| 摘要 |
<p>A magnet apparatus (6) for use in a magnetic resonance imaging system includes a first superconducting coil assembly (26), arranged radially outside a bore (7), for generating a first magnetic field in a working volume (18). An active magnetic shield (27) which includes a second superconducting coil assembly for generating a second magnetic field, the direction of which is opposite to that of the first magnetic field, in the working volume (18), is arranged radially outside the bore (7). A yoke magnetic shield (19) formed of a ferromagnetic material is arranged radially outside the first superconducting coil assembly (26) and the active magnetic shield (27). Magnetic fluxes of the first and second magnetic fields leaking outside the bore cancel each other to be attenuated, and are absorbed in the yoke magnetic shield (19). A magnetic fringe field is reduced by a combination of the active and yoke magnetic shields (27, 19), and a magnetic field in the working volume (18) is set at a high homogeneity.</p> |
