NOVEL HIGH-FREQUENCY RESONATOR FOR NMR IMAGING AND SPECTROSCOPY

A new type of RF coil for NMR imaging and spectroscopy is described. The resonator is simple to assemble and is particularly suited to high RF frequencies. The principle of the design is based on the standing wave present in an RF-driven transmission line with an open (or shorted) end. The RF field is produced by the inner conductors of such lines, preferably at 1 4λ from the open end. At this position the outer conductors are enlarged and coincide to serve as a Faraday shield, enclosing the inner conductors which are positioned on a sleeve around the measurement region. The generated RF field shows good homogeneity. The coil is very efficient, has minimum electric coupling, and is capable of handling high RF powers. By adjusting the total length of the transmission lines it is possible to manipulate for any given frequency the capacitance of, and consequently the maximum voltage over, the tuning capacitor in the resonant situation. The characteristics for a 270 MHz coil with inner diameter of 7 cm are given, and experimental in vivo NMR results using this probe in a horizontal-bore 6.3 T animal system are presented. © 1990.