Concomitant magnetic field gradients and their effects on imaging at low magnetic field strengths.

Low-field NMR imaging systems which use large amplitude field gradient pulses (e.g., in flow velocity encoding) may be subject to the undesirable effects of concomitant gradients. We demonstrate the effects of these extra gradients, which arise from Maxwell's equations, and show that the resultant image phase shifts and amplitude changes are consistent with theory.