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Quantitative Comparison of Multi-Echo Spin Echo and Multi-Echo Gradient Echo Myelin Water Imaging in a Panel of Mbp
Vladimir Grouza1,2, Yawen Shi1,2,3, Sean Goldfarb2,4
1McConnell Brain Imaging Centre, Montreal Neurological Institute and Hospital, Montreal, Quebec, Canada.
Purpose:
To evaluate the correspondence between myelin water fraction (MWF) estimates derived from multi-echo spin echo (MESE) and multi-echo gradient echo (MGRE) imaging in fixed mouse brain tissue, using a panel of myelin basic protein (Mbp) enhancer-edited mouse lines exhibiting graded hypomyelination.
Methods:
Fifteen mouse brains from five genetically modified mouse lines were imaged using ex vivo 7 T MRI with high-resolution 3D MESE and MGRE protocols. MWF maps were computed from the MESE approach using regularized non-negative least squares (NNLS) decomposition, and from the MGRE approach using robust principal component analysis (rPCA). MWF values were then parcellated across major white matter tracts using an atlas-based pipeline and validated against biological markers, including Mbp gene expression and FluoroMyelin fluorescence intensity.
Results:
Both MESE- and MGRE-derived MWF maps exhibited high sensitivity to myelin content and resolved mouse line-dependent differences across white matter tracts. Region-specific MWF estimates were highly correlated across contrasts (r = 0.96), with MGRE yielding consistently higher MWF values, particularly in smaller tracts. MESE derived MWF values showed subtle underestimation of myelin content in hypomyelinated white matter regions. Both MWF measures showed strong correlations with Mbp messenger ribonucleic acid (mRNA) (r = 0.72-0.97) and FluoroMyelin staining (r = 0.50-0.92), with stronger histological correlations for MGRE-derived values.
Conclusion:
Both MESE and MGRE sequences provide biologically meaningful estimates of myelin content in fixed tissue but exhibit contrast-specific sensitivities and biases. MGRE combined with rPCA offers time efficient imaging and robustness in fine white matter structures, supporting its utility for high-resolution preclinical myelin mapping.
Insights
Multi-echo gradient echo (MGRE) and multi-echo spin echo (MESE) MRI methods accurately map myelin content in mouse brains. MGRE offers robust, time-efficient myelin mapping in preclinical research.
Area of Science:
- Neuroimaging
- Biomedical Engineering
- Neuroscience
Background:
- Myelin water fraction (MWF) is a key MRI biomarker for myelin content.
- Assessing MWF in preclinical models requires reliable and sensitive imaging techniques.
- Comparing different MRI sequences is crucial for optimizing myelin mapping.
Purpose of the Study:
- To compare myelin water fraction (MWF) estimates from multi-echo spin echo (MESE) and multi-echo gradient echo (MGRE) MRI.
- To evaluate these MWF estimates in fixed mouse brain tissue with varying myelin levels.
- To validate MRI-derived MWF against biological markers of myelination.
Main Methods:
- Ex vivo 7T MRI scans of 15 mouse brains from five genetically modified lines.
- High-resolution 3D MESE and MGRE imaging protocols were employed.
- MWF maps were generated using regularized non-negative least squares (NNLS) for MESE and robust principal component analysis (rPCA) for MGRE.
- Atlas-based parcellation and correlation with Mbp gene expression and FluoroMyelin staining were performed.
Main Results:
- Both MESE and MGRE MWF maps showed high sensitivity to myelin content and mouse line differences.
- MWF estimates from both methods were highly correlated (r=0.96).
- MGRE yielded higher MWF values, particularly in smaller tracts, and showed stronger histological correlations.
- MESE MWF values slightly underestimated myelin in hypomyelinated regions.
Conclusions:
- Both MESE and MGRE MRI provide biologically meaningful myelin content estimates in fixed tissue.
- MGRE with rPCA is time-efficient and robust for fine white matter structures.
- MGRE is suitable for high-resolution preclinical myelin mapping.
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