Detection and correction of frequency instabilities for volumetric 1 H echo‐planar spectroscopic imaging

Spectral quality in 1 H magnetic resonance spectroscopic imaging (MRSI) critically depends on the stability of the main magnetic field. For echo‐planar MRSI implemented at 3 T, temperature variation in the passive steel shims of the magnet system can lead to a significant drift in the resonance frequency. A method is presented that incorporates interleaved measurement of the instantaneous resonance frequency of a reference water signal into a volumetric MRSI sequence and allows correction for the drift during postprocessing. Results from normal human brain at 3 T indicate that the correction largely removes lineshape distortions, recovers metabolite signal loss, and improves spectral quality by reducing the width of spectral lines; however, particularly in inferior regions, other sources of distortion may be present that cause broadening of spectral lines. Magn Reson Med 53:465–469, 2005. © 2005 Wiley‐Liss, Inc.