Wireless tissue palpation: Proof of concept for a single degree of freedom

Palpating tissues and organs to identify hidden tumors or to detect buried vessels is not a viable option in laparoscopic surgery due to lack of force feedback. So far, research toward restoring tactile and kinesthetic sensations in minimally invasive surgery has focused on the distal sensing element or on the proximal rendering of haptic cues. In this work we present a pilot study to assess the feasibility of wireless tissue palpation, where a magnetic device is deployed through a standard surgical trocar and operated to perform tissue palpation without requiring a dedicated entry port. The setup consists of a wireless intra-body device and an external robotic manipulator holding a load cell and a permanent magnet. Embedded in the wireless cylindrical device (12.7 mm in diameter and 27.5 mm in height) is a sensing module, a wireless microcontroller, a battery and a permanent magnet. This preliminary study assessed the precision in reconstructing the indentation depth based on magnetic field measurements at the wireless device (i.e., 0.1 mm accuracy). Experimental trials demonstrated the effectiveness of wireless vertical indentation in detecting the elastic modulus of three different silicone tissue simulators (elastic modulus ranging from 50 kPa to 93 kPa), showing a maximum relative error below 3%. Finally, wireless palpation was used to identify differences in tissue stiffness from a lump embedded into a porcine liver. The reported results have the potential to open a new paradigm in the field of palpation devices, where direct physical connection across the abdominal wall is no longer required.