Dynamic shimming method of multi-order harmonics for magnetic resonance imaging

The invention discloses a method for carrying out dynamic and real-time shimming on any multi-order harmonic component in a selected area for magnetic resonance imaging, and the method can be used for improving the uniformity degree of a main magnetic field in an imaging area through cancelling out non-uniform harmonic items. According to the method provided by the invention, the weight distribution of any-order harmonic of the main magnetic field in the selected area can be analyzed once through phase information of images which are acquired by a three-dimensional gradient echo sequence twice, wherein a series of technical means of carrying out water-fat phase synchronization, eliminating low-signal noise pollution by virtue of an amplitude template and unwinding a three-dimensional phase are adopted, so that the weight component coefficient of any-order harmonic in the selected imaging area can be accurately and rapidly analyzed; a reversed compensating current is added into a corresponding harmonic shimming coil so as to accurately cancel out non-uniform high-order harmonics and only reserve zero-order harmonics, namely a uniform field; and the method provided by the invention has the advantage of maximally improving the uniformity degree of the main magnetic field by combining owned hardware conditions.