A Hybrid Model Method for Accurate Surface Deformation and Incision Based on FEM and PBD

In some simulations like virtual surgery, an accurate surface deformation method is needed. Many deformation methods focus on the whole model swing and twist. Few methods focus on surface deformation. For the surface deformation method, two necessary characteristics are needed: the accuracy and real-time performance. Some traditional methods, such as position-based dynamics (PBD) and mass-spring method (MSM), focus more on the real-time performance. Others like the finite element method (FEM) focus more on the accuracy. To balance these two characteristics, we propose a hybrid mesh deformation method for accurate surface deformation based on FEM and PBD. Firstly, we construct a hybrid mesh, which is composed of a coarse volume mesh and a fine surface mesh. Secondly, we implement FEM on coarse volume mesh and PBD on fine surface mesh, and the deformation of fine surface mesh is constrained by the displacement of the coarse volume mesh. Thirdly, we introduced a small incision process for our proposed method. Finally, we implemented our method on a simple deformation simulation and a small incision simulation. The result shows an accurate surface deformation performance by implementing our method. The incision effect shows the compatibility of our proposed method. In conclusion, our proposed method acquires a better trade-off between accuracy and real-time performance.

Virtual Surgical Planning: Modeling from the Present to the Future

Virtual surgery planning is a non-invasive procedure, which uses digital clinical data for diagnostic, procedure selection and treatment planning purposes, including the forecast of potential outcomes. The technique begins with 3D data acquisition, using various methods, which may or may not utilize ionizing radiation, such as 3D stereophotogrammetry, 3D cone-beam CT scans, etc. Regardless of the imaging technique selected, landmark selection, whether it is manual or automated, is the key to transforming clinical data into objects that can be interrogated in virtual space. As a prerequisite, the data require alignment and correspondence such that pre- and post-operative configurations can be compared in real and statistical shape space. In addition, these data permit predictive modeling, using either model-based, data-based or hybrid modeling. These approaches provide perspectives for the development of customized surgical procedures and medical devices with accuracy, precision and intelligence. Therefore, this review briefly summarizes the current state of virtual surgery planning.

Is a Video Worth a Thousand Words? Educating Preclinical Medical Students on Sterile Scrubbing, Gowning, and Gloving Virtually and In-Person

Introduction. Programs that offer early exposure to surgery for medical students foster interest in and positive perceptions of surgery. The COVID-19 pandemic led to suspension of these activities at our institution, the University of Kansas School of Medicine. In response to the lack of virtual alternatives, a pilot virtual surgery enrichment program was implemented for first-year students in place of in-person surgical exposure. The aim of this study was to compare the efficacy of in-person and virtual-based surgical education programs to expose preclinical medical students about the surgical realm of medicine. Methods.First-year medical students participated in either a virtual (Group A) or in-person (Group B) week-long surgical enrichment program. Group assignments were dictated by COVID restrictions on each of our three medical school campuses: Salina, Wichita, and Kansas City. Pre- and post-surveys with a 14-question multiple-choice assessment of surgical knowledge were distributed to participants. Paired Wilcoxon Signed Rank tests and Mann-Whitney-U tests were used for statistical analysis. Results. There were 14 participants in Group A and 7 participants in Group B. Both groups improved significantly from pre- to post-assessment score. (Group A, p = 0.01; Group B, p = 0.04). There was no difference between groups in the magnitude of score improvement from pre- to post-assessment (p = 0.59). Conclusion. This pilot program demonstrated that virtual platforms can be a method to provide meaningful clinical experiences in surgery to preclinical medical students restricted from clinical activities. Further development of mentorship in virtual surgical programs and assessment of subjective experience is needed.

Hemodynamics After Fontan Procedure are Determined by Patient Characteristics and Anastomosis Placement Not Graft Selection: a Patient-Specific Multiscale Computational Study

Objectives: Patient-specific multiscale modeling simulates virtual surgeries of the Fontan procedure using three different graft options. Predictive modeling details post-operative outcomes that can help inform clinical decision support. Methods: Six patients underwent preoperative cardiac magnetic resonance imaging and catheterization. Virtual surgery is carried out for each patient to test the resulting hemodynamics of three Fontan graft options: ECC, 9mm Y-graft, and 12mm Y-graft. Results: 1) one-way ANOVA p>0.998 in all systemic pressures and flows between graft options, 2) p=0.706 for hepatic flow distribution between graft options, 3) local power loss differences do not affect the systemic circulation, 4) anastomosis positioning modification of the same Y-graft in the same patient changed left PA hepatic distribution from 0.66 to 0.49 Conclusions: Systemic pressures and blood flow after the Fontan procedure are not affected by graft selection but are well influenced by patient pulmonary vascular impedance. The hepatic distribution can be affected by anastomosis placement.

Virtual dissection of the real brain: integration of photographic 3D models into virtual reality and its effect on neurosurgical resident education

OBJECTIVE Virtual reality (VR) is increasingly being used for education and surgical simulation in neurosurgery. So far, the 3D sources for VR simulation have been derived from medical images, which lack real color. The authors made photographic 3D models from dissected cadavers and integrated them into the VR platform. This study aimed to introduce a method of developing a photograph-integrated VR and to evaluate the educational effect of these models. METHODS A silicone-injected cadaver head was prepared. A CT scan of the specimen was taken, and the soft tissue and skull were segmented to 3D objects. The cadaver was dissected layer by layer, and each layer was 3D scanned by a photogrammetric method. The objects were imported to a free VR application and layered. Using the head-mounted display and controllers, the various neurosurgical approaches were demonstrated to neurosurgical residents. After performing hands-on virtual surgery with photographic 3D models, a feedback survey was collected from 31 participants. RESULTS Photographic 3D models were seamlessly integrated into the VR platform. Various skull base approaches were successfully performed with photograph-integrated VR. During virtual dissection, the landmark anatomical structures were identified based on their color and shape. Respondents rated a higher score for photographic 3D models than for conventional 3D models (4.3 ± 0.8 vs 3.2 ± 1.1, respectively; p = 0.001). They responded that performing virtual surgery with photographic 3D models would help to improve their surgical skills and to develop and study new surgical approaches. CONCLUSIONS The authors introduced photographic 3D models to the virtual surgery platform for the first time. Integrating photographs with the 3D model and layering technique enhanced the educational effect of the 3D models. In the future, as computer technology advances, more realistic simulations will be possible.

Predictability of maxillary positioning: a 3D comparison of virtual and conventional orthognathic surgery planning

Background Virtual surgery planning (VSP) is believed to reduce inaccuracies in maxillary positioning compared to conventional surgery planning (CSP) due to the elimination of face-bow transfer and laboratory steps. However, there is still a lack of comparative studies for the accuracy of splint-based maxillary positioning in CSP versus VSP. Therefore, the objective of this retrospective, observational study was to compare if splints produced by VSP and CSP reach postoperative outcomes within clinically acceptable limits. Methods The planned and actual postoperative results of 52 patients (VSP: n = 26; CSP: n = 26) with a mean age of 24.4 ± 6.2 years were investigated by three-dimensional (3D) alignment with planning software. The conventional treatment plan was digitized, so that the evaluation of both methods was performed in the same manner using the same coordinate system. Inaccuracies were measured by sagittal, vertical and transversal deviations of the upper central incisors and the inclination of the maxillary occlusal plane between the planned and achieved maxillary positions. Results Both methods demonstrated significant differences between the planned and actual outcome. The highest inaccuracies were observed in vertical impaction and midline correction. No significant differences between CSP and VSP were observed in any dimension. Errors in vertical and sagittal dimension intensified each other. Conclusions In conclusion, splint-based surgeries reached similar results regardless of the applied planning method and splint production.

A study of real-time simulation of liver of virtual surgical robot based on biologically position-based dynamic model

Virtual surgery robot can accurately modeling of surgical instruments and human organs, and realistic simulation of various surgical phenomena such as deformation of organic tissues, surgery simulation system can provide operators with reusable virtual training and simulation environment. To meet the requirement of virtual surgery robot for the authenticity and real-time of soft tissue deformation and surgical simulation in liver surgery, a new method is proposed to simulate the deformation of soft tissue. This method combines the spring force, the external force of the system, and the constraint force produced by the constraint function of the position-based dynamics. Based on the position-based dynamics, an improved three-parameter mass-spring model is added. In the calculation of the elastic force, the nonlinearity and viscoelasticity of the soft tissue are introduced, and the joint force of the constraint projection process and the constraint force of the position-based dynamics is used to modify mass points movement. The method of position-based dynamics based on biological characteristics, not only considers the biomechanical properties of biological soft tissue as an organic polymer such as viscoelasticity, nonlinearity, and incompressibility but also retains the rapidity and stability of the position based dynamic method. Through the simulation data, the optimal side length of tetrahedral mesh in the improved three-parameter model is obtained, and the physical properties of the model are proved. The real-time simulation of the liver and other organs is completed by using the Geomagic touch force feedback device, which proves the practicability and effectiveness of this method.

Three-Dimensional Modeling and Simulation of Muscle Tissue Puncture Process

Needle biopsy is an important part of modern clinical medicine. The puncture accuracy and sampling success rate of puncture surgery can be effectively improved through virtual surgery. Because fewer puncture existing three-dimensional(3D) model, it is impossible to guide the operation under complicated working conditions, which limits the development of virtual surgery. In this paper, 3D simulation of muscle tissue puncture process is studied. Firstly, the parameters of muscle tissue are measured. Considering the fitting accuracy and calculation speed, the M-R model is selected. Subsequently, an accurate 3D dynamic puncture model is established. The failure criterion is used to define the breaking characteristics of the muscle, and the bilinear cohesion model defines the breaking process. Experiments with different puncture speeds are carried out through the built in vitro puncture platform. The experimental results are compared with the simulation results. The accuracy of the model is verified by the high degree of agreement between the two curves. Finally, the model under different parameters is studied. Analyze the simulation results of different puncture depths and puncture speeds. The 3D puncture model can provide a more accurate model support for virtual surgery and help improve the success rate of puncture surgery.