Reconstruction of the Gastro-oesophageal Junction Based on Ultra-mill Imaging for Biomechanical Analysis

Abstract

The gastro-oesophageal junction (GOJ) connects the oesophagus and the stomach. The GOJ regulates the passage of food through a pressure barrier. Contraction of the surrounding circular and longitudinal muscle layers result in changes of intraluminal pressure gradient for allowing antegrade passage of food. Dysfunction of the GOJ lead to common upper gastrointestinal (GI) disorders such as achalasia and gastro-oesophageal reflux disease (GORD). The main aim of thesis was to develop a subject specific GOJ finite element model based on unique ultra-mill image data of the human GOJ. The geometry was constructed by taking nodes at the boundary of the segmented images at consistent angular intervals relative to the centroid. Elements were created using uniform tessellations patterns. The constructed anatomy was compared to an existing GOJ model constructed from the visible human dataset. The new ultra-mill model contained a decreased intraluminal cavity (1,324 vs. 5,400 mm3) and muscle volumes (1,540 vs. 15,700 mm3), and a reduced length (48.3 vs. 24.5 mm). The biomechanical analysis revealed that the ultra-mill model developed a lower pressure than the visible human model (0.419 vs. 4.360 kPa). Changing material law parameters yielded indeterminant relationships with the pressure developed. However, the variables of wall thickness, length, width, and size had strong positive linear relationships with pressure, thought to be due increases in cavity volume. Further investigation revealed a difference in degree of influence between variables after adjusting for cavity volume. Aside from size, length was the most influential factor, followed by width, then muscle wall thickness. The results suggest that tissue preparation method and geometry length have a large influence on pressure developed. In conclusion, the work presented in this thesis provides insight into for the inter-individual variability in GOJ pressure. The model lays the groundwork for more sophisticated simulations predicting the dysfunctions associated with the GOJ.