This study characterizes the sensitivity of noninvasive measurements of cerebral blood flow (CBF) by using frequency-domain near-infrared spectroscopy (FD-NIRS) and coherent hemodynamics spectroscopy (CHS). We considered six FD-NIRS methods: single-distance intensity and phase (SDI and SDϕ), single-slope intensity and phase (SSI and SSϕ), and dual-slope intensity and phase (DSI and DSϕ). Cerebrovascular reactivity (CVR) was obtained from the relative change in measured CBF during a step hypercapnic challenge. Greater measured values of CVR are assigned to a greater sensitivity to cerebral hemodynamics. In a first experiment with eight subjects, CVR_SDϕ was greater than CVR_SDI (p < 0.01), whereas CVR_DSI and CVR_DSϕ showed no significant difference (p > 0.5). In a second experiment with four subjects, a 5 mm scattering layer was added between the optical probe and the scalp tissue to increase the extracerebral layer thickness (L_ec), which caused CVR_DSϕ to become significantly greater than CVR_DSI (p < 0.05). CVR_SS measurements yielded similar results as CVR_DS measurements but with a greater variability, possibly resulting from instrumental artifacts in SS measurements. Theoretical simulations with two-layered media confirmed that, if the top (extracerebral) layer is more scattering than the bottom (brain) layer, the relative values of CVR_DSI and CVR_DSϕ depend on L_ec. Specifically, the sensitivity to the brain is greater for DSI than DSϕ for a thin extracerebral layer (L_ec < 13 mm), whereas it is greater for DSϕ than DSI for a thicker extracerebral layer.

中文翻译：

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频域光学测量对脑血流动力学的敏感性：高碳酸血症期间脑血流的模拟和人体研究

本研究通过使用频域近红外光谱 (FD-NIRS) 和相干血流动力学光谱 (CHS) 来表征脑血流 (CBF) 无创测量的灵敏度。我们考虑了六种 FD-NIRS 方法：单距离强度和相位（SDI 和 SD Φ）、单斜率强度和相位（SSI 和 SS Φ）以及双斜率强度和相位（DSI 和 DS Φ）。脑血管反应性 (CVR) 是通过在步骤高碳酸血症挑战期间测量的 CBF 的相对变化获得的。CVR 测量值越大，对脑血流动力学的敏感性越高。在对 8 名受试者进行的第一个实验中，CVR _{SD Φ}大于 CVR _SDI ( p < 0.01)，而 CVR _DSI和 CVR _{DS Φ}无显着差异 ( p > 0.5)。在对四名受试者进行的第二个实验中，在光学探头和头皮组织之间添加了 5 mm 的散射层，以增加脑外层厚度 ( L _ec )，这导致 CVR _DS显着大于 CVR _DSI ( p < 0.05) 。CVR _SS测量产生与 CVR _DS测量相似的结果，但变异性更大，可能是由于 SS 测量中的仪器伪影造成的。两层介质的理论模拟证实，如果顶部（脑外）层比底部（大脑）层散射更多，则 CVR _DSI和 CVR _DSψ的相对值取决于L _ec。具体而言，对于较薄的脑外层（L _ec < 13 mm）， DSI 对大脑的敏感性高于 DS phi ，而对于较厚的脑外层， DS phi的敏感性高于DSI。