New approach to epilepsy - magnetic fields guide surgery
Electrical signals from nerves in the brain cause weak magnetic fields which can be measured by means of magnetoencephalography (MEG). A project supported by the Austrian Science Fund (FWF) has investigated the extent to which direct measurement of neural electrical activity can be coupled with MEG to diagnose and treat epilepsy. The findings are important in view of today's spiralling health care costs, as the apparatus used to detect magnetic fields in the brain is 30 times as expensive as that used to measure electrical signals directly.
About three percent of all Europeans develop epilepsy in the course of their lifetimes. In Austria 64,000 people are currently suffering from the disease. The illness is typically caused by unusual activity in the nerve cells in certain regions of the brain. This can be measured by electroencephalography (EEG) - a technique that has been around for over 70 years - or MEG which is a much more recent development. Professor Christoph Baumgartner of the Neurological University Clinic at Vienna General Hospital has looked into the effect of combining both methods on the accuracy with which the affected parts of the brain can be localised. The results of the research, which was supported by the FWF, indicate that the new approach is better than either EEG or MEG alone at localising the hyperactive regions of the brain. It also has the advantage that the risky "invasive" methods - introducing electrodes into the brain - do not have to be used as often.
In epilepsy cases that do not adequately respond to medication the only option is surgery, and for this the affected areas of the brain must first be localised. As Baumgartner puts it: "Although highly effective drugs are now available, about 20 percent of all patients do not respond to them. Surgery is an effective alternative for most sufferers. This involves removing the irregular parts of the brain. But to ensure that seizure freedom achieved in this way does not come at the cost of neurological deficits, the affected area must be precisely localised before the operation."
Surface EEG - a non-invasive method - is one of the mapping techniques that can be used for this purpose. However, the accuracy of the measurements is limited by the fact that the scalp and the skull act as insulators. A non-involved reference is also needed to interpret the electrical signals. However, this is often subject to other distorting factors, making it difficult to pinpoint the hyperactive regions of the brain.
Implantation or combined measurement
Because of this, it is currently necessary to implant electrodes in the brain to obtain the necessary spatial resolution, and hence reliable results. However, according to Baumgartner: "Instead of this procedure, which is extremely unpleasant for the patient and involves a risky operation, MEG can be used in tandem with EEG. Both methods are based on the same physiological process - changes in the potentials of nerve fibre ends - but they measure different effects and can thus complement each other."
As part of the FWF project, the research team developed a biophysical model that enables the measurement results to be related to spatial data generated by magnetic resonance tomography, thus achieving the necessary precision. As to the financial side of this improved form of care, Baumgartner noted: "At present an MEG costs EUR 1.5 million, whereas a modern EEG can be had for as little as EUR 30,000. So for cost reasons, too, it is important to know where MEG scores, and use it only when it is really necessary." FWF President Professor Georg Wick commented: "One of the functions of basic research - and hence of the FWF, too - is investigating the potential applications of innovative ideas and technologies. In a high-tech society like ours, this plays a particularly important economic role."
Prof. Christoph Baumgartner
Neurological University Clinic
Vienna General Hospital
Währinger Gürtel 18-20
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Vienna, October 6, 2003