Biomagnetic systems for clinical use

Abstract We present two multichannel systems based on a superconducting quantum interference device (SQUID) for biomagnetic measurements, installed at the University of Chieti. Both systems have been designed for clinical and routine use and have been developed owing to an international cooperation. The main issues in the instrument implementation were field sensitivity and spatial resolution, as well as flexibility and stability during operation. The first system is a planar system and is devised for magnetocardiographic measurements. This system is composed of 74 dc SQUID integrated magnetometers contained in a low-noise dewar: 55 sensors are measurement channels and 21 are placed far from the subject and are used as reference channels to create software gradiometers. The second system is a helmet system and consists of 165 dc SQUID integrated magnetometers to perform magnetoencephalographic recordings; 153 channels are distributed over a surface covering the whole scalp and 12 channels are used as references. The field noise of the SQUID magnetometers is about 5fTHz−1/2. Each system is placed in a magnetically shielded room for eddy current shielding and magnetic shielding. The magnetic field is recorded with sampling frequencies up to 10 kHz. The analogue-to-digital converted data are processed on line by means of an array of digital signal processors, allowing bandpass filtering, decimation and noise compensation.