| The signal-to-noise ratio (SNR) is a fundamental measure of the quality of the signals obtained in Magnetic Resonance (MR) Technology. The primary focus of this dissertation is the optimization of MR coils and antennas to maximize SNR, using analytical methods and field calculations by numerical electromagnetic method of moments (MoM) as well as experimental validation.;First, a biopsy needle MR imaging (MRI) antenna to collect biopsy samples from internal organs is developed. It can perform MRI at the needle position, for device tracking and high resolution imaging.;Second, a tunable planar strip array antenna that can be tuned with a size matched to specific MRI applications is developed. Then, a single element of the tunable planar strip array is analyzed by field calculations to optimize the SNR performance with respect to its geometric and electric parameters. The findings are summarized as design rules of thumb.;Third, the SNR performances of the following quadrature surface detectors are evaluated: (i) figure'8'/butterfly shaped loops combined with circular loop elements; (ii) a novel quadrature MRI detector that we developed comprised of a strip detector and a circular; and (iii) an overlapped array of two loops. The SNR is optimized for each pair and the SNR performance compared for detectors optimized to the same depth. The SNR-optimized figure-8 detector has a loop radius r8∼0.6d, so r8/r0∼1.3 in an optimized quadrature detector. The optimized butterfly coil has side length ∼ d and cross-over angle of ≥ 150° at the center.;Finally, detector noise figures (NFs) are used to characterize the SNR limits of circular loop coils. Loops made of copper wire and copper tapes are considered in the analysis. Losses from conductors, capacitors, solder joints, eddy currents in overlapped array coils and sample losses from 40-400 MHz are estimated using analytical and numerical electromagnetic calculations and measurements. From the analysis it is found that loops made of wire and tape, perform similarly, but tape coils in arrays have substantial eddy current losses.;The analysis involving numerical, analytical and experimental methods resulted in optimal MR resonator designs that can be incorporated in the modern day MR systems. |
