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Strongly coupled versus uncoupled spin response to radio frequency interference effects: application to glutamate and glutamine in spectroscopic imaging
Author(s) -
Snyder Jeff,
Thompson Richard B.,
Wild Jim M.,
Wilman Alan H.
Publication year - 2008
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.1214
Subject(s) - glutamine , metabolite , nuclear magnetic resonance , choline , glutamate receptor , radio frequency , chemistry , biophysics , physics , biology , amino acid , biochemistry , telecommunications , receptor , computer science
It is well known that comparable radio frequency (RF) wavelengths and human head dimensions at high fields can lead to an inhomogeneous RF field when using standard RF transmission. However, the impact of RF inhomogeneity on potential differences in quantification between coupled and uncoupled spins at longer echo times has not been investigated thoroughly. The consequence of this RF interference on metabolite quantification in spectroscopic imaging at 4.7 T was investigated for the strongly coupled spin systems of glutamate and glutamine at an echo time of 120 ms, and compared with the singlet response of choline. These effects were studied using a single‐voxel PRESS sequence ( α –2 α –2 α ) with varying flip angle ( α ) from 90° to 65° in simulation, phantom, and in vivo experiments. Phantom metabolite yield decreased to 57% for choline and 27% for glutamate/glutamine in agreement with the simulations. Even a minor reduction from α = 85° to 80° produced a large difference between coupled and uncoupled yields, with a reduction of 7% for choline and 17% for glutamate/glutamine. Anecdotal in vivo spectroscopic imaging studies show similar trends, with large differences between choline and glutamate/glutamine yield over a small, 2.2 cm, region. These results demonstrate severe effects on metabolite yield due to RF variation between strongly coupled and uncoupled spin systems at long echo time, which complicates metabolite quantification. Copyright © 2007 John Wiley & Sons, Ltd.