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-cool ed MRI receiver coil and DC SQUID pre-amplifier. Comparison of images of a non-conducting room temperature test object collected with the SQ UID-based system and those collected with an equivalent-area room-temp erature 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 im proved SNRs over those of the room-temperature coil, this time by a fa ctor of between two and three, and as a result reveal greater anatomic al detail. We show that the performance is currently limited by induct ively 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 f actor of between 2.8 and 4.5. We believe that these are the first magn etic resonance images of a living sample to have been produced with a SQUID-based receiver.