S. Raith et al., "Finite Element Simulation of the Deformation of the Female Breast Based on MRI Data and 3-D Surface Scanning: An In-Vivo Method to Assess Biomechanical Material Parameter Sets", in Proc. of 3rd Int. Conf. on 3D Body Scanning Technologies, Lugano, Switzerland, 2012, pp. 196-203, http://dx.doi.org/10.15221/12.196.
Finite Element Simulation of the Deformation of the Female Breast Based on MRI Data and 3-D Surface Scanning: An In-Vivo Method to Assess Biomechanical Material Parameter Sets
Stefan RAITH 1, Maximilian EDER 1, Fee VON WALDENFELS 1, Jalil JALALI 2, Alexander VOLF 1, Laszlo KOVACS 1
1 Research Group CAPS (Computer Aided Plastic Surgery) - Department of Plastic Surgery and Hand Surgery, Klinikum rechts der Isar, Technische Universität München, Germany;
2 Institute of Medical Engineering at the Technische Universität München (IMETUM), Garching, Germany
Introduction: Biomechanical studies of the mechanical deformations of the human body often use numerical simulations, such as the finite element analysis (FEA). Especially the shape changes of the female breast under varying load conditions are a current area of interest, both in the computational engineering science and the medical sector. During radiological diagnostics the breast is exposed to different mechanical loading conditions than later at the stage of the operation planning and in the operation room. For better operation planning, a prediction of these mechanical deformations on the computer is desired. However, to generate realistic results that consider the physics of biological materials, it is essential to have a sufficient understanding of the theoretical constitutive models and the material parameters that describe the soft tissue of the breast. Although numerous studies have been performed to acquire material parameters, yet no consensus of reliable parameter sets could be generated yet. We think that three-dimensional body scanning can have a decisive role for the determination of soft tissue parameters of the breast.
Materials and Methods: In the presented study, twelve different parameter sets for material properties that have been proposed in literature references are employed to biomechanical simulation models. These 3-D anatomical models are derived from prone MRI datasets of 18 healthy volunteers. With the aid of FEA a force free reference state is calculated, using an iterative heuristic approach to overcome the deformations caused by unavoidable gravity loading. Starting from the obtained gravity free model the shape of the breast in upright position is calculated. The obtained result is then compared to the real volunteers' breast surfaces acquired with a 3-D surface scanner in order to evaluate the applicability of the simulation procedure.
Results: It could be shown, that hyper-elastic constitutive models perform superior to linear elastic models that cannot exceed the linear Hookean domain. Within the group of hyper-elastic material models, proposed in literature, those found by Tanner at al. (2006) and Rajagopal at al. (2008), perform significantly (p < 0.01) better than the other material parameter sets evaluated. Variations in boundary conditions have shown a minor influence on the calculation outcome compared to the variation of material parameters.
Conclusion: The advantage of the here presented method is its non-invasive character as a combination of volume imaging (MRI) and 3-D surface scanning (Laser triangulation) and the involvement of the computer for the actual simulation. Since the whole workflow of simulation and data evaluation is automated, multitudes of simulations can be performed with few additional efforts. Thus, optimizations of material parameters can be performed beyond the limits of parameter settings from previous studies that permit patient individual adjustment of material parameters. Thus, reliable biomechanical breast model based on the presented methods can be applied to derive patient specific material parameter sets. This data might be helpful in oncology for tumor tracking by integrating comparison of multimodality images into the simulation model and could improve plastic and reconstructive breast surgery planning.
3-D scan, MRI, Finite Element Simulation, material parameters, standardization
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