Significance: The use of diffuse correlation spectroscopy (DCS) has shown efficacy in research studies as a technique capable of noninvasively monitoring blood flow in tissue with applications in neuromonitoring, exercise science, and breast cancer management. The ability of DCS to resolve blood flow in these tissues is related to the optical sensitivity and signal-to-noise ratio (SNR) of the measurements, which in some cases, particularly adult cerebral blood flow measurements, is inadequate in a significant portion of the population. Improvements to DCS sensitivity and SNR could allow for greater clinical translation of this technique. Aim: Interferometric diffuse correlation spectroscopy (iDCS) was characterized and compared to traditional homodyne DCS to determine possible benefits of utilizing heterodyne detection. Approach: An iDCS system was constructed by modifying a homodyne DCS system with fused fiber couplers to create a Mach–Zehnder interferometer. Comparisons between homodyne and heterodyne detection were performed using an intralipid phantom characterized at two extended source–detector separations (2.4, 3.6 cm), different photon count rates, and a range of reference arm power levels. Characterization of the iDCS signal mixing was compared to theory. Precision of the estimation of the diffusion coefficient and SNR of the autocorrelation curve were compared between different measurement conditions that mimicked what would be seen in vivo. Results: The mixture of signals present in the heterodyne autocorrelation function was found to agree with the derived theory and resulted in accurate measurement of the diffusion coefficient of the phantom. Improvement of the SNR of the autocorrelation curve up to ∼2 × and up to 80% reduction in the variability of the diffusion coefficient fit were observed for all measurement cases as a function of increased reference arm power. Conclusions: iDCS has the potential to improve characterization of blood flow in tissue at extended source–detector separations, enhancing depth sensitivity and SNR.

中文翻译：

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干涉漫相关光谱改善了源-探测器长距离和低光子计数率下的测量


意义：弥散相关光谱 (DCS) 的使用已在研究中显示出功效，作为一种能够无创监测组织中血流的技术，可应用于神经监测、运动科学和乳腺癌管理。 DCS 解析这些组织中血流的能力与测量的光学灵敏度和信噪比 (SNR) 有关，在某些情况下，特别是成人脑血流测量，在很大一部分情况下是不够的。人口。 DCS 灵敏度和 SNR 的改进可以使该技术获得更大的临床转化。目的：对干涉漫相关光谱 (iDCS) 进行表征，并将其与传统的零差 DCS 进行比较，以确定利用外差检测的可能优势。方法：通过修改带有熔融光纤耦合器的零差 DCS 系统来构建 iDCS 系统，以创建马赫-曾德干涉仪。使用脂肪乳模体进行零差和外差检测之间的比较，其特征在于两个扩展的源-检测器间隔（2.4、3.6 cm）、不同的光子计数率和一系列参考臂功率水平。将 iDCS 信号混合的表征与理论进行了比较。在模拟体内观察到的不同测量条件之间比较了自相关曲线的扩散系数和信噪比的估计精度。结果：发现外差自相关函数中存在的信号混合与推导的理论一致，并导致体模扩散系数的精确测量。 在所有测量情况下，随着参考臂功率的增加，自相关曲线的 SNR 提高了 ∼2 ×，扩散系数拟合的变异性降低了 80%。结论：iDCS 有潜力在扩展源-探测器分离时改善组织中血流的表征，从而提高深度灵敏度和信噪比。