Effects of sensor calibration, balancing and parametrization on the signal space separation method

Signal space separation (SSS) is a novel method for processing multichannel biomagnetic data. It is useful for a variety of applications including interference suppression, movement compensation and conversion of measurements between sensor arrays. The performance of SSS has been examined mainly on a 306-channel whole-head magnetoencephalography system. To facilitate the adaptation of the method to other biomagnetometer systems, the effect of various properties of the sensor array on its performance needs to be studied. To this end, we examined the effects of gradiometer imbalance, sensor calibration errors and erroneous sensor geometry information on SSS using simulations. The results indicate that depending on the application, gradiometer balance on the level of 0.1% to 0.5% may be needed for satisfactory SSS performance. For wire-wound gradiometers, this requires very careful attention in manufacturing. Errors in calibration coefficients and geometry information were found to have less significance.