• Shantanu Sinha, Usha Sinha, Vadim Malis, Valmik Bhargava, Kyoko Sakamoto, and Mahadevan Rajasekaran.
• Muscle Imaging and Modeling Laboratory, Department of Radiology, University of California, San Diego, California, USA.
• J Magn Reson Imaging. 2018 Oct 1; 48 (4): 1002-1011.

BackgroundUrinary incontinence is a major clinical problem arising primarily from age-related degenerative changes to the sphincter muscles. However, the precise anatomy of the normal male sphincter muscles has yet to be established. Diffusion tensor imaging (DTI) may offer a unique insight into muscle microstructure and fiber architecture.PurposeTo explore the anatomy of the urethral sphincter muscles pertinent to urinary continence function using DT-MRI.Study TypeProspective cohort study.SubjectsEleven normal male subjects (mean age: 25.4 years); two subjects were scanned in three separate sessions to assess reproducibility.Field Strength/Sequence3T; using a diffusion-weighted spin echo planar sequence.AssessmentDT parameters including fractional anisotropy (FA), primary (λ1 ), secondary (λ2 ), and tertiary (λ3 ) eigenvalues, Apparent diffusion coefficient and radial diffusivity were analyzed statistically, while tracked muscle fibers were assessed visually.Statistical TestsRegional differences (sphincters and longitudinal muscle of the urethra) in the DTI indices were assessed by one-way analysis of variance. A Tukey post-hoc test was used to identify significant differences between muscle regions.ResultsTwo sphincter muscles, one proximal near the base of the bladder, corresponding to the lisso-sphincter, and the other distal to the end of the prostate corresponding to the rhabdo-sphincter, surrounding a central urethral muscle fiber bundle, were clearly identified. FA was higher and λ3 lower in the proximal sphincter muscle compared to the central urethral muscle and the distal sphincter (P < 0.05). The average coefficient of variation ranged from 5-12% for the DTI indices.Data ConclusionSince DTI values are known to reflect underlying tissue microarchitecture, significant differences in DTI indices identified here between the muscles of the urethral complex may potentially arise from differences in tissue microarchitecture that may in turn be related to the specific function of the sphincter and other muscles.Level Of Evidence1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1002-1011.© 2018 International Society for Magnetic Resonance in Medicine.

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