Soft tissue navigation using needle-shaped markers: Evaluation of navigation aid tracking accuracy and CT registration

摘要

We evaluate two core modules of a novel soft tissue navigation system. The system estimates the position of a hidden target (e.g. a tumor) during a minimally invasive intervention from the location of a set of optically tracked needle-shaped navigation aids which are placed in the vicinity of the target. The initial position of the target relative to the navigation aids is obtained from a CT scan. The accuracy of the entire system depends on (a) the accuracy for locating a set of navigation aids in a CT image, (b) the accuracy for determining the positions of the navigation aids during the intervention by means of optical tracking, (c) the accuracy for tracking the applicator (e.g. the biopsy needle), and (d) the accuracy of the real-time deformation model which continuously computes the location of the initially determined target point from the current positions of the navigation aids. In this paper, we focus on the first two aspects. We introduce the navigation aids we constructed for our system and show that the needle tips can be tracked with submillimeter accuracy. Furthermore, we present and evaluate three methods for registering a set of navigation aid models with a given CT image. The fully-automatic algorithm outperforms both the manual method and the semi-automatic algorithm, yielding an average distance of 0.27 ± 0.08 mm between the estimated needle tip position and the reference position.