Premium
Water saturation shift referencing (WASSR) for chemical exchange saturation transfer (CEST) experiments
Author(s) -
Kim Mina,
Gillen Joseph,
Landman Bennett A.,
Zhou Jinyuan,
van Zijl Peter C.M.
Publication year - 2009
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21873
Subject(s) - saturation (graph theory) , chemistry , nuclear magnetic resonance , voxel , laser linewidth , monte carlo method , analytical chemistry (journal) , magnetization transfer , asymmetry , computational physics , molecular physics , atomic physics , physics , optics , laser , magnetic resonance imaging , mathematics , medicine , statistics , chromatography , combinatorics , artificial intelligence , computer science , radiology , quantum mechanics
Chemical exchange saturation transfer (CEST) is a contrast mechanism that exploits exchange‐based magnetization transfer (MT) between solute and water protons. CEST effects compete with direct water saturation and conventional MT processes, and generally can only be quantified through an asymmetry analysis of the water saturation spectrum ( Z ‐spectrum) with respect to the water frequency, a process that is exquisitely sensitive to magnetic field inhomogeneities. Here it is shown that direct water saturation imaging allows measurement of the absolute water frequency in each voxel, allowing proper centering of Z ‐spectra on a voxel‐by‐voxel basis independently of spatial B 0 field variations. Optimal acquisition parameters for this “water saturation shift referencing” (WASSR) approach were estimated using Monte Carlo simulations and later confirmed experimentally. The optimal ratio of the WASSR sweep width to the linewidth of the direct saturation curve was found to be 3.3–4.0, requiring a sampling of 16–32 points. The frequency error was smaller than 1 Hz at signal‐to‐noise ratios of 40 or higher. The WASSR method was applied to study glycogen, where the chemical shift difference between the hydroxyl (OH) protons and bulk water protons at 3T is so small (0.75–1.25 ppm) that the CEST spectrum is inconclusive without proper referencing. Magn Reson Med, 2008. © 2009 Wiley‐Liss, Inc.