Real-time simulation of soft tissue deformation for surgical simulation

Surgical simulation plays an important role in the training, planning and evaluation of many surgical procedures. It requires realistic and real-time simulation of soft tissue deformation under interaction with surgical tools. However, it is challenging to satisfy both of these conflicting requirements. On one hand, biological soft tissues are complex in terms of material compositions, structural formations, and mechanical behaviours, resulting in nonlinear deformation characteristics under an external load. Due to the involvement of both material and geometric nonlinearities, the use of nonlinear elasticity causes a highly expensive computational load, leading to the difficulty to achieve the real-time computational performance required by surgical simulation. On the other hand, in order to satisfy the real-time computational requirement, most of the existing methods are mainly based on linear elasticity under the assumptions of small deformation and homogeneity to describe deformation of soft tissues. Such simplifications allow reduced runtime computation; however, they are inadequate for modelling nonlinear material properties such as anisotropy, heterogeneity and large deformation of soft tissues. In general, the two conflicting requirements of surgical simulation raise immense complexity in modelling of soft tissue deformation. This thesis focuses on establishment of new methodologies for modelling of soft tissue deformation for surgical simulation. Due to geometric and material nonlinearities in soft tissue deformation, the existing methods have only limited capabilities in achieving nonlinear soft tissue deformation in real-time. In this thesis, the main focus is devoted to the real-time and realistic modelling of nonlinear soft tissue deformation for surgical simulation. New methodologies, namely new ChainMail algorithms, energy propagation method, and energy balance method, are proposed to address soft tissue deformation. Results demonstrate that the proposed methods can simulate the typical soft tissue mechanical properties, accommodate isotropic and homogeneous, anisotropic and heterogeneous materials, handle incompressibility and viscoelastic behaviours, conserve system energy, and achieve realistic, real-time and stable deformation. In the future, it is projected to extend the proposed methodologies to handle surgical operations, such as cutting, joining and suturing, for topology changes occurred in surgical simulation

Numerical Study For Acoustic Micro-Imaging Of Three Dimensional Microelectronic Packages

Complex structures and multiple interfaces of modern microelectronic packages complicate the interpretation of acoustic data. This study has four novel contributions. 1) Contributions to the finite element method. 2) Novel approaches to reduce computational cost. 3) New post processing technologies to interpret the simulation data. 4) Formation of theoretical guidance for acoustic image interpretation. The impact of simulation resolution on the numerical dispersion error and the exploration of quadrilateral infinite boundaries make up the first part of this thesis's contributions. The former focuses on establishing the convergence score of varying resolution densities in the time and spatial domain against a very high fidelity numerical solution. The latter evaluates the configuration of quadrilateral infinite boundaries in comparison against traditional circular infinite boundaries and quadrilateral Perfectly Matched Layers. The second part of this study features the modelling of a flip chip with a 140µm solder bump assembly, which is implemented with a 230MHz virtual raster scanning transducer with a spot size of 17µm. The Virtual Transducer was designed to reduce the total numerical elements from hundreds of millions to hundreds of thousands. Thirdly, two techniques are invented to analyze and evaluate simulated acoustic data: 1) The C-Line plot is a 2D max plot of specific gate interfaces that allows quantitative characterization of acoustic phenomena. 2) The Acoustic Propagation Map, contour maps an overall summary of intra sample wave propagation across the time domain in one image. Lastly, combining all the developments. The physical mechanics of edge effects was studied and verified against experimental data. A direct relationship between transducer spot size and edge effect severity was established. At regions with edge effect, the acoustic pulse interfacing with the solder bump edge is scattered mainly along the horizontal axis. The edge effect did not manifest in solder bump models without Under Bump Metallization (UBM). Measurements found acoustic penetration improvements of up to 44% with the removal of (UBM). Other acoustic mechanisms were also discovered and explored. Defect detection mechanism was investigated by modelling crack propagation in the solder bump assembly. Gradual progression of the crack was found have a predictable influence on the edge effect profile. By exploiting this feature, the progress of crack propagation from experimental data can be interpreted by evaluating the C-Scan image