IMPROVEMENTS ON AN IN-VIVO AUTOMATIC SHIMMING METHOD (FASTERMAP)

Improvements on a localized, automatic shimming method described by Gr uetter and Boesch (J. Magn. Reson. 96, 323-334 (1992)) and Gruetter (M agn. Reson. Med. 29, 804-811 (1993)) are presented. A spin-echo sequen ce employing a double sech refocusing scheme is used to acquire a fiel d map along linear projections that improves the signal-to-noise ratio by at least a factor of two over the stimulated echo sequence previou sly used. To further improve the reliability of shim adjustments, a va riance-weighted polynomial regression analysis is performed. This also extends the scope of application of this technique to global shimming . Localized H-1 spectra of human brain shimmed by this method are pres ented.