Abstract
Several MRI measures have been proposed as in vivo biomarkers of myelin, each with applications ranging from plasticity to pathology. Despite the availability of these myelin-sensitive modalities, specificity and sensitivity have been a matter of discussion. Debate about which MRI measure is the most suitable for quantifying myelin is still ongoing. In this study, we performed a systematic review of published quantitative validation studies to clarify how different these measures are when compared to the underlying histology. We analysed the results from 43 studies applying meta-analysis tools, controlling for study sample size and using interactive visualization (https://neurolibre.github.io/myelin-meta-analysis). We report the overall estimates and the prediction intervals for the coefficient of determination and find that MT and relaxometry-based measures exhibit the highest correlations with myelin content. We also show which measures are, and which measures are not statistically different regarding their relationship with histology.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
- Revised discussion; - Added a new repeated measures meta-regression analysis; - Fixed a typo in the data spreadsheet.
Abbreviations and mathematical symbols
- AD
- axial diffusivity
- AK
- axial kurtosis
- AWF
- axonal water fraction
- FA
- fraction anisotropy
- ihMTR
- inhomogeneous magnetization transfer ratio
- k_fm
- free water-macromolecular exchange rate
- k_mf
- macromolecular-free water exchange rate
- M0m
- macromolecular pool magnetization fraction
- MD
- mean diffusivity
- MK
- mean kurtosis
- MPF
- macromolecular pool fraction
- MT
- magnetization transfer
- MTR
- magnetization transfer ratio
- MTR-UTE
- magnetization transfer ratio (using ultra-short echo time)
- MTV
- macromolecular tissue volume
- MVF-MT
- myelin volume fraction (estimated from MT)
- MVF-T2
- myelin volume fraction (estimated from T2)
- MWF
- myelin water fraction
- PD
- proton density
- PN
- peripheral nerve
- PRISMA
- Preferred Reporting Items for Systematic Reviews and Meta-Analyses
- QSM
- quantitative susceptibility mapping
- R1f
- free water pool longitudinal relaxation rate
- R2*
- apparent transverse relaxation rate
- RAFF
- relaxation along a fictitious field
- RD
- radial diffusivity
- RD-DBSI
- radial diffusivity (from diffusion basis spectrum imaging)
- RDe
- extra-cellular compartment radial diffusivity
- RK
- radial kurtosis
- rSPF
- relative semi-solid proton fraction
- SC
- spinal cord
- T1
- longitudinal relaxation time
- T1p
- adiabatic longitudinal relaxation time
- T1sat
- longitudinal relaxation time under magnetization transfer irradiation
- T2
- transverse relaxation time
- T2f
- free water pool transverse relaxation time
- T2int
- transverse relaxation intermediate component
- T2m
- macromolecular pool transverse relaxation rate
- T2p
- adiabatic transverse relaxation time