. Age-related metabolic transition points were identified using classification and regression tree (CART) models. Multivariable regression analyses were performed to assess association between BMI and testicular FDG uptake. RESULTS: In 377 boys (mean age, 8.0 ± 5.3 years), testicular 18F-FDG uptake increased with age, correlating strongly with SUVmax (r = 0.792) and SUVmean (r = 0.753), moderately with TLR (r = 0.506), (all P < 0.001). Three age-related metabolic patterns were identified: low uptake at 0-8 years, transitional increase at 9-12 years, and sustained higher uptake at 13-18 years. Corresponding SUVmax 97.5th percentiles were 2.5-2.9, 5.2-5.3, and 5.9-6.5. CART identified a metabolic transition at 10.5-12.5 years. Multivariate analysis identified age as the dominant predictor for testicular FDG uptake (SUVmax: β = 0.689, SUVmean: β = 0.638, TLR: β = 0.501; all P < 0.001). After age adjustment, higher BMI remained independently associated with increased uptake (SUVmax: r = 0.398; SUVmean: r = 0.412; both P < 0.001). Metabolic transition points varied among BMI groups, with 10.5, 11.5, and 12.5 years in the overweight, normal-weight, and underweight groups, respectively. CONCLUSION: Physiological testicular 18F-FDG uptake demonstrates distinct age-related patterns across childhood and adolescence. Age-stratified descriptive values provide quantitative reference data for pediatric PET interpretation. BMI is independently associated with testicular FDG uptake.