ANALYSIS OF THE EDDY-CURRENT INDUCED ARTIFACTS AND THE TEMPORAL COMPENSATION IN NUCLEAR-MAGNETIC-RESONANCE IMAGING

Effects of eddy currents in nuclear magnetic resonance imaging (NMR) are investigated from the solution of Maxwell's equations. The point spread functions affected by the eddy currents appear broader and shifted, resulting in resolution degradation as well as misregisteration. The intensity and phase variations caused by the eddy currents can also generate problems associated with intensity and phase-sensitive imaging techniques. In this paper, reduction of eddy currents by a temporal compensation of the input current waveform to the gradient coil is studied with analytic solution. The limitation of the temporal compensation due to the spatially variant eddy currents is also investigated for both whole body diagnostic imaging system and small bore NMR microscopy system. Within a limited imaging volume of less than 60% of the gradient coil diameter, it appeared that most of eddy current problems can be solved by the temporal compensation technique.