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  • Title: Detection and correction of frequency instabilities for volumetric 1H echo-planar spectroscopic imaging.
    Author: Ebel A, Maudsley AA.
    Journal: Magn Reson Med; 2005 Feb; 53(2):465-9. PubMed ID: 15678549.
    Abstract:
    Spectral quality in 1H 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.
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