Diffusion tensor imaging of the anal canal at 3 tesla: Feasibility and reproducibility of anisotropy measures

Purpose: To assess the feasibility and reproducibility of 3-tesla diffusion tensor imaging (DTI) of the anal canal. Materials and Methods: DTI was performed in 25 men with no clinical history of anal canal disease undergoing MRI for prostate cancer. Analysis of fractional anisotropy (FA), relative anisotropy (RA), and apparent diffusion coefficient (ADC) were determined for the epithelial/subepithelial layer, internal sphincter, external sphincter, and puborectalis. The directionality of diffusion was recorded from colorcoded tractography maps. Obturator internus and gluteus maximus served as reference muscles. Mean (SD) of values for FA, RA, and ADC were compared using analysis of variance. Intra and inter-rater agreement and test reproducibility (n 5) was assessed by Bland-Altman statistics. Results: Mean (SD) for the epithelial/subepithelial layer, internal, external sphincter, and puborectalis were as follows: FA: 0.283 (0.099); 0.337 (0.049); 0.415 (0.072); and 0.407 (0.062), respectively. RA: 0.241 (0.094); 0.292 (0.050); 0.371 (0.083); 0.361 (0.067), respectively; and ADC: 1.49 (0.23); 1.59 (0.19); 1.51 (0.28); and 1.54 (0.29) x 10(-3) mm(2)/s, respectively. Good overall intra and inter-rater agreement and test-retest reproducibility was noted (coefficient of variation of 4.8-19.4% and 5.9-12.9%, respectively). Conclusion: Anisotropy is evident in the anal canal with good inter-rater agreement and test reproducibility.