Ning Li, Jindong Tan, PhD. The University of Tennessee
Background and Objective: Fully insertable laparoscopic cameras, compared to conventional trocar-based laparoscopes, feature more locomotive flexibility in a larger workspace and thus represent a promising trending of laparoscopic imaging devices. These cameras, typically anchored against the interior abdominal wall and manipulated through magnetic coupling, although have shown their technical feasibility in terms of actuation and imaging, none of them are getting close to clinical application due to concerns about safety.
One common problem lies in that the stress distribution on the abdominal wall tissue caused by camera-tissue interaction is completely unknown, not to mention controlled. The patient could be exposed to a high risk of being injured due to inappropriate camera-tissue interaction force.
Therefore, this abstract aims to model and simulate the stress distribution on the abdominal wall tissue for a magnetic actuated laparoscopic camera during operation, which will facilitate closed-loop laparoscopic camera control and surgical safety.
Fig. 1 Concept of the magnetic actuated fully insertable laparoscopic camera
Modelling Approach: The Kelvin-Voigt model has been adopted to study the mechanical properties of the abdominal wall tissue. The contact profile between the camera and the tissue is depicted using two sectional views as shown in Fig.2. The tissue surface is in close contact with the camera between A and B as well as C and D. Beyond those points, the tissue leaves contact with the camera and the deformation w(x/y) decays along X/Y exponentially. The vertical stress component could be given as 1. Since the camera is anchored still in a quasi-static state, dw(x/y,t) could be ignored and q(x/y) is simplified as 2, where E=1/ ∑4i=1(1/Ei) is the equivalent modulus of elasticity of the tissue. The horizontal stress p(x/y) could be easily computed using the constraint that the resultant stress at each point should be perpendicular to the tissue profile.
q(x/y,t) = (w(y,t) + ∑4i=1Tidwi(y,t)/dt) / ∑4i=1(1/Ei) (1)
q(x/y) = w(x/y) / ∑4i=1(1/Ei) = Ew(x/y) (2)
Fig. 2 Longitudinal and latitudinal sectional views of tissue deformation
Simulation Results: The camera resemble a cylinder of Φ16mm x 81mm. The simulations were performed using Matlab in a tissue area of 20mm × 100mm at an indentation of h = 0.25r = 0.002m with an approximated E of 200000N/m3. The vertical stress q(x,y) distribution is shown in the left of Fig. 3, with the maximum stress values of 400Pa at the deepest part of the tissue. The right of Fig. 3 shows the horizontal stresses p(x,y). Different from the vertical stress distribution, the lowest values of 0Pa were found at the deepest part of the tissue, while the maximum values 88.057Pa occurred where the tissue leaves contact with the camera.
Fig. 3 Simulated vertical and horizontal stress distribution
Conclusions and Future: This abstract proposes a modelling approach for stress distribution during the interaction between an insertable laparoscopic camera and the abdominal wall tissue. The effectiveness of the method has been verified by simulation results. These stresses will be integrated to get the interaction force and thus establish the relation between them in the future.
Presented at the SAGES 2017 Annual Meeting in Houston, TX.
Abstract ID: 98697
Program Number: ETP728
Presentation Session: Emerging Technology Poster Session (Non CME)
Presentation Type: Poster