Functional near-infrared spectroscopy (fNIRS) estimates the functional oscillations of oxyhemoglobin and deoxyhemoglobin in the cortex through scalp-located multiwavelength recordings. Hemoglobin oscillations are inferred through temporal changes in continuous-wave (CW) light attenuation. However, because of the diffusive multilayered head tissue structures, the photon path is longer than the source-detector separation, complicating hemoglobin evaluation. This aspect is incorporated in the modified Beer-Lambert law where the source-detector distance is multiplied by the differential pathlength factor (DPF). Since DPF estimation requires photons' time-of-flight information, DPF is assumed a priori in CW-fNIRS. Importantly, errors in the DPF spectrum induce hemoglobin cross talk, which is detrimental for fNIRS. We propose to estimate subject-specific DPF spectral dependence relying on multidistance high-density measurements. The procedure estimates the effective attenuation coefficient (EAC), which is proportional to the geometric mean of absorption and reduced scattering. Since DPF depends on the scattering-to-absorption ratio, EAC limits the spectral dependence assumption to scattering. This approach was compared to a standard frequency-domain multidistance procedure. A good association between the two methods ( r 2 = 0.69 ) was obtained. This approach could estimate low-resolution maps of the DPF spectral dependence through large field of view, high-density systems, reducing hemoglobin cross talk, and increasing fNIRS sensitivity and specificity to brain activity without instrumentation modification.

中文翻译：

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连续波功能近红外光谱中的差分光程因子：减少高密度记录中的血红蛋白串扰。

功能近红外光谱（fNIRS）通过头皮定位的多波长记录来估计皮层中氧合血红蛋白和脱氧血红蛋白的功能振荡。血红蛋白振荡是通过连续波（CW）光衰减的时间变化来推断的。但是，由于头颅组织层具有扩散性，因此光子路径比源探测器分离器更长，从而使血红蛋白评估复杂化。这方面被纳入修改的比尔-朗伯定律中，其中源-检测器距离乘以差分路径长度因子（DPF）。由于DPF估计需要光子的飞行时间信息，因此在CW-fNIRS中假定DPF为先验。重要的是，DPF谱图中的错误会引起血红蛋白串扰，这对fNIRS有害。我们建议依靠多距离高密度测量来估计特定于受试者的DPF光谱依赖性。该程序估算有效衰减系数（EAC），该系数与吸收和减少的散射的几何平均值成正比。由于DPF取决于散射吸收比，因此EAC将光谱依赖性假设限制为散射。将该方法与标准频域多距离程序进行了比较。两种方法之间的相关性很好（r 2 = 0.69）。这种方法可以通过大视野，高密度系统，减少血红蛋白串扰，提高fNIRS对大脑活动的敏感性和特异性而无需对仪器进行修改即可估计DPF光谱依赖性的低分辨率图。