[Expanded reality in head surgery].

The preoperative planning of complex craniofacial surgical interventions is increasingly realized with the aid of appropriate planning systems in order to achieve high precision, minimal invasion and protection of risk areas. But the most important step from the planning to the actual intervention consists of providing the planning data intraoperatively in a reasonable and easy to handle way. In this regard, augmented reality is one of the most challenging and promising techniques to solve this problem.

[Multi-value regulatory systems for extracorporeal circulation].

Extracorporeal perfusion is the standard technique in cardiac surgery. It is controlled by perfusionists on the basis of their clinical experience and on the available data collected pre- and intra-operatively. But in spite of intensive monitoring postoperative complications occur.

["Computer- and Sensor-Assisted Surgery" Special Research Area 414--goals and concepts].

This paper presents an overview of our research in computer assisted surgery within the "Sonderforschungsbereich 414--Information Technology in Medicine: Computer and Sensor Supported Surgery". The overall goal is to achieve improved operation methods including higher quality, more safety and also more economy due to shorter operation time and less postoperative treatment. The SFB 414 is divided into three different sections focusing on projects concerning the heart, projects supporting cranio-facial interventions and interconnecting projects that serve both categories.

Design of a system for contact-free measurement of the conductivity of biological tissue.

The electrical impedance of tissue can give important informations about the viability of the tissue. A non-invasive and contact-free measuring system using an inductive sensor is presented. Using a single pick-up coil the system is not sensitive enough for measuring the small changes in conductivity of biological tissue.

Modeling force development in the sarcomere in consideration of electromechanical coupling.

Models of the cellular force development simulate the contractive behavior of the sarcomere. In conjunction with electrophysiological models they can contribute to a better comprehension of physiology and pathologies. Aim of this study is to examine the coupling of cellular electrophysiological processes and force development.

Hyperelastic description of elastomechanic properties of the heart: a new material law and its application.

Knowledge concerning passive mechanic cardiac properties is necessary to model behavior of whole hearts. Commonly, a continuum mechanics based description is chosen in conjunction with the finite element method. The aim of this work is to summarize, derive and evaluate hyperelastic material laws for inhomogeneous, anisotropic myocardium.

Development and characterisation of a ceramic HF-resonator for the MR-tomography.

Future trends in magnetic resonance imaging (MRI) lead to higher magnetic field strengths of the static magnetic fields and as an implication of that to much higher frequencies. Nowadays a common model of a send-receive coil is the birdcage resonator. However it is very difficult to find an optimal L/C-relation for the capacities and inductivities at frequencies above 300 MHz.

Simulation of a birdcage and a ceramic cavity HF-resonator for high magnetic fields in magnetic resonance imaging.

The aim of this work was the 3D-simulation of a dielectric resonator for high-field-MRI. A 12-rod-bird-cage-resonator was simulated in a first step, in order to verify the capability of the commercial simulation software MAFIA to simulate homogeneous, transversal B-fields in resonators. The second step was the simulation of frequency-independent dielectric ceramic resonators for static magnetic field strengths of 7 T and 12 T (294 MHz and 504 MHz respectively).

Thermal heating of human tissue induced by electromagnetic fields of magnetic resonance imaging.

The paper presents a simulation of the transient temperature distribution in the human body caused by induced eddy currents during magnetic resonance imaging (MRI). In a first simulation the validity of the used heat conduction equation was proven using a simple example of a cool-down-process of a sphere. Thereafter the heating of a phantom model with an implanted electrode placed in a MRI-System (active body coil) was examined.

Numerical calculations of switched magnetic field gradients during magnetic resonance imaging.

During magnetic resonance imaging (MRI) pulse-sequences the human body is exposed to switched magnetic gradient fields. These gradients become stronger and are switched faster for fast imaging. Effects resulting from these fields with trapezoidal waveforms are on the one hand sensory perception of induced currents and on the other hand muscular and cardiac stimulation.

Development of a cost-effective and MRI compatible temperature measurement system.

A reliable temperature measurement system working inside a MRI-system is required in order to determine the amount of local temperature rise during application of radiofrequency fields on medical implants and thus to ensure patient safety. Hence the aim of this study was to develop a cost-effective temperature measurement system suitable for use in a MRI system to investigate this heating having mainly phantom experiments in mind. Three active temperature measurement systems were set up, the first using a PTC as the temperature sensor, the other two with platinum resistors of 100 omega and 1000 omega.

Magnetic resonance imaging with implanted neurostimulators: numerical calculation of the induced heating.

Magnetic resonance imaging (MRI) is still contraindicated in patients with implanted active medical devices, as the applied radiofrequency (RF) fields can lead to significant heating of the implants and the electrodes. A head model with an implanted deep brain stimulation electrode (DBS) was exposed to a continuous RF-field similar to the excitational field used in MRI at a frequency of 64 MHz. In this study a two-step procedure for the accurate estimation of electrode-heating during MRI is presented.

Mobile patient simulator for resuscitation training with automatic external defibrillators.

Resuscitation training has to be performed under most realistic conditions. This includes both usual CPR measures (breathing and chest compressions) and advanced measures, e.g.

[Hardware implementation in VT/VF detection algorithms for AED (automatic external defibrillators)].

The automatic external defibrillator (AED) should carry out the diagnosis of the patient in a cardiac emergency when medical professionals are not present. The decision about defibrillation should be made without the help of first responder. To fulfill these requirements special algorithms are needed.

Imaging characteristics of different multichannel magnetocardiographic systems.

In this study a comparison of multichannel magnetocardiographic systems is performed with respect to the "detectable" information content. We investigate the lead-field matrices, the slope of the singular values and the source spaces of three different devices: the VectorView (Neuromag: magnetometer-gradiometer mixed device) of the BioMag Laboratory, Helsinki University Central Hospital (HUCH), the arrangement of electronically coupled magnetometers of the Physikalisch-Technische Bundesanstalt Berlin (PTB) and a virtual sensor geometry which was optimized for an improved slope of the singular values at the Institute of Biomedical Engineering, Karlsruhe.

[Development of Bluetooth wireless sensors].

Wireless communication could help to overcome current obstacles in medical devices and could enable medical services to offer completely new scenarios in health care. The Bluetooth technology which is the upcoming global market leader in wireless communication turned out to be perfectly suited not only for consumer market products but also in the medical environment [1]. It offers a low power, low cost connection in the medium range of 1-100 m with a bandwidth of currently 723.

[Coupling ventilation and defibrillation].

Fibrillation of the heart is one of the most common reasons for sudden death. In case of fibrillation, the brain gets damaged by hypoxia within minutes. Only a concept that bothly regards the cardial and pulmonal problem can be successful.

Symmetry considerations for volumetric implant-planning.

Symmetry Considerations can be used not only to plan the desired shape of reconstructured bone structures, but also to generate prototypes for soft tissue implants. The paper describes a system which allows to calculate a symmetry plane in the facial area automatically and computes proposals for implants or transplants. This is done by using a Simulated Annealing algorithm to determine the best reflection and morphologig operators to calculate the implant.

Simulation of non-contact measurement of the electrical impedance using an anatomical model.

The measurement of the impedance of biological tissue can be a non-invasive method to find new data of diagnostic relevance. A system for a non-contact measurement of the electrical impedance of biological tissue is presented. The system consists of an excitation coil and two sensing coils, an upper and a lower coil.

Calculation of the dielectric properties of biological tissue using simple models of cell patches.

The measurement of the dielectric properties of biological tissue is of increasing scientific relevance. Models for the comprehension of the dielectric properties at various frequencies have been successfully set up. However, students often have problems in understanding the effects taking place on cellular level which lead to the observed dispersion.