A 4.2 K receiver coil and SQUID amplifier used to improve the SNR of low-field magnetic resonance images of the human arm

We describe the design and use of a 48 mm diameter, liquid-helium-cooled MRI receiver coil and DC SQUID pre-amplifier. Comparison of images of a non-conducting room temperature test object collected with the SQUID-based system and those collected with an equivalent-area room-temperature surface coil show that the SQUID system SNR is approximately a factor of four greater, despite a 15 mm vacuum gap between sample and coil in the SQUID case. SQUID images of the lower arm also display improved SNRs over those of the room-temperature coil, this time by a factor of between two and three, and as a result reveal greater anatomical detail. We show that the performance is currently limited by inductively coupled losses from metal components in the imager, but that, by using the same system in a whole-body imager, the SNR of SQUID images of the arm will exceed the room-temperature coil's performance by a factor of between 2.8 and 4.5. We believe that these are the first magnetic resonance images of a living sample to have been produced with a SQUID-based receiver.