Using analytical redundancy to increase safety of a synergistic manually guided instrument for craniotomy

In this paper, two methods for bridging line of sight interruptions occurring during the use of the synergistically operated semiautomatic trepanation system (STS) are presented. In the STS, position information is acquired using an optical tracking system with the disadvantage of possible line-of-sight interruptions. Their compensation is crucial, as a real-time control system automatically adjusts the cutting depth of the instrument on the basis of position information and a-priori data. The surgeon is only responsible for guiding the instrument along the resection line. Hence, availability of position information is crucial for depth control, set point generation, and thus for patient safety. In favour of enhancing reliability of position and orientation acquisition, two approaches were developed which are intended to estimate the position during line of sight interruptions on the basis of a-priori system information and process parameters. To assure patient´s safety during this procedure, several parameters of the system (e.g. cutting radius, skull gradient) are used in order to estimate the possible cutting error while the redundant system is activated. These two algorithms and the online risk assessment were implemented, and afterwards evaluated. The evaluation was performed using a skull phantom, and yielded promising results.