RADIOFREQUENCY MAP OF AN NMR COIL BY IMAGING

We propose a new imaging method to obtain a map of the radiofrequency (RF) field amplitude over a sample. The sequence contains three RF pul ses (alpha, 2alpha, and alpha) and produces two images by a classical spin echo and a stimulated echo. A third image is computed and gives t he distribution of the flip angle a, and so the RF amplitude, over the sample. The accuracy of the flip angle determination is verified on a n homogeneous sample and results show a good correlation between exper imental and theoretical flip angles in the range of 50-degrees to 130- degrees. Experiments with a surface coil and a resonator show the meth od is available in an inhomogeneous RF field. Images obtained on the c alf of a volunteer confirms the independence of the computed RF distri bution from proton density, T1, or T2 contrast.