Preoperative Planning And Soft Tissue Modeling For Virtual Surgery Simulation System

With the increasing clinical application of robot-assisted surgery systems,the training of surgeons and pre-operative planning have become an urgent problem to be solved.As a new way to solve these problems,virtual surgery simulation system has become a research hotspot.The virtual surgery simulation system can solve many limitations in traditional surgical training,and surgical planning process can also be realized quickly based on three-dimensional reconstruction of soft tissue.The preoperative planning process is the preparation of the surgery,and it is crucial for the surgical simulation.In addition,master operator is controlled by surgeons under the guidance of virtual vision in the traditional robot-assisted virtual training system,and the virtual microdevice is controlled to perform the surgical operation.This method relies mainly on vision,and multi-dimensional force sensing is lack.The lack of multi-dimensional force situation makes lack of sense of presence and immersion.Related researchs on preoperative planning and soft tissue modeling techniques have important significance for the development of virtual surgical simulation system.This dissertation is supported by the National Natural Science Foundation of China(61203358)and the Natural Science Foundation of Heilongjiang Province(F2015034).This dissertation focuses on the preoperative planning problems and the lack of immersion in the virtual surgery simulation system.Theoretical analysis and experimental have carried on dynamics modeling and analysis,preoperative planning optimization methods,mechanical properties of soft tissue and virtual soft tissue modeling and so on.Specific work includes:Firstly,the robot assisted surgery system is introduced.The dynamic models of instrument arm and laparoscopic arm are established based on the Lagrange equation.The correctness of dynamic models is verified by virtual prototype simulation.Considering the trocar force between the mechanical arm and the abdominal wall during the surgical operation,a strategy based on the complete dynamic model to estimate the trocar force of the laparoscopic arm is proposed.A simple mechanical model of soft tissue is established by indentation test,which is added to the dynamic model of robotic arm to establish a complete dynamic model to analyze the influence of breath and joint clearances on the trocar point during the operation.An external force estimation strategy is proposed based on the complete dynamic model of instrument arm.Secondly,for the trocar point adjustment mechanism,the dexterity and the mean position error of trocar point in the global space are used as the optimization objective,and the dimensional parameters are optimized to improve the positioning performance.By establishing the mathematical model of the abdominal wall,a surgical incision optimization algorithm based on the characteristic parameters of the lesion is proposed.The surgical incision position is optimized by using the laparoscopic incision feature parameter index and the optimal triangle criterion.Extra-abdominal collaboration space index is proposed by normalizing the surgical system coordinate system.A positioning algorithm of multi-arm system is proposed based on double collaboration space and the optimal surgical incision position.The effectiveness of the optimization method is verified by simulation and established virtual positioning system.Thirdly,the quasi-static response of liver tissue is obtained by non-slip compression test.The stress relaxation response is obtained by unconfined compression experiments.The inverse finite element parameter inversion based on multi-population genetic algorithm is used to obtain constitutive model parameters.Based on the model parameters,the influence of friction in unconfined compression experiments on soft tissue mechanical response is studied by finite element analysis,and the percentage difference in radial deformation is proposed.The friction estimation model coefficients based on percentage difference is determined by finite element analysis,and the estimation accuracy verification is completed.Aiming at the preloading force problem in unconfined compression experiments,an elimation method based on linear loading region is proposed to eliminate the influence of preloading force on elastic response of soft tissue,and the effectiveness of the method is verified by experiments.Finally,aiming at the master-slave control of the laparoscopic arm and instrument arm,two different master-slave mapping methods are adopted.A method to eliminate the jitter problem in the master-slave motion control process is proposed.The dynamic model of rovotic arm is used to verify the effectiveness of this method.A virtual surgical simulation system including virtual soft tissue and surgical execution system model is established.The collision detection between the virtual micro-device and the virtual soft tissue is realized by using hybrid bounding box.The finite element model is established by using the real mechanical properties of soft tissue.The mathematical model between the loading displacement and the deformation radius is established.By comparing the mechanical response of the discrete unit combination model and the finite element model,the parameters of the basic discrete unit are obtained and used as physical model parameters of virtual soft tissue.The phantom manipulator and the virtual surgical system are used for simulation to realize the pressing and stretching operations on the soft tissue,and provide technical foundation for further developing a surgical simulation system with more realistic visual feedback and force feedback.