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Abstract: The effects of tissue resistivities on EEG amplitudes were studied using an anatomically accurate computer model based on the finite difference method (FDM) and lead field analysis covering the whole brain area with 180 000 nodes. Five tissue types and three lead fields were considered for analysis. The changes in sensitivity distribution are directly comparable to changes in the potential distribution on the scalp. The results indicate that a 10% decrease in any tissue resistivity caused 3.0–4.1% differences in the sensitivity distributions of the selected EEG leads. The applied 10% decrease in the resistivity values covers only a fraction of the range of variation of 50% to 100% reported in the literature. The use of a 55% decreased skull resistivity value or a commonly applied three-compartment model increased the differences to 28% and 33%, respectively. In conclusion, both a realistic anatomy and accurate resistivity data are important in EEG head models.

Abstract: The paper describes the application of new semi-automatic segmentation software to the task of detection of anatomical structures and lesion an their threedimensional (3D) visualisation in 23 patients with secondary progressive multiple sclerosis (MS). The purpose is to study the correlation between magnetic resonance imaging (MRI) parameters (volumes of plaques and cerebrospinal fluid spaces) and clinical deficits (neurological deficits in the form of EDSS and RFSS scores, and neuropsychological deficits). The software operates in PC/Windows and PC/NeXTstep environments and utilises graphical user interfaces. Quantitative accuracy is measured by performing segmentation of fluid-filled syringes (relative error of 1.5%), and reproducibility is measured by intra- and inter-observer studies (3% and 7% variability, respectively). The mean volumes of MS plaques show significant correlations with the total RFSS scores (p=0.04). Relative intracranial cerebrospinal fluid (CSF) space volumes show statistically significant correlation with EDSS scores (p=0.01). The mean volume of MS plaques shows a significant correlation with the overall neuropsychological deficits (p=0.03). 3D visualisation helps to understand the relationship of lesions to the surrounding brain structures. The use of semiautomatic segmentation techniques is recommended in the clinical diagnosis of MS patients.

The aim of this study was to examine the neuronographic findings of electrical and transcranial magnetic stimulation of the facial nerve and to compare their ability to predict clinical recovery from idiopathic facial nerve palsy (Bell's palsy). Eighty-six patients were examined clinically and neurophysiologically immediately on presentation to Tampere University Hospital. Electroneuronography (ENoG) and transcranial magnetic stimulation (TMS) were performed 1–6 times for each patient. The time interval between each examination varied from 2 to 7 days. Seventy-eight patients were followed for a median period of 13 months after the onset of palsy. Facial nerve function was graded according to the House-Brackmann grading system. Relative amplitude differences of ENoG and TMS during the acute phase were then correlated with clinical outcome. Statistical analysis of the results showed that a TMS response elicitable during the first 5 days of the palsy was correlatable with a good prognosis. ENoG results correlated with clinical outcome at a later time from onset of symptoms. TMS was well tolerated and no adverse effects were seen. These results indicate that TMS is a useful method for the early prediction of outcome in patients with Bell's palsy.

Abstract: Segmentation software is described, developed for medical image processing and run on Windows. The software applies basic image processing techniques through a graphical user interface. For particular applications, such as brain lesion segmentation, the software enables the combination of different segmentation techniques to improve its efficiency. The program is applied for magnetic resonance imaging, computed tomography and optical images of cryosections. The software can be utilised in numerous applications, including pre-processing for three-dimensional presentations, volumetric analysis and construction of volume conductor models.

Magnetic stimulation provides a method to stimulate the facial nerve transcranially. With this method, the stimulation can be directed to the intracranial part of the facial nerve, whereas conventional electric stimuli are delivered to a more peripheral part of the nerve. In 40 healthy subjects, ipsilateral responses with latencies of 4.5 ± 0.4 ms were recorded on the nasolabial folds. The latencies were 1.1 ms longer than those elicited at the stylomastoid foramen by electric stimulation. Furthermore, a response with a mean latency of 12 ms (range 10-16 ms) appeared in 6 out of 10 healthy subjects and a polyphasic response with a mean latency of 32 ms in 9 out of 10 of these subjects. Transcranial magnetic stimulation seems to allow the examination of motor conduction through the proximal part of the facial nerve. In addition, the method may give further information concerning the facial activation mechanisms possibly by other central pathways.

A computer model has been designed for the calculation of the electrical fields in the head, based on the finite difference method. This method has not previous& been applied for head modelling. The model was validated by using three concentric spheres and comparing it with an analytic model. Three levels of accuracy were tested. The forward solutions show that the finite difference algorithm work correct& and, by selecting the size of the volume elements properly, accurate results are obtained. The model will be applied to accurate and realistic geometries of the human head obtained from magnetic resonance images.