Human vs. robotic tactile sensing: Detecting lumps in soft tissue

Abstract

Humans can localize lumps in soft tissue using the distributed tactile feedback and processing afforded by the fingers and brain. This task becomes extremely difficult when the fingers are not in direct contact with the tissue, such as in laparoscopic or robot-assisted procedures. Tactile sensors have been proposed to characterize and detect lumps in robot-assisted palpation. In this work, we compare the performance of a capacitive tactile sensor with that of the human finger. We evaluate the response of the sensor as it pertains to robot-assisted palpation and compare the sensor performance to that of human subjects performing an equivalent task on the same set of artificial tissue models. Furthermore, we investigate the effects of various tissue parameters (lump size, lump depth, and surrounding tissue stiffness) on the performance of both the human finger and the tactile sensor. Using signal detection theory for determining tactile sensor lump detection thresholds, the tactile sensor outperforms the human finger in a palpation task.

Lump detection with a gelsight sensor

“…For each trial, a particular phantom was placed below the GelSight device, and the pad was pressed against the phantom with a given amount of force. Following, Gwilliam et al [6], we express the force in gram equivalent units. Table 2 shows the conversion to Newton.…”

“…and the DigiTacts Sensor Gwilliam et al [6] introduced a lump detection experiment using the DigiTacts II capacitive sensor. Phantoms used in their experiments are similar to what we have used for testing the GelSight sensor, but they focused their work on larger lumps with shallower depths than we did.…”

“…As will be described, this can be detected by measuring the change in surface geometry under increasing force. Following Gwilliam et al [6], we constructed phantoms using Ecoflex 0030 silicone rubber from Smooth-On Inc. This rubber has a Shore 00 harness of 30, and is similar to soft human tissue.…”

“…From the clinical data in [7], [11], [12], we can know that lumps are significantly stiffer than surrounding tissues. Such contrast of stiffness can assist doctors in the localization and assessment of lumps during lump examinations, when the doctors' fingertips are in direct contact with the tissue [6].…”

“…Gwilliam et al [6], studied lump detection using an artificial touch sensor based on a capacitive array [13]. They constructed phantoms of soft silicone rubber containing hard embedded balls of various sizes and depths, and derived pressure distributions as they pressed the sensor on the phantom.…”