| 摘要 |
<p>A method for minimizing the inhomogeneity of a static magnetic field, produced by a main magnet, over a selected arbitrary volume, by operation of a plurality N of shimming coils each independently producing an associated shimming magnetic field having an associated inhomogeneity which is a function of spatial location over that same volume, uses the steps of: measuring the magnitude of the main magnet field, in the absence of all shimming fields, at a plurality of locations X1 upon the surface of an imaginary sphere enclosing the arbitrary volume; measuring the polarity and magnitude of each of the N shimming fields, with respect to the polarity and magnitude of a D.C. current flowing throught the associated shimming coil, at the same plurality of locations Xi upon the imaginary sphere surface; determining the weighted mean-square variation of the total field at each of another plurality of points Ywithin the volume of said imaginary sphere; and - (d) selecting the current magnitudes and polarities for each of the N shimming coils to provide each of the N associated shimming fields with magnitude and polarity to minimize the inhomogeneity of the main magnetic field in the arbitrary volume. The set of weighting coefficients may be selected to all be equal, or to emphasize at least one desired region of the arbitrary volume.</p> |
