Okada Eiji, Delpy David T
Department of Electronics and Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
Appl Opt. 2003 Jun 1;42(16):2915-22. doi: 10.1364/ao.42.002915.
It is important for near-infrared spectroscopy (NIRS) and imaging to estimate the sensitivity of the detected signal to the change in hemoglobin that results from brain activation and the volume of tissue interrogated for a specific source-detector fiber spacing. In this study light propagation in adult head models is predicted by Monte Carlo simulation to investigate the effect of the superficial tissue thickness on the partial optical path length in the brain and on the spatial sensitivity profile. In the case of source-detector spacing of 30 mm, the partial optical path length depends mainly on the depth of the inner skull surface whereas the spatial sensitivity profile is significantly affected by the thickness of the cerebrospinal fluid layer. The mean optical path length that can be measured by time-resolved experiments increases when the skull thickness increases whereas the partial mean optical path length in the brain decreases when the skull thickness increases. These results indicate that it is not appropriate to use the mean optical path length as an alternative to the partial optical path length to compensate the NIRS signal for the difference in sensitivity caused by variation of the superficial tissue thickness.
对于近红外光谱（NIRS）和成像而言，针对特定源探测器光纤间距，估算检测信号对因大脑激活导致的血红蛋白变化以及被询问组织体积的敏感度非常重要。在本研究中，通过蒙特卡罗模拟预测成人头部模型中的光传播，以研究浅表组织厚度对大脑中部分光程长度以及空间敏感度分布的影响。在源探测器间距为30毫米的情况下，部分光程长度主要取决于内颅骨表面的深度，而空间敏感度分布则受到脑脊液层厚度的显著影响。当颅骨厚度增加时，通过时间分辨实验可测量的平均光程长度会增加，而大脑中的部分平均光程长度会减少。这些结果表明，使用平均光程长度替代部分光程长度来补偿因浅表组织厚度变化导致的敏感度差异对NIRS信号进行补偿是不合适的。
