Purpose of reviewMyelin water imaging (MWI) is generally regarded as the most rigorous approach for noninvasive, in-vivo measurement of myelin content, which has been histopathologically validated. As such, it has been increasingly applied to neurological diseases with white matter involvement, especially those affecting myelin. This review provides an overview of the most recent research applying MWI in neurological syndromes.Recent findingsMyelin water imaging has been applied in neurological syndromes including multiple sclerosis, Alzheimer's disease, Huntington's disease, traumatic brain injury, Parkinson's disease, cerebral small vessel disease, leukodystrophies and HIV. These syndromes generally showed alterations observable with MWI, with decreased myelin content tending to correlate with lower cognitive scores and worse clinical presentation. MWI has also been correlated with genetic variation in the APOE and PLP1 genes, demonstrating genetic factors related to myelin health.SummaryMWI can detect and quantify changes not observable with conventional imaging, thereby providing insight into the pathophysiology and disease mechanisms of a diverse range of neurological syndromes.

The standard myelin water imaging (MWI) sequence for cervical spinal cord, 3D gradient and spin echo (GRASE), was modified to allow scanning in “normal mode” (limiting imaging parameters that may cause physiologic stress) for patients who may not tolerate peripheral nerve stimulation or tissue heating due to MR-conditional implants or medical issues. Traditional 32-echo GRASE was replaced with 48-echo GRASE in normal mode. Myelin water fraction maps from the new sequence had better repeatability than the standard sequence. 48-echo GRASE is the recommended sequence for MWI in spinal cord, particularly for subjects who cannot be scanned outside of normal mode.

A single hemisphere of postmortem brain tissue from a subject with multiple sclerosis (MS) was scanned at high (Philips Elition 3T) and low (Hyperfine Swoop 64mT) field strength to determine whether lesions could be detected using a portable low field MRI system. T2-weighted scans were acquired at both field strengths with matching resolutions to assess the impact of low field. Comparisons with a high resolution 3T scan showed that of 17 visible lesions, 11 were seen on the lower resolution 3T and 10 were seen on the 64mT scan, demonstrating the feasibility of lesion detection at low field.

Myelin water fraction (MWF) quantifies myelin content in the central nervous system. MWF analysis typically assumes there is no water exchange between different water pools in tissue during the measurement. Here we investigate the effect of incorporating a two-pool model of exchange in a study of MWF in multiple sclerosis (MS) spinal cord and compare with results from the original algorithm. Including exchange resulted in higher MWF values and myelin water residence times that were correlated with MWF, but maintained the expected relationship in MWF between MS subtypes and controls.