Description of a haptic user interface for remote palpation

Precise detection of tumor boundaries critically influences outcome quality of tumor excision surgery. While stiffness is a suitable indicator for discrimination between healthy and diseased tissue, this tool is available to surgeons only to a limited extent during minimally invasive surgery or robotically assisted surgery. Haptic feedback can be a valuable addition to the current use of visual cues and reduced haptic sensations, and provides the opportunity to display measured tissue stiffness directly. We propose a method to provide stiffness information for remote palpation using a device with a series elastic actuator and describe an implementation in detail. The device’s pose is tracked to palpate a virtual object in the form of a stiffness point cloud, acquired from automated force and indentation depth measurements. Two tracking methods, one based on a sensorized, passive kinematic chain, and one based on ArUco markers and a webcam, are described. In preliminary tests, the device and tracking showed promise regarding their suitability for stiffness display of data collected from a soft silicone tissue phantom with a stiffer inclusion. The two tracking methods are compared to a CNC machine as reference, with mean euclidean distances of [1.54+-0.92,12.17+-5.73]mm between reference and the marker and kinematic chain methods, respectively. The haptic device is able to display force errors <10% in a range of 1 to 6N. Technical evaluation and optimization of the complete implementation remain in progress. A user study is planned to quantify the method’s suitability for inclusion boundary detection.