A 'Hi-Fi' Cartesian feedback spectrometer for precise quantitation and superior performance.
The use of Cartesian electronic feedback for effecting a major improvement in the functioning of magnetic resonance instrumentation is reported. The dependences of both flip angle and signal strength upon probe loading, matching, and tuning are virtually eliminated. Thus, for a chosen probe, sample geometry and flip angle, the free induction decay signal strength is rendered solely dependent upon the number of nuclei. The instrument therefore becomes capable of absolute calibration. In addition, phase and amplitude distortion of selective pulses, introduced by crossed diodes, power amplifier heating, etc., is virtually eliminated, as are radiation damping and phase modulation caused by probe vibration. The use of multiple probes at the same frequency, for example quadrature probes and phased arrays, is also simplified as the effects of interactions between such probes are typically reduced by two orders of magnitude.