In spite of the computational load of FEM; it is still the most popular method to model physically realistic deformations for soft tissue. While it is easier to solve linear FEM equations in real-time; it is observed that soft tissues have non-linear behaviour; such that the linear deformation becomes un-realistic if the size of the deformation exceeds a threshold (typically 10% of the original tissue size). In addition to non-linearity; soft tissues may also have various complex behaviours like visco-elasticity and anisotropicity increasing the computational burden. If tissue cutting is also to be simulated; the model should be updated both physically and virtually; which makes the real time simulations even harder.
To reach a compromise between the necessity of high haptic refresh rates and the computational burden of the FEM; several optimization techniques such as condensation [Bro-Nielsen and Cotin 1996]; pre-computation [Cotin et al. 1999; Sedef et al. 2006; Sela et al. 2007]; level of detail [Debunne et al. 2001]; and exploitation of the sparse matrix structure have been introduced in simulations. Current simulators; however; still have to either sacrifice one property of real tissues such as non-linearity; anisotropicity or visco-elasticity; or apply force interpolation or extrapolation techniques to reach a sufficient haptic refresh rate (1 kHz). Therefore solution of large FEM systems in real-time to be used in soft-tissue deformations is still a challenge for which new solutions are being sought.
Keywords: Soft tissue deformation; surgery simulation; FEM
SIGRAD 2008. The Annual SIGRAD Conference Special Theme: Interaction; November 27-28; 2008 Stockholm; Sweden
BRO-NIELSEN; M.; AND COTIN; S. 1996. Real-time volumetric deformable models for surgery simulation using finite elemets and condensation. In Computer Graphics Forum; 57‚Äď66.
COTIN; S.; DELINGETTE; H.; AND AYACHE; N. 1999. Real-time elastic deformations of soft tissues for surgery simulation. IEEE Transactions on Visualization and Computer Graphics; 62‚Äď73.
DEBUNNE; G.; DESBRUN; M.; CANI; M.-P.; AND BARR; A. H. 2001. Dynamic real-time deformations using space and time adaptive sampling. In SIGGRAPH ‚Äô01: Proceedings of the 28th annual conference on Computer graphics and interactive techniques; 31‚Äď36.
SEDEF; M.; SAMUR; E.; AND BASDOGAN; C. 2006. Real-time finite-element simulation of linear viscoelastic tissue behavior based on experimental data. IEEE Computer Graphics and Applications; 58‚Äď68.
SELA; G.; SUBAG; J.; LINDBLAD; A.; ALBOCHER; D.; SCHEIN; S.; AND ELBER; G. 2007. Real-time haptic incision simulation using fem-based discontinuous free-form deformation. Computer Aided Design; 685‚Äď693.