PubMed Health⌕ Search

Biomedical subjects

A van Oosterom

Publications and source records attributed to A van Oosterom.

At least 19 recordsLinked to original sources
PubMed1998

Lead system transformation of body surface map data.

Multicenter application of body surface map data (multilead electrocardiographic [ECG] data) is hampered by the fact that the centers involved in body surface mapping use lead systems differing in lead placement as well as in the number of leads. In this study, the performance of two methods for converting multilead ECGs from one lead system to another is evaluated in their application to the major lead systems presently in use throughout the world. The first method is based on Laplacian interpolation, and the second method is derived from the correlations between the signals in an extensive lead system. Through analyzing the representation errors, it was found that, for lead systems incorporating over 60 leads, both methods work well, yielding errors comparable to interbeat differences in individuals. For lead systems incorporating fewer leads, the correlation method is to be preferred.

Adult↗
PubMed1997

Botryomycosis mimicking a liposarcoma.

Botryomycosis is an atypical reaction of the host to a common bacterial infection. A case of botryomycosis mimicking a liposarcoma as suspected on clinical and radiological grounds is described. The diagnosis was made by biopsy and culture of the lesion. A review of the literature is given.

Abdomen↗
PubMed1996

The surface Laplacian of the potential: theory and application.

The use of the surface Laplacian of the potential (Ls) in bioelectricity is discussed. Different estimates of Ls, in particular the field measured by coaxial electrodes, are compared to that of the true Laplacian. A method to compute Ls on the surface of an inhomogeneous volume conductor of arbitrary shape resulting from assumed electrical sources in introduced. In two applications the sensitivity of the body surface Laplacian is carried to that of body surface potentials. This comparison is carried out for dipolar sources within the human brain as well as for distributed sources within the heart.

Body Surface Potential Mapping↗
PubMed1995

Lead system transformation for pooling of body surface map data: a surface Laplacian approach.

In this paper, a method is described to transform Body Surface Map (BSM) data from one lead system to that of another. This enables pooling of BSM data between different centres. The transformation tool is based upon Laplacian interpolation. It is evaluated by inspecting transformations from lead systems having few leads to one having many leads.

Body Surface Potential Mapping↗
PubMed1994

Application of the boundary element method to the solution of anisotropic electromagnetic problems.

The paper discusses the application of the boundary element method to the computation of the electric potential and magnetic field generated by bioelectric sources in an anisotropic inhomogeneous volume conductor, using a proper coordinate transformation. It is shown that the co-ordinate transformation generally not only affects the conductivity and geometry of the volume conductor under consideration, but also the current source term and the continuity relation on the interfaces bounding regions of different conductivity. To illustrate these results, the electric potentials in an anisotropic finite length cylinder and in an anisotropic volume conductor of irregular (torso) shape, computed by the boundary element method, are compared with the results obtained by the analytical solution and the finite element method, respectively.

Anisotropy↗
PubMed1994

Docetaxel (Taxotere) in advanced renal cell cancer. A phase II trial of the EORTC Early Clinical Trials Group.

Docetaxel (Taxotere), an analogue of paclitaxel, was tested in a phase II study in advanced renal cell carcinoma. Consenting patients with measurable lesions, adequate organ functions and no prior chemotherapy received 100 mg/m2 of docetaxel as a 1-h infusion every 3 weeks. No premedication to avoid hypersensitivity reactions or nausea and emesis was given. 32 eligible patients received 100 treatment cycles. Short-lasting neutropenia was the dose-limiting toxicity. Acute hypersensitivity reactions (HSR), oedema and skin changes were other important side-effects. HSRs regressed spontaneously or were treated with antihistamines with or without corticosteroids. One partial remission was documented. At the dose and schedule used, docetaxel has only low activity against renal cell carcinoma.

Adult↗
PubMed1993

The number of signals in multilead ECGs in individuals.

The number of independent signals in multilead electrocardiograms (ECGs) (body surface maps) of individuals have been determined by using two different methods. Both methods are based on an analysis of the eigenvalues of the spatial covariance matrix corresponding to the individual multilead ECG. One method takes only the noise level into account (threshold method). The other method is based on an information theoretic criterion (minimum description length) and uses explicitly the statistical properties of the noise (noise covariance). The analysis was performed on the QRS complexes and ST-T complexes of the multilead ECG of 61 subjects. The noise was estimated from three isoelectric intervals (PQ interval). For the different subjects, 0-14 signals (with a mean of 7 signals) were detected in the QRS interval and 0-9 signals (with a mean of 3 signals) were detected in the ST-T interval.

Electrocardiography↗
PubMed1993

Coping with toxicities of docetaxel (Taxotere).

BACKGROUND: In phase II studies of the EORTC-ECTG, acute hypersensitivity reaction, edema and skin toxicity were important side effects of docetaxel (TaxotereTM). PATIENTS AND METHODS: Fifty patients with solid tumors were treated with docetaxel at the University Hospital of Antwerp. Of these, 28% developed an acute hypersensitivity reaction and 20% edema. Twelve and three hours before the next docetaxel administrations those with the acute hypersensitivity reaction were subsequently pretreated orally with 32 mg of methylprednisolone, 10 mg of cetirizine and 1 mg of ketotifen. CONCLUSIONS: The acute hypersensitivity reaction could be completely blocked in all but in 1 of 14 patients, and this pretreatment schedule had an important prophylactic effect on edema formation. Skin toxicity was successfully treated with an ointment of glycerin and chlorhexidine.

Antineoplastic Agents, Phytogenic↗
PubMed1992

Heart position and orientation in forward and inverse electrocardiography.

A study has been made of the influence of the position and orientation of the heart within the thorax on computed ECG waveforms (forward model) and on computed activation sequences (inverse model) in three normal cases. Results show that differences in heart position and orientation, associated with shifts relative to the precordium of the order of 0.5 cm, may result in amplitude differences or QRS waveforms of typically tenths or millivolts, which constitute part of the observed interindividual variability of the ECG. The inverse study shows that, in spite of similar errors in estimated heart position and orientation, stable solutions of the ventricular activation sequence can still be found. However, in the case where the heart is very close to precordial leads, the stability of the inverse solution is found to be intrinsically poor.

Electrocardiography↗
PubMed1992

Implicit and explicit constraints in inverse electrocardiography.

This paper reviews the major distributed source models that have been postulated over the years to support the interpretation of observed body surface potentials: double-layer models, the source description in terms of epicardial (ie, pericardial) potentials, and its equivalent: the distributed monolayer. This includes a presentation and discussion of a source model that has been developed over the past decade: the uniform double-layer model. The properties of this model are contrasted to those of other distributed source models from the perspective of their inherent capacity for imposing the constraints that are essential for regularizing the involved inverse problem.

Electrocardiography↗
PubMed1992

Electrical impedance tomography. Solving anisotropic mixed boundary value problems by means of the boundary element method.

In a previous study we have shown that an anisotropic volume conduction problem involving the Neumann condition at the outer surface of a volume conductor can be solved by means of the boundary element method by applying an appropriate coordinate transformation (Zhou and van Oosterom 1991). In this paper we will show that this approach can also be applied to solve the anisotropic mixed boundary value condition problems studied in electrical impedance tomography (EIT). Results are presented of numerical computations, which were carried out for a volume conductor of irregular (torso) shape.

Electric Conductivity↗
PubMed1992

Application of electrical impedance tomography to the determination of lung volume.

Trans-thoracical electrical impedance measurements on a human subject have been performed using the Sheffield equipment. These measured transfer impedances are compared with computed ones, based on an inhomogeneous, torso-shaped volume conductor, for different values of the overall electrical conductivities sigma l and sigma r of left and right lung. Each measured set of impedances is compared with all calculated sets. The remaining (minimum) residual difference epsilon is used as a measure of the goodness of fit, and the values of sigma l and sigma r for which epsilon is minimal are taken as representing the overall conductivities of the lungs. For data measured at various stages within the respiratory cycle, sigma l and sigma r have been determined. The results are found to relate well to physiology: for a measurement taken at maximum expiration sigma l and sigma r indicate almost homogeneity, whereas for end inspiratory level sigma l and sigma r tend towards values of 0.2, which is a realistic value for the relative conductivity of lung tissue.

Electric Conductivity↗
PubMed1992

Computation of the potential distribution in a four-layer anisotropic concentric spherical volume conductor.

A method for solving the potential distribution in a multilayer anisotropic concentric spherical volume conductor, which has recently been described in the literature, has been tested and found to be numerically unstable. In this paper it is demonstrated how these numerical difficulties can be avoided. Moreover, the method is extended by lifting the previously imposed restriction on the innermost region to be isotropic. A convergence criterion for determining the required number of terms in the final series expansion is proposed. The influences of radial and tangential conductivity values of the skull and brain tissue on the dipole-induced potential are investigated.

Algorithms↗
PubMed1992

Experience with ifosfamide in the EORTC Soft Tissue and Bone Sarcoma Group.

The Soft Tissue and Bone Sarcoma Group of the European Organization on Research and Treatment of Cancer has conducted a number of studies of chemotherapy in advanced disease over the past 15 years. Following the discovery that the CYVADIC regimen (cyclophosphamide/vincristine/doxorubicin/dimethyl imidazole carboxamide) was less active than had been reported originally, the individual components of CYVADIC were studied. This showed that doxorubicin had considerable activity and that ifosfamide 5 g/m2 given over 24 hours was at least as active as cyclophosphamide. Subsequent studies have therefore centered on a combination of doxorubicin and ifosfamide. A large randomized trial showed no significant benefit of doxorubicin/ifosfamide over single-agent doxorubicin, but the doses of doxorubicin were different. More recently, using bone marrow growth factors, it has been possible to increase the doxorubicin dose to that given as a single agent and also maintain the ifosfamide dose. This is now being tested in a randomized trial to determine whether improved response rates and other indicators of outcome will be seen.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1992

On the detection of the number of signals in multi-lead ECGs.

New methods which have been developed in the field of signal processing to detect the number of intrinsic source signals in a set of multiple signals have been studied in their application to the analysis of multilead ECGs (body surface maps). All these methods are based on the analysis of the eigenvalues of the covariance matrix related to the observed data. By using artificial multilead ECGs in which the properties of the signal and noise parts were known, the effect of taking into account these properties was investigated. It was found that the method based on information-theoretic criteria was superior in detecting the number of signal components, in the case that the noise in the data is non-white, as compared to a simple threshold method.

Data Interpretation, Statistical↗