Biomechanic characterization of normal urethra using uro-dynamic MRI during voiding

INTRODUCTION: Dynamic volumetric MRI was used to non-invasively assess urethral biomechanics in a single healthy male subject during voiding. METHODS: Volumetric lower urinary tract (LUT) images were obtained throughout the voiding effort using the uro-dynamic MRI methodology. These were subsequently segmented using MIMICS. Segmented urethral volumes were divided into prostatic, membranous, penile and bulbous urethra and were used to quantify urethral diameters over time, length and different phases of flow. Idealized instantaneous resistances were calculated for the posterior (prostatic and membranous) urethra. RESULTS: The analysis was separated into time and length averaged, and step-by-step analysis. Step-by-step analysis revealed more variation in the initial flow and terminal flow than during robust flow. Time and length averaged analysis showed the membranous urethra had the narrowest lumen and greatest resistance to flow. Correlation of urethral diameters with flow showed strong correlations with both the prostatic and membranous urethral segments. CONCLUSION: This single-subject study confirms the potential of uro-dynamic MRI to provide noninvasive assessment of lower urinary tract anatomy and urethral biomechanics during voiding.