Three‐dimensional biomechanical properties of the human rectum evaluated with magnetic resonance imaging

A method to evaluate the three‐dimensional (3‐D) geometry of the human gastrointestinal wall may be valuable for understanding tissue biomechanics, mechano‐sensation and function. In this paper we present a magnetic resonance imaging (MRI) based method to determine rectal geometry and validation of data obtained in three volunteers. A specially designed rectal bag was filled in a stepwise manner while MRI and bag pressure were recorded. 3‐D models of curvatures, radii of curvature, tension and stress were generated and the circumferential and longitudinal strains were calculated. The computed bag volumes corresponded to the infused volumes. A pronounced bag elongation and decrease in wall thickness was observed during the bag filling. The spatial distributions of the biomechanical parameters were distinctly different between individuals and non‐homogeneous throughout the rectal wall due to its complex geometry. The average tension and stress increased as a function of infused volume and circumferential strain. The present study provides a method for characterizing the complex in vivo 3‐D geometry of the human rectum. The non‐homogenous spatial curvature distribution suggests that simple estimates of tension based on pressure and volume do not reflect the true 3‐D biomechanical properties of the rectum.