High‐resolution quantitative MRI of multiple sclerosis spinal cord lesions

Abstract

The myelin sheath is an extended and modified plasma membrane wrapped around axons in a spiral fashion. 1 Myelin is composed of about 40% water, whereas the dry mass consists of about 80% lipids, primarily the glycolipid galactocerebroside, and 20% protein. 2 Due to its importance for normal function of the nervous system, and severe consequences of myelin damage in demyelinating diseases (such as multiple sclerosis [MS]), the noninvasive

Accurate actual flip angle imaging (AFI) in the presence of fat

“…In our experiments, the fat ghosting caused substantial errors in the non‐processed B 1 maps, with errors reaching 25% at 3T in some subjects. The errors caused by ghosting may significantly affect many established quantitative MRI methods that rely on AFI‐based flip angle calibration 16–18 . In practice, B 1 maps from AFI and other methods are often smoothed in the post‐processing stage to reduce noise (Figure 7) and bulk motion artifacts that, in the case of Cartesian sampling, also manifest as signal ghosting.…”

“…The errors caused by ghosting may significantly affect many established quantitative MRI methods that rely on AFI-based flip angle calibration. [16][17][18] In practice, B 1 maps from AFI and other methods are often smoothed in the post-processing stage to reduce noise (Figure 7) and bulk motion artifacts that, in the case of Cartesian sampling, also manifest as signal ghosting. Yet, the smoothing cannot always remove the observed fat ghosting, especially its low spatial frequency components (Figure 8).…”

Advanced spinal cord MRI in multiple sclerosis: Current techniques and future directions

“…Moreover, Dvorak et al (2021) compared T 2 -based MWI methods in controls and people with MS (pwMS; mcDESPOT vs GRASE), and discussed both with regards to sensitivity to MS-related demyelination in brain and CSC. Use of MWI in the SC in MS is supported by ongoing work on histological validation in both healthy and MS brain and cord tissue (see Laule and Moore, 2018 for a review), including making use of UHF ( Laule et al, 2016 , McDowell et al, 2022 ), as well as a substantial body of work on acquisition strategies, algorithm stability, and intra- and inter-site reproducibility ( Alonso-Ortiz et al, 2015 ).…”