Hüseyin Kemâl Çakmak

Endoscopic surgery training using virtual reality and deformable tissue simulation

Abstract Surgical training systems based on virtual reality (VR) and simulation techniques for tissue deformation may represent a more cost-effective and efficient alternative to traditional training methods. Additionally, VR is a technology that can teach surgeons new procedures and can determine their level of competence before they operate on patients. At Forschungszentrum Karlsruhe (FZK), a virtual reality training system for minimally invasive surgery (MIS), based on the simulation software KISMET, has been developed. An overview of the current state of development for the “Karlsruhe Endoscopic Surgery Trainer” is presented. For quick and easy creation of surgical scenes containing deformable anatomical organ models, the spline-based modeller KisMo has been developed, which generates beside the geometry also a spatial mass–spring network of the objects for the elastodynamic simulation in KISMET. The MIS trainer provides several surgical interaction modules for deformable objects like grasping, application of clips, cutting, coagulation, injection and suturing. Additionally, it is possible to perform irrigation and suction in the operation area. Active deformable objects are used for the morphodynamic simulation of the stomach and the intestines. Furthermore, a hierarchical pulse simulation in virtual arterial vessel trees has been realized, which enables the palpation of the pulse with a force-feedback device. The pulse simulation is coupled with an arterial bleeding simulation, which gets activated by injuries of arteries and stopped by application of clips. The simulation system has been applied to minimally invasive surgery training in gynaecology and laparoscopy. Special attention is addressed to elastodynamically deformable tissue models and geometric modelling techniques for graphical real-time performance.

Vision-based Hand Representation and Intuitive Virtual Object Manipulation in Mixed Reality

In this paper we introduce a method for representation of the human hand in virtual or mixed environments and interaction with virtual objects. We use a head-mounted display with two cameras installed on top to record the user s hand, which is then cut out and shown in the virtual environment. Extracted features like silhouette and fingertip positions enable direct visual interaction with objects in virtual worlds. Applications of the approach are presented and feature extraction methods, the overlay technique and the hardwareand software setup of the system are described. Finally the benefits and limitations of the approach are discussed.

Illusory Hand Ownership Induced by an MRI Compatible Immersive Virtual Reality Device

In this paper, we introduce a virtual reality based setup for triggering and studying illusory sensations of limb ownership as known from the popular rubber hand illusion. Unlike a similar setup introduced recently, this experiment is triggered by software automatically, which provides for a good synchrony and for high accuracy of visuotactile stimulation. The system is usable inside a magnetic resonance scanner which allows observing cortical activations at the same time. We tested two participants, one highly and the other lowly susceptible to the induction of illusory limb ownership, assessing their subjective experiences as well as their brain activity using functional magnetic resonance imaging. We present preliminary results suggesting that our setup induces illusory ownership experiences for a virtual limb successfully, accompanied by neuronal activation in integrative brain areas.

A Matlab-Based Simulation Tool For The Analysis Of Unsymmetrical Power System Transients In Large Networks

This paper presents an extendable Matlab-based phasortime domain toolbox for modeling, simulation and analysis of unsymmetrical power system transients in large networks. Unlike most of the existing transient stability simulators which represent the transmission network on a per phase positive sequence basis, the new simulation function introduced in this paper is based on the symmetrical component technique which employs the three sequence networks. This representation allows consideration of network imbalances in order to include a wide range of disturbances during transient stability studies. The main aim of this paper is to describe the model details of the power system components required for unsymmetrical transients analysis and the solution methodology in the introduced simulation function. The performance of the simulation function is tested using standard IEEE test network models and the promising results are positively compared to respective results in DIgSILENT PowerFactory in terms of accuracy.

Poster Abstract: Implementation of an extended generator subsystem in OpenModelica and comparative analysis with DIgSILENT PowerFactory

Mathematical modeling is a key step in the analysis of power system stability. In view of model accuracy, this process should include all relevant details that affect the transient behavior of the power system. To this aim, an extension of the generator subsystem model is introduced in OpenModelica by adding a new turbine-governor model. Taking advantage of the multi-domain modeling property of OpenModelica, two libraries are coupled to interconnect the mechanical and electrical domains of the generator subsystem. The new generator subsystem is tested using the standard IEEE 9-Bus test feeder and the simulation results in OpenModelica are furthermore compared to respective results in DIgSILENT PowerFactory. The new generator subsystem model is integrated into the validated 20 kV power grid model of KIT-Campus North and respective results are presented for abrupt load changes.

Enhancing model interchangeability for powerflow studies : An example of a new Hungarian network model in powerfactory and Easimov

The article presents a comparison of basic powerflow studies, performed with a market available and a new self-developed power grid analysis software suite. The example of the Hungarian power system is used to show a blueprint process for creating computer models of large-scale electric systems, using dominantly openly available data sources. The first part of the article introduces the Hungarian power systems, and details how topological, consumption and generation data are collected. The second part presents the implementation of these raw data in DIgSILENT PowerFactory and eASiMOV, highlighting the interoperability of the softwares and the additional value of model data conversion.

Entwicklung eines Bewertungssystems für Virtual Reality-Simulatoren in der Chirurgie

Zusammenfassung Chirurgische Fertigkeiten im Bereich der minimal invasiven Chirurgie können an Virtual Reality-Simulatoren geübt werden. Für ein zielgerichtetes Training ist die Bewertung der Übungsausführung wichtig. Deshalb werden neue Methoden zur Entwicklung eines Bewertungssystems für die automatisierte Beurteilung von Trainierenden eingeführt. Zwei Studien haben die Eignung des neuen Konzeptes gezeigt. Abstract Currently, essential skills for minimal access surgery can be practised on a virtual reality-simulator outside the operating room. For effective training, it is important to assess the training process. Therefore, new methods are introduced to develop an assessment system for an automated evaluation of trainees. Two different studies demonstrate the quality of the new concept.