title: Diffusion-mediated dephasing in the dipole field around a single spherical magnetic object.
abstract: In this work, the time evolution of the free induction decay caused by the local dipole field of a spherical magnetic perturber is analyzed. The complicated treatment of the diffusion process is replaced by the strong-collision-approximation that allows a determination of the free induction decay in dependence of the underlying microscopic tissue parameters such as diffusion coefficient, sphere radius and susceptibility difference. The interplay between susceptibility- and diffusion-mediated effects yields several dephasing regimes of which, so far, only the classical regimes of motional narrowing and static dephasing for dominant and negligible diffusion, respectively, were extensively examined. Due to the asymmetric form of the dipole field for spherical objects, the free induction decay exhibits a complex component in contradiction to the cylindrical case, where the symmetric local dipole field only causes a purely real induction decay. Knowledge of the shape of the corresponding frequency distribution is necessary for the evaluation of more sophisticated pulse sequences and a detailed understanding of the off-resonance distribution allows improved quantification of transverse relaxation.
authors.affiliation: German Cancer Research Center, E010 Radiology, INF 280, D-69120 Heidelberg, Germany.
authors.forename: Lukas R
authors.initials: LR
authors.lastname: Buschle
authors.affiliation: German Cancer Research Center, E010 Radiology, INF 280, D-69120 Heidelberg, Germany; Division of Neuroradiology, University of Heidelberg, INF 400, D-69120 Heidelberg, Germany.
authors.forename: Felix T
authors.initials: FT
authors.lastname: Kurz
authors.affiliation: Department of Experimental Physics 5, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kampf
authors.affiliation: Research Center for Magnetic Resonance Bavaria e.V. (MRB), Am Hubland, D-97074 Würzburg, Germany; Translational Lung Research Center, Member of the German Center for Lung Research (DZL), Aulweg 130, D-35392 Gießen, Germany; Department of Diagnostic and Interventional Radiology, University of Heidelberg, INF 110, D-69120 Heidelberg, Germany.
authors.forename: Simon M F
authors.initials: SMF
authors.lastname: Triphan
authors.affiliation: German Cancer Research Center, E010 Radiology, INF 280, D-69120 Heidelberg, Germany.
authors.forename: Heinz-Peter
authors.initials: HP
authors.lastname: Schlemmer
authors.affiliation: German Cancer Research Center, E010 Radiology, INF 280, D-69120 Heidelberg, Germany; Division of Neuroradiology, University of Heidelberg, INF 400, D-69120 Heidelberg, Germany. Electronic address: c.ziener@dkfz-heidelberg.de.
authors.forename: Christian Herbert
authors.initials: CH
authors.lastname: Ziener
mesh_terms: D004058:Diffusion; D006801:Humans; D008168:Lung / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging; D008280:Magnetics
keywords: Dipole field; Frequency density of states; Line broadening; Lung tissue; Susceptibility effects