No abstract

The ability to measure myelin in vivo has great consequences for furthering our knowledge of normal development, as well as for understanding a wide range of neurological disorders. The following review summarizes the current state of myelin imaging using MR. We consider five MR techniques that have been used to study myelin: 1) conventional MR, 2) MR spectroscopy, 3) diffusion, 4) magnetization transfer, and 5) T2 relaxation. Fundamental studies involving peripheral nerve and MR/histology comparisons have aided in the interpretation and validation of MR data. We highlight a number of important findings related to myelin development, damage, and repair, and we conclude with a critical summary of the current techniques available and their potential to image myelin in vivo.

Quantitative myelin content imaging provides novel and pertinent information related to underlying pathogenetic mechanisms of myelin-related disease, or disorders arising from aberrant connectivity. Multicomponent Driven Equilibrium Single Pulse Observation of T1 and T2 (mcDESPOT) is a time-efficient multicomponent relaxation analysis technique that provides estimates of the myelin water fraction (MWF), a surrogate measure of myelin volume. Unfortunately, mcDESPOT relies on a two water-pool model (myelin-associated water, and intra/extra cellular water), which is inadequate within partial-volume voxels, i.e. containing brain tissue and ventricle or meninges, resulting in MWF under-estimation. To address this, a third, non-exchanging ‘free-water’ component was introduced to the mcDESPOT model. Numerical simulations and experimental in vivo data show the model to perform advantageously within partial volume regions whilst providing robust and reproducible results. It is concluded that this model is preferable for future studies and analysis.