通过半傅立叶快速采集弛豫增强磁共振成像研究正常胎儿大脑发育规律

目的 利用半傅立叶（half-Fourier）快速采集弛豫增强（rapid acquisition with relaxation enhancement，RARE）磁共振成像序列分析胎儿大脑的正常发育。方法 用半傅立叶RARE成像方法检查25例12-38孕周的宫内正常胎儿大脑。根据胎龄评估脑回的成熟度、灰白质的分界情况、脑室与脑横径比率和蛛网膜下腔的大小。结果 在12-23孕周，胎儿脑表面光滑，大脑皮层分为2，3层。在24-26孕周，中央沟内见数个小的浅沟，所有胎儿的大脑皮层都可分为未成熟的皮质、中间带和胚胎基质3层。在27-29孕周，脑实质不同区域均可观察到不同程度的脑沟形成，胚胎基质基本消失。从30孕周开始，整个大脑皮层均可见脑沟形成。但是，33孕周之前，脑皮质并未折叠（infolding），岛盖（opercular formation）也未形成。23孕周之前，脑室较大，然后逐渐缩小。在整个孕期内，覆盖于脑皮质表面的蛛网膜下腔轻度扩大，在21-26孕周最明显。结论 半傅立叶RARE MR成像可准确评价胎儿大脑随着孕龄有规律发育成熟过程中的变化。

Development of normal fetal brain by MRI with a half-Fourier rapid acquisition with relaxation enhancement sequence

Objective To evaluate normal maturation of the fetal brain with half-Fourier rapid acquisition with relaxation enhancement(RARE) MRI.Methods The normal brains of 25 fetuses of 12-38 weeks gestational age were examined in utero with half-Fourier RARE imaging.Gyrus maturation,gray and white matter differentiation,ventricle-to-brain diameter ratio,and subarachnoid space size were evaluated with respect to gestational age.Results At 12-23 weeks,the brain had a smooth surface,and two or three layers were differentiated in the cerebral cortex.At 24-26 weeks,only a few shallow grooves were seen in the central sulcus,and three layers,including the immature cortex,intermediate zone,and germinal matrix,were differentiated in all fetuses.At 27-29 weeks,sulcus formation was observed in various regions of the brain parenchyma,and the germinal matrix became invisible.Sulcation was seen in the whole cerebral cortex from 30 weeks on.However,the cortex did not undergo infolding,and opercular formation was not seen before 33 weeks.At 23 weeks and earlier,the cerebral ventricles were large;thereafter,they gradually became smaller.The subarachnoid space overlying the cortical convexities was slightly dilated at all gestational ages,most markedly at 21-26 weeks.Conclusion Changes in brain maturation proceed through stages in an orderly and predictable fashion and can be evaluated reliably with half-Fourier RARE MRI.