Researcher: Sedef, Mert
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Sedef, Mert
Sedef, Lütfi Mert
Sedef, Lütfi Mert
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Publication Metadata only Real-time visio-haptic interaction with static soft tissue models having geometric and material nonlinearity(Elsevier, 2010) Peterlik, Igor; Matyska, Luděk; N/A; Department of Mechanical Engineering; Sedef, Mert; Başdoğan, Çağatay; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 125489Realistic soft tissue models running in real-time are required for the development of computer-based surgical training systems. To construct a realistic soft tissue model, finite element (FE) modeling techniques are preferred over the particle-based techniques since the material properties can be integrated directly into the FE model to provide more accurate visual and haptic feedback to a user during the simulations. However, running even a static (time-independent) nonlinear FE model in real-time is a highly challenging task because the resulting stiffness matrix (K) is not constant and varies with the depth of penetration into the model. We propose a new computational approach allowing visio-haptic interaction with an FE model of a human liver having both nonlinear geometric and material properties. Our computational approach consists of two main steps: a pre-computation of the configuration space of all deformation configurations of the model, followed by the interpolation of the precomputed data for the calculation of the nodal displacements and reaction forces that are displayed to the user during the real-time interactions through a visual display and a haptic device, respectively. For the implementation of the proposed approach, no a priori assumptions or modeling simplifications about the mathematical complexity of the underlying soft tissue model, size and irregularity of the FE mesh are necessary. Moreover, it turns out that the deformation and force responses of the liver in the simulations are heavily influenced by the selected simulation parameters, such as the material model, boundary conditions and loading path, but the stability of the visual and haptic rendering in our approach does not depend on these parameters. In addition to showing the stability of our approach, the length of the precomputations as well as the accuracy of the interpolation scheme are evaluated for different interpolation functions and configuration space densities.Publication Metadata only A robotic indenter for minimally invasive characterization of soft tissues(Elsevier Science Bv, 2005) Avtan, Levent; Düzgün, Oktay; N/A; N/A; Department of Mechanical Engineering; Samur, Evren; Sedef, Mert; Başdoğan, Çağatay; Master Student; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering College of Engineering; 192890; N/A; 125489We have developed a robotic indenter for minimally invasive measurement of tissue properties during a laparoscopic surgery. Using the indenter, we conducted animal experiments in situ and successfully measured the force versus displacement response of pig liver under static and dynamic loading conditions. Using the small deformation assumption, we estimated the effective Young's modulus of pig liver around 15 kPa from the force-displacement data of static indentations. We also obtained the relaxation function, describing the variation of force response with respect to time, from the data of stress relaxation experiments. We observed that pig liver shows linear viscoelastic behavior.Publication Metadata only A robotic indenter for minimally invasive measurement and characterization of soft tissue response(Elsevier, 2007) Avtan, Levent; Düzgün, Oktay; N/A; N/A; Department of Mechanical Engineering; Samur, Evren; Sedef, Mert; Başdoğan, Çağatay; Master Student; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering College of Engineering; 192890; N/A; 125489The lack of experimental data in current literature on material properties of soft tissues in living condition has been a significant obstacle in the development of realistic soft tissue models for virtual reality based surgical simulators used in medical training. A robotic indenter was developed for minimally invasive measurement of soft tissue properties in abdominal region during a laparoscopic surgery. Using the robotic indenter, force versus displacement and force versus time responses of pig liver under static and dynamic loading conditions were successfully measured to characterize its material properties in three consecutive steps. First, the effective elastic modulus of pig liver was estimated as 10-15 kPa from the force versus displacement data of static indentations based on the small deformation assumption. Then, the stress relaxation function, relating the variation of stress with respect to time, was determined from the force versus time response data via curve fitting. Finally, an inverse finite element solution was developed using ANSYS finite element package to estimate the optimum values of viscoelastic and nonlinear hyperelastic material properties of pig liver through iterations. The initial estimates of the material properties for the iterations were extracted from the experimental data for faster convergence of the solutions.Publication Metadata only Visual and haptic simulation of linear viscoelastic tissue behavior based on experimental data(IEEE Computer Soc, 2006) N/A; N/A; Department of Mechanical Engineering; Sedef, Mert; Samur, Evren; Başdoğan, Çağatay; Master Student; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 192890; 125489We have developed a new numerical scheme for simulating linear viscoelastic tissue behavior modeled by FEM. We have integrated experimentally-measured viscoelastic tissue properties into our model for realistic force feedback to the user. A new precomputation method based on superposition principle was proposed for real-time computation of nodal displacements and interaction forces. We achieved stable haptic interactions by executing the viscoelastic model at 100Hz while the haptic loop was updated at 1KHz. The developed model and the proposed pre-computation approach have been both validated using ANSYS.Publication Metadata only VR-based simulators for training in minimally invasive surgery(IEEE Computer Soc, 2007) Harders, Matthias; Wesarg, Stefan; Department of Mechanical Engineering; Başdoğan, Çağatay; Sedef, Mert; Faculty Member; Master Student; Department of Mechanical Engineering; College of Engineering; Graduate School of Sciences and Engineering; 125489; N/APublication Metadata only Real-time finite-element simulation of linear viscoelastic tissue behavior based on experimental data(Ieee Computer Soc, 2006) N/A; N/A; N/A; Department of Mechanical Engineering; Sedef, Mert; Samur, Evren; Başdoğan, Çağatay; Master Student; Master Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 125489N/A