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Biomedical subjects

B Vanrumste

Publications and source records attributed to B Vanrumste.

7 recordsLinked to original sources
PubMed2000

Dipole location errors in electroencephalogram source analysis due to volume conductor model errors.

An examination is made of dipole location errors in electroencephalogram (EEG) source analysis, due to not incorporating the ventricular system (VS), omitting a hole in the skull and underestimating skull conductivity. The simulations are performed for a large number of test dipoles in 3D using the finite difference method. The maximum dipole location error encountered, utilising 27 and 53 electrodes is 7.6 mm and 6.1 mm, respectively when omitting the VS, 5.6 mm and 5.2 mm, respectively when neglecting the hole in the skull, and 33.4 mm and 28.0 mm, respectively when underestimating skull conductivity. The largest location errors due to neglecting the VS can be found in the vicinity of the VS. The largest location errors due to omitting a hole can be found in the vicinity of the hole. At these positions the fitted dipoles are found close to the hole. When skull conductivity is underestimated, the dipole is fitted close to the skull-brain border in a radial direction for all test dipoles. It was found that the location errors due to underestimating skull conductivity are typically higher than those found due to neglecting the VS or neglecting a hole in the skull.

Electric Conductivity↗
PubMed2000

Influence of measurement noise and electrode mislocalisation on EEG dipole-source localisation.

Measurement noise in the electro-encephalogram (EEG) and inaccurate information about the locations of the EEG electrodes on the head induce localisation errors in the results of EEG dipole source analysis. These errors are studied by performing dipole source localisation for simulated electrode potentials in a spherical head model, for a range of different dipole locations and for two different numbers (27 and 148) of electrodes. Dipole source localisation is performed by iteratively minimising the residual energy (RE), using the simplex algorithm. The ratio of the dipole localisation error (cm) to the noise level (%) of Gaussian measurement noise amounts to 0.15 cm/% and 0.047 cm/% for the 27 and 148 electrode configurations, respectively, for a radial dipole with 40% eccentricity The localisation error due to noise can be reduced by taking into account multiple time instants of the measured potentials. In the case of random displacements of the EEG electrodes, the ratio of dipole localisation errors to electrode location errors amounts to 0.78 cm-1 cm and 0.27 cm-1 cm for the 27 and 148 electrode configurations, respectively. It is concluded that it is important to reduce the measurement noise, and particularly the electrode mislocalisation, as the influence of the latter is not reduced by taking into account multiple time instants.

Electricity↗
PubMed2000

Automatic localization of EEG electrode markers within 3D MR data.

The electrical activity of the brain can be monitored using ElectroEncephaloGraphy (EEG). From the positions of the EEG electrodes, it is possible to localize focal brain activity. Thereby, the accuracy of the localization strongly depends on the accuracy with which the positions of the electrodes can be determined. In this work, we present an automatic, simple, and accurate scheme that detects EEG electrode markers from 3D MR data of the human head.

Electrodes↗
PubMed2000

EEG dipole source localization using artificial neural networks.

Localization of focal electrical activity in the brain using dipole source analysis of the electroencephalogram (EEG), is usually performed by iteratively determining the location and orientation of the dipole source, until optimal correspondence is reached between the dipole source and the measured potential distribution on the head. In this paper, we investigate the use of feed-forward layered artificial neural networks (ANNs) to replace the iterative localization procedure, in order to decrease the calculation time. The localization accuracy of the ANN approach is studied within spherical and realistic head models. Additionally, we investigate the robustness of both the iterative and the ANN approach by observing the influence on the localization error of both noise in the scalp potentials and scalp electrode mislocalizations. Finally, after choosing the ANN structure and size that provides a good trade off between low localization errors and short computation times, we compare the calculation times involved with both the iterative and ANN methods. An average localization error of about 3.5 mm is obtained for both spherical and realistic head models. Moreover, the ANN localization approach appears to be robust to noise and electrode mislocations. In comparison with the iterative localization, the ANN provides a major speed-up of dipole source localization. We conclude that an artificial neural network is a very suitable alternative for iterative dipole source localization in applications where large numbers of dipole localizations have to be performed, provided that an increase of the localization errors by a few millimetres is acceptable.

Brain↗
PubMed1999

Source localization in refractory partial epilepsy.

In this paper, 51 patients with refractory complex partial seizures (CPS) and intracranial structural abnormalities demonstrated with optimum MR (space-occupying: n = 16; atrophic: n = 32; dysplastic: n = 3) were studied. Video-EEG monitoring showed CPS in all patients. In 13 patients, additional intracranial EEG monitoring demonstrated hippocampal seizure onset in 12 and medial occipital ictal onset in 1 patient. Interictal and ictal dipole modeling using a spherical head model and realistic electrode coordinates were performed. Spatiotemporal dipole mapping of interictal epileptic discharges revealed two distinct dipole patterns. Patients with lesions located in the medial temporal lobe (n = 41) and medial occipital lobe (n = 2) uniformly presented a dipole with an elevation of more than 15 degrees relative to the axial plane. Eight out of ten patients with extratemporal lesions and 1 patient with a pure neocortical temporal lesion had a less stable dipole with an elevation less than 15 degrees relative to the axial plane. Dipole modeling of epochs of early ictal discharges revealed a striking correspondence with the interictal findings in individual patients. Ictal dipole modeling identified the ictal onset zone correctly when compared with intracranial EEG recordings from bilateral hippocampal depth electrodes in patients with medial temporal seizure onset. Mapping of dipoles on MR images of individual patients facilitated clinical interpretation of the EEG data. Interictal and ictal dipole mapping provided additional and clinically relevant information and may obviate the need for intracranial EEG studies in some surgical candidates for refractory CPS.

Adolescent↗
PubMed1999

Epilepsy surgery in Belgium, the experience in Gent.

Between January 1992 and July 1998, 320 patients were presurgically evaluated for medically refractory epilepsy at the University Hospital of Gent. All patients underwent a comprehensive presurgical evaluation, including extensive neurological history and examination, video-EEG monitoring of interictal EEG and habitual seizures, and optimum magnetic resonance (MR). In a large subgroup of these patients, a comprehensive neuropsychological examination and interictal 18FDG-PET were performed. Subsequently, a bilateral carotid angiography and intracarotid amytal procedure (Wada-test) were planned in 49 patients to establish hemispheric language dominance and bilateral memory function. After proper selection, 23 patients underwent invasive video-EEG monitoring with intracranial implantation of parenchymal and/or subdural electrodes to further document the area of seizure onset. From the initial group of 320 potential surgical candidates, 75 patients (42 males, 33 females) with mean age of 29 years (range: 2 months-55 years) and mean duration of uncontrolled seizures of 15 years (range: 2 weeks-38 years) eventually underwent a surgical procedure. Sixty of 75 patients were on high dose antiepileptic polytherapy. Optimum MR detected structural abnormalities, confined to a limited brain area, in 71 patients. These abnormalities were of space-occupying nature in 31 cases; an atrophic lesion was suspected in 39 patients; a combination of space-occupying and atrophic lesion was seen in 1 case. Structural abnormalities were most frequently located in the temporal lobe (n = 53) and the frontal lobe (n = 10). Video-EEG monitoring documented complex partial seizures in 67 patients with occasional secondary generalisation in 32. Most patients had complex partial seizures of temporal lobe as defined by clinical and EEG criteria. Two patients had only simple partial seizures. Ultimately, an area of seizure onset could be determined in all patients. Temporal lobectomy with hippocampectomy was the most commonly performed procedure (n = 42). In 13 patients, complete lesionectomies were performed for epileptogenic structural lesions in and outside the temporal lobe. In 2 patients, only partial lesionectomies were possible; in 5 patients, only biopsies in combination with partial lesionectomies could be performed. Anterior 2/3 callosotomy was performed in 4 patients and hemispherectomy was performed in 2 patients. Postsurgical seizure control, after average follow-up of 50 months (range: 12-98 months), was excellent in 49 patients who became seizure-free. In these patients, antiepileptic therapy was tapered 2 years after surgery. Patients in whom only biopsies or partial lesionectomies were performed have poor seizure control. Epilepsy surgery is a rewarding therapeutic alternative for patients with medically refractory epilepsy. Comprehensive presurgical evaluation and epilepsy surgery provide excellent neurological, neurophysiological, neuropsychological and imaging research opportunities.

Adolescent↗