Recently, finite element models based on Biot's displacement (u,U) formulation for poroelastic materials have been extensively used to predict the acoustical and structural behavior of multilayer structures. These models while accurate lead to large frequency dependent matrices for three-dimensional problems necessitating important setup time, computer storage and solution time. In this paper, a novel exact mixed displacement pressure (u,p) formulation is presented. The formulation derives directly from Biot's poroelasticity equations. It has the form of a classical coupled fluid-structure problem involving the dynamic equations of the skeleton in vacuo and the equivalent fluid in the rigid skeleton limit. The governing (u,p) equations and their weak integral form are given together with the coupling conditions with acoustic media. The numerical implementation of the presented approach in a finite element code is discussed. Examples are presented to show the accuracy and effectiveness of the presented formulation.
This paper presents the boundary conditions that apply to the weak integral formulation of the Biot mixed (u_,p) poroelasticity equations. These boundary conditions are derived from the classical boundary conditions of the Biot displacement (u_,U_) poroelasticity equations. They are applied to the surface integrals of the associated weak form to account for exterior excitations, supports, and couplings with exterior elastic, acoustic, poroelastic media, and a septum. It will be shown that the derived boundary conditions for the (u_,p) formulation lead to simpler finite element equations compared to those obtained from the (u_,U_) formulation. Finally, two numerical examples are presented to validate the poroelastic-septum coupling condition, and to highlight the limitations of the free edge condition on a poroelastic medium.
We have conducted a pilot validation study for the NeuroTouch tumor resection scenario and demonstrated for the first time, face, content and construct validity of a VR neurosurgical simulation exercise. Future full-scale studies will be conducted in noncompetitive settings and incorporate expert participants.
BACKGROUND:
A virtual reality (VR) neurosurgical simulator with haptic feedback may provide the best model for training and perfecting surgical techniques for transsphenoidal approaches to the sella turcica and cranial base. Currently there are 2 commercially available simulators: NeuroTouch (Cranio and Endo) developed by the National Research Council of Canada in collaboration with surgeons at teaching hospitals in Canada, and the Immersive Touch. Work in progress on other simulators at additional institutions is currently unpublished.
OBJECTIVE:
This article describes a newly developed application of the NeuroTouch simulator that facilitates the performance and assessment of technical skills for endoscopic endonasal transsphenoidal surgical procedures as well as plans for collecting metrics during its early use.
METHODS:
The main components of the NeuroTouch-Endo VR neurosurgical simulator are a stereovision system, bimanual haptic tool manipulators, and high-end computers. The software engine continues to evolve, allowing additional surgical tasks to be performed in the VR environment. Device utility for efficient practice and performance metrics continue to be developed by its originators in collaboration with neurosurgeons at several teaching hospitals in the United States. Training tasks are being developed for teaching 1- and 2-nostril endonasal transsphenoidal approaches. Practice sessions benefit from anatomic labeling of normal structures along the surgical approach and inclusion (for avoidance) of critical structures, such as the internal carotid arteries and optic nerves.
CONCLUSION:
The simulation software for NeuroTouch-Endo VR simulation of transsphenoidal surgery provides an opportunity for beta testing, validation, and evaluation of performance metrics for use in neurosurgical residency training.
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