Characterization of soft tissue cutting for haptic display: experiments and computational models

Real-time medical simulation for robotic surgery planning and surgery training requires realistic yet computationally fast models of the mechanical behavior of soft tissue. This work presents a study to develop such a model to enable fast haptics display in simulation of softtissue cutting. An apparatus was developed and experiments were conducted to generate force-displacement data for cutting of soft tissue such as pig liver. The force-displacement curve of cutting pig liver revealed a characteristic pattern: the overall curve is formed by repeating units consisting of a local deformation segment followed by a local crack-growth segment. The modeling effort reported here focused on characterizing the tissue in the local deformation segment for fast haptic display. The deformation resistance of the tissue was quantified in terms of the local effective modulus (LEM) consistent with experimental forcedisplacement data. An algorithm was developed to determine LEM by solving an inverse problem with iterative finite element models. To enable faster simulation of cutting of a threedimensional (3D) liver specimen of naturally varying thickness, three levels of model order reduction were studied. Additionally, the variation of the LEM with cutting speed was determined. The values of LEM decreased as the cutting speed increased. This thesis also includes the characteristic response of soft tissue to the growth of a cut (cracking) with a scalpel blade. The experimentally measured cut-force versus cut-length data was used to determine the soft tissue’s resistance to fracture (resistance to crack extension) in scalpel cutting. The resistance to fracture of the soft tissue is defined as the amount of mechanical work needed to cause a cut (crack) to extend for a unit length in a soft-tissue sample of unit thickness. The equipment, method, and model are applicable for all soft tissue.Finally, the method of determining the property of the pig liver tissue during cutting was verified. Dual C-arm fluoroscopes were used to obtain the motion of the beads embedded inside the specimen during cutting. The experimentally measured displacement field was compared to the displacement field obtained through finite element model based on the LEM values at each localized area.Ph.D., Mechanical Engineering and Mechanics -- Drexel University, 200

3D and 2D finite element analysis in soft tissue cutting for haptic display

Paper presented at the 2005 International Conference on Advanced Robotics, ICAR '05, Seattle, WA.Real-time medical simulation for robotic surgery planning and surgery training requires realistic yet computationally fast models of the mechanical behavior of soft tissue. This paper presents a study to develop such a model to enable fast haptics display in simulation of softtissue cutting. An apparatus was developed and experiments were conducted to generate force-displacement data for cutting of soft tissue such as pig liver. The forcedisplacement curve of cutting pig liver revealed a characteristic pattern: the overall curve is formed by repeating units consisting of a local deformation segment followed by a local crack-growth segment. The modeling effort reported here focused on characterizing the tissue in the local deformation segment in a way suitable for fast haptic display. The deformation resistance of the tissue was quantified in terms of the local effective modulus (LEM) consistent with experimental force-displacement data. An algorithm was developed to determine LEM by solving an inverse problem with iterative finite element models. To enable faster simulation of cutting of a three-dimensional (3D) liver specimen of naturally varying thickness, three levels of model order reduction were studied. Firstly, a 3D quadratic-element model reduced to uniform thickness but otherwise haptics-equivalent (have identical forcedisplacement feedback) to a 3D model with varying thickness matching that of the liver was used. Next, hapticsequivalent 2D quadratic-element models were used. Finally, haptics-equivalent 2D linear-element models were used. These three models had a model reduction in the ratio of 1.0:0.3:0.04 but all preserved the same input-output (displacement, force) behavior measured in the experiments. The values of the LEM determined using the three levels of model reduction are close to one another. Additionally, the variation of the LEM with cutting speed was determined. The values of LEM decreased as the cutting speed increased

Determining fracture characteristics in scalpel cutting of soft tissue

Paper presented at the First IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics, BioRob 2006, Pisa, Italy.This paper addresses the characteristic response of soft tissue to the growth of a cut (cracking) with a scalpel blade. We present our experimental equipment, experiments, and the results for scalpel cutting of soft tissue. The experimentally measured cut-force versus cut-length data was used to determine the soft tissue’s resistance to fracture (resistance to crack extension) in scalpel cutting. The resistance to fracture (the toughness) of the soft tissue is quantified by the measure R defined as the amount of mechanical work needed to cause a cut (crack) to extend for a unit length in a soft-tissue sample of unit thickness. The equipment, method, and model are applicable for all soft tissue. We used pig liver as soft-tissue samples for our experiments

Comparison of Ortho-planar Spring design optimization based on Linear Elastic and Hyper Elastic Materials

In this paper, compliant Ortho-planar spring was designed based on a three-dimensional topology optimization method. The computation was developed using MATLAB programming. The objective of this work was to apply dual method to design an Ortho-planar spring while the design should have minimum mass and at the same time satisfy a set of constrained displacement. Throughout this paper, we analyzed a method for designing an Ortho-planar spring using linear elastic material and hyperelastic material. The results showed that under small displacement conditions, the output displacement, maximum stress magnitude, and the maximum stress of linear elastic assumption and hyper-elastic material were relatively close to each other. However, the mass fraction and the layout as the result of the optimization process was different. As for larger displacement, the maximum stress of linear elastic material appeared 2.59 times higher than the maximum stress of the hyper-elastic material model. The topology optimization output based on linear material was invalid because the topology of the computed Ortho-planar spring was not appeared as a one-piece layout while the design based on nonlinear material looked promising

Comparison of Ortho-planar Spring design optimization based on Linear Elastic and Hyper Elastic Materials

In this paper, compliant Ortho-planar spring was designed based on a three-dimensional topology optimization method. The computation was developed using MATLAB programming. The objective of this work was to apply dual method to design an Ortho-planar spring while the design should have minimum mass and at the same time satisfy a set of constrained displacement. Throughout this paper, we analyzed a method for designing an Ortho-planar spring using linear elastic material and hyperelastic material. The results showed that under small displacement conditions, the output displacement, maximum stress magnitude, and the maximum stress of linear elastic assumption and hyper-elastic material were relatively close to each other. However, the mass fraction and the layout as the result of the optimization process was different. As for larger displacement, the maximum stress of linear elastic material appeared 2.59 times higher than the maximum stress of the hyper-elastic material model. The topology optimization output based on linear material was invalid because the topology of the computed Ortho-planar spring was not appeared as a one-piece layout while the design based on nonlinear material looked promising

Modeling and analysis of coagulated liver tissue and its interaction with a scalpel blade

10.1007/s11517-013-1038-5Medical and Biological Engineering and Computing516687-695MBEC