title: Spectroscopic imaging with volume selection by unpaired adiabatic pi pulses: theory and application.
abstract: In NMR spectroscopy, volume selection can be advantageously achieved using adiabatic pi pulses, which enable high bandwidth and B(1) insensitivity. In order to avoid the generation of non-linear phase profiles and the subsequent signal loss caused by incoherent averaging, adiabatic pi pulses are usually used in pairs for volume selection in each spatial dimension. Alternatively, when performing spectroscopic imaging (SI), a high enough spatial resolution results in negligible phase dispersion within each pixel. This allows using only one pulse per selected spatial dimension, resulting in a reduced echo-time and reduced power deposition. In this work, the feasibility of such an approach is explored theoretically and numerically, allowing the derivation of explicit conditions to obtain SI images without artifact. Adequate spatial and spectral post-processing procedures are described to compensate for the effect of non-linear phase profiles. These developments are applied to SI in the rat brain at 9.4 T, using a new adiabatic sequence named Pseudo-LASER.
authors.affiliation: Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, 2021 Sixth Street SE, Minneapolis, MN 55455, USA. julien@cmrr.umn.edu
authors.forename: Julien
authors.initials: J
authors.lastname: Valette
authors.forename: Jang-Yeon
authors.initials: JY
authors.lastname: Park
authors.forename: Olli
authors.initials: O
authors.lastname: Gröhn
authors.forename: Kāmil
authors.initials: K
authors.lastname: Uğurbil
authors.forename: Michael
authors.initials: M
authors.lastname: Garwood
authors.forename: Pierre-Gilles
authors.initials: PG
authors.lastname: Henry
mesh_terms: D000465:Algorithms; D000818:Animals; D001921:Brain / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051381:Rats