Pubovisceralis Muscle Fiber Architecture Determination: Comparison Between Biomechanical Modeling and Diffusion...

Biomechanical analysis of pelvic floor dysfunction requires knowledge of certain biomechanical parameters, such as muscle fiber direction, in order to adequately model function. Magnetic resonance (MR) diffusion tensor imaging (DTI) provides an estimate of overall muscle fiber directionality based on the mathematical description of water diffusivity. This work aimed at evaluating the concurrence between pubovisceralis muscle fiber representations obtained from DTI, and the maximum principal stress lines obtained through the finite element method. Seven datasets from axial T2-weighted images were used to build numerical models, and muscle fiber orientation estimated from the DT images. The in-plane projections of the first eigenvector of both vector fields describing muscle fiber orientation were extracted and compared. The directional consistency was evaluated by calculating the angle between the normalized vectors for the entire muscle and also for the right and left insertions, middle portions, and anorectal area. The values varied between 28° ± 6 (right middle portion) and 34° ± 9 (anorectal area), and were higher than the angular precision of the DT estimates, evaluated using wild bootstrapping analysis. Angular dispersion ranged from 17° ± 4 (left middle portion) to 23° ± 5 (anorectal area). Further studies are needed to examine acceptability of these differences when integrating the vectors estimated from DTI in the numerical analysis.