F. B. Sachse

Development of a human body model for numerical calculation of electrical fields

Knowledge of the distribution of electrical fields in the human body is of importance for scientists, engineers and physicians. This paper shows one way to achieve this knowledge by numerical calculation based on macroscopic models of the human body. An anatomical model is created by preprocessing, segmentation and classification of the digital images within the Visible Man data set. Conductivity models are derived, which describe the distribution of electrical conductivity in the human body. A conductivity model is applied to solve an exemplary forward problem in electrophysiology, which consist of the calculation of the electrical field distribution arising from cardiac sources. The cardiac sources are obtained by a model of the excitation process within the heart. The calculation of electrical fields is carried out numerically by employing the finite difference method.

Modeling of fiber orientation in the ventricular myocardium with MR diffusion imaging

A numerical simulation of the electrical and mechanical behavior of the heart requires appropriate anatomical models. Suitable for this are models that describe the macroscopic anatomy, including information concerning the averaged local fiber direction. This work describes methods to create anatomical macroscopic models using different techniques of magnetic resonance (MR) imaging, i.e. proton density and diffusion tensor imaging, with techniques of digital image processing. An example model of canine ventricles is developed and presented using 3D visualization.

Creation of a Human Heart, Model and its Customisation using Ultrasound Images

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.

A model based approach to assignment of myocardial fibre orientation

A model based method is presented to assign the fibre orientation in the human heart. The approach uses anatomical models, which are derivable from medical tomographic images. These models describe the geometry of the atria and ventricles. The approach extends the models by applying information from morphological measurements, which examine the fibre orientation for the different anatomical structures in the dissected normal hearts. The orientation of myocardial fibres is interpolated based on restrictions, which are determined with automatic methods inside and on the surface of myocardial structures. For each structure a different rulebased method is chosen. The method is illustrated with an exemplary anatomical model, which was constructed with techniques of digital image processing based on the Visible Female data set.

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. Hence, different material laws were set up and their parameters were determined taking measurement data in literature into account. The material laws were compared from a theoretical and numerical point of view. Furthermore, the application of continuum mechanics based methods is evaluated concerning aspects of numerical solution and spatial discretisation. In further work the laws will be implemented and integrated in an existing software environment, which allows the calculation of deformations in complex geometries.

DEFORMATION OF SURFACE NETS FOR INTERACTIVE SEGMENTATION OF TOMOGRAPHIC DATA

3D tomographic data created in the every day routine of hospitals and research facilities is characterized by a high level of diagnostic Information and usually is made up of extensive volumes of data. Processing of this data is largely up to trained professionals since digital image processing by means of automatic, Computer based algorithms generally does not produce useful results. Extensive input from human experts for image preprocessing is therefore still required. A possible solution is to provide an environment in which automatic image processing will succeed. This can be achieved by a time efficient presegmentation. Our solution lies in the intuitive and interactive deformation of surface nets by human input (mouse, drag and drop). This allows to quickly create masking volumes for threshold or region growth algorithms [1] to work in or to set starting configurations for edge oriented segmenatation methods like active contours [2] [3] [4].

Comparison of regularization techniques for the reconstruction of transmembrane potentials in the heart.

Computer simulations to reconstruct the transmembrane potential distribution were performed for an anisotropic finite element model of the heart. Transmembrane potential was reconstructed in the form of 3D patches. Test patterns generated with a cellular automaton were used. Tikhonov 0-order and 2-order reconstruction techniques were compared. Tikhonov 2-order regularization was shown to deliver better solutions; this is demonstrated by the inspection of the source space of the inverse problem and by the comparison of the correlation coefficients between the reconstructed and original distributions. Time information was incorporated into the regularization.

Electro-mechanical modeling of the myocardium: coupling and feedback mechanisms

Computer-aided simulations of the heart provide knowledge for cardiological diagnosis and therapy. A model of the myocardium is presented which allows the reconstruction of electrical and mechanical processes with the 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. The results of simulations show the connection between the electrical excitation process and the following mechanical deformation in a 3D anisotropic area of the myocardium.

Entwicklung eines 4-Kamera-Systems zur Lokalisation einer Elektrodenanordnung auf dem Thorax.

Die Multikanal-EKG-Ableitung und auch die Impedanztomographie erfordern das Anlegen von Elektroden am menschlichen Korper. An diesen Elektroden werden Potentiale gemessen und Strome eingespeist. Die resultierenden Informationen spielen eine wichtige Rolle in der medizinischen Diagnostik. Die vorliegende Arbeit behandelt die Lokalisation von den bei diesen Verfahren benotigten Elektroden ausgehend von Stereofarbaufnahmen. Die Lokalisation unterteilt sich in die Kamerakalibrierung mit einem hierfur konstruierten dreidimensionalen Referenzobjekt und die Bestimmung der dreidimensionalen Elektrodenpositionen. Die Farbaufnahmen werden von vier unterschiedlich positionierten CCDKameras erzeugt. Im Unterschied zu bereits bekannten Entwicklungen [1] bietet das System die Moglichkeit, sowohl frontale als auch dorsale Elektroden in einem einheitlichen Koordinatensystem zu lokalisieren.

Modeling of force development in the human heart with a cellular automaton parameterized by numerical simulations

Models of the human heart are introduced which describe the anatomy, electrical excitation propagation and force development. The anatomical models were constructed with methods of digital image processing based on photographic images delivered by the Visible Human Project, National Library of Medicine, USA. Cardiac excitation propagation, cellular electrophysiology and force development are modeled with a cellular automaton. A parameterization of the cellular automaton is performed by mathematical models at the cellular level based on differential equations. Appropriate models of electrophysiology, force development and excitation propagation are chosen subject to the tissue types. The models are applied to simulate electrical and mechanical processes in the heart.