Graded Hypercapnia-Calibrated BOLD: Beyond the Iso-metabolic Hypercapnic Assumption.
Graded Hypercapnia-Calibrated BOLD: Beyond the Iso-metabolic Hypercapnic Assumption.
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DOI：
10.3389/fnins.2017.00276
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发表时间：
2017
影响因子：
4.3
通讯作者：
Murphy K
中科院分区：
文献类型：
--
作者：
Driver ID;Wise RG;Murphy K
校准BOLD是一种很有前途的技术，它克服了传统fMRI对脑血管状态的敏感性；测量脑代谢耗氧量（cro2）的基础水平或任务诱导反应。校准后的BOLD方法容易受到校准参数M测量误差的影响，如果去除所有脱氧血红蛋白，理论上BOLD信号会发生变化。测量M的原始和最流行的方法是使用高碳酸血症（动脉中二氧化碳的增加），假设它不影响cmo2。这一假设受到了挑战，最近的研究使用了一个纠正术语，基于文献值的基础ccro2与高碳酸血症的降低。这并不理想，因为这个值可能因受试者和大脑区域而异，并取决于所达到的高碳酸血症水平。在这里，我们提出了一种新的方法，使用分级高碳酸血症设计，并假设cmcro2随高碳酸血症水平线性变化，这样我们就可以在不假设cmcro2变化规模的前提下测量M。通过使用分级高碳酸气体挑战，我们能够消除高碳酸期间基础cro2减少造成的偏差，同时计算高碳酸时剂量方向的cro2变化。与假设cmoro2没有变化相比，该方法导致视觉和运动皮质的m值显著降低，这是由于基础cmoro2的剂量依赖性高碳酸降低，分别为1.5±0.6%/mmHg（视觉）和1.8±0.7%/mmHg（运动），其中mmHg是大潮末二氧化碳水平的单位变化。与以往使用文献值的校正方法不同，该方法考虑了实验差异和受试者间差异导致的基础ccro2对高碳酸血症反应的可变性。通过在测量m值时结合测量和校正高碳酸血症期间基础cmoro2的减少，应用我们的方法将校正cmoro2任务响应值和绝对cmoro2的高估。
Calibrated BOLD is a promising technique that overcomes the sensitivity of conventional fMRI to the cerebrovascular state; measuring either the basal level, or the task-induced response of cerebral metabolic rate of oxygen consumption (CMRO2). The calibrated BOLD method is susceptible to errors in the measurement of the calibration parameter M, the theoretical BOLD signal change that would occur if all deoxygenated hemoglobin were removed. The original and most popular method for measuring M uses hypercapnia (an increase in arterial CO2), making the assumption that it does not affect CMRO2. This assumption has since been challenged and recent studies have used a corrective term, based on literature values of a reduction in basal CMRO2 with hypercapnia. This is not ideal, as this value may vary across subjects and regions of the brain, and will depend on the level of hypercapnia achieved. Here we propose a new approach, using a graded hypercapnia design and the assumption that CMRO2 changes linearly with hypercapnia level, such that we can measure M without assuming prior knowledge of the scale of CMRO2 change. Through use of a graded hypercapnia gas challenge, we are able to remove the bias caused by a reduction in basal CMRO2 during hypercapnia, whilst simultaneously calculating the dose-wise CMRO2 change with hypercapnia. When compared with assuming no change in CMRO2, this approach resulted in significantly lower M-values in both visual and motor cortices, arising from significant dose-dependent hypercapnia reductions in basal CMRO2 of 1.5 ± 0.6%/mmHg (visual) and 1.8 ± 0.7%/mmHg (motor), where mmHg is the unit change in end-tidal CO2 level. Variability in the basal CMRO2 response to hypercapnia, due to experimental differences and inter-subject variability, is accounted for in this approach, unlike previous correction approaches, which use literature values. By incorporating measurement of, and correction for, the reduction in basal CMRO2 during hypercapnia in the measurement of M-values, application of our approach will correct for an overestimation in both CMRO2 task-response values and absolute CMRO2.