Biomagnetic systems for clinical use

We present two multichannel systems based on a superconducting quantum inte rference device (SQUID) for biomagnetic measurements, installed at the Univ ersity 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 fir st system is a planar system and is devised for magnetocardiographic measur ements. This system is composed of 74 de SQUID integrated magnetometers con tained 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 s oftware gradiometers. The second system is a helmet system and consists of 165 de SQUID integrated magnetometers to perform magnetoencephalographic re cordings; 153 channels are distributed over a surface covering the whole sc alp and 12 channels are used as references. The field noise of the SQUID ma gnetometers is about 5 fT Hz(-1/2). Each system is placed in a magnetically shielded room for eddy current shielding and magnetic shielding. The magne tic 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 dig ital signal processors, allowing bandpass filtering, decimation and noise c ompensation.