All 15 volunteers completed each of the four scans at the appropriate time. Study 2 (within 24 h of ejaculation) was performed at a mean of 11.13 h post reported ejaculation (median 11, range 2–21, interquartile range 8–15 h). For one subject, there was a technical failure of diffusion-weighted imaging on the day 1 scan and the results were excluded from the ADC analysis.
The mean prostate volume measured on day 3 was 22.45 cm3 (median 23.28 cm3, range 13.04–31.21 cm3). No correlation was demonstrated between prostate volume and age; Spearman’s rank Rho −0.035. There was no change in whole-gland prostate volume between the four studies: baseline, 22.46 cm3; day 1, 22.47 cm3; day 2, 22.53 cm3 and day 3, 22.45 cm3 (p = 0.89–0.99); Table 2.
The average total seminal vesicle volume including wall and fluid volume was 12.47 cm3 (median 11.82 cm3, range 5.44–28.81 cm3) as measured on day 3, i.e. following a uniform ejaculatory preparation time. There was no significant difference in overall average volume of the right (6.35 cm3) and left (6.13 cm3) seminal vesicles, with the difference ranging from 0.21 to 2.17 cm3; p = 0.50. As expected, there was no change in SV wall volume between the studies: baseline, 6.31 cm3; day 1, 6.61 cm3; day 2, 6.59 cm3 and day 3, 6.65 cm3; p = 0.38–0.49.
The average seminal vesicle fluid volume on day 3 with a standardised preparation time was 5.82 cm3 (median 5.25 cm3, range 2.1–14.52 cm3). There was no significant correlation between age and seminal vesicle fluid volume, Rho 0.171. There was a reduction in seminal vesicle fluid volume in 13 of 15 subjects from baseline to day 1, with a general trend for increasing volumes on subsequent days (Fig. 2). The two patients without SV volume reduction showed volume increases of 1.05 cm3 (8.4%) and 0.02 cm3 (0.9%), respectively. There was no significant correlation between reported ejaculation time and subsequent change in SV fluid volume at day 1, Rho −0.147. SV fluid volume significantly reduced from 6.45 cm3 at baseline to 4.80 cm3 at day 1 (25.6% reduction, p < 0.001) and to 5.28 cm3 at day 2 (18.1% reduction, p = 0.002); Fig. 3. There was subsequently a significant increase in volume to 5.82 cm3 at day 3 post-ejaculation from 4.80 cm3 at day 1 (35.1% increase, p = 0.006) and from 5.28 cm3 at day 2 (10.2% increase, p = 0.022); Table 3.
Whole-gland T2 signal intensity measurements
The mean whole-gland T2 signal intensity normalised to muscle measured 2.45 (ratio; unitless) at baseline and 2.49 on day 1, 2.48 on day 2 and 2.46 on day 3. There was no significant difference using t test comparisons between any combination of days (p = 0.74–0.92).
Quantitative whole-gland ADC measurements
The mean whole-prostate ADC value on day 3 was 1.074 cm3 × 10−3 mm2/s (median 1.071, range 0.947–1.229 × 10−3 mm2/s). There was a reduction ADC value in 10 of 14 subjects from baseline to day 1 (Supplemental Table 1), with a significant mean reduction from 1.105 × 10−3 mm2/s at baseline to 1.056 × 10−3 mm2/s at day 2 (4.3% reduction, p = 0.009); Fig. 4. There was a general trend for ADC values to subsequently increase from day 2 to 3, but this was not significant (Table 4).