Remote palpation instruments for minimally invasive surgery

New minimally invasive surgical techniques prevent surgeons from directly touching and palpating internal tissue. Palpation tasks that are trivial to complete with the fingers are time consuming or impossible with current surgical tools. Remote palpation systems are needed to allow surgeons to use their highly developed sense of touch. These systems include tactile sensors to measure distributed contact information as the tissue is probed, signal processing algorithms to determine what the surgeon's finger would feel if it were touching the tissue, and tactile displays that recreate this information on the finger. Development of these devices is difficult due to the complexity of palpation and the human sense of touch. This thesis investigates design specifications for remote palpation instruments. A three-prong approach is taken. First, palpation is studied through observation and measurement. Second, design specifications are determined, and third, prototypes are designed, constructed, and tested based on these principles. To focus the research, a target application of locating hard nodules in the lung during thoracic surgery was chosen. To provide insight to the sensitivity requirements of the tactile sensor, an experiment measured the tactile stimulus on the finger when a lump could just be detected. Based on these results, the prototype sensor was designed to measure distributed pressure. One important design parameter for tactile displays is temporal bandwidth. Adequate speed is required for the display to produce correct tactile sensations as the finger moves over a structural feature. A human factors experiment measured maximum finger velocities during a lump localization task, and it was determined that a 30 Hz bandwidth display is needed. The surgical instrument carries the tactile feedback and allows internal tissues to be probed. Effective designs must allow the surgeon to use natural hand and finger motions. To provide insight for the design process, a taxonomy of palpation was developed to characterize hand configurations and finger motions used during surgery. The prototype remote palpation instrument incorporating all of the components was able to locate lumps in rubber models using minimally invasive techniques.