Haptic Perception of Distance-To-Break for Compliant Tissues in a Surgical Simulator

Abstract

In minimally invasive surgery (MIS), it is critical to have the ability to accurately interpret haptic information and apply appropriate force magnitudes onto soft tissue in order to minimize tissue trauma. The surgeon's administration of force onto tissue reveals useful perceptual information which guides further haptic interaction making the force perception in MIS a dynamic process. It has been hypothesized that the compliant nature of soft tissue during force application provides biomechanical information denoting tissue failure. Specifically, the relationship between applied force and material deformation rate specifies the distance remaining until the tissue will fail, which is termed distance-to-break (DTB). Two experiments explored sensitivity to DTB; one with an exploratory task and the other using a unidirectional task. Findings revealed that observers could reliably perceive DTB in simulated biological tissues in the exploratory task but they were unable to perform the unidirectional task. It was also found that the perception of DTB can be improved through feedback training. Implications for optimizing training in MIS simulators are discussed.

Learning to perceive haptic distance-to-break in the presence of friction.

“…Although Long et al (2014) were able to demonstrate that DTB can be perceived, several other factors were not taken into consideration that may affect an observer’s perception of nonlinear material break point. For example, trocars are a sealing mechanism at the incision sites during MIS that act as a portal for tools to access the body and which maintain pressure within the body cavity.…”

“…Just as past research has identified the haptic invariant subserving the perception of object length and weight by wielding, we have identified DTB as a haptic invariant that specifies the immanent break point of a nonlinear material that an observer is probing or stretching (Long et al, 2014). DTB is a form of haptic “looming,” in that it is based on the increasing amount of force needed to probe into or to stretch a material with an exponential force-displacement relationship.…”

“…As force is applied, the change in reactive force relative to the magnitude of the force specifies to the operator how much further the material can be deformed before it will break (see Figure 1). Using nine different material profiles with varying deformation distances and forces required to break each material, preliminary work by Long et al (2014) demonstrated that novice participants are sensitive to DTB when pushing a tool against simulated materials. The goal of the present work was to extend this initial finding with a different set of materials, test if the sensitivity to DTB would persist when varying levels of friction were added to the movement of the tool, test if sensitivity to DTB could be improved through training (for a theoretical framework see; Jacobs & Michaels, 2007; Wagman, Shockley, Riley, & Turvey, 2001; Withagen & Michaels, 2005), and test if sensitivity to DTB occurs in a similar fashion when the tool is manipulated with a pulling motion instead of a pushing motion…”

“…In addition, the current experiment included a control group that did not receive the visual feedback training to allow for investigation of training effects. No control group was employed by Long et al (2014).…”

“…Many embed the natural exponential function y = be ax where a, b are positive constants, e is the natural base, and x is the displacement (a real number). As described below, the rate of change in the exponential model of the force-displacement function was shown to provide the haptic system with an invariant that specifies how much displacement remains before the tissue will rupture or break (Long et al, 2014). This “distance-to-break” (DTB) indicates how much farther one can manipulate a material until failure occurs.…”