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Real‐time motion and B 0 correction for localized adiabatic selective refocusing (LASER) MRSI using echo planar imaging volumetric navigators
Author(s) -
Hess Aaron T.,
Andronesi Ovidiu C.,
Dylan Tisdall M.,
Gregory Sorensen A.,
Kouwe André J. W.,
Meintjes Ernesta M.
Publication year - 2012
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.1756
Subject(s) - adiabatic process , echo (communications protocol) , planar , nuclear magnetic resonance , laser , materials science , motion (physics) , echo planar imaging , physics , optics , magnetic resonance imaging , computer science , medicine , radiology , computer network , computer graphics (images) , classical mechanics , thermodynamics
A method is presented to correct the effects of motion and motion‐related B 0 perturbations on spectroscopic imaging in real time through the use of a volumetric navigator. It is demonstrated that, for an axial slice, lifting the chin significantly disrupts the B 0 homogeneity in the zero‐order (frequency), first‐order Y (coronal) axis and second‐order ZY term. This volumetric navigator is able to measure and correct in real time both head pose and zero‐ to first‐order B 0 inhomogeneities. The volumetric navigator was validated in six volunteers who deliberately lifted and then dropped their chin during the scan. These scans show that motion correction alone is not sufficient to recover the spectral quality. By applying real‐time shim adjustments, spectral quality was fully recovered to linewidths below 0.08 ppm and the signal‐to‐noise ratio to within acceptable limits in five of six subjects. In the sixth subject, 83% of the spectra within the volume of interest were recovered, compared with the worst case nonshim‐corrected scan, where none of the voxels fell within these quality bounds. It is shown that the use of a volumetric navigator comes at no additional cost to the scan time or spectral signal‐to‐noise ratio. Copyright © 2011 John Wiley & Sons, Ltd.