New Jersey Institute of Technology, Biomedical Engineering Department, New Jersey 07102, USA.
J Biomed Opt. 2013 Jul;18(7):075001. doi: 10.1117/1.JBO.18.7.075001.
Near-infrared (NIR) lasers find applications in neuro-medicine both for diagnostic and treatment purposes. Penetration depth and profile into neural tissue are critical parameters to be considered in these applications. Published data on the optical properties of rodent neural tissue are rare, despite the frequent use of rats as an animal model. The aim of this study was to measure the light intensity profile inside the rat brain using a direct method, while the medium is being illuminated by an NIR laser beam, and compare the results with in vitro measurements of transmittance in the rat brain slices. The intensity profile along the vertical axis had an exponential decline with multiple regions that could be approximated with different coefficients. The Monte Carlo method that was used to simulate light-tissue interactions and predict the scattering coefficient of brain tissue from the measurements suggested that more scattering occurred in deeper layers of the cortex. A single scattering coefficient of 125 cm-1 was estimated for cortical layers from 300 to 1500 μm and a gradually increasing value from 125 to 370 cm-1 for depths of 1500 to 3000 μm. The deviations of in vivo results from the in vitro transmittance measurements, as well as the postmortem in vivo results from the alive measurements were significant.
近红外（NIR）激光在神经医学中具有诊断和治疗用途。在这些应用中，穿透深度和进入神经组织的形态是需要考虑的关键参数。尽管大鼠经常被用作动物模型，但关于啮齿动物神经组织的光学特性的公开数据很少。本研究的目的是使用直接方法测量大鼠大脑内的光强分布，同时用近红外激光束照射介质，并将结果与大鼠脑片的体外透射率测量进行比较。沿垂直轴的强度分布呈指数下降，有多个区域可以用不同的系数来近似。用于模拟光-组织相互作用并根据测量值预测脑组织散射系数的蒙特卡罗方法表明，更多的散射发生在皮质的较深层。从测量值估计皮质层的单个散射系数为 125 cm-1，从 300 到 1500 μm 深度的散射系数逐渐增加到 125 到 370 cm-1，从 1500 到 3000 μm 深度的散射系数逐渐增加。体内结果与体外透射率测量值的偏差，以及死后体内结果与活体测量值的偏差均具有显著意义。
