¹⁸F-FDG Uptake of Human Testis on PET/CT: Correlation with Age, Sex Hormones, and Vasectomy

Purpose: The purpose of this study was to evaluate glucose metabolism of normal human testis on ¹⁸F-FDG PET/CT and to assess possible correlations among age, the serum levels of sex hormones, and vasectomy. Methods: ¹⁸F-FDG PET/CT was performed in 66 normal healthy men (50.8 ± 13.6 years, range 22-81), and mean standard uptake values (SUV) of ¹⁸F-FDG in testis and adductor muscle were measured. Testis-muscle SUV ratios (T/M ratios) were calculated. Serum levels of total testosterone, free testosterone, estradiol, and of sex-hormone binding globulin (SHBG) were measured. We searched for correlations between T/M ratios and age and the serum concentrations of sex hormones. ¹⁸F-FDG PET/CT was also performed in 32 vasectomized men (55.7 ± 7.8 years, range 38-71) and 52 nonvasectomized men (55.4 ± 11.6 years, range 37-72). Mean SUVs of testis and adductor muscle were measured, and T/M ratios were calculated. Results: A significant age-related decline was found in T/M ratio (r = -0.509, p < 0.0001). Serum levels of total testosterone and free testosterone were also found to be positively correlated with T/M ratio (r = 0.427, p = 0.0003; r = 0.435, p = 0.0003, respectively). The mean SUV and T/M ratio of vasectomized men were significantly lower than those of nonvasectomized men (p < 0.0378 and p = 0.0001, respectively). Conclusions: Glucose metabolism in the testis in an adult population was found to be correlated with age, serum sex hormone level, and vasectomy history. These results indicate that testicular ¹⁸F-FDG uptake may have attributed to testicular function and testicular histology. Our findings may have important implications for the interpretation of testicular ¹⁸F-FDG uptake in the normal adult population.