Quantitative MRI-based assessment of the ultrastructural compactness of myelin lamellae
Efficient neuronal communication relying on rapid saltatory conduction depends not only on the amount of myelin wrapping axons but also on myelin compact organisation. Yet, current quantitative MRI myelin imaging methods, such as Myelin Water Imaging (MWI) and quantitative Magnetization Transfer (qMT), are designed to estimate myelin content and are often treated as interchangeable, overlooking…
Quantitative MRI techniques like Myelin Water Imaging (MWI) and quantitative Magnetization Transfer (qMT) are utilized to gauge myelin content in neuronal communication. However, these methods don't account for the organisation of myelin layers, which is crucial for efficient saltatory conduction. The new Structural Myelin Integrity (SMI) metric, introduced in this study, discerns myelin compact organisation from content by merging the distinct biophysical attributes of MWI and qMT.
SMI separates water confined between myelin layers from the total myelin membrane mass. In rodent models of myelin decompaction and remyelination, SMI detected structural abnormalities in compact organisation, even when myelin membranes remained largely intact. Unlike myelin-content metrics, SMI values in remyelination models approached healthy levels earlier, suggesting the formation of thin yet compact sheaths.
The study concludes that myelin organisation and content can diverge, making SMI a promising non-invasive marker for detecting white matter changes in clinical MRI, which may currently go unnoticed.
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