Ning G, Malisza K L, Del Bigio M R, Bascaramurty S, Kozlowski P, Tuor U I
Institute for Biodiagnostics, National Research Council Canada, Winnipeg.
Pediatr Res. 1999 Feb;45(2):173-9. doi: 10.1203/00006450-199902000-00003.
We investigated whether the changes detectable with magnetic resonance imaging techniques during and after an episode of cerebral hypoxia-ischemia differ in immature and older brain. Diffusion weighted (DW) and T2-weighted (T2W) images were repeatedly acquired before, during, and after an episode of cerebral hypoxia-ischemia (unilateral carotid artery occlusion plus hypoxia) in 2- and 4-wk-old rats lightly anesthetized with isoflurane. Areas of increased brightness were detected in DW images from both 2- and 4-wk-old rats by 10-20 min after the start of hypoxia. These hyperintense areas increased during hypoxia, comprising 60.8+/-4.9% and 30.5+/-2.7% of the brain image at the level of the thalamus in 2-wk-old and 4-wk-old animals, respectively (p < 0.003). Hyperintense areas (e.g. 27.0+/-8.3%) also appeared in T2W images during hypoxia-ischemia in 2-wk-old animals, but these did not occur in 4-wk-old animals (p < 0.02). This observation was reflected in T2, which increased during hypoxia-ischemia in the 2-wk-old but not the 4-wk-old group. By 60 min after the termination of hypoxia-ischemia in either age group, areas of hyperintensity resolved and then reappeared 24 h later on both DW and T2W images. Thus, irrespective of age, magnetic resonance imaging changes during transient hypoxia-ischemia generally recover with a delayed or secondary increase in DW and T2W hyperintensity hours later. Immature brain differs from older brain primarily with respect to some combination of hypoxic/ischemic cellular or biochemical changes, that are detectable as increases in T2 within 2-wk-old but not 4-wk-old animals.
我们研究了在脑缺氧缺血发作期间及之后，通过磁共振成像技术检测到的变化在未成熟脑和成熟脑中是否存在差异。在2周龄和4周龄的大鼠中，用异氟烷轻度麻醉后，在脑缺氧缺血发作（单侧颈动脉闭塞加缺氧）之前、期间和之后反复采集扩散加权（DW）和T2加权（T2W）图像。在缺氧开始后10 - 20分钟，在2周龄和4周龄大鼠的DW图像中均检测到亮度增加的区域。这些高强度区域在缺氧期间增加，在2周龄和4周龄动物中，丘脑水平的高强度区域分别占脑图像的60.8±4.9%和30.5±2.7%（p < 0.003）。在2周龄动物的缺氧缺血期间，T2W图像中也出现了高强度区域（如27.0±8.3%），但在4周龄动物中未出现（p < 0.02）。这一观察结果反映在T2值上，T2值在2周龄组的缺氧缺血期间增加，而在4周龄组未增加。在任何一个年龄组中，缺氧缺血终止后60分钟，高强度区域消失，然后在24小时后在DW和T2W图像上再次出现。因此，无论年龄大小，短暂性缺氧缺血期间的磁共振成像变化通常会恢复，但随后会延迟或在数小时后出现DW和T2W高强度的二次增加。未成熟脑与成熟脑的主要区别在于缺氧/缺血细胞或生化变化的某种组合，这种变化在2周龄动物中可检测为T2增加，而在4周龄动物中则不可检测。
