Towards force sensing based on instrument-tissue interaction

Abstract

The missing haptic feedback in minimally invasive and robotic surgery has prompted the development of a number of approaches to estimate the force acting on the instruments. Modifications of the instrument can be costly, fragile, and harder to sterilize. We propose a method to estimate the forces from the tissue deformation, hence working with multiple instruments and avoiding any modification to their design. Using optical coherence tomography to get precise deformation estimates, we have studied the deformations for different instrument trajectories and mechanical tissue properties. Surface deformation profiles for three different soft tissue phantoms and the resulting forces where monitored. Our results show a systematic and constant relationship between deformation and interaction force. Different tissue elasticities result in different but consistent deformation-force mappings. For a series of independent measurements the root-mean-square-error between estimated and measured force was below 3 mN. The results indicate that it is possible to estimate the force acting between tissue and instrument based on the deformation caused by the instrument. Given that in robotic surgery the pose of the instrument head is known and hence the respective tissue deformation caused by the instrument can be measured in a well-defined relative position, the method allows for force estimation without any changes to the instruments.