Abstract:

BACKGROUND: Middle latency auditory evoked responses (MLAER) as a measure of depth of sedation are critically dependent on data quality and the analysis technique used. Manual peak labeling is subject to observer bias. This study investigated whether a user-independent index based on wavelet transform can be derived to discriminate between awake and unresponsive states during propofol sedation. METHODS: After obtaining ethics committee approval and written informed consent, 13 volunteers and 40 patients were studied. In all subjects, propofol was titrated to loss of response to verbal command. The volunteers were allowed to recover, then propofol was titrated again to the same end point, and subjects were finally allowed to recover. From three MLAER waveforms at each stage, latencies and amplitudes of peaks Pa and Nb were measured manually. In addition, wavelet transform for analysis of MLAER was applied. Wavelet transform gives both frequency and time information by calculation of coefficients related to different frequency contents of the signal. Three coefficients of the so-called wavelet detail level 4 were transformed into a single index (Db3d4) using logistic regression analysis, which was also used for calculation of indices for Pa, Nb, and Pa/Nb latencies. Prediction probabilities for discrimination between awake and unresponsive states were calculated for all MLAER indices. RESULTS: During propofol infusion, subjects were unresponsive, and MLAER components were significantly depressed when compared with the awake states (P < 0.001). The wavelet index Db3d4 was positive for awake and negative for unresponsive subjects with a prediction probability of 0.92. CONCLUSION: These data show that automated wavelet analysis may be used to differentiate between awake and unresponsive states. The threshold value for the wavelet index allows easy recognition of awake versus unresponsive subjects. In addition, it is independent of subjective peak identification and offers the advantage of easy implementation into monitoring devices.

Abstract:

The implementation and first in vivo results of a novel coronary magnetic resonance angiography (MRA) protocol allowing simultaneous acquisition of multiple geometrically independent 3D imaging stacks are presented. Each imaging stack is acquired in a separate cardiac phase using an individual magnetization preparation and navigator-based gating and prospective motion correction. Each stack covers one of the main coronary vessels. Thus, an improvement of scan efficiency was achieved, which was used in this study to reduce total scan time at standard image quality. Experiments performed in healthy volunteers and in patients using a two-stack approach yielded a total scan time reduction of 50% with an image quality equivalent to standard single-stack coronary MRA.

Abstract:

Computer aided simulations of the heart provide knowledge for cardiologic diagnosis and therapy. A model of the myocardium is presented which allows the reconstruction of electrical and mechanical processes with inclusion of feedback mechanisms. The model combines detailed models of cellular electrophysiology and force development with models of the electrical current flow and the mechanical behavior of the myocardium. Results of simulations show the connection between the electrical excitation process and the following mechanical deformation in a three dimensional, anisotropic area of the myocardium. Keywords: Mechano-Electrical Feedback, Electro-Mechanical Feedback, Cellular Models, Electrophysiology, Excitation-Propagation

Abstract:

Knowledge of tissue distribution allows the creation of anatomical models of the human body. Anatomically based models are of increasing interest e.g. in the field of medical education, development of therapies and research on the risks of electro smog.The motivation for this work was the creation of a female 3D anatomical model with high accuracy and resolution. The purpose of this anatomical model is to simulate the human physical behavior through the numerical calculation of fields.The objectives were the segmentation of the Visible Female thorax applying digital image processing techniques and the evaluation of existing tools for segmentation and classification. This evaluation should deliver solutions to achieve better accuracy, to reduce the time on manual segmentation and to allow an adaptation of existing tools.

Abstract:

The inverse problem of electrocardiology might provide a powerful clinical investigation method for visualising the electrical activity of the heart. To use this method one requires accurate models of the human torso and heart. The objective of this work was to create an accurate model of the human ventricles including the valves from images recorded using Magnetic Resonance Imaging (MRI). This model is used as a "generic" model, and is adapted to a given individual with a host mesh fit to spatially registered Ultrasound (US) images.

Abstract:

The effect of the modelling errors on the solution of the inverseproblem of electrocardiographyis investigated. The electrocardiographicsignal is simulated using ajnite element model of human torso and realistic source patterns gained with a cellular automaton. Noise is added to simulated measurementsand the inverseproblem is solved. Modelling errors consist offalse conductivity assumptions, changed anisotropy ratio of skeletal muscles and geometric errors. The effect of modeling errors on optimal regulariza- tion parameter determination is investigated. The changes in muscle anisotropy and heart position are shown to have the highest effect on reconstructed epicardial potentials. CRESO and L-curve criteria for optimal regularization parameter estimation are compared.

Abstract:

In der Medizintechnik hat die Virtuelle Realita &#776;t in den letzten Jahren zunehmend an Bedeutung gewonnen. Gerade im Bereich Operationsplanung und in der Aus- bildung von praktizierenden A &#776;rzten und angehenden A &#776;rzten im Studium kann hier eine vielversprechende Mo &#776;glichkeit geboten werden, die Qualita &#776;t der Operationen zu steigern. Gerade die Erweiterung der Mensch-Maschine-Schnittstelle um Technolo- gien, die es ermo &#776;glichen, neben dem visuellen auch den taktilen Sinn anzusprechen, stellen eine deutliche Verbesserung fu &#776;r eine realistische Simulation dar. Gegenstand dieser Arbeit war die Entwicklung einer Benutzerschnittstelle zur intuitiven Durch- fu &#776;hrung von Simulationen im Bereich der Radiofrequenz-Ablation in der Kardiologie mit einem haptischen Interface. Die Simulationen sollen auch Laien eine rasche Ein- arbeitung in das Themengebiet ermo &#776;glichen. Meine wesentlichen Ta &#776;tigkeiten waren: Die Gestaltung der Benutzeroberfla &#776;che. Hier wurde besonderer Wert auf eine intuitive Benutzerfu &#776;hrung gelegt. Die Integration aller wa &#776;hrend der Simulation ausgefu &#776;hrten Programme. Diese werden alle direkt durch die Benutzeroberfla &#776;che ausgefu &#776;hrt und auch wieder beendet. Eine einfache Bedienung der Gesamtsimulation ist somit gewa &#776;hrlei- stet. Die Modellierung von pathologischen Erregungen des Herzens mit einem zellu- la &#776;ren Automaten. Der Benutzer kann menu &#776;gefu &#776;hrt u &#776;ber die Benutzerschnitt- stelle die gewu &#776;nschte pathologische Erregungsausbreitung aus verschiedenen Pathologien auswa &#776;hlen. Die Benutzeroberfla &#776;che fu &#776;r das eingesetzte haptische Interface wird aus der Hauptbenutzeroberfla &#776;che gestartet und auch wieder beendet. Die Simulation der Radiofrequenz-Ablation eines Herzens mit Vorhofflattern mit dem Ziel der Terminierung der pathologischen Erregungsausbreitung. Hier wurde eine kreisende Erregungen des menschlichen Herzens von mir auf dem Vorhof simuliert. Eine anschließende Radiofrequenz-Ablation brachte als Er- gebnis eine Terminierung des simulierten Vorhofflatterns und ein Wiederein- setzen des physiologischen Sinusrhythmus.

Abstract:

A generic model of the human ventricles is created from Magnetic Resonance Images (MRI) and customised to a given patients heart using Ultrasound data with a host mesh fitting procedure. The motivation for this work is to provide individual and accurate models for the solution of the inverse problem in electro- cardiology.The first objective was the creation of a surface model of the human ven- tricles. This was constrained by several factors, due to the desired application for the inverse problem. A bi-cubic Hermite basis function with quadri-lateral elements is chosen, which is an efficient shape descriptor with first and second order continuity across element boundaries. The ventricles and the valve plane is modelled with three independent surface meshes. The whole model is closed to fulfil the boundary conditions of the inverse problem.The second objective was the adaption of this surface model to a given patients heart. MRI is the most accurate, but also most expensive imaging technology. 3D Ultrasound is cheap, but some areas are barely visible, e.g. the right ventricular free wall. Thus Ultrasound alone is insufficient to develop a complete model from. The host mesh fitting procedure combines the advantages of both imaging technologies. In areas with Ultrasound data the model gets adapted to the new positions and elsewhere the generic model is used to fill in the missing features.The generic model is first embedded as a slave mesh inside the host mesh by making the nodes relative to the &#958;-coordinates of the host mesh. After a gross alignment, the Ultrasound data is projected onto the surfaces of the slave mesh yielding pairs of points for the subsequent fitting procedure of the host mesh. Finally, the slave mesh is updated to the new host mesh.An additional objective of this work was the creation of a volumetric model of the ventricular walls. This uses a tri-cubic Hermite interpolation function. The main constraint of this model in the creation is in retaining consistency in its &#958;-directions, leading to a complicated mesh topology.