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Developing Reality-Based Soft-Tissue Models for Real-Time Surgical Simulation

Main Participants

J. P. Desai, Z. Gao, A. Lau, and K. Lister

Sponsor

This project is sponsored by NIH.

Keywords

Surgical simulation, soft-tissue modeling, ex vivo test, in vivo test, finite element simulation

Motivation

The implementation of complex surgical procedures has driven the need in the medical community for the development of surgical simulators with accurate visual and haptic feedback. This need, coupled with recent advances in computational power, has stimulated research in the area of more complex, and realistic constitutive models for soft tissue deformation. In our research, we have been focusing on developing a biomechanical model of the liver with the ultimate goal of using this model for local tool-tissue interaction tasks and providing feedback to the surgeon through a haptic display.

Overview of Approach

1. Characterization and constitutive modeling of ex vivo liver tissue under finite deformation Ex vivo experiments on porcine liver tissue: In actual deformation of soft-tissue during surgical intervention, the tissue is subject to tension, compression, and shear. Therefore, characterization of soft-tissue in all these three deformation modes is necessary. We have conducted two types of pure shear test, unconfined compression and uniaxial tension tests extensively on ex vivo porcine liver tissue. Novel strain measurement and analyses: In the tension and pure shear tests, the natural textures on the sample surface are excellent full-field markers for imaging. We used digital image correlation (DIC) technique to track these textures and calculate the strain in the specimen. A new method to estimate the zero strain state was proposed according to the maximum stretching band observed on the relative strain field. Constitutive modeling of liver tissue: Based on the experimental results, two hyperelastic models were developed to describe the liver tissue properties. The combined exponential/logarithmic Ogden model can represent the general deformation of liver tissue in full range of compression, tension and pure shear. The Ogden model fitted from experimental result can be used directly in a commercially available FEM software such as Abaqus.

2. In vivo porcine liver experiment and 3D finite element simulation Design and building of the experimental setup for in vivo tests: An in-vivo testing device has been developed for probing, cutting and electrocauterizing porcine liver tissue. The device can provide controlled linear motion in the speed range of 0-4 in/s while the reaction forces imparted on the surgical tool are recorded. Additionally, an optical pattern tracking system is used in conjunction with this device to allow for real-time tracking of the tissue deformation during experimentation as well as the generation of accurate three-dimensional (3D) profile for the organ geometry. In vivo characterization of porcine liver: The mechanical response of liver under probing (or indentation) can be collected in vivo. The probing speed can be adjusted in the range that is typical for a surgical intervention. The 3D deformation of the liver surface close to the probing site will be measured in real-time during the experiments. The force, deformation and 3D surface profile of the liver will be used in later finite element analysis. Modeling and prediction of liver deformation based on in-vivo data: The mechanical properties of soft tissue in its natural state (in-vivo) are different from those in ex-vivo state due to blood perfusion and other reasons. The ex-vivo tissue model will be modified to account for the blood perfusion and strain rate dependent effect. The 3D finite element simulation result will be compared with those measured from the experiments.

3. Development of a GPU driven real-time surgical simulator for soft-tissue probing Preprocessing of probing: In this iteration of the probing simulator, the finite element analysis was preprocessed in Abaqus. This approach allowed for superior accuracy by the ability to use the more detailed Ogden material model as well as a more detailed mesh. Following the analysis, the resulted were uploaded into a simulator that could replicate the probing task in real time with accurate graphics and force feedback. Development of real-time GPU driven simulator: Previous work has been conducted in the area of developing a real-time GPU based approach for deformation of complex hyperelastic models such as the Ogden model. This approach will be utilized to develop a compressive simulator for probing of soft-tissue. By utilizing the GPU, the preprocessing step will not be required, thereby eliminating the need for the tool path to discrete paths.

4. Development of a GPU driven real time surgical simulator for scalpel cutting Development of scalpel cutting model: A fracture mechanics approach will be implemented in developing a model for scalpel cutting of pig liver in both the ex-vivo and in-vivo contexts. A testing device has been developed to measure the parameters required for the modeling process through surface deformation tracking. Development of real-time GPU driven simulator: The fracture mechanics based model will be added to the previously developed real-time probing simulator. This will allow the simulation of the scalpel cutting process along arbitrary tool paths. The proposed device will contain realistic visual displays and haptic feedback, which can be used to train surgeons in scalpel cutting procedures.

Relevant publications

Zhan Gao, and Jaydev P. Desai, “Estimating zero-strain states of very soft tissue under gravity loading using digital image correlation”, Medical Image Analysis, DOI: 10.1016/j.media.2009.11.002, 2010.

Zhan Gao, Kevin Lister, and Jaydev P. Desai, “Constitutive modeling of liver tissue: experiment and theory”, Annals Biomedical Engineering, DOI: 10.1007/s10439-009-9812-0, 2010.

Lister Kevin, and Jaydev P. Desai, “Real-time, haptics-enabled simulator for probing ex vivo liver tissue”, Engineering in Medicine and Biology Society, 2009. EMBC 2009. Annual International Conference of the IEEE, pp 1196-1199, September, 2009.

Zhan Gao, Theodore Kim, Doug L. James, Jaydev P. Desai, “Semi-automated soft-tissue acquisition and modeling for surgical simulation”, 5th Annual IEEE Conference on Automation Science and Engineering, CASE 2009, pp. 268-273, August 22-25, 2009.

Zhan Gao, Kevin Lister, Jaydev P. Desai, “Constitutive Modeling of Liver Tissue: Experiment and Theory”, Second biennial IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics—BioRob, October 2008.

Contact

Prof. Jaydev P. Desai
Director—Robotics, Automation, and Medical Systems Laboratory
Department of Mechanical Engineering
0160 Glenn L. Martin Hall
University of Maryland College Park, MD-20742
Phone: 301-405-4427
Email: jaydev (at) umd.edu
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