TY - JOUR
T1 - Shimmed matching pulses
T2 - Simultaneous control of rf and static gradients for inhomogeneity correction
AU - Franck, John M.
AU - Demas, Vasiliki
AU - Martin, Rachel W.
AU - Bouchard, Louis S.
AU - Pines, Alexander
PY - 2009/12/1
Y1 - 2009/12/1
N2 - Portable NMR systems generally suffer from poor field homogeneity and are therefore used more commonly for imaging and relaxation measurements rather than for spectroscopy. In recent years, various approaches have been proposed to increase the sample volume that is usable for spectroscopy. These include approaches based on manual shimming and those based on clever combinations of modulated radio frequency and gradient fields. However, this volume remains small and, therefore, of limited utility. We present improved pulses designed to correct for inhomogeneous dispersion across wide ranges of frequency offsets without eliminating chemical shift or spatial encoding. This method, based on the adiabatic double passage, combines the relatively larger corrections available from spatially matched rf gradients [C. Meriles, J. Magn. Reson. 164, 177 (2003)]. with the adjustable corrections available from time-modulated static field gradients [D. Topgaard, Proc. Natl. Acad. Sci. U.S.A. 101, 17576 (2004)]. We explain the origins of these corrections with a theoretical model that simplifies and expedites the design of the pulse waveforms. We also present a generalized method for evaluating and comparing pulses designed for inhomogeneity correction. Experiments validate this method and support simulations that offer new possibilities for significantly enhanced performance in portable environments.
AB - Portable NMR systems generally suffer from poor field homogeneity and are therefore used more commonly for imaging and relaxation measurements rather than for spectroscopy. In recent years, various approaches have been proposed to increase the sample volume that is usable for spectroscopy. These include approaches based on manual shimming and those based on clever combinations of modulated radio frequency and gradient fields. However, this volume remains small and, therefore, of limited utility. We present improved pulses designed to correct for inhomogeneous dispersion across wide ranges of frequency offsets without eliminating chemical shift or spatial encoding. This method, based on the adiabatic double passage, combines the relatively larger corrections available from spatially matched rf gradients [C. Meriles, J. Magn. Reson. 164, 177 (2003)]. with the adjustable corrections available from time-modulated static field gradients [D. Topgaard, Proc. Natl. Acad. Sci. U.S.A. 101, 17576 (2004)]. We explain the origins of these corrections with a theoretical model that simplifies and expedites the design of the pulse waveforms. We also present a generalized method for evaluating and comparing pulses designed for inhomogeneity correction. Experiments validate this method and support simulations that offer new possibilities for significantly enhanced performance in portable environments.
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U2 - 10.1063/1.3243850
DO - 10.1063/1.3243850
M3 - Article
C2 - 20025334
AN - SCOPUS:73449131223
VL - 131
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 23
M1 - 234506
ER -