Blaney Giles, Bottoni Martina, Sassaroli Angelo, Fernandez Cristianne, Fantini Sergio
Department of Biomedical Engineering, Tufts University 4 Colby St, Medford, MA 02155, USA.
Department of Biomedical Engineering, Politecnico di Torino 24 Corso Duca degli Abruzzi, Torino, TO 10129, Italy.
J Innov Opt Health Sci. 2022 May;15(3). doi: 10.1142/s1793545822500201. Epub 2022 Apr 7.
We investigated the relationship between chromophore concentrations in two-layered scattering media and the apparent chromophore concentrations measured with broadband optical spectroscopy in conjunction with commonly used homogeneous medium inverse models. We used diffusion theory togenerate optical data from a two-layered distribution of relevant tissue absorbers, namely, oxyhemoglobin, deoxyhemoglobin, water, and lipids, with a top-layer thickness in the range 1-15 mm. The generated data consisted of broadband continuous-wave (CW) diffuse reflectance in the wavelength range 650-1024 nm, and frequency-domain (FD) diffuse reflectance at 690 and 830 nm; two source-detector distances of 25 and 35 mm were used to simulate a dual-slope technique. The data were inverted using diffusion theory for a semi-infinite homogeneous medium to generate reduced scattering coefficients at 690 and 830 nm (from FD data) and effective absorption spectra in the range 650-1024 nm (from CW data). The absorption spectra were then converted into effective total concentration and oxygen saturation of hemoglobin, as well as water and lipid concentrations. For absolute values, it was found that the effective hemoglobin parameters are typically representative of the bottom layer, whereas water and lipid represent some average of the respective concentrations in the two layers. For concentration changes, lipid showed a significant cross-talk with other absorber concentrations, thus indicating that lipid dynamics obtained in these conditions may not be reliable. These systematic simulations of broadband spectroscopy of two-layered media provide guidance on how to interpret effective optical properties measured with similar instrumental setups under the assumption of medium homogeneity.
我们研究了两层散射介质中发色团浓度与通过宽带光学光谱结合常用的均匀介质反演模型测量的表观发色团浓度之间的关系。我们使用扩散理论从相关组织吸收体（即氧合血红蛋白、脱氧血红蛋白、水和脂质）的两层分布生成光学数据，顶层厚度范围为1 - 15毫米。生成的数据包括波长范围在650 - 1024纳米的宽带连续波（CW）漫反射率，以及690和830纳米处的频域（FD）漫反射率；使用25和35毫米的两个源 - 探测器距离来模拟双斜率技术。利用半无限均匀介质的扩散理论对数据进行反演，以生成690和830纳米处的约化散射系数（来自FD数据）以及650 - 1024纳米范围内的有效吸收光谱（来自CW数据）。然后将吸收光谱转换为血红蛋白的有效总浓度和氧饱和度，以及水和脂质浓度。对于绝对值，发现有效血红蛋白参数通常代表底层，而水和脂质代表两层中各自浓度的某种平均值。对于浓度变化，脂质与其他吸收体浓度表现出显著的串扰，因此表明在这些条件下获得的脂质动力学可能不可靠。这些两层介质宽带光谱的系统模拟为在介质均匀性假设下如何解释使用类似仪器设置测量的有效光学性质提供了指导。
