| 摘要 |
<p>A method of monitoring spatial variations in the primary magnetic field produced in an NMR system is provided. The method comprises the steps of: obtaining first and second images of a sample positioned within the primary magnetic field, each image being obtained by applying a radio frequency (RF) excitation pulse and a decoding gradient pulse separated temporally by an evolution time so as to produce a gradient echo signal, and at least one encoding gradient pulse, the at least one encoding gradient pulse being applied during the evolution time, wherein said first image is obtained using a first evolution time and said second image is obtained using a second evolution time, the first and second evolution times being different, and; using said first and second images to monitor spatial variations in the primary magnetic field produced in the NMR system. The time period between the application of the at least one encoding gradient pulse and the decoding gradient pulse is the same for each image, such that the effects of eddy currents produced by the at least one encoding gradient pulse in the monitored spatial variations are reduced.</p> |
