Purpose

To evaluate the effect of rectal distension on the quality of anatomical and functional prostate multiparametric (mp) MRI.

Materials and methods

Multiparametric (mp) 3T-MRI images of 173 patients were independently evaluated by two radiologists in this retrospective study. Planimetry rectal volumes were derived and a subjective assessment of rectal distension was made using a 5-point Likert scale (1 = no stool/gas, 5 = large amount of stool/gas). Image quality of diffusion-weighted imaging (DWI) was evaluated using a 5-point Likert scale. DWI was further scored for distortion and artefact. T2W images were evaluated for image sharpness and the presence of motion artefact. The stability of the dynamic contrast-enhancement acquisition was assessed by recording the number of corrupt data points during the wash-out phase.

Results

There was a strong correlation between subjective scoring of rectal loading and objectively measured rectal volume (r = 0.82), p < 0.001. A significant correlation was shown between increased rectal distension and both reduced DW image quality (r = −0.628, p < 0.001), and increased DW image distortion (r = 0.814, p < 0.001). There was also a significant trend for rectal distension to increase artefact at DWI (r = 0.154, p = 0.042). Increased rectal distension led to increased motion artefact on T2 (p = 0.0096), but did not have a significant effect on T2-sharpness (p = 0.0638). There was no relationship between rectal distension and DCE image quality (p = 0.693). 63 patients underwent lesion-targeted biopsy post MRI, there was a trend to higher positive predictive values in patients with minor rectal distension (34/38, 89.5%) compared to those with moderate/marked distension (18/25, 72%), p = 0.09.

Conclusion

Rectal distension has a significant negative effect on the quality of both T2W and DW images. Consideration should therefore be given to bowel preparation prior to prostate mpMRI to optimise image quality.