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Coupling effects in volume selective 1 H spectroscopy of major brain metabolites
Author(s) -
Ernst Th.,
Hennig J.
Publication year - 1991
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.1910210111
Subject(s) - spins , chemistry , spectroscopy , spectral line , nuclear magnetic resonance , attenuation , polarization (electrochemistry) , nuclear magnetic resonance spectroscopy , magnetization transfer , coupling (piping) , atomic physics , physics , condensed matter physics , materials science , optics , quantum mechanics , magnetic resonance imaging , medicine , metallurgy , radiology
The effect of PRESS and STEAM sequences on the spectra of coupled substances are discussed using the examples of weakly coupled AX and A 2 X systems. Maximum differences compared to uncoupled spins occur if the RF pulses are applied to antiphase magnetization. In this case, the spin echo of the PRESS experiment shows a modified dependence on the refocusing flip angle, which may lead to an attenuation of the acquired signal. In STEAM spectroscopy the evolution within the middle interval t m is dominated by zero quantum coherences and longitudinal polarization, whose maximum efficiencies are 25 and 12.5%, respectively. Zero quantum coherences may lead to strong modulations when the t m value is varied. The effects on the spectra of important coupled metabolites of the human brain such as glutamate, GABA, inositol, and particularly lactate, are demonstrated. The observed modulations seem to make the quantification of the spectra rather difficult at echo times above 50 ms. © 1991 Academic Press, Inc.