Effects of white matter microstructure on phase and susceptibility maps

Abstract

Purpose: To investigate the effects on quantitative susceptibility mapping (QSM) and susceptibility tensor imaging (STI) of the frequency variation produced by the microstructure of white matter (WM). Methods: The frequency offsets in a WM tissue sample that are not explained by the effect of bulk isotropic or anisotropic magnetic susceptibility, but rather result from the local microstructure, were characterized for the first time. QSM and STI were then applied to simulated frequency maps that were calculated using a digitized whole-brain, WM model formed from anatomical and diffusion tensor imaging data acquired from a volunteer. In this model, the magnitudes of the frequency contributions due to anisotropy and microstructure were derived from the results of the tissue experiments. Results: The simulations suggest that the frequency contribution of microstructure is much larger than that due to bulk effects of anisotropic magnetic susceptibility. In QSM, the microstructure contribution introduced artificial WM heterogeneity. For the STI processing, the microstructure contribution caused the susceptibility anisotropy to be significantly overestimated. Conclusion: Microstructure-related phase offsets in WM yield artifacts in the calculated susceptibility maps. If susceptibility mapping is to become a robust MRI technique, further research should be carried out to reduce the confounding effects of microstructure-related frequency contributions.

Nuclei‐specific deposits of iron and calcium in the rat thalamus after status epilepticus revealed with quantitative susceptibility mapping (QSM)

“…Susceptibility contrast in the thalamus can be affected by myelin content. 45 However, due to the TE-dependent and anisotropic effect of myelinated fibers and white matter microstructure on measured susceptibility, 46,47 histological correlation with myelin staining is not straightforward. Further, focal mineralization in the lesions can be accompanied by varying degrees of demyelination, thus the contribution of myelin to QSM contrast in thalamic gray matter nuclei is expected to be weak in comparison to the effects of pathological iron and calcium accumulations.…”

Advanced magnetic resonance spectroscopy and imaging techniques applied to brain development and animal models of perinatal injury

“…A similar contrast can be obtained using Quantitative Susceptibility Mapping (QSM), where phase data are processed to extract the underlying magnetic susceptibility () distribution, resulting in a novel quantitative anatomical contrast of an intrinsic physical tissue property (de Rochefort et al, 2010). Fiber direction, iron and/or myelin are known to influence the susceptibility contrast, although the exact origin of this contrast is not fully understood (Wharton and Bowtell, 2015). Phase and susceptibility contrasts are based on spatial susceptibility distribution.…”

“…Phase and susceptibility contrasts are based on spatial susceptibility distribution. Recently it was suggested that white matter structure such as axonal microstructure may also have an impact on phase and susceptibility contrasts (Wharton and Bowtell, 2015). Both of these MR modalities are of great interest in the field of perinatal brain injury since it is frequently associated with myelination impairment and neuronal/axonal disease (Ferriero, 2004;Volpe, 2009).…”

“…QSM is an important tool for probing brain microstructure, providing an excellent contrast between white matter and grey matter (de Rochefort et al, 2010). Although myelin and iron are important components in the origin of phase/susceptibility contrast, contrast also depends on the orientation of the fibers compared to the direction of the main magnetic field B 0 (Marques et al, 2009;Wharton and Bowtell, 2015), as well as of the axonal structure/compaction (Wharton and Bowtell, 2015).…”

“…While the origin of phase contrast is not fully understood, it is related to the magnetic susceptibility of the tissues. Several putative assumptions have been made, including an effect of iron, myelin or lipid content, as well as an effect of fiber orientation compared to the main magnetic field strength or packing of axons (Wharton and Bowtell, 2015). Phase contrast imaging has been recently used to assess the myelination process in the developing mouse brain, making it a powerful tool to assess myelination deficits, a hallmark of preterm brain injury (Lodygensky et al, 2012).…”