INFLUENCE OF DETECTOR GEOMETRY ON MEG AND MCG MEASUREMENTS

During the last few years, multichannel systems have significantly improved the diagnostic quality of biomagnetic measurements. However, the shape of the sensor array and the number of channels necessary are the subjects of ongoing discussion. Using simulation experiments we demonstrate that the spacing of the sensor coils depends on the highest spatial frequency in the magnetic field distribution and consequently on the type and position of the sources to be measured. Then the number of channels is determined by the total measurement area required to cover the object under investigation. Because of the strong dependence of the biomagnetic field on the distance from the source, an array with a shape matched to the surface of the object is generally required. However, this criterion would result in different array curvatures for brain and heart investigations. Our simulations confirm that slight deviations from the ideal shape lead to a reduction of localization accuracy, but even when restricting a biomagnetic investigation to the brain, different curvatures am present and thus an array matched to all measurement conditions cannot be realized. The use of a curvature smaller than the ideal value generally gives a localization accuracy worse than obtained with a flat arrangement. We conclude that a flat detector array is suitable for both MEG and MCG measurements.