High-Tc SQUID vs. Low-Tc SQUID-Based Recordings on a Head Phantom: Benchmarking for Magnetoencephalography

We explore the potential that high critical-temperature (high-T-c) superconducting quantum interference device (SQUID) technology has for magnetic recordings of brain activity, i.e., magnetoencephalography (MEG). To this end, we performed a series of benchmarking experiments to directly compare recordings with a commercial (low-T-c SQUID-based) 306-channel MEG system (Elekta Neuromag TRIUX, courtesy of NatMEG) and a single channel high-T-c SQUID system. The source on which we recorded is a head phantom including 32 artificial current dipoles housed inside a half-spherical shell (courtesy Elekta Oy) for calibrating MEG systems. The high-T-c SQUID magnetometer consisted of a single layer YBa2Cu3O7-x (YBCO) film on a 10 mm x 10 mm bicrystal substrate with a magnetic field sensitivity of similar to 40 fT/root Hz down to 10 Hz. We recorded serial activations of eight tangential current dipoles located at different depths from the surface of the head phantom. Results indicate that our individual high-T-c SQUID demonstrated signal-to-noise ratios (SNRs) about 7-14 times lower than that of similarly-positioned low-T-c SQUIDs in a commercial MEG system. Only considering single-channel SNR, high-T-c SQUIDs with resolution better than 18 fT/root Hz would be required to outperform the low-Tc system for shallow dipole sources. This work demonstrates a proof of principle study for future multichannel high-T-c MEG system development.