Microengineering department
VRAI Group
Diploma project, Winter 2000
Prof. Reymond Clavel
Ass. Gaëtan Marti, Dr. Charles Baur

3D reconstruction of the bile ducts

by Patrick Ramer

Lausanne, February 2001

The goal of the project

This project aims to provide a new tool for endoscopic surgery, particularly for interventions concerning the liver and the pancreas. In the case of partial excision of liver segments, not only the surface and the tissue of the organ have to be considered, but also the distribution of the vessels (arteries and veins) and the bile ducts in the liver. The bile duct system is reconstructed in 3D from two 2D X-ray images acquired with per-operative cholangiography. This 3D model of the ducts can then be superimposed on the endoscopic image in real-time. This will allow to “see through” the liver and to locate the bile ducts directly on the endoscopic image.

Reconstruction steps

The entire process consists of three steps:

1. Image acquisition and feature extraction
2. Correspondence problem between the two images and 3D reconstruction
3. Fusion with endoscopic images 

Feature extraction

Feature extraction is manual and is performed on both projection images separately. Several propositions are made for an automatic extraction.
Extracted features are the centerlines of the ducts, bifurcation and terminal points and segments. Feature points serve as reference for the reconstruction step. 
A sequence of angiographies is acquired during injection of the X-ray contrast agent. The propagation of the flux provides valuable information to identify ambiguities.

3D reconstruction

Several criteria are presented to exclude wrong correspondences from the final solution. The concept of epipolar geometry plays an important role at this stage and is also used for back-projection of matched points to construct the 3D model. The two images are matched using a recursive scheme adapted for tree-like structures.

Surgical applications

Surgical applications include partial hepatectomy in the case of cancer, metastasis and malformation or for transplantation; further the treatment of echinococcosis and chronic pancreatitis. 

13.3.2001, Patrick Ramer