Cábez Manuel Blesa, Vaher Kadi, York Elizabeth N, Galdi Paola, Sullivan Gemma, Stoye David Q, Hall Jill, Corrigan Amy E, Quigley Alan J, Waldman Adam D, Bastin Mark E, Thrippleton Michael J, Boardman James P
MRC Centre for Reproductive Health, Institute for Regeneration and Repair, University of Edinburgh, Edinburgh BioQuarter, United Kingdom.
Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom.
Imaging Neurosci (Camb). 2023 Sep 12;1. doi: 10.1162/imag_a_00017. eCollection 2023.
A cardinal feature of the encephalopathy of prematurity is dysmaturation of developing white matter and subsequent hypomyelination. Magnetisation transfer imaging (MTI) offers surrogate markers for myelination, including magnetisation transfer ratio (MTR) and magnetisation transfer saturation (MTsat). Using data from 105 neonates, we characterise MTR and MTsat in the developing brain and investigate how these markers are affected by gestational age at scan and preterm birth. We explore correlations of the two measures with fractional anisotropy (FA), radial diffusivity (RD) and T1w/T2w ratio which are commonly used markers of white matter integrity in early life. We used two complementary analysis methods: voxel-wise analysis across the white matter skeleton, and tract-of-interest analysis across 16 major white matter tracts. We found that MTR and MTsat positively correlate with gestational age at scan. Preterm infants at term-equivalent age had lower values of MTsat in the genu and splenium of the corpus callosum, while MTR was higher in central white matter regions, the corticospinal tract and the uncinate fasciculus. Correlations of MTI metrics with other MRI parameters revealed that there were moderate positive correlations between T1w/T2w and MTsat and MTR at voxel level, but at tract level FA had stronger positive correlations with these metrics. RD had the strongest correlations with MTI metrics, particularly with MTsat in major white matter tracts. The observed changes in MTI metrics are consistent with an increase in myelin density during early postnatal life, and lower myelination and cellular/axonal density in preterm infants at term-equivalent age compared to term controls. Furthermore, correlations between MTI-derived features and conventional measures from diffusion MRI provide new understanding about the contribution of myelination to non-specific imaging metrics that are often used to characterise early brain development.
早产儿脑病的一个主要特征是发育中的白质成熟障碍及随后的髓鞘形成不足。磁化传递成像（MTI）可提供髓鞘形成的替代标志物，包括磁化传递率（MTR）和磁化传递饱和度（MTsat）。利用105例新生儿的数据，我们对发育中大脑的MTR和MTsat进行了特征描述，并研究了这些标志物在扫描时的胎龄和早产如何影响它们。我们探讨了这两种测量方法与分数各向异性（FA）、径向扩散率（RD）和T1w/T2w比值的相关性，这些是早期生命中白质完整性的常用标志物。我们使用了两种互补的分析方法：跨白质骨架的体素分析和跨16条主要白质束的感兴趣束分析。我们发现MTR和MTsat与扫描时的胎龄呈正相关。足月等效年龄的早产儿胼胝体膝部和压部的MTsat值较低，而中央白质区域、皮质脊髓束和钩束的MTR较高。MTI指标与其他MRI参数的相关性表明，在体素水平上T1w/T2w与MTsat和MTR之间存在中度正相关，但在束水平上FA与这些指标的正相关性更强。RD与MTI指标的相关性最强，特别是在主要白质束中与MTsat的相关性。观察到的MTI指标变化与出生后早期髓鞘密度增加一致，与足月对照组相比，足月等效年龄的早产儿髓鞘形成和细胞/轴突密度较低。此外，MTI衍生特征与扩散MRI常规测量之间的相关性为髓鞘形成对常用于表征早期脑发育的非特异性成像指标的贡献提供了新的认识。
