title: Real-time motion and B0 correction for localized adiabatic selective refocusing (LASER) MRSI using echo planar imaging volumetric navigators.
abstract: 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.
authors.affiliation: MRC/UCT Medical Imaging Research Unit, Department of Human Biology, University of Cape Town, South Africa. hess.aaron@gmail.com
authors.forename: Aaron T
authors.initials: AT
authors.lastname: Hess
authors.forename: Ovidiu C
authors.initials: OC
authors.lastname: Andronesi
authors.forename: M Dylan
authors.initials: MD
authors.lastname: Tisdall
authors.forename: A Gregory
authors.initials: AG
authors.lastname: Sorensen
authors.forename: André J W
authors.initials: AJ
authors.lastname: van der Kouwe
authors.forename: Ernesta M
authors.initials: EM
authors.lastname: Meintjes
mesh_terms: D016477:Artifacts; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D003401:Creatine / Q000378:metabolism; D017352:Echo-Planar Imaging / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation* / Q000379:methods*; D021621:Imaging, Three-Dimensional; D009038:Motion; D009068:Movement; D015203:Reproducibility of Results; D012399:Rotation; D059629:Signal-To-Noise Ratio; D013997:Time Factors
chemical_list: D001224:Aspartic Acid; C000179:N-acetylaspartate; D003401:Creatine