Measurements of scattering and absorption changes in muscle and brain
Measurements of scattering and absorption changes in muscle and brain
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DOI：
10.1098/rstb.1997.0055
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发表时间：
1997-06-29
期刊：
影响因子：
--
通讯作者：
Fabiani, M
中科院分区：
文献类型：
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作者：
Gratton, E;Fantini, S;Fabiani, M
最近提出了基于血红蛋白含量变化或血红蛋白饱和度变化来研究人脑功能的非侵入性技术。在新方法中，近红外透射和反射测量可能具有显著的优势，并补充了功能磁共振成像和正电子发射断层扫描等成熟的方法。近红外测量可以非常快，在速度上与电生理测量相当，但更好地定位。我们将展示人脑在刺激视觉皮层后所产生的毫秒信号的测量。然而，主要的未解决的问题仍然是关于观测到的信号的起源。对暴露在外的动物皮质的光学测量表明，吸收系数和散射系数都受到神经活动的影响。模型计算表明，我们检测到的信号可能来自于头皮以下1 ~ 2cm区域散射系数的快速变化。我们讨论了基于频域仪器的测量方案，以及在整个光学响应中分离吸收和散射贡献的算法。我们的方法在相对均匀的质量（如大肌肉）中可以很好地分离散射和吸收。我们的测量方案的外推到一个复杂的结构，如人类头部是严格评估。
Non-invasive techniques for the study of human brain function based on changes of the haemoglobin content or on changes of haemoglobin saturation have recently been proposed. Among the new methods, near-infrared transmission and reflection measurements may have significant advantages and complement well-established methods such as functional magnetic resonance imaging and positron emission tomography. Near-infrared measurements can be very fast, comparable in speed to electrophysiological measurements, but are better localized. We will present the demonstration of measurements of millisecond signals due to brain activity in humans following stimulation of the visual cortex. However, major unresolved questions remain about the origin of the signals observed. Optical measurements on exposed cortex in animals show that both the absorption and the scattering coefficient are affected by neural activity. Model calculations show that the signals we detected may originate from rapid changes of the scattering coefficient in a region about 1 to 2 cm below the scalp. We discuss our measurement protocol, which is based on a frequency-domain instrument, and the algorithm to separate the absorption from the scattering contribution in the overall optical response. Our method produces excellent separation between scattering and absorption in relatively homogeneous masses such as large muscles. The extrapolation of our measurement protocol to a complex structure such as the human head is critically evaluated.