Chan Kevin C, Khong Pek-Lan, Lau Ho-Fai, Cheung Pik-To, Wu Ed X
Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
Int J Dev Neurosci. 2009 Oct;27(6):607-15. doi: 10.1016/j.ijdevneu.2009.05.012. Epub 2009 Jun 6.
Neonatal hypoxic-ischemic encephalopathy is a major cause of brain damage in infants, and is associated with periventricular white matter injury and chronic neurological dysfunctions. However, the mechanisms of the chronic white matter injury and reorganization are still unclear. In this study, in vivo diffusion tensor imaging (DTI) was employed to evaluate the late changes of white matter microstructural integrity in the rat brains at 10 weeks after severe neonatal hypoxic-ischemic insults at postnatal day 7. In the fractional anisotropy directionality map, qualitative evaluation showed that a dorsoventrally oriented fiber bundle extended from the corpus callosum into the cyst in the anterior brain, whilst the posterior peri-infarct areas had similar fiber orientations as the contralateral internal capsule, optic tract and fimbria of hippocampus. Compared to the contralateral hemisphere, significantly higher fractional anisotropy, axial diffusivity and diffusion trace value were observed quantitatively in the distal end of the extended fiber bundle connecting the anterior and posterior white matters rostrocaudally. A significantly lower fractional anisotropy but higher axial and radial diffusivities and trace were also found in the ipsilateral corpus callosum, proximal external capsule and anterior commissure, while slightly lower fractional anisotropy and axial diffusivity were noticed in the ipsilateral internal capsule and optic nerve. It was suggested that increased fractional anisotropy, axial diffusivity and trace characterize white matter reorganization in chronic neonatal hypoxic-ischemic insults, whereas reduction in fractional anisotropy appears to characterize two types of white matter lesions, with significantly higher axial and radial diffusivities and trace being primary and slightly lower axial diffusivity being secondary. Combined with fractional anisotropy directionality map, in vivo DTI provides important indices to differentiate the chronic effects of severe neonatal hypoxic-ischemic injury and recovery globally, quantitatively and non-invasively.
新生儿缺氧缺血性脑病是婴儿脑损伤的主要原因，与脑室周围白质损伤和慢性神经功能障碍有关。然而，慢性白质损伤和重组的机制仍不清楚。在本研究中，采用活体扩散张量成像（DTI）评估出生后第7天严重新生儿缺氧缺血性损伤后10周大鼠脑白质微观结构完整性的后期变化。在分数各向异性方向性图中，定性评估显示，一个从胼胝体向腹背方向延伸的纤维束进入前脑囊肿，而后侧梗死周围区域的纤维方向与对侧内囊、视束和海马伞相似。与对侧半球相比，在前后白质之间沿头尾方向连接的延伸纤维束远端，定量观察到分数各向异性、轴向扩散率和扩散轨迹值显著更高。在同侧胼胝体、近端外囊和前连合中也发现分数各向异性显著降低，但轴向和径向扩散率及轨迹更高，而在同侧内囊和视神经中分数各向异性和轴向扩散率略低。提示分数各向异性、轴向扩散率和轨迹增加是慢性新生儿缺氧缺血性损伤中白质重组的特征，而分数各向异性降低似乎是两种白质病变的特征，其中轴向和径向扩散率及轨迹显著更高是主要的，轴向扩散率略低是次要的。结合分数各向异性方向性图，活体DTI提供了重要指标，可在全球范围内、定量且无创地区分严重新生儿缺氧缺血性损伤的慢性影响和恢复情况。
