Microscope Embedded Neurosurgical Training and Intraoperative System

In the recent years, neurosurgery has been strongly influenced by new technologies. Computer Aided Surgery (CAS) offers several benefits for patients\u27 safety but fine techniques targeted to obtain minimally invasive and traumatic treatments are required, since intra-operative false movements can be devastating, resulting in patients deaths. The precision of the surgical gesture is related both to accuracy of the available technological instruments and surgeon\u27s experience. In this frame, medical training is particularly important. From a technological point of view, the use of Virtual Reality (VR) for surgeon training and Augmented Reality (AR) for intra-operative treatments offer the best results. In addition, traditional techniques for training in surgery include the use of animals, phantoms and cadavers. The main limitation of these approaches is that live tissue has different properties from dead tissue and that animal anatomy is significantly different from the human. From the medical point of view, Low-Grade Gliomas (LGGs) are intrinsic brain tumours that typically occur in younger adults. The objective of related treatment is to remove as much of the tumour as possible while minimizing damage to the healthy brain. Pathological tissue may closely resemble normal brain parenchyma when looked at through the neurosurgical microscope. The tactile appreciation of the different consistency of the tumour compared to normal brain requires considerable experience on the part of the neurosurgeon and it is a vital point. The first part of this PhD thesis presents a system for realistic simulation (visual and haptic) of the spatula palpation of the LGG. This is the first prototype of a training system using VR, haptics and a real microscope for neurosurgery. This architecture can be also adapted for intra-operative purposes. In this instance, a surgeon needs the basic setup for the Image Guided Therapy (IGT) interventions: microscope, monitors and navigated surgical instruments. The same virtual environment can be AR rendered onto the microscope optics. The objective is to enhance the surgeon\u27s ability for a better intra-operative orientation by giving him a three-dimensional view and other information necessary for a safe navigation inside the patient. The last considerations have served as motivation for the second part of this work which has been devoted to improving a prototype of an AR stereoscopic microscope for neurosurgical interventions, developed in our institute in a previous work. A completely new software has been developed in order to reuse the microscope hardware, enhancing both rendering performances and usability. Since both AR and VR share the same platform, the system can be referred to as Mixed Reality System for neurosurgery. All the components are open source or at least based on a GPL license

Collision Detection and Merging of Deformable B-Spline Surfaces in Virtual Reality Environment

This thesis presents a computational framework for representing, manipulating and merging rigid and deformable freeform objects in virtual reality (VR) environment. The core algorithms for collision detection, merging, and physics-based modeling used within this framework assume that all 3D deformable objects are B-spline surfaces. The interactive design tool can be represented as a B-spline surface, an implicit surface or a point, to allow the user a variety of rigid or deformable tools. The collision detection system utilizes the fact that the blending matrices used to discretize the B-spline surface are independent of the position of the control points and, therefore, can be pre-calculated. Complex B-spline surfaces can be generated by merging various B-spline surface patches using the B-spline surface patches merging algorithm presented in this thesis. Finally, the physics-based modeling system uses the mass-spring representation to determine the deformation and the reaction force values provided to the user. This helps to simulate realistic material behaviour of the model and assist the user in validating the design before performing extensive product detailing or finite element analysis using commercially available CAD software. The novelty of the proposed method stems from the pre-calculated blending matrices used to generate the points for graphical rendering, collision detection, merging of B-spline patches, and nodes for the mass spring system. This approach reduces computational time by avoiding the need to solve complex equations for blending functions of B-splines and perform the inversion of large matrices. This alternative approach to the mechanical concept design will also help to do away with the need to build prototypes for conceptualization and preliminary validation of the idea thereby reducing the time and cost of concept design phase and the wastage of resources

Passive Realizations of Series Elastic Actuation: Effects of Plant and Controller Dynamics on Haptic Rendering Performance

We introduce minimal passive physical equivalents of series (damped) elastic actuation (S(D)EA) under closed-loop control to determine the effect of different plant parameters and controller gains on the closed-loop performance of the system and to help establish an intuitive understanding of the passivity bounds. Furthermore, we explicitly derive the feasibility conditions for these passive physical equivalents and compare them to the necessary and sufficient conditions for the passivity of S(D)EA under velocity sourced impedance control (VSIC) to establish their relationship. Through the passive physical equivalents, we rigorously compare the effect of different plant dynamics (e.g., SEA and SDEA) on the system performance. We demonstrate that passive physical equivalents make the effect of controller gains explicit and establish a natural means for effective impedance analysis. We also show that passive physical equivalents promote co-design thinking by enforcing simultaneous and unbiased consideration of (possibly negative) controller gains and plant parameters. We demonstrate the usefulness of negative controller gains when coupled to properly designed plant dynamics. Finally, we provide experimental validations of our theoretical results and characterizations of the haptic rendering performance of S(D)EA under VSIC

Haptic feedback from human tissues of various stiffness and homogeneity

This work presents methods for haptic modelling of soft and hard tissue with varying stiffness. The model provides visualization of deformation and calculates force feedback during simulated epidural needle insertion. A spring-mass-damper (SMD) network is configured from magnetic resonance image (MRI) slices of patient’s lumbar region to represent varying stiffness throughout tissue structure. Reaction force is calculated from the SMD network and a haptic device is configured to produce a needle insertion simulation. The user can feel the changing forces as the needle is inserted through tissue layers and ligaments. Methods for calculating the force feedback at various depths of needle insertion are presented. Voxelization is used to fill ligament surface meshes with spring mass damper assemblies for simulated needle insertion into soft and hard tissues. Modelled vertebrae cannot be pierced by the needle. Graphs were produced during simulated needle insertions to compare the applied force to haptic reaction force. Preliminary saline pressure measurements during Tuohy epidural needle insertion are also used as a basis for forces generated in the simulation

Large Deformation Object Modeling Using Finite Element Method And Proper Orthogonal Decomposition For Haptic Robots

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalışmada, hissedici arabirimler ve bu arabirimlerde kullanılan hesaplama metotları incelenmiştir. Bu amaçla doğrultusunda, yüksek deformasyon özelliğine sahip doğrusal olmayan bir kirişin modeli sonlu elemanlar metodu kullanılarak elde edilmiştir ve bu model gerçek zamalı olarak PHANTOM® Premium 6 DOF hissedici arabirimi ile etkileşime geçirilmiştir. Etkileşimi elde etmek amacıyla, kiriş modeli OpenGL kütüphanesi kullanılarak görselleştirilmiştir ve cihaza OpenHaptics kütüphanesinin HDAPI fonksiyonları kullanılarak hükmedilmiştir. Hissedici cihazların ihtiyaç duyduğu yüksek hesaplama hızlarını elde edebilmek amacıyla uygun ortogonal ayrıştırma metodunu kullanarak düşük mertebeli model elde edilmiştir. Her iki modelin davranışı incelendiginde uygun orthogonal ayrıştırma metodunun, orjinal model davranışı gösterdiği saptanmış ve hesaplama zamanlarının büyük oranda azaldığı görülmüştür.In this study, haptic systems are introduced with investigation of haptic interfaces and haptic rendering. To this end, a large deformation real time beam model is developed and integrated with the PHANTOM® Premium 6 DOF haptic robot. OpenGL library is used as a visualization tool of the model and the haptic robot is manipulated using libraries of OpenHaptics named as HDAPI. In order to obtain high computational demands of the haptic systems, Proper Orthogonal Decomposition method is used to obtain a low order model. Investigations of both models have revealed that lower order model behaves exactly in a similar manner as the original model with reduced computational effort.Yüksek LisansM.Sc

Representing the model of impedance controlled robot interaction with feedback delay in polytopic LPV form: TP model transformation based approach

The aim of this paper is to transform the model of the impedance controlled robot interaction with feedback delay to a Tensor Product (TP) type polytopic LPV model whereupon Linear Matrix Inequality (LMI) based control design can be immediately executed. The paper proves that the impedance model can be exactly represented by a finite element TP type polytopic model under certain constrains. The paper also determines various further TP models with different advantages for control design. First, it derives the exact Higher Order Singular Value Decomposition (HOSVD) based canonical form, then it performs complexity trade-off to yield a model with less number of components but rather effective for LMI design. Then the paper presents various different types of convex TP model representations based on the non-exact model in order to investigate how convex hull manipulation can be performed on the model. Finally the presented models are analyzed to validate the accuracy of the transformation and the resulting TP type polytopic LPV models. The paper concludes that these prepared models are ready for convex hull manipulation and LMI based control design