Superconducting single and phased-array probes for clinical and research MRI

Significant improvement of the signal-to-noise ratio (SNR) for magnetic resonance imaging (MRI) applications, in which the thermal noise of the rf receiver probe dominates the system noise can be achieved by cooling down a normal metal probe or by using superconductors. In this work, the SNR enhancement expected from using superconductors for single coil and/or phased array designs are calculated, discussed and compared with some experimental results. We also report on the design and fabrication of a 63.8 MHz probe (1.5 Tesla) consisting of patterned, copper or YBCO films deposited on both sides on a 5 cm LaAlO₃ substrate. The unloaded Q of the normal metal probe at room temperature and at 77 K was about 400 and 1000, respectively, while the YBCO probe exhibited a Q of 40 000 at 77 K. Five-cm diameter probes cooled to 77 K were superior to their identically designed room temperature equivalents, and provided SNR gains at 1.5 Tesla of 3 and 2 times for YBCO and cooled normal metal, respectively. The application of superconducting coils in conjunction with recently developed techniques for significant reduction of MRI acquisition times by using parallel processing with phased array probes is discussed.