Fredriksson Ingemar, Larsson Marcus, Strömberg Tomas
Linköping University, Department of Biomedical Engineering, University Hospital, S-581 85 Linköping, Sweden.
Microvasc Res. 2009 Jun;78(1):4-13. doi: 10.1016/j.mvr.2009.02.008. Epub 2009 Mar 10.
A new method for estimating the measurement depth and volume in laser Doppler flowmetry (LDF) is presented. The method is based on Monte Carlo simulations of light propagation in tissue. The contribution from each individual Doppler shift is calculated and thereby multiple Doppler shifts are handled correctly. Different LDF setups for both probe based (0.0, 0.25, 0.5, and 1.2 mm source-detector separation) and imaging systems (0.5 and 2.0 mm beam diameter) are considered, at the wavelengths 543 nm, 633 nm, and 780 nm. Non-linear speckle pattern effects are accounted for in the imaging system setups. The effects of tissue optical properties, blood concentration, and blood oxygen saturation are evaluated using both homogeneous tissue models and a layered skin model. The results show that the effect on the measurement depth of changing tissue properties is comparable to the effect of changing the system setup, e.g. source-detector separation and wavelength. Skin pigmentation was found to have a negligible effect on the measurement depth. Examples of measurement depths are (values are given for a probe based system with 0.25 mm source-detector separation and an imaging system with a 0.5 mm beam diameter, respectively, both operating at 780 nm): muscle - 0.55/0.79 mm; liver - 0.40/0.53 mm; gray matter - 0.48/0.68 mm; white matter - 0.20/0.20 mm; index finger pulp - 0.41/0.53 mm; forearm skin - 0.53/0.56 mm; heat provoked forearm skin - 0.66/0.67 mm.
本文提出了一种估算激光多普勒血流仪（LDF）测量深度和体积的新方法。该方法基于光在组织中传播的蒙特卡罗模拟。计算了每个单独多普勒频移的贡献，从而正确处理了多个多普勒频移。考虑了基于探头（源 - 探测器间距为0.0、0.25、0.5和1.2 mm）和成像系统（光束直径为0.5和2.0 mm）的不同LDF设置，波长分别为543 nm、633 nm和780 nm。在成像系统设置中考虑了非线性散斑图案效应。使用均匀组织模型和分层皮肤模型评估了组织光学特性、血液浓度和血氧饱和度的影响。结果表明，组织特性变化对测量深度的影响与系统设置变化（如源 - 探测器间距和波长）的影响相当。发现皮肤色素沉着对测量深度的影响可忽略不计。测量深度的示例如下（分别给出了源 - 探测器间距为0.25 mm的基于探头的系统和光束直径为0.5 mm的成像系统在780 nm下运行时的值）：肌肉 - 0.55/0.79 mm；肝脏 - 0.40/0.53 mm；灰质 - 0.48/0.68 mm；白质 - 0.20/0.20 mm；食指指腹 - 0.41/0.53 mm；前臂皮肤 - 0.53/0.56 mm；热刺激后的前臂皮肤 - 0.66/0.67 mm。
