Quantitative Mechanics of the Bladder During Voiding Using MRI.

Abstract

Purpose: Uro-Dynamic MRI was used to non-invasively quantify bladder biomechanics, characterizing the fundamental relationship between bladder wall surface area and bladder volume during voiding.

Methods: Differential Subsampling with Cartesian Ordering MRI sequence was used to acquire multiple volumetric bladder images during the voiding in five normal male subjects. Images were imported into MIMICS. Bladder volume and bladder wall surface area were obtained using threshold-based image segmentation and the main axes of bladder wall deformation were measured/tracked throughout voiding. Linear anatomical measurements yielded bladder volume estimation using a generalized ellipsoid approximation and facilitated direct comparison with the metrics obtained from the 3D renderings.

Results: Ellipsoid volume approximation showed high agreement with volume from 3D renderings; however, this agreement does not hold for flow rates derived from both approaches. Analysis of changes in volume and surface area from 3D renderings show bladder deformation that varies throughout voiding, behaving closer to an idealized spherical bladder past the point of maximum flow. Further analysis suggests an asymmetrical and nonconstant change of bladder dimensions in relation to changes in bladder volume, and a generalized concentric contraction of the bladder wall past maximum flow during the voiding event.

Conclusion: Uro-Dynamic MRI allowed time-resolved analysis of the relationship between changes in anatomy-based measurements, volume and surface area of the bladder. This methodology highlights the use of Uro-Dynamic MRI as a powerful tool to comprehensively extract anatomical information of the bladder and correlate this information with novel Noninvasive metrics to evaluate patient specific biomechanics.

Clinical trial registration: The patients recruited for this study and data collected for this manuscript are not part of a clinical trial.