Lo E H, Rogowska J, Batchelder K F, Wolf G L
Center for Imaging and Pharmaceutical Research, Harvard Medical School, Charlestown, MA, USA.
Neurol Res. 1996 Apr;18(2):150-6. doi: 10.1080/01616412.1996.11740394.
We describe a novel approach for analysing the hemodynamic alterations that result after focal cerebral ischemia. This approach utilizes a temporal correlation analysis of first pass transit data obtained with functional imaging. First pass transits of injected contrast agents are measured with dynamic CT scanning. Normal transit profiles are obtained from contralateral cortical regions to serve as reference profiles. Normalized correlations are then calculated to compare transit profiles from each individual pixel within the brain to the normal reference profile. The normalized correlation coefficient is used as a measure of temporal similarity to quantitatively assess deviations from normal hemodynamics. The method is based on the premise that perturbed hemodynamics are manifested as changes in the shape of the cerebral transit profiles. Correlation maps are produced that display regional alterations in cerebral hemodynamics. Results from rabbit (n=4) and rat (n=4) models of focal ischemia are presented. In the normal contralateral hemisphere, correlation values range from 0.83-0.93 with coefficients of variation of less than 3-4% . The ischemic core is comprised of regions without significant bolus transit. The peripheral zones that lie between normal brain and the ischemic core are composed of intermediate correlation values. By setting statistical thresholds (mean minus 2SD, p < 0.05), we quantitatively define these intermediate zones as the hemodynamic penumbra, i.e. regions where the shape of the first pass transit profile has been altered. The resulting correlation maps clearly image gradients of altered cerebral hemodynamics. Perfusion indices calculated based on transit profile peaks revealed that the penumbral zones possess reduced perfusion on the order of about 40 percent of contralateral values. In summary, we believe that temporal correlation analysis of first pass transit profiles can be used to image the hemodynamic penumbra in focal cerebral ischemia.
我们描述了一种用于分析局灶性脑缺血后所导致的血流动力学改变的新方法。该方法利用对功能成像获得的首过通过数据进行时间相关性分析。通过动态CT扫描测量注入造影剂的首过通过情况。从对侧皮质区域获取正常通过曲线作为参考曲线。然后计算归一化相关性，以比较脑内每个单独像素的通过曲线与正常参考曲线。归一化相关系数用作时间相似性的度量，以定量评估与正常血流动力学的偏差。该方法基于这样一个前提，即血流动力学紊乱表现为脑通过曲线形状的变化。生成相关图，显示脑血流动力学的区域改变。给出了兔（n = 4）和大鼠（n = 4）局灶性缺血模型的结果。在正常对侧半球，相关值范围为0.83 - 0.93，变异系数小于3 - 4%。缺血核心由无明显团块通过的区域组成。位于正常脑和缺血核心之间的周边区域由中间相关值组成。通过设置统计阈值（均值减去2倍标准差，p < 0.05），我们将这些中间区域定量定义为血流动力学半暗带，即首过通过曲线形状已改变的区域。由此产生的相关图清晰地显示了脑血流动力学改变的梯度。基于通过曲线峰值计算的灌注指数显示，半暗带区域的灌注减少，约为对侧值的40%。总之，我们认为首过通过曲线的时间相关性分析可用于对局灶性脑缺血中的血流动力学半暗带进行成像。
