Rectal distension may lead to poor quality results on prostate multiparametric magnetic resonance imaging (mpMRI), according to a new study.
The imaging modality employs T2-weighted images (T2W), diffusion-weighted images (DWI), and dynamic contrast-enhanced images (DCE).
For the study, two blinded radiologists independently assessed the quality of prostate mp MRI 3T images using various scales. The 173 patients had various indications, most commonly an elevated PSA or previous negative systematic biopsy or were on active surveillance.
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Rectal distension was graded separately on a 5-point Likert scale, from 1 (no stool or gas) to 5 (large amounts). According to results published in the European Journal of Radiology, rectal loading correlated with rectal volume. As rectal loading increased, the quality of DWI decreased significantly and displayed greater distortion. Radiologists also observed increased artifact. Greater rectal distension also led to increased motion artifact on T2W. It did not affect the sharpness of T2W images nor DCE quality.
A subset of 63 patients subsequently underwent targeted biopsy. The positive predictive value of the test was higher for patients with mild rather than moderate/severe rectal distension.
“Rectal distension has a significant negative effect on the quality of both T2W and DW Images,” concluded Iztok Caglic, an MD-PhD student at Addenbrooke’s Hospital and University of Cambridge in Cambridge, UK, and colleagues. “Consideration should therefore be given to bowel preparation prior to prostate mpMRI to optimise image quality.”
Dr Caglic and the team postulated that the absence of an endorectal coil in mpMRI allows for rectal distension and movement and may lead to artifact. Evacuating the bowels before MRI may help and should be formally tested, they suggested. They also noted other possible strategies, such as different DWI techniques, prone imaging, correcting the inhomogeneous magnetic field during its acquisition, or post-processing techniques that correct distortion.
Notably, use of a cleansing enema did not significantly improve mpMRI image quality in a small study of 28 patients published in the Journal of Magnetic Resonance Imaging (2015;42:689-697). In that study, few patients had moderate to severe rectal distension, compared with 38% of patients in the current study.
Reference
1. Caglic I, Hansen NL, Slough RA, Patterson AJ, Barrett T. Evaluating the effect of rectal distension on prostate multiparametric MRI image quality. Eur J Radiol. http://dx.doi.org/10.1016/j.ejrad.2017.02.029
