Objective: To prospectively investigate the longitudinal effect of ejaculatory abstinence on MRI-measured seminal vesicle (SV) volume and whole-prostate ADC over consecutive days.
Methods: 15 healthy male volunteers (mean 35.9 years, range 27–53) underwent 3-T MRI at baseline and 1, 2 and 3 days post-ejaculation. Prostate and SV volumes were derived by volume segmentation and whole-gland apparent diffusion coefficient (ADC) values calculated. A mixed-effects linear regression compared ADC values and prostate/seminal vesicle volumes in each volunteer between studies in a pairwise manner.
Results: All subjects completed the four MRIs. Mean prostate volume was 22.45 cm³ (range 13.04–31.21 cm³), with no change between the four studies (p = 0.89–0.99). 13⁄15 subjects showed SV volume reduction from baseline to day 1, with group-mean decreasing from 6.45 to 4.80 cm³ (−25.6%, p < 0.001), and a significant reduction from baseline to day 2 (−18.1%, p = 0.002). There was a significant volume increase from both day 1 (+21.3%, p = 0.006) and day 2 (+10.2%, p = 0.022) to day 3 post-ejaculation. There was a significant reduction in ADC from 1.105 at baseline to 1.056 × 10⁻³ mm²/s at day 1 (mean −4.3%, p = 0.009).
Conclusion: The longitudinal effect of ejaculation on SV volume was demonstrated. Significant reductions in SV volume and whole-gland ADC were observed post-ejaculation, supporting a 3-day period of abstinence before prostate MRI.