RF FRONT-END FOR A 4.1-TESLA CLINICAL NMR SPECTROMETER

With increased signal-to-noise, spatial, temporal, and spectral resolu tion, blood oxygenation level contrast, and other benefits of high fie ld NMR, 4T NMR systems enhance the potential for using multinuclear im aging and spectroscopy for medical science and clinical diagnostics. A new NMR spectrometer is needed however. The magnet aside, the key dif ference between present clinical or animal systems, and 4T+ clinical s ystems is the RF front end. Including the power amplifier, transmit/re ceive (T/R) switch, preamplifier, and RF coils, the front end is requi red to operate at power levels, bandwidths, and circuit lengths unique in the NMR field. New technology has been developed for these compone nts to optimize the performance of the spectrometer. To cover broader spectral bandwidths, and to compensate for chemical shift dispersion e rror, two 15kW solid stare amplifiers have been developed for implemen tation on a ''home-built'' 4.1T clinical system. A stripline transform ed, nonmagnetic, tuned GaAsFET preamp has been built for achieving hig h gain and low noise at the RF coil. A nonmagnetic dual quadrature hyb rid-PIN diode T/R switch was developed to isolate the RF power amplifi er from the receiver. New high frequency coils have made use of tuned cavities and transmission lines.