Patent ID: 7394255

Claim:
Magnetic resonance apparatus comprising a magnet having a plurality of pairs of air-cored coils arranged in respective substantially parallel planes, the air-cored coils in each pair being adapted to be operated in a counter-running manner when in use so as to generate a region of magnetic field spaced apart from said planes, having sufficient uniformity to enable magnetic resonance signals to be obtained from a target within the region and having a magnetic field direction Z lying substantially parallel to said planes, wherein each of the air-cored coils is elongate in a direction X substantially parallel to said planes, and wherein two pairs of said air-cored coils have a relatively short elongation in the direction X and two pairs of said air-cored counter-running coils have a relatively long elongation in the direction X, the current being arranged to flow in one sense in one of the pairs of each length, and in the opposite sense in the other of the pairs of each length so as to substantially cancel the second and fourth derivatives of the magnetic field with respect to the direction X at the centre of the said region.