[Design of active shimming coils on mini-type permanent magnetic resonance imaging system].

The homogeneity of magnetic field is a key parameter in nuclear magnetic resonance system (NMRI); it can be refined by active shimming. In this work, the authors analyze the theory of active shimming, carry out data processing and simulation, and design an active shimming system which can work on permanent mini-type MRI system. The shimming coils are placed on both out-sides of the receiving shielding box, so the gap of the coils is constant. The system improves the homogeneity of magnetic field (i. e. the decrease of heterogeneity from 10 ppm to 1.4 ppm) on NMI20 mini-type MRI instrument.