ABSTRACT 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.
Grouza et al. (Sun,) studied this question.