慢性脑血管狭窄患者脑血流量与氧摄取分数关系的初步研究

The changes of oxygen extraction fraction and cerebral blood flow of brain parenchyma in patients with unilateral cerebral vessel stenosis： initial experience of the quantative measurements

目的初步探讨梯度回波采样白旋回波序列（GESSE）评价慢性脑血管狭窄患者脑氧摄取分数（OEF）的价值，以及研究脑血流量（CBF）与OEF变化的相互关系。方法选取8名正常志愿者及16例慢性单侧颈内动脉或颅内血管狭窄的患者，进行颅脑MR扫描，扫描序列包括T2WI、MRA、GESSE序列以及动脉自旋标记（ASL）序列。GESSE扫描得到的数据在Matlab软件下应用北京大学交叉学科研究院研发的后处理程序进行后处理得到OEF图，将双侧脑实质分别分为前、中、后共6个ROI，测量各个区域脑实质OEF值。ASL序列扫描数据也在该软件下进行后处理，选择与GESSE序列相同层面，并计算该层面上述ROI的CBF值，将患侧ROI的CBF与对侧对称ROI的CBF的比值定义为相对CBF（rCBF）。将病变侧CBF值较对侧下降的ROI纳入研究范围。以rCBF=0．50为分割点，将所有研究范围内ROI的OEF值分为两组并采用t检验比较两者OEF值之间差异。正常志愿者的OEF值为标准，元±2s为上下限范围，患者的OEF值与该范围进行比较。通过泊松相关分析检验rCBF与OEF的相关性。结果8名正常志愿者平均脑组织OEF值为0．318±0．023，正常值上限为0．364，正常值下限为0．272。16例单侧血管狭窄的患者中，8例患者为单侧脑组织OEF值升高，共得到12个ROI，DSA或MRA上显示患者血管狭窄的情况为单侧多支血管狭窄或颅内主干血管多处狭窄。另外8例患者脑组织OEF值在正常范围内，共得到14个ROI，DSA或MRA上显示患者血管狭窄的情况为单支血管狭窄。以rCBF=0．50为分界点，将OEF值分为两组进行比较，rCBF≥0．50组的平均OEF值为0．325±0．028，rCBF〈0．50组的平均OEF值为0．397±0．010。两组之间的差异具有统计学意义（t=-8．840，P=0．000）。相关分析发现rCBF与OEF之间存在负相关（r=-0．851，P=0．000）。结论慢性单侧颈内动脉和（或）颅内血管狭窄患者脑组织OEF值可能升高或在正常范围内，CBF值下降越明显，OEF值上升越明显。

Objective Using gradient-echo sampling of spin-echo （GESSE） sequence to study the change of oxygen extraction fraction （OEF） in patients with unilateral cerebral vessel stenosis and the relationship between OEF and cerebral blood flow （CBF）. Methods Eight normal volunteers and 16 patients with unilateral cerebra/ vessel stenosis were enrolled in this study. Written infformed consents were obtained from all subjects. Routine MRI, GESSE and arterial spin labeling （ASL） sequences were performed for all patients. Raw data from GESSE and VE-ASL sequences were transferred to PC to conduct postprocessing. To obtain quantitative OEF and CBF of the brain parenchyma, 6 ROIs were placed respectively in the anterior, middle and posterior part of both hemispheres. The relalive CBF （rCBF） was defined as the ratio of CBF of ischemic hemisphere to that of contralateral hemisphere. T test was used for statistics. Results The mean value and normal range of OEF in the volunteers were 0. 318 ± 0. 023 and 0. 272-43. 364, respectively. In the 16 patients with unilateral cerebral vessel stenosis, 8 patients had ROIs with greater OEF in unilateral hemisphere than those in contralateral hemisphere. These cases presented multiple intracranial main arterial stenoses in digital subtraction angiography （DSA） or MR angiography （MRA） examination. The other 8 patients had normal OEF in all ROIs. And they only had single arterial stenosis in DSA or MRA. Set rCBF = 0. 50 as a dividing point, the mean OEF value was 0. 397 ＋0. 010 in the patients with rCBF 〈 0. 50. In the patients with rCBF 〉I 0. 5, the mean OEF value was 0. 325 ± 0. 028. The difference between the two groups was statistically significant （ t = - 8. 840, P = 0. 000 ）. Conclusion Patients with chronic cerebral ischemia may present with various hemodynamic impairment. The more CBF decreases, the more OEF increases. Those with increased OEF tended to have more than one lesion in the major intracranial arteries.