Superconducting Probe Coils for Ultra Low-Field MRI

Two types of magnetic-resonance-imaging (MRI) machines -- specifically, the Picker/NordstarMerit machine operating with Overhauser enhancement and the pulsed-field machine under developmentat Stanford University -- will use readout field strengths less than or equal to 0.01 T. At thecorresponding low readout field strengths less than or equal to 0.01 T. At the corresponding lowreadout frequencies (less then 400 kHz), the noise voltage generated by a 20-cm normal-metal coil ismore than 18 times the tissue-generated noise. Thus, a signal-to-noise enhancement of 18 could beobtained through the use of low-noise superconducting coils. Conductus has already demonstratedsuperconducting coils for low-field MRI at 4 MHz (0.1T). Reaching the sub-MHz frequencies ofultralow-field MRI requires much larger inductances and/or capacitances in the tuned coil. In the PhaseI effort, two methods of reaching these low frequencies with high-Q coils will be examined, prototypeswill be designed, and initial measurements will be made. In Phase II, coils will be delivered to the twoinstrument developers for evaluation.