title: Symmetry of the gradient profile as second experimental dimension in the short-time expansion of the apparent diffusion coefficient as measured with NMR diffusometry.
abstract: The time-dependent apparent diffusion coefficient as measured by pulsed gradient NMR can be used to estimate parameters of porous structures including the surface-to-volume ratio and the mean curvature of pores. In this work, the short-time diffusion limit and in particular the influence of the temporal profile of diffusion gradients on the expansion as proposed by Mitra et al. (1993) is investigated. It is shown that flow-compensated waveforms, i.e. those whose first moment is zero, are blind to the term linear in observation time, which is the term that is proportional to mean curvature and surface permeability. A gradient waveform that smoothly interpolates between flow-compensated and bipolar waveform is proposed and the degree of flow-compensation is used as a second experimental dimension. This two-dimensional ansatz is shown to yield an improved precision when characterizing the confining domain. This technique is demonstrated with simulations and in experiments performed with cylindrical capillaries of 100 μm radius.
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, 69121 Heidelberg, Germany. Electronic address: f.laun@dkfz.de.
authors.forename: Frederik Bernd
authors.initials: FB
authors.lastname: Laun
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center, Im Neuenheimer Feld 280, 69121 Heidelberg, Germany. Electronic address: t.kuder@dkfz.de.
authors.forename: Tristan Anselm
authors.initials: TA
authors.lastname: Kuder
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand. Electronic address: fangrong.zong@vuw.ac.nz.
authors.forename: Fangrong
authors.initials: F
authors.lastname: Zong
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand. Electronic address: stefan.hertel@vuw.ac.nz.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hertel
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand. Electronic address: Petrik.Galvosas@vuw.ac.nz.
authors.forename: Petrik
authors.initials: P
authors.lastname: Galvosas
keywords: Diffusion; Gradient profile; Short-time limit; Surface-to-volume ratio; Waveform