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

Abstract

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.

Biomechanical functional and sensory modelling of the gastrointestinal tract

“…Advances in imaging are being introduced initially as research tools and subsequently as clinical diagnostic tests. Medical imaging-based three-dimensional models of in vivo GI organs have characterized the oesophagus, stomach, small intestine, sigmoid colon and rectum using ultrasonography, computed tomography (CT) or MRI (Li et al 1994;Liao et al 2004a;Frokjaer et al 2005Frokjaer et al , 2007Jeays et al 2007a,b;Pal et al 2007). Figure 2 shows an example of reconstruction of the stomach shape obtained by three-dimensional ultrasonography.…”

“…With the identified inner and outer wall boundaries of each cross-sectional two-dimensional image, a data cloud of a three-dimensional model was then obtained by using a segmentation technique. For GI organs, such as the stomach (Liao et al 2004a), rectum (Frokjaer et al 2005) or sigmoid colon ; figure 3), the centre line of the organs is curved. When the organ is deformed, it is deformed along the curved axis.…”

“…The main methods we used for the three-dimensional GI geometric modelling establishment are briefly described below. More detailed description of the methods can be found in our previous literature in Liao et al (2004aLiao et al ( , 2005 and Frokjaer et al (2005Frokjaer et al ( , 2007. (i) Medical imaging-based three-dimensional model reconstruction…”

“…In the healthcare sector, this approach is not common but is evolving Hunter & Nielsen 2005;Clapworthy & Viceconti 2007). Exploration of the human body has dramatically improved by the introduction of medical imaging modalities such as magnetic resonance imaging (MRI) and ultrasonography (Frokjaer et al 2005(Frokjaer et al , 2006Gilja et al 2007). These techniques have revolutionized the way in which many conditions are diagnosed and treated.…”

“…The challenge is to develop mathematical and computational models of structurefunction relations appropriate to each (limited) spatial and temporal domain and then to link the parameters of a model at one scale to a more detailed description of structure and function on the adjacent levels. Two-dimensional cross-sectional imaging (CT, MRI and ultrasonography)-based modelling has been used to characterize biomechanics, function and sensory responses in the stomach (Liao et al 2004b, the rectum and sigmoid colon (Frokjaer et al 2005, cardiovascular system and computer-aided orthopaedic surgery. The present analytical tool can thus be integrated in order to analyse complex structures for understanding biomechanical properties and visceral perception in other visceral organs and further to be integrated as a global GI model.…”