Myelin quantification with MRI: A systematic review of accuracy and reproducibility.
OBJECTIVES
Currently, multiple sclerosis is treated with anti-inflammatory therapies, but these treatments lack efficacy in progressive disease. New treatment strategies aim to repair myelin damage and efficacy evaluation of such new therapies would benefit from validated myelin imaging techniques. Several MRI methods for quantification of myelin density are available now. This systematic review aims to analyse the performance of these MRI methods.


METHODS
Studies comparing myelin quantification by MRI with histology, the current gold standard, or assessing reproducibility were retrieved from PubMed/MEDLINE and Embase (until December 2019). Included studies assessed both myelin histology and MRI quantitatively. Correlation or variance measurements were extracted from the studies. Non-parametric tests were used to analyse differences in study methodologies.


RESULTS
The search yielded 1348 unique articles. Twenty-two animal studies and 13 human studies correlated myelin MRI with histology. Eighteen clinical studies analysed the reproducibility. Overall bias risk was low or unclear. All MRI methods performed comparably, with a mean correlation between MRI and histology of R2=0.54 (SD=0.30) for animal studies, and R2=0.54 (SD=0.18) for human studies. Reproducibility for the MRI methods was good (ICC=0.75-0.93, R2=0.90-0.98, COV=1.3-27%), except for MTR (ICC=0.05-0.51).


CONCLUSIONS
Overall, MRI-based myelin imaging methods show a fairly good correlation with histology and a good reproducibility. However, the amount of validation data is too limited and the variability in performance between studies is too large to select the optimal MRI method for myelin quantification yet.
['van der Weijden|Chris W J|CWJ|', 'García|David Vállez|DV|', 'Borra|Ronald J H|RJH|', 'Thurner|Patrick|P|', 'Meilof|Jan F|JF|', 'van Laar|Peter-Jan|PJ|', 'Dierckx|Rudi A J O|RAJO|', 'Gutmann|Ingomar W|IW|', 'de Vries|Erik F J|EFJ|']
D000818:Animals D001921:Brain D006801:Humans D008279:Magnetic Resonance Imaging D009103:Multiple Sclerosis D009186:Myelin Sheath D015203:Reproducibility of Results D013116:Spinal Cord
Multiple sclerosis Demyelinating diseases Magnetic resonance imaging Myelin sheath Neurodegenerative diseases