Hoshi Yoko, Shimada Miho, Sato Chie, Iguchi Yoshinobu
Tokyo Institute of Psychiatry, Department of Integrated Neuroscience, 2-1-8 Kamikitazawa, Setagaya-ku, Tokyo 156-8585, Japan.
J Biomed Opt. 2005 Nov-Dec;10(6):064032. doi: 10.1117/1.2142325.
Using both experimental and theoretical methods, we examine the contribution of different parts of the head to near-IR (NIR) signal. Time-resolved spectroscopy is employed to measure the mean optical path length (PL), and the absorption (mu(a)) and reduced scattering (mu(s)') coefficients in multiple positions of the human head. Monte Carlo simulations are performed on four-layered head models based on an individual magnetic resonance imaging (MRI) scan to determine mu(a) and mu(s)' in each layer of the head by solving inverse problems, and to estimate the partial path length in the brain (p-PL) and the spatial sensitivity to regions in the brain at the source-detector separation of 30 mm. The PL is closely related to the thickness of the scalp, but not to that of other layers of the head. The p-PL is negatively related to the PL and its contribution ratio to the PL is 5 to 22% when the differential path length factor is 6. Most of the signal attributed to the brain comes from the upper 1 to 2 mm of the cortical surface. These results indicate that the NIR signal is very sensitive to hemodynamic changes associated with functional brain activation in the case that changes in the extracerebral tissue are ignorable.
我们使用实验和理论方法，研究了头部不同部位对近红外（NIR）信号的贡献。采用时间分辨光谱法测量人体头部多个位置的平均光程长度（PL）、吸收系数（μ(a)）和约化散射系数（μ(s)'）。基于个体磁共振成像（MRI）扫描对四层头部模型进行蒙特卡罗模拟，通过求解反问题确定头部各层的μ(a)和μ(s)'，并在源 - 探测器间距为30 mm时估计脑内的部分光程长度（p - PL）以及对脑内区域的空间敏感性。PL与头皮厚度密切相关，但与头部其他层的厚度无关。当微分路径长度因子为6时，p - PL与PL呈负相关，其对PL的贡献率为5%至22%。归因于大脑的大部分信号来自皮质表面上方1至2毫米处。这些结果表明，在忽略脑外组织变化的情况下，近红外信号对与脑功能激活相关的血流动力学变化非常敏感。
