Diffuse Correlation Spectroscopy Beyond the Water Peak Enabled by Cross-Correlation of the Signals From InGaAs/InP Single Photon Detectors.
Diffuse Correlation Spectroscopy Beyond the Water Peak Enabled by Cross-Correlation of the Signals From InGaAs/InP Single Photon Detectors.
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DOI：
10.1109/tbme.2021.3131353
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发表时间：
2022-06
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扩散相关光谱（DCS）是一种光学技术，允许无创测量血流。最近的工作表明，利用传统NIR范围以外的更长波长可以显著提高信噪比（SNR）。然而，既对较长波长敏感又适合于临床应用的电流检测器（InGaAs/InP SPAD）遭受次优后脉冲和暗噪声特性。为了克服这些障碍，我们引入了一个互相关的方法，更准确地恢复使用InGaAs/InP SPAD的血流信息。两个InGaAs/InP SPAD探测器用于在体外和体内DCS测量。对来自每个探测器的光子流进行互相关以计算相关函数。改变检测器操作参数以确定使测量SNR最大化的参数。进行状态空间建模以确定每个操作点的检测器特性。在整个操作条件范围内对检测器特性进行了评价。对检测器噪声对相关函数的影响进行建模提供了一种纠正相关曲线失真的方法，从而准确恢复由参考检测器确认的流量信息。通过来自两个检测器的信号的互相关、检测器响应的基于模型的表征以及检测器操作参数的优化的组合，该方法允许对真实血流指数的准确估计。重要性：这项工作提出了一种方法，DCS可以在较长的近红外波长与现有的检测器技术，利用增加的SNR。
Diffuse correlation spectroscopy (DCS) is an optical technique that allows for the non-invasive measurement of blood flow. Recent work has shown that utilizing longer wavelengths beyond the traditional NIR range provides a significant improvement to signal-to-noise ratio (SNR). However, current detectors both sensitive to longer wavelengths and suitable for clinical applications (InGaAs/InP SPADs) suffer from suboptimal afterpulsing and dark noise characteristics. To overcome these barriers, we introduce a cross correlation method to more accurately recover blood flow information using InGaAs/InP SPADs. Two InGaAs/InP SPAD detectors were used for during in vitro and in vivo DCS measurements. Cross correlation of the photon streams from each detector was performed to calculate the correlation function. Detector operating parameters were varied to determine parameters which maximized measurement SNR. State-space modeling was performed to determine the detector characteristics at each operating point. Evaluation of detector characteristics was performed across the range of operating conditions. Modeling the effects of the detector noise on the correlation function provided a method to correct the distortion of the correlation curve, yielding accurate recovery of flow information as confirmed by a reference detector. Through a combination of cross-correlation of the signals from two detectors, model-based characterization of detector response, and optimization of detector operating parameters, the method allows for the accurate estimation of the true blood flow index. Significance: This work presents a method by which DCS can be performed at longer NIR wavelengths with existing detector technology, taking advantage of the increased SNR.