A programmable pre‐emphasis system

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Abstract
MRI systems often use magnetic field gradient and shim pulse‐shaping networks (pre‐emphasis) to correct for magnetic field distortions caused by eddy currents. A pre‐emphasis system that uses up to 16 fixed resistor‐capacitor (RC) time constants per channel with programmable amplitude coefficients is described. The magnetic fields induced by the pre‐emphasis RC time constants serve as a set of basis functions for compensating eddy‐current fields induced by the gradient set. The resultant time‐varying magnetic field gradient accurately reflects the gradient specified by the pulse programmer. Reductions in eddy‐current fields are demonstrated for actively shielded and unshielded gradient sets.