title: Diffusion tensor imaging of the anal canal at 3 tesla: feasibility and reproducibility of anisotropy measures.
abstract: OBJECTIVE
  To assess the feasibility and reproducibility of 3-tesla diffusion tensor imaging (DTI) of the anal canal.
  
  
  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 color-coded 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) × 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).
  
  
  CONCLUSIONS
  Anisotropy is evident in the anal canal with good inter-rater agreement and test reproducibility.
authors: Paul Strickland Scanner Centre, Mount Vernon Hospital, Northwood, Middlesex, United Kingdom. vicky.goh@kcl.ac.uk
authors: Vicky
authors: V
authors: Goh
authors: Emily
authors: E
authors: Tam
authors: N Jane
authors: NJ
authors: Taylor
authors: J James
authors: JJ
authors: Stirling
authors: Ian C
authors: IC
authors: Simcock
authors: Robert Glynne
authors: RG
authors: Jones
authors: Anwar R
authors: AR
authors: Padhani
mesh_terms: D000368:Aged; D000465:Algorithms; D001003:Anal Canal / Q000033:anatomy & histology*; D016880:Anisotropy; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005240:Feasibility Studies; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity