Synopsis

Magnetic resonance imaging relies on the use of magnetic field gradients – that is a magnetic field, B (r) which varies linearly withposition, r, such that B (r) = G.r – to spatially encode the NMR signal. Such gradients are generated by passing currents throughspecially arranged coils of wire, placed on a former that surrounds the imaging subject. Three separate coils are needed in order toproduce a linear variation of the z-component of the magnetic field along each of the three Cartesian directions (x, y and z). Theperformance of the gradient coils and the amplifiers that are used to drive them dictates the kind of gradient waveforms that can beused in an MR scanner, particularly controlling the maximum gradient strength and rate of change of gradient with time that can be employed. Since the use of strong and rapidly switched gradients generally improves image quality and the speed of imagea cquisition, considerable benefits can result from optimising gradient coil performance.