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We report on the design of a planar 200MHz superconducting two-resonator array for magnetic resonance imaging (MRI) applications. The array was made out of a double-sided thin YBa2Cu3O7−x film on r-cut sapphire substrate and consists of two 24mm diameter resonators with built-in planar capacitors for coupling to the tuning and matching electronics. Required for the performance of the MRI array, rf isolation of two resonators was accomplished by built-in planar capacitors, and the mechanism of resonator-to-resonator decoupling was analyzed. The signal-to-noise gain as a result of using high-Tc superconductor resonators/arrays was calculated and compared with experimental data.

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 LaAlO 3 substrate. The unloaded of the normal metal probe at room temperature and at 77 K was about 400 and 1000, respectively, while the YBCO probe exhibited a 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.

T h e p e r f o r m a n c e o f s m a I I-v o I u m e Magnetic Resonance Imaging (M R I) d e p e n d s on t h e s y s t e m n o i s e determined by noise of a probe and/or of a preamplifier (not by the body noise). Several demonstrations confirmed that, for selected applications, high-TC superconductor MRI receiver coils have superior properties to those of comparable copper coils. W e report on the outstanding performance of modified twin horseshoe Y B C O r f surface probes in a 2 Tesla s c a n n e r operating at 77 K. They were used for MR imaging of spinal cord injuries in rats and for imaging of brain of small animals. The probes were designed with a virtual ground plane, thus reducing the coil-to-ground dielectric losses and making its resonant frequency less sensitive to the body proximity. Each coil was fabricated using large area 500 nm thick double-sided YBaZCu30, films deposited on sapphire r-cut substrates. W e c o m p a r e t h e p e r f o r m a n c e o f t h e 2 T e s l a high critical temperature superconductor (HTS) probe with that made of a copper coil. Designing and cryo-packaging of HTS MRI probes is discussed.

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