A superconducting magnet (01, 02) suitable for use in a MRI system, the magnet having a stepped diameter bore (114, 115, 116; 214, 215, 216) extending along an axis of the magnet and being capable of producing a magnetic field of at least 1.5 Tesla in an imaging region within the bore, the magnet comprising a primary coil structure having at least first (105a, 105b; 205a, 205b), second (106a, 106b; 206a, 206b) and third (107; 207) sets of coils positioned along the axis and coaxially aligned along the axis, each set having one or more primary coils arranged around the bore and each set of coils having a different inner diameter to the other sets, wherein a primary coil (105a; 205a) in the first set is located adjacent to a first axial end of the magnet, a primary coil (107; 207) in the third set is located adjacent to a second axial end of the magnet being opposite to the first axial end, and the second set of coils is located between the first and third sets of coils, and the inner diameter of the or each coil of the second set is less the inner diameter of the or each coil of the first set but greater than the inner diameter of the or each coil of the third set, wherein each of the first, second and third sets of coils are arranged on first (101; 201), second (102; 202) and third (103; 303) former portions, respectively, surrounding the bore, wherein the second former portion has an average inside diameter which is less than the inside diameter of the first former portion but greater than the inside diameter of the third former portion, and wherein each of the former potions defines a respective step of the bore, and wherein the first, second and third sets of coils are configured such that the imaging region is close enough to the second axial end of the magnet for access of an extremity of a subject, while maintaining suitable access for a shoulder of the subject from the first axial end to allow a head and shoulder of a subject access to the imaging region from the first axial end of the magnet, and to allow an extremity of the subject access to the imaging region from the second axial end of the magnet. a primary coil (105a; 205a) in the first set is located adjacent to a first axial end of the magnet, a primary coil (107; 207) in the third set is located adjacent to a second axial end of the magnet being opposite to the first axial end, and the second set of coils is located between the first and third sets of coils, and the inner diameter of the or each coil of the second set is less the inner diameter of the or each coil of the first set but greater than the inner diameter of the or each coil of the third set, wherein each of the first, second and third sets of coils are arranged on first (101; 201), second (102; 202) and third (103; 303) former portions, respectively, surrounding the bore, wherein the second former portion has an average inside diameter which is less than the inside diameter of the first former portion but greater than the inside diameter of the third former portion, and wherein each of the former potions defines a respective step of the bore, and wherein the first, second and third sets of coils are configured such that the imaging region is close enough to the second axial end of the magnet for access of an extremity of a subject, while maintaining suitable access for a shoulder of the subject from the first axial end to allow a head and shoulder of a subject access to the imaging region from the first axial end of the magnet, and to allow an extremity of the subject access to the imaging region from the second axial end of the magnet.