title: B0 -orientation dependent magnetic susceptibility-induced white matter contrast in the human brainstem at 11.7T.
abstract: To investigate B0 -field-orientation dependent white matter contrast in the human brainstem based on R2 * and frequency difference (Δf) mapping from gradient echo (GRE) imaging at 11.7T.
  
  
  
  Multi-echo GRE data were acquired from two fixed human brainstem specimens at multiple orientations with respect to the static B0 field. The B0 -orientation dependent modulation curves of R2 * and Δf measurements between short and long echo time regimes were used to reconstruct maps of three-dimensional (3D) white matter orientation vectors. The results were compared with maps from diffusion MRI, susceptibility tensor imaging, and histological staining of the same specimens.
  
  
  
  R2 * and Δf maps demonstrated distinct and significant contrast modulation between the corticospinal tract (CST) and transverse pontine fibers (TPF) dependent on B0 orientation. Interleaved fiber orientations of the CST and TPF could be sensitively resolved based on field-orientation-dependent fitting of the R2 * and Δf measurements. The fitted 3D orientation vector maps and peak-to-peak amplitude of R2 * and Δf modulation exhibited close correspondence to primary eigenvector and anisotropy maps derived from diffusion MRI. The amplitude of B0 -orientation dependent R2 * modulation was significantly (P < 0.005) higher in the CST compared with TPF, while fractional anisotropies were comparable.
  
  
  
  The findings of this study demonstrate the potential of B0 -orientation dependent susceptibility-induced R2 * and Δf contrasts to probe tract-specific orientation and microstructure in white matter. Magn Reson Med 75:2455-2463, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Manisha
authors.initials: M
authors.lastname: Aggarwal
authors.affiliation: Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kageyama
authors.affiliation: F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
authors.forename: Xu
authors.initials: X
authors.lastname: Li
authors.affiliation: F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: van Zijl
mesh_terms: D000328:Adult; D000465:Algorithms; D016880:Anisotropy; D001933:Brain Stem / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011712:Pyramidal Tracts / Q000000981:diagnostic imaging; D066127:White Matter / Q000000981:diagnostic imaging*
keywords: R2*; anisotropy; frequency difference; magnetic susceptibility; microstructure; white matter