Mudra R, Nadler A, Keller E, Niederer P
Institute of Biomedical Engineering, University and ETH Zürich, Gloriastrasse 35, 8092 Zürich, Switzerland.
J Biomed Opt. 2006 Jul-Aug;11(4):044009. doi: 10.1117/1.2341652.
Near-infrared spectroscopy (NIRS) combined with indocyanine green (ICG) dilution is applied externally on the head to determine the cerebral hemodynamics of neurointensive care patients. We applied Monte Carlo simulation for the analysis of a number of problems associated with this method. First, the contamination of the optical density (OD) signal due to the extracerebral tissue was assessed. Second, the measured OD signal depends essentially on the relative blood content (with respect to its absorption) in the various transilluminated tissues. To take this into account, we weighted the calculated densities of the photon distribution under baseline conditions within the different tissues with the changes and aberration of the relative blood volumes that are typically observed under healthy and pathologic conditions. Third, in case of NIRS ICG dye dilution, an ICG bolus replaces part of the blood such that a transient change of absorption in the brain tissues occurs that can be recorded in the OD signal. Our results indicate that for an exchange fraction of Delta=30% of the relative blood volume within the intracerebral tissue, the OD signal is determined from 64 to 74% by the gray matter and between 8 to 16% by the white matter maximally for a distance of d=4.5 cm.
近红外光谱（NIRS）结合吲哚菁绿（ICG）稀释法被应用于头部外部，以测定神经重症监护患者的脑血流动力学。我们应用蒙特卡罗模拟来分析与该方法相关的一些问题。首先，评估了由于脑外组织导致的光密度（OD）信号污染。其次，测量得到的OD信号本质上取决于不同透射组织中（相对于其吸收而言）的相对血液含量。为了考虑这一点，我们用在健康和病理条件下通常观察到的相对血容量的变化和偏差，对不同组织在基线条件下计算得到的光子分布密度进行加权。第三，在NIRS ICG染料稀释的情况下，ICG团注会替代部分血液，从而导致脑组织中吸收的瞬态变化，这可以在OD信号中记录下来。我们的结果表明，对于脑内组织中相对血容量的交换分数Δ = 30%，在距离d = 4.5 cm时，OD信号最大程度上由灰质决定64%至74%，由白质决定8%至16%。
