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The signal profile measured in balanced steady-state free precession has been shown to exhibit tissue-dependent asymmetries that were hypothesized to relate to properties of the tissue microenvironment. It was proposed that balanced steady-state free precession asymmetry may reflect subtle features of the frequency distribution in tissue. The present work investigates the large balanced steady-state free precession asymmetries observed in white matter. First, maps quantifying the asymmetry are presented, which demonstrate considerable heterogeneity within white matter, with some tracts exhibiting significant asymmetry and others having a nearly symmetric profile. These maps are compared with a diffusion-tensor atlas and indicate that the highest asymmetry is found in tracts oriented perpendicular to the main magnetic field. Measurements conducted at multiple repetition times suggest that the asymmetries are characterized by relatively small frequency shifts. These results are discussed in the context of previous work studying gradient-recalled echo (GRE) signal behavior in white matter, and it is suggested that these two techniques are detecting closely related phenomena.

Original publication

DOI

10.1002/mrm.22249

Type

Journal article

Journal

Magnetic resonance in medicine

Publication Date

02/2010

Volume

63

Pages

396 - 406

Addresses

Centre for Functional MRI of the Brain, University of Oxford, Oxford, UK. karla@fmrib.ox.ac.uk

Keywords

Brain, Nerve Fibers, Myelinated, Humans, Image Interpretation, Computer-Assisted, Imaging, Three-Dimensional, Magnetic Resonance Imaging, Image Enhancement, Sensitivity and Specificity, Reproducibility of Results, Phantoms, Imaging, Algorithms, Models, Biological, Computer Simulation