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Correction of frequency and phase variations induced by eddy currents in localized spectroscopy with multiple echo times
Author(s) -
Zhang Yan,
Marenco Stefano,
Shen Jun
Publication year - 2007
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21265
Subject(s) - spectroscopy , echo (communications protocol) , spins , nuclear magnetic resonance , signal (programming language) , phase (matter) , spectral line , chemistry , low frequency , creatine , intensity (physics) , atomic physics , physics , optics , condensed matter physics , computer science , computer network , biochemistry , organic chemistry , quantum mechanics , astronomy , programming language
As a consequence of the time‐varying magnetic field induced by eddy currents, frequency drifting occurs when the sampling window of localized spectroscopy continuously shifts. The frequency drifting and the concomitant phase variations can severely affect spectroscopy results when data are acquired with multiple echo times (TEs), such as in the measurement of glutamate (Glu) concentration using the TE‐averaged method. Specifically, the averaged spectra are further broadened and distorted in the presence of residual eddy currents, and editing of the coupled spins of Glu C4 protons is affected, resulting in errors in the measured relative intensity ratio. Postacquisition correction using unsuppressed water as reference can effectively minimize this detrimental effect, as manifested by the significantly enhanced signal intensity. Also, it is demonstrated that the methyl signals of creatine (Cr) at 3.0 ppm and choline (Cho) at 3.2 ppm can be used as internal references in finding frequency and phase disparities between different TEs. Magn Reson Med 58:174–178, 2007. © 2007 Wiley‐Liss, Inc.