Apparatus (10) for use in MRIS includes a coil arrangement having drive coils (20), shield coils (30) and a power supply unit (PSU) (40). The drive coils (20) and the shield coils (30) are connected in series to the PSU (40) to form a circuit. The shield coils (30) are connected between a first and second length of the drive coils (20) so as to straddle a virtual earth of the circuit. This is advantageous in minimising potential differences within the shield coil (30) assembly and thereby in minimising partial discharge therewithin. Partial discharge between adjacent parts of the drive coils (20) is minimised by spatially arranging those coils (20) such that parts thereof that are at a high electrical potential are spatially adjacent parts thereof that are simultaneously at a potential of the same polarity of at a low electrical potential of either polarity.