Banerjee Soumyodeep, Sarkar Sandip, Karmakar Subhajit
University Science Instrumentation Center, The University of Burdwan, Bardhaman, India.
Applied Nuclear Physics Division, Saha Institute of Nuclear Physics, Kolkata, India.
Biomed Phys Eng Express. 2021 Apr 1;7(3). doi: 10.1088/2057-1976/abf052.
Optical penetration inside human skin is constrained by the wavelength dependent scattering and absorption losses by tissue microstructure and chromophores. This computational study investigates whether the signature of hematocrit variation from plexus i.e., the first skin layer having very small blood volume percentage distributed in capillary vessels, is retained by the detected photoacoustic response. Theskin phantom is irradiated by a light source equivalent to a small footprint and low power (below 5 W) continuous wave LASER diode. As the low fluence can be compensated by exploiting strong absorption by targeted chromophores (hemoglobin molecules), an irradiation of wavelength 405 nm has been used to generate detectable pressure from capillary blood vessels of plexus. Optical energy deposition inside the tissue has been modelled using Monte Carlo technique and the pressure wave is computed using k-wave. It is found that with the increase in hematocrit from 10% to 50%, photoacoustic amplitude monotonically increases and gets almost doubled. The increment is about 30% in the range of hematocrit of physiological interest (from 30% to 50%). The variation follows a quadratic relationship for the entire hematocrit range. This photoacoustic signature of hematocrit variation has further been validated against minimum detectable pressure (800 Pa). This numerical model is expected to be an important basis to realize the idea of low cost small footprintphotoacoustic hematocrit measurement device.
人体皮肤内的光穿透受到组织微观结构和发色团引起的与波长相关的散射和吸收损耗的限制。这项计算研究调查了从丛状层（即毛细血管中血容量百分比非常小的第一层皮肤）的血细胞比容变化特征是否能被检测到的光声响应保留。用一个等效于小光斑和低功率（低于5瓦）连续波激光二极管的光源照射皮肤模型。由于低能量密度可以通过利用目标发色团（血红蛋白分子）的强吸收来补偿，因此使用波长405纳米的辐射从丛状层的毛细血管中产生可检测的压力。利用蒙特卡罗技术对组织内的光能沉积进行了建模，并使用k波计算了压力波。结果发现，随着血细胞比容从10%增加到50%，光声振幅单调增加，几乎翻倍。在生理感兴趣的血细胞比容范围内（从30%到50%），增量约为30%。在整个血细胞比容范围内，这种变化呈二次关系。血细胞比容变化的这种光声特征已针对最小可检测压力（800帕）进行了进一步验证。这个数值模型有望成为实现低成本小光斑光声血细胞比容测量装置这一想法的重要基础。
