弥散张量成像在胎儿脑发育中的研究进展

胎脑从妊娠第3周末一个简单的神经管结构发育成出生后功能结构复杂的脑组织,期间经历了脑原始诱导发育、神经细胞增殖、神经元移行、两侧大脑半球皮质层状结构形成、脑室、沟、裂、脑回发育,以及白质纤维出现到成熟的髓鞘化过程。这些发育过程极其精确复杂,但是遵从严格的顺序。产前超声仅能筛查早期胎脑较明显的先天异常,无法评估这些细微的脑结构发育情况。近年来发展的磁共振成像技术为胎脑发育的研究提供了有用工具,尤其是弥散张量成像技术通过检测脑组织的水分子弥散运动,提供了从微观结构层面观察胎脑信息的视角,同胎脑组织学研究形成互补。本文将简要介绍弥散张量成像(diffusion tensor imaging,DTI)技术应用于胎脑方面的优势及其主要应用手段,DTI对皮质层状结构的显示,以及显示白质纤维束出现的时间、顺序、胎脑纤维束连接的变化、白质髓鞘化前成熟过程等,还总结了目前DTI技术用于胎儿脑成像的主要技术难题与解决办法,为进一步应用弥散张量成像研究正常胎儿脑发育奠定理论基础。

Advances of diffusion tensor imaging in fetal brain development

Fetal brain is extraordinarily complex and functional, yet its origin is a simple tubular structure at the end of 3 gestational week. During this period, it undergoes brain primitive induction development, nerve cells proliferation, neuronal migration, bilateral cerebral hemisphere stratum formation, ditch, crack, brain development, white matter fibers appearance and myelination. These developmental processes are extremely precise and complex, but follow a strict sequence. Prenatal ultrasound can only screen obvious congenital anomalies during early pregnancy, but has not yet assessed the development of these subtle brain structure. In recent years, the development of magnetic resonance imaging technology for the development of fetal brain provides a useful tool, in particular, diffusion tensor imaging provides a microstructure observation of fetal brain information perspective by detecting water dispersion movement of brain tissue. Histopathologic examination can provide complementary information. The advantages and application of DTI in fetal brain will be briefly introduced in this review. DTI can display the cortical lamellar structure and the time and sequence of white matter fiber bundles, the changes of connective fiber bundles of fetal brain, myelin maturation process and so on. The main technical problems and solutions of DTI technique for fetal brain imaging are also summarized, which will lay a theoretical foundation for the further application of diffusion tensor imaging in normal fetal brain development.