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Biomedical subjects

A van Oosterom

Publications and source records attributed to A van Oosterom.

At least 73 records · Page 4Linked to original sources
PubMed1990

The magnetocardiogram as derived from electrocardiographic data.

Magnetocardiographic signals, as present outside the thorax and generated by the depolarization process within the ventricles of the human heart, have been computed by using a model that incorporates the uniform double layer as the exclusive primary source. The volume conductor effects are treated by using an inhomogeneous, multicompartmental model of the thorax, based on "tailored" geometry derived from magnetic resonance imaging. The required activation function, specifying the timing of the ventricular depolarization process, was derived from an inverse procedure that uses as input data electric signals measured at the body surface. Next, the magnetic signals from the same subjects were measured. A close correspondence between computed and measured magnetic signals was observed (relative root mean square residual difference of 0.37). These results demonstrate that magnetocardiograms and electrocardiograms have a common basis and that it is unlikely that prominent sources exist that are electrically silent and yet active in the genesis of the magnetic fields associated with the depolarization process of the heart. Moreover, fresh support is implied for the usefulness of the classical uniform double layer as the electrical source model during ventricular depolarization. The contributions of the secondary sources have previously been found to be a major component of the electric signals; they are now also shown to be a major component of the magnetic signals.

Electrocardiography↗
PubMed1990

The role of computer modeling in electrocardiography.

This paper introduces some levels at which the computer has been incorporated in the research into the basis of electrocardiography. The emphasis lies on the modeling of the heart as an electrical current generator and of the properties of the body as a volume conductor, both playing a major role in the shaping of the electrocardiographic waveforms recorded at the body surface. It is claimed that the Forward-Problem of electrocardiography is no longer a problem. Several source models of cardiac electrical activity are considered, one of which can be directly interpreted in terms of the underlying electrophysiology (the depolarization sequence of the ventricles). The importance of using tailored rather than textbook geometry in inverse procedures is stressed.

Computer Simulation↗
PubMed1989

The effect of torso inhomogeneities on body surface potentials quantified using "tailored" geometry.

The effect of torso inhomogeneities on the electrocardiographic body surface potentials in general, and the waveform of the QRS complex in the standard leads in particular, were studied by using an inhomogeneous, numerical model of the torso including the (lower) conductivity of the lungs and the (higher) conductivity of the ventricular cavities. The relevant geometry was derived from actual data as measured from NMR scans of the subjects studied. The simulated potentials were compared to the body surface potentials recorded in the same individuals. In view of the observed high quality of the correspondence in the fully inhomogeneous case, the quantitative results of the study of the effects of the involved inhomogeneities attain a high level of credibility. To facilitate this analysis a new tool is introduced: the contribution maps.

Action Potentials↗
PubMed1989

The fetal ECG throughout the second half of gestation.

The results of a study in which multi-lead simultaneous recordings of the abdominal fetal electrocardiogram (FECG) have been made are presented. A homogeneous volume conduction model based on the actual recorded geometry was made. Using this model, fetal vectorcardiograms (FVCGS) were computed. Before 28 weeks of gestation the inter- and intra-individual variability of the observed signals could be removed by computing FVCGs in a fetal reference frame. This opens up the possibility of using the shape of the QRS complex for diagnostic purposes.

Abdomen↗
PubMed1989

The effect of changes in the conductive medium on the fetal ECG throughout gestation.

The electrical conduction of the ECG from the fetal heart to the maternal abdomen has been modelled by using volume conductor models based on the measured actual geometry. The models have been verified by means of multi-lead recordings of the fetal ECG. The results show that early in pregnancy (less than 28 weeks) the conduction can successfully be described by an electrically homogeneous model. Based on this model, a description of the fetal ECG that is independent of the position of the fetus is derived. In late pregnancies, the conduction is dominated by the isolating effect of the vernix caseosa. As the distribution of the vernix over the fetal body is unknown, the shape of the fetal ECG is disturbed in an unintelligible way. As a consequence, caution has to be applied when using the shape of the fetal ECG for diagnostic means.

Electric Conductivity↗
PubMed1989

Lead systems for the abdominal fetal electrocardiogram.

The literature on abdominal FECG has been studied for design principals of a lead system for recording FECG signals at the maternal abdomen. The indications are compared, contrasted, and combined with the results obtained from basic FECG data collected in a recent study on the modelling of the FECG.

Electrocardiography↗
PubMed1989

Source parameter estimation in inhomogeneous volume conductors of arbitrary shape.

In this paper it is demonstrated that the use of a direct matrix inverse in the solution of the forward problem in volume conduction problems greatly facilitates the application of standard, nonlinear parameter estimation procedures for finding the strength as well as the location of current sources inside an inhomogeneous volume conductor of arbitrary shape from potential measurements at the outer surface (inverse procedure). This, in turn, facilitates the inclusion of a priori constraints. Where possible, the performance of the method is compared to that of the Gabor-Nelson method. Applications are in the fields of bioelectricity (e.g., electrocardiography and electroencephalography).

Electric Conductivity↗
PubMed1989

Tailored versus realistic geometry in the inverse problem of electrocardiography.

The stability and applicability of a previously developed inverse procedure for the noninvasive determination of the activation sequence of the human heart has been evaluated. In particular, the possibility of using a standard geometrical configuration representing the heart and the inhomogeneous volume conductor in this procedure has been tested. Results show that in order to obtain reliable inverse solutions, true "tailored" geometry should be used.

Electric Conductivity↗
PubMed1989

On the numerical accuracy of the boundary element method.

The numerical accuracy of the boundary element (BE) method used to solve the volume conduction problem of nested compartments, each having a homogeneous conductivity, is studied. The following techniques for improving this accuracy are discussed: the handling of the auto solid angle element omega ii, the overall refinement of the level of discreteness, the use of a locally refined discrete grid, the isolated problem approach, and an adaptive refined computation of the discrete surface integrals involved in the BE method. The effects of these techniques on the numerical accuracy of the computed electrical potentials are illustrated by taking a volume conductor consisting of four concentric spheres representing the head since for this model an analytical (exact) solution is available. The techniques are of importance for numerically computed electroencephalograms (EEG's) since the numerically computed surface EEG's are severely affected by the relatively low conductivity of the compartment representing the skull.

Brain↗