Ultra-low field Magnetic Resonance Imaging using high-Tc SQUIDs

A measurement system for ultra-low field Magnetic Resonance Imaging (ulf-MRI) has been built and programmed and a few proof-of- principle 2D images of water phantoms have been acquired at 89.3 μT measurement field. The smallest detectable volume of water has been de- termined to be 0.3 cm3. A single-shot NMR spectrum of a water sample has been detected and the signal-to-noise ratio of the resonant peak has been determined to be 60 with a linewidth of 0.9 Hz at 3.8 kHz. A few dif- ferent pulsing sequences have been tried and the most promising has been determined to be a prepolarization pulse that is turned off non-adiabatically. Some obstacles towards building a full-fledged ulf-MRI measurement sys- tem have been identified and partially addressed, such as the external mag- netic fluctuations of around 200 nT and that an unshielded SQUID detector has problems performing reliably after the prepolarization pulse