Upper gastrointestinal model for ERCP simulation

Abstract

ERCP is a minimally invasive technique for diagnosing and treating pathologic conditions of the bile duct and pancreatic duct. This thesis aims at developing real-time, interactive simulation of ERCP which helps training of skills to physicians. The upper gastrointestinal model in ERCP simulation is large and tubular shaped but the collision region and the viewed region are relatively small. Centerline based modeling is suitable for identifying that region by using centerline and circular indices. Proposed method creates centerline-based model with segmentation of the entire original model by constructing a hexagon lattice structure. By using linear interpolation while ray-casting, this method preserves proper ordering of indices in the large curvature region. This method also creates uniform meshes despite of varying model diameter. Further, in collision detection, since no additional model like BVH is used, refitting of additional model is not required. The duodenal papilla is modeled by using FEM. For simulating interactions between duodenal papilla and various tools or gallstone, a multi-contact model is using mass-spring membrane. The membrane is generated at the local region where contacts occur, which is identical to local triangular surface mesh of the finite element model. Then the membrane is deformed by contact with the tool. This method determines the position constraints of deformable objects and prevents interpenetration. On comparing with two previous real-time multi contact methods, this multi-contact model has small position error, where the error is determined in reference to the dense mesh system. The developed methods are used together to simulate the ERCP procedure. Also, both methods can be used not only in ERCP simulation but also for other deformable object simulation.