Super-Q Detection of Transient Magnetic Resonance Signals

The signal-to-noise ratio (SNR) improvements with increasing detection coil quality factor, Q, are examined for the detection of known magnetic resonance signals in noise. It is found that in the absence of amplifier noise, SNR continues to increase with increasing Q even in the super-Q limit, when the bandwidth of the tuned detection circuit is smaller than that of the signal to be detected. In the super-Q limit, the maximum obtainable SNR is thus limited by noise from the amplifiers in the system. This contrasts with typical NMR measurements where the ultimate SNR is limited by thermal noise from the detection circuit. Explicit expressions are derived and are compared to experiments performed using electronically simulated spin echo signals