Vascular steal explains early paradoxical blood oxygen level-dependent cerebrovascular response in brain regions with delayed arterial transit times.
Vascular steal explains early paradoxical blood oxygen level-dependent cerebrovascular response in brain regions with delayed arterial transit times.
复制标题
DOI：
10.1159/000348841
复制
发表时间：
2013
影响因子：
1.9
通讯作者：
Crawley AP
中科院分区：
文献类型：
--
作者：
Poublanc J;Han JS;Mandell DM;Conklin J;Stainsby JA;Fisher JA;Mikulis DJ;Crawley AP
吸入二氧化碳(CO2)操作过程中的血氧水平依赖(BOLD)磁共振成像(MRI)可用于测量脑血管反应性(CVR)和绘制脑血管储备耗竭区域图。这些区域对吸入的二氧化碳表现出减少或消极的大胆反应。在这项研究中，我们试图通过调查消极大胆反应的时间延迟(TD)来阐明其背后的机制。以注射造影剂的动态磁化率对比(DSC)MRI作为金标准，测量CVR的到达时间，并与之进行比较。我们假设，如果消极的大胆反应是偷窃现象的结果，那么它们应该与健康脑组织的积极大胆反应同步，即使血液到达的时间会推迟。在3Tesla磁共振系统上，收集了19例狭窄闭塞性脑血管病患者的BOLD CVR和DSC图像。对于每个患者，我们通过将BOLD信号与呼气末二氧化碳分压(PETCO2)回归来生成CVR幅度图，并通过提取BOLD信号与PETCO2之间最大互相关的时间来生成CVR TD图。此外，通过用伽马变量函数对DSC信号进行拟合来生成血液到达时间图。构建了与不同反应程度相对应的ROI掩模。在这些面罩中，提取了19名患者的平均CVR幅度、CVR Td和DSC血液到达时间的平均值。然后绘制CVR幅度和CVR Td与DSC血液到达时间的关系图。结果表明，CVR的大小与DSC的血液到达时间高度相关。正如预期的那样，血液到达时间最长的受损组织的CVR幅度最低(最负)。然而，CVR-Td与DSC的血液到达时间呈非连续关系。对于阳性反应性的组织，CVRTd与DSC的血液到达时间(p<；0.0001)有很好的相关性，但对于阴性反应性的组织，CVRTD不能保持这一趋势。阴性反应区的CVR Td与健康区相似。这些结果支持这样一种假设，即消极反应是偷窃现象的结果，当大脑较健康的部分开始反应并增加血流量时，大胆的信号就会降低。BOLD CVR MRI能够识别这种窃取分布，这具有特殊的诊断意义，因为它代表了流向已经受损组织的实际减少。
Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) during manipulation of inhaled carbon dioxide (CO2) can be used to measure cerebrovascular reactivity (CVR) and map regions of exhausted cerebrovascular reserve. These regions exhibit a reduced or negative BOLD response to inhaled CO2. In this study, we sought to clarify the mechanism behind the negative BOLD response by investigating its time delay (TD). Dynamic susceptibility contrast (DSC) MRI with the injection of a contrast agent was used as the gold standard in order to provide measurement of the blood arrival time to which CVR TD could be compared. We hypothesize that if negative BOLD responses are the result of a steal phenomenon, they should be synchronized with positive BOLD responses from healthy brain tissue, even though the blood arrival time would be delayed. On a 3-tesla MRI system, BOLD CVR and DSC images were collected in a group of 19 patients with steno-occlusive cerebrovascular disease. For each patient, we generated a CVR magnitude map by regressing the BOLD signal with the end-tidal partial pressure of CO2 (PETCO2), and a CVR TD map by extracting the time of maximum cross-correlation between the BOLD signal and PETCO2. In addition, a blood arrival time map was generated by fitting the DSC signal with a gamma variate function. ROI masks corresponding to varying degrees of reactivity were constructed. Within these masks, the mean CVR magnitude, CVR TD and DSC blood arrival time were extracted and averaged over the 19 patients. CVR magnitude and CVR TD were then plotted against DSC blood arrival time. The results show that CVR magnitude is highly correlated to DSC blood arrival time. As expected, the most compromised tissues with the longest blood arrival time have the lowest (most negative) CVR magnitude. However, CVR TD shows a noncontinuous relationship with DSC blood arrival time. CVR TD is well correlated to DSC blood arrival time (p < 0.0001) for tissue of positive reactivity, but fails to maintain this trend for tissue of negative reactivity. Regions with negative reactivity have similar CVR TD than healthy regions. These results support the hypothesis that negative reactivity is the result of a steal phenomenon, lowering the BOLD signal as soon as healthier parts of the brain start to react and augment their blood flow. BOLD CVR MRI is capable of identifying this steal distribution, which has particular diagnostic significance as it represents an actual reduction in flow to already compromised tissue.