Concerning the matching of magnetic susceptibility differences for the compensation of background gradients in anisotropic diffusion fibre phantoms

Abstract

Artificial, anisotropic fibre phantoms are nowadays increasingly used in the field of diffusion-weighted MRI. Such phantoms represent useful tools for, among others, the calibration of pulse sequences and validation of diffusion models since they can mimic well-known structural features of brain tissue on the one hand, but exhibit a reduced complexity, on the other. Among all materials, polyethylene fibres have been widely used due to their excellent properties regarding the restriction of water diffusion and surface relaxation properties. Yet the magnetic susceptibility of polyethylene can be distinctly lower than that of distilled water. This difference produces strong microscopic, background field gradients in the vicinity of fibre bundles which are not parallel to the static magnetic field. This, in turn, modulates the MRI signal behaviour. In the present work we investigate an approach to reduce the susceptibility-induced background gradients via reducing the heterogeneity in the internal magnetic susceptibility. An aqueous solution of magnesium chloride hexahydrate (MgCl2·6H2O) is used for this purpose. Its performance is demonstrated in dedicated anisotropic fibre phantoms with different geometrical configurations.

Design and Validation of Diffusion MRI Models of White Matter

“…While it used reasonable diameters (20 µm) the drawback was that it only modeled the extra-axonal space. Better magnetic susceptibility matching between water and the Dyneema material can be achieved using magnesium chloride (Farrher et al, 2017). A complementary phantom design of the intra-axonal space has recently been proposed using co-electrospun fibers that produce a hollow honeycomb-like arrangement and a distribution of diameters of about 9.5 µm (Hubbard et al, 2015).…”

Dedicated diffusion phantoms for the investigation of free water elimination and mapping: insights into the influence of T2 relaxation properties

“…In the following subsections we discuss each of these features in the context of each phantom. ‘Is well characterised in terms of its microstructural properties'. Both phantoms were constructed with polyethylene fibres, which have been successfully used for the construction of several phantoms for DW MRI applications and have well known physical properties regarding water diffusion and relaxation ‘Is easy to assemble and reproducible'.…”

“…Differences between the magnetic susceptibility of the fibres and the surrounding bulk liquid generate field gradients, which in turn produce image distortions due to the bias in the phase accumulated towards the end of the EPI readout. In the case of Dyneema fibres, the difference in magnetic susceptibility between the fibres and distilled water is ~1 ppm . Yet, as observed in our results, this difference does not lead to appreciable image distortions, compared with the distortions that one normally observes in vivo induced by the presence of air, which has a difference in the magnetic susceptibility of nearly 8.5 ppm compared with tissue …”

“…In contrast to the cylindrical design of the phantom in Reference , the sections of fibre bundles in our design are straight and can, therefore, be positioned at a given angle with respect to the external magnetic field. This, in turn, enables the susceptibility‐induced, background gradients to be controlled …”

Recent Developments in Fast Kurtosis Imaging

“…Such studies have been carried out for experimental stroke [5,90], stress and depression [60,91], and kidney fibrosis [62] to name a few. Furthermore, studies have been performed to elucidate the relation between DKI metrics and tissue magnetic susceptibility [92,93] with results suggesting a susceptibility contribution in DKI metrics warranting further investigation. Similarly, studies have been performed to optimize diffusion sampling schemes for DKI [3] and to assess the DKI metric reproducibility across field strengths [94].…”