Development of a Monte Carlo-wave model to simulate time domain diffuse correlation spectroscopy measurements from first principles.

Cheng, Chen, Sie, Marsili, Boas (2022) Development of a Monte Carlo-wave model to simulate time domain diffuse correlation spectroscopy measurements from first principles. J Biomed Opt 27(8)


Diffuse correlation spectroscopy (DCS) is an optical technique that measures blood flow non-invasively and continuously. The time-domain (TD) variant of DCS, namely, TD-DCS has demonstrated a potential to improve brain depth sensitivity and to distinguish superficial from deeper blood flow by utilizing pulsed laser sources and a gating strategy to select photons with different pathlengths within the scattering tissue using a single source-detector separation. A quantitative tool to predict the performance of TD-DCS that can be compared with traditional continuous wave DCS (CW-DCS) currently does not exist but is crucial to provide guidance for the continued development and application of these DCS systems.We aim to establish a model to simulate TD-DCS measurements from first principles, which enables analysis of the impact of measurement noise that can be utilized to quantify the performance for any particular TD-DCS system and measurement geometry.We have integrated the Monte Carlo simulation describing photon scattering in biological tissue with the wave model that calculates the speckle intensity fluctuations due to tissue dynamics to simulate TD-DCS measurements from first principles.Our model is capable of simulating photon counts received at the detector as a function of time for both CW-DCS and TD-DCS measurements. The effects of the laser coherence, instrument response function, detector gate delay, gate width, intrinsic noise arising from speckle statistics, and shot noise are incorporated in the model. We have demonstrated the ability of our model to simulate TD-DCS measurements under different conditions, and the use of our model to compare the performance of TD-DCS and CW-DCS under a few typical measurement conditions.We have established a Monte Carlo-Wave model that is capable of simulating CW-DCS and TD-DCS measurements from first principles. In our exploration of the parameter space, we could not find realistic measurement conditions under which TD-DCS outperformed CW-DCS. However, the parameter space for the optimization of the contrast to noise ratio of TD-DCS is large and complex, so our results do not imply that TD-DCS cannot indeed outperform CW-DCS under different conditions. We made our code available publicly for others in the field to find use cases favorable to TD-DCS. TD-DCS also provides a promising way to measure deep brain tissue dynamics using a short source-detector separation, which will benefit the development of technologies including high density DCS systems and image reconstruction using a limited number of source-detector pairs.

扩散相关光谱 (DCS) 是一种光学技术,可以无创地连续测量血流。 DCS 的时域 (TD) 变体,即 TD-DCS,通过利用脉冲激光源和门控策略在脑内选择具有不同路径长度的光子,已证明具有提高脑深度敏感性和区分浅层血流和深层血流的潜力。使用单源-检测器分离散射组织。目前尚不存在可与传统连续波 DCS (CW-DCS) 进行比较的预测 TD-DCS 性能的定量工具,但对于为这些 DCS 系统的持续开发和应用提供指导至关重要。我们旨在建立从第一原理模拟 TD-DCS 测量的模型,可以分析测量噪声的影响,可用于量化任何特定 TD-DCS 系统和测量几何的性能。我们集成了描述光子散射的蒙特卡罗模拟在生物组织中,使用波模型计算由于组织动力学引起的散斑强度波动,以从第一原理模拟 TD-DCS 测量。我们的模型能够模拟在探测器处接收到的光子计数作为 CW-DCS 和TD-DCS 测量。激光相干性、仪器响应函数、探测器门延迟、门宽度、散斑统计产生的固有噪声和散粒噪声的影响都包含在模型中。我们已经展示了我们的模型在不同条件下模拟 TD-DCS 测量的能力,并使用我们的模型比较了 TD-DCS 和 CW-DCS 在一些典型测量条件下的性能。我们建立了蒙特卡罗-能够从第一原理模拟 CW-DCS 和 TD-DCS 测量的波浪模型。在我们对参数空间的探索中,我们找不到 TD-DCS 优于 CW-DCS 的实际测量条件。然而,TD-DCS 对比度噪声比优化的参数空间大且复杂,因此我们的结果并不意味着 TD-DCS 在不同条件下确实不能优于 CW-DCS。我们向该领域的其他人公开了我们的代码,以找到有利于 TD-DCS 的用例。 TD-DCS 还提供了一种使用短源-检测器分离测量深部脑组织动力学的有前景的方法,这将有利于技术的发展,包括高密度 DCS 系统和使用有限数量的源-检测器对进行图像重建。


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