title: Orientation dependence of magnetization transfer parameters in human white matter.
abstract: Quantification of magnetization-transfer (MT) experiments is typically based on a model comprising a liquid pool "a" of free water and a semisolid pool "b" of motionally restricted macromolecules or membrane compounds. By a comprehensive fitting approach, high quality MT parameter maps of the human brain are obtained. In particular, a distinct correlation between the diffusion-tensor orientation with respect to the B0-magnetic field and the apparent transverse relaxation time, T2(b), of the semisolid pool (i.e., the width of its absorption line) is observed. This orientation dependence is quantitatively explained by a refined dipolar lineshape for pool b that explicitly considers the specific geometrical arrangement of lipid bilayers wrapped around a cylindrical axon. The model inherently reduces the myelin membrane to its lipid constituents, which is motivated by previous studies on efficient interaction sites (e.g., cholesterol or galactocerebrosides) in the myelin membrane and on the origin of ultrashort T2 signals in cerebral white matter. The agreement between MT orientation effects and corresponding forward simulations using empirical diffusion imaging results as input as well as results from fits employing the novel lineshape support previous suggestions that the fiber orientation distribution in a voxel can be modeled as a scaled Bingham distribution.
authors: Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany. Electronic address: anpa@cbs.mpg.de.
authors: André
authors: A
authors: Pampel
authors: Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany. Electronic address: dirk.mueller1@tu-dresden.de.
authors: Dirk K
authors: DK
authors: Müller
authors: Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany. Electronic address: anwander@cbs.mpg.de.
authors: Alfred
authors: A
authors: Anwander
authors: Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany. Electronic address: marschner@cbs.mpg.de.
authors: Henrik
authors: H
authors: Marschner
authors: Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstr. 1a, 04103 Leipzig, Germany. Electronic address: moeller@cbs.mpg.de.
authors: Harald E
authors: HE
authors: Möller
mesh_terms: D000328:Adult; D001923:Brain Chemistry; D003198:Computer Simulation; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D060526:Magnetic Fields; D008297:Male; D008959:Models, Neurological; D009186:Myelin Sheath / Q000737:chemistry*; D066127:White Matter / Q000737:chemistry*; D055815:Young Adult
keywords: Absorption lineshape; Anisotropy; Bingham distribution function; Cerebral white matter; Fiber orientation distribution; Orientation dependence; Quantitative magnetization-transfer imaging; Super-Lorentzian lineshape