Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 58, Issue 1, Pages 167-173Publisher
JOHN WILEY & SONS INC
DOI: 10.1002/mrm.21251
Keywords
Hadamard encoding; high field; magnetic resonance spectroscopic imaging (MRSI); selective pulses; chemical shift displacement
Funding
- NCI NIH HHS [CA111911] Funding Source: Medline
- NIBIB NIH HHS [EB001015] Funding Source: Medline
- NINDS NIH HHS [NS050520] Funding Source: Medline
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Proton MR spectroscopic imaging (MRSI) at higher magnetic fields (B-0) suffers metabolite localization errors from different chemical-shift displacements (CSDs) if spatially-selective excitation is used. This phenomenon is exacerbated by the decreasing radiofrequency (RF) field strength, B-1, at higher B(0)s, precluding its suppression with stronger gradients. To address this, two new methods are proposed: 1) segmenting the volume-of-interest (VOI) into several slabs, allowing proportionally stronger slice-select gradients; and 2) sequentially cascading rather than superposing the components of the Hadamard selective pulses used for reasons of better point-spread function (PSF) to localize the few slices within each slab. This can reduce the peak B, to that of a single slice. Combining these approaches permits us to increase the selective gradient four- to eightfold per given B1, to 12 or 18mT/m for 4- or 2-cm VOIs. This brute force approach reduces the CSD to under 0.05 cm/ppm at 7T, or less than half that at 3T. Magn Reson Med 58: 167-173, 2007. (c) 2007 Wiley-Liss, Inc.
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