Ultra-low field SQUID magnetic resonance for biomedical research

We are developing a SQUID (Superconducting QUantum Interference Device)-magnetometer system operating at 4K, for electron paramagnetic resonance (EPR) detection from room temperature samples in magnetic fields of the order of a Gauss. The magnetometer consists of a home-built, a second order gradiometer pick-up coil inductively coupled to the input of a commercially available two-stage dc SQUID amplifier with high bandwidth suitable for EPR, as well as NMR detection at wide range of frequencies up to a few MHz. Preliminary tests were done on samples of Pt powder at 4K and NMR signals have been detected in fields of few tens of gauss, with a minimum system sensitivity for spin concentration of $\sim $10$^{\mathrm{17}}$. We are currently developing an optimal SQUID gradiometer and a low temperature dewar for the EPR measurements. We plan to operate at low EPR excitation frequencies of a few MHz with the advantages of negligible sample heating and high penetration depth in biological systems. We discuss the prospects for \textit{in vivo} biomedical EPR imaging.