A simple method of measuring gradient induced eddy currents to set compensation networks

We describe a technique for measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time-dependent magnetic field gradients. The EC measuring technique uses a sample with short T1, T2 and many rf excitation pulses and free induction decays (FIDs) to measure the out-of-phase component of the FIDs, which are proportional to gamma delta B, the amount by which the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and useful for setting preemphasis compensation networks.