From Haptics
Research/Tissue Modeling and Simulation
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Overview
Appropriate models for accurate planning and simulation
The development a high-fidelity surgical simulation or planning software involves many steps, including: determining the constitutive law that describes an organ's response to applied loads, building a computational models that simulates tool-tissue interaction behavior in real time, generating visual and haptic displays that present the user with tool-tissue interaction responses, and creating a curriculum and/or feedback mechanisms that aim to improve operator performance. Validation of surgical simulators is essential to motivate their application as a method for training and pre- or intra-operative planning. As part of this research we propose that each state of surgical simulation development process acts as a "filter" in which about force-motion relationships are lost or transfered.
Our current research focus involves investigating the modeling factors while transitioning from a complex tissue model to a simplified simulation model. Specifically we have looked at differences between linear and nonlinear elasticity-based models for surgical simulators with force feedback and also importance of organ anatomy and connective tissue for surgical planners.
Eye surgery simulation
Phacoemulsification cataract surgery, a minimally invasive technique to remove a cloudy lens from the eye, is one of the most commonly performed surgical procedures in the western world. Conventional training for this procedure involves didactic lectures and practice on pig and human cadaver eyes, none of which allow trainees to form an accurate predictive model of human tissue behavior during surgery. A virtual environment simulator for capsulorrhexis, one of the first steps in cataract surgery, has been developed that allows a trainee to use surgical instruments to excise a circle of tissue on the anterior side of the lens capsule through tearing. The simulator invokes a deformable mass-spring-damper mesh model of the tissue that can be grasped and torn via shearing. A novel algorithm for mesh division and maintenance enables realistic tearing behavior.
The trainee controls tool motion using a 3-degree-of-freedom haptic device, and haptic feedback is provided from the virtual tissue. Although the haptic feedback in a real capsulorrhexis procedure is below the human threshold of haptic sensing, this simulator enables an experiment to determine the effectiveness of “haptic training wheels” – the idea of haptic training for a task without haptic feedback.
Cutting with scissors
Modeling forces applied to scissors during cutting of biological materials is useful for surgical simulation. Previous approaches to haptic display of scissor cutting are based on recording and replaying measured data. We have developed an analytical model based on the concepts of contact mechanics and fracture mechanics to calculate forces applied to scissors during cutting of a slab of material. The model considers the process of cutting as a sequence of deformation and fracture phases. During deformation phases, forces applied to the scissors are calculated from a torque-angle response model synthesized from measurement data multiplied by a ratio that depends on the position of the cutting crack edge and the curve of the blades. Using the principle of conservation of energy, the forces of fracture are related to the fracture toughness of the material and the geometry of the blades of the scissors. The forces applied to scissors generally include high-frequency fluctuations. We show that the analytical model accurately predicts the average applied force. The cutting model is computationally efficient, so it can be used for real-time computations such as haptic rendering. Experimental results from cutting samples of paper, plastic, cloth, and chicken skin confirm the model, and the model is rendered in a haptic virtual environment.thin objects in daily tasks.
People
- PI: Allison Okamura
- Laura Doyle
- Sarthak Misra
- Collaborating faculty: KT Ramesh
- Undergraduate researcher: Kathryn Smith
- Clinical: Saras Ramanathan, K. Macura
- Previous: Mohsen Mahvash, Kathryn Smith, Diana Kim, Kristin Jeung, Vanessa Chial
Publications
Journal Publications
- S. Misra, K. J. Macura, K. T. Ramesh, and A. M. Okamura, "The Importance of Organ Geometry and Boundary Constraints during Surgical Planning", In Preparation.
- S. Misra, K. T. Ramesh, and A. M. Okamura, "Modeling of Tool-Tissue Interactions for Computer-Based Surgical Simulation: A Literature Review", Under Review.
Conference Publications
- L.A. Doyle, N.R. Gauthier, S. Ramanathan and A.M. Okamura, "A Simulator to Explore the Role of Haptic Feedback in Cataract Surgery Training", Medicine Meets Virtual Reality (MMVR) 15, Jan 29 – Feb 1, 2008, Long Beach, CA, USA. (oral presentation, paper)
- S. Misra, K. T. Ramesh, and A. M. Okamura, "Physically Valid Surgical Simulators: Linear versus Nonlinear Tissue Models", Accepted to Medicine Meets Virtual Reality (MMVR) 16 Conference, Long Beach, USA, January 2008. (Best Poster Award)
- S. Misra, A. M. Okamura, and K. T. Ramesh, "Force Feedback is Noticeably Different for Linear versus Nonlinear Elastic Tissue Models", 2nd Joint EuroHaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems (IEEE), pages 519-524, Tsukuba, Japan, March 2007.
Support
Eye surgery simulation work is supported by the Johns Hopkins University, National Institutes of Health grant no. R01 EB002004, and National Science Foundation grant no. IIS-0347464.
