Elimination of visually evoked BOLD responses during carbogen inhalation: Implications for calibrated MRI
Elimination of visually evoked BOLD responses during carbogen inhalation: Implications for calibrated MRI
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DOI：
10.1016/j.neuroimage.2010.09.059
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发表时间：
2011-01-15
期刊：
影响因子：
5.7
通讯作者：
Hoge, R. D.
中科院分区：
文献类型：
--
作者：
Gauthier, C. J.;Madjar, C.;Hoge, R. D.
呼吸10%CO2与90%O-2的混合物（此处称为Carbogen-10）由于CO2的血管舒张作用而增加血流量，并且由于富氧水平而提高血液O-2饱和度。这些效应都倾向于降低脑组织中脱氧血红蛋白的水平，从而降低BOLD对比度进一步增加的可能性。在本研究中，强烈视觉刺激（60 s）的块呈现在较长的块（180 s）中，在此期间，受试者呼吸用医用空气稀释的不同分数浓度（0-100%）的carbogen-10。当呼吸未稀释的carbogen-10时，BOLD对视觉刺激的反应降低到低于carbogen-10反应背景的噪声水平。在这些浓度下，总（视觉+ carbogen）BOLD响应幅度（7.5 +/-1.0%，n = 6）向单独使用carbogen时观察到的幅度（7.5 +/-1.0%，n = 6）收敛。尽管几乎完全消除了视觉BOLD反应，但对单独队列的伪连续动脉自旋标记表明灌注反应基本保留（89 +/-34%，n = 5）。先前讨论的观察结果表明在吸入Carbogen-10期间静脉饱和度可以被驱动到非常高的水平，这一发现对校准的MRI技术具有重要意义。后一种方法涉及通过表达激活诱导的BOLD信号增加作为静脉饱和度接近100%时观察到的最大BOLD信号M的一部分来估计静脉O-2饱和度的相对变化。虽然M的值通常是从使用高碳酸血症或高氧引起的小得多的BOLD反应中推断出来的，但我们的研究结果表明，这些影响可以通过吸入carbogen来结合，以获得基于较大BOLD增加的M估计值。使用混合BOLD校准模型，考虑到血流和动脉氧合的变化，我们估计吸入carbogen-10导致平均静脉饱和度为91%，使我们能够计算出9.5%的估计M值。(C)2010年爱思唯尔公司All rights reserved.
Breathing a mixture of 10% CO2 with 90% O-2 (referred to here as carbogen-10) increases blood flow due to the vasodilatory effect of CO2, and raises blood O-2 saturation due to the enriched oxygen level. These effects both tend to reduce the level of deoxygenated hemoglobin in brain tissues, thereby reducing the potential for further increases in BOLD contrast. In the present study, blocks of intense visual stimulation (60 s) were presented amid longer blocks (180 s) during which subjects breathed various fractional concentrations (0-100%) of carbogen-10 diluted with medical air. When breathing undiluted carbogen-10, the BOLD response to visual stimulation was reduced below the level of noise against the background of the carbogen-10 response. At these concentrations, the total (visual + carbogen) BOLD response amplitude (7.5 +/- 1.0%, n = 6) converged toward that seen with carbogen alone (7.5 +/- 1.0%, n = 6). In spite of the almost complete elimination of the visual BOLD response, pseudo-continuous arterial spin-labeling on a separate cohort indicated a largely preserved perfusion response (89 +/- 34%, n = 5) to the visual stimulus during inhalation of carbogen-10.The previously discussed observations suggest that venous saturation can be driven to very high levels during carbogen inhalation, a finding which has significant implications for calibrated MRI techniques. The latter methods involve estimation of the relative change in venous O-2 saturation by expressing activation-induced BOLD signal increases as a fraction of the maximal BOLD signal M that would be observed as venous saturation approaches 100%. While the value of M has generally been extrapolated from much smaller BOLD responses induced using hypercapnia or hyperoxia, our results suggest that these effects could be combined through carbogen inhalation to obtain estimates of M based on larger BOLD increases. Using a hybrid BOLD calibration model taking into account changes in both blood flow and arterial oxygenation, we estimated that inhalation of carbogen-10 led to an average venous saturation of 91%, allowing us to compute an estimated M value of 9.5%. (C) 2010 Elsevier Inc. All rights reserved.