A 16-channel SQUID-device for biomagnetic investigations of small objects

Biomagnetic investigations in basic physiological research using animals re quire measurement devices different from commercial biomagnetometers used i n human investigations. Two major problems have to be tackled in the design of such biomagnetometers. First, the spatial sampling needs to be much hig her. Second, the distance between pick-up coils and the sources needs to be much shorter in order to compensate the worse signal-to-noise ratio (SNR) due to the smaller pick-up coils. We designed and built a 16-channel biomagnetic measurement system meeting t hese design criteria. The pick-up coil diameter of this new biomagnetometer is 6.7 mm, thus allowing 16 channels on an area of 3.2x3.2 cm(2). The pick -up coils are located 3 mm above the dewar outer bottom, hence the closest distance to the cortical surface can be a few millimetres. We provide as an example of first measurements performed with the new bioma gnetometer investigations of epileptic spikes in adult rabbits by simultane ous magnetoencephalogram (MEG) and electrocorticogram (ECoG) recordings. Th e high SNR of the recorded MEG and the simultaneously detected electric pot entials allow investigations of the spatio-temporal pattern of neuronal pro cesses of epileptiform spikes with signal strengths of about 3.5 pT. (C) 19 99 IPEM. Published by Elsevier Science Ltd. All rights reserved.