Abstract: A gated amplifier drives a gradient coil when the gate signal is applied and the gate signal also controls an FET switch to disconnect a shim power supply from shim coils and connects the shim power supply instead to a dummy load. When the gate signal is removed, the shim coil is restored to operation from the shim power supply.

Abstract: In nuclear spin tomography disturbances are encountered as a result of the insertion of the gradient fields, which disturbances are due to the generation of eddy currents and lead to field distortions making themselves felt, among other things, in the rapid decay of the echo signals of spin echo pulse sequences, i.e. in disturbances of the rephasing conditions. According to the invention, the rephasing conditions required for generating spin echo impulse sequences can be established either by varying the value of the static magnetic field between the excitation pulse and the next following rf pulse of a spin echo pulse sequence, or else by adjusting the interval between the excitation pulse and the next following rf pulse to a value different from half the interval between the subsequent rf pulses.