Zhang Quan, Brown Emery N, Strangman Gary E
Harvard Medical School, Massachusetts General Hospital, Neural Systems Group, 13th Street, Building 149, Room 2651, Charlestown, Massachusetts 02129, USA.
J Biomed Opt. 2007 Jul-Aug;12(4):044014. doi: 10.1117/1.2754714.
The sensitivity of near-infrared spectroscopy (NIRS) to evoked brain activity is reduced by physiological interference in at least two locations: 1. the superficial scalp and skull layers, and 2. in brain tissue itself. These interferences are generally termed as "global interferences" or "systemic interferences," and arise from cardiac activity, respiration, and other homeostatic processes. We present a novel method for global interference reduction and real-time recovery of evoked brain activity, based on the combination of a multiseparation probe configuration and adaptive filtering. Monte Carlo simulations demonstrate that this method can be effective in reducing the global interference and recovering otherwise obscured evoked brain activity. We also demonstrate that the physiological interference in the superficial layers is the major component of global interference. Thus, a measurement of superficial layer hemodynamics (e.g., using a short source-detector separation) makes a good reference in adaptive interference cancellation. The adaptive-filtering-based algorithm is shown to be resistant to errors in source-detector position information as well as to errors in the differential pathlength factor (DPF). The technique can be performed in real time, an important feature required for applications such as brain activity localization, biofeedback, and potential neuroprosthetic devices.
近红外光谱技术（NIRS）对诱发脑活动的敏感性在至少两个位置会因生理干扰而降低：1. 头皮和颅骨表层；2. 脑组织本身。这些干扰通常被称为“全局干扰”或“系统干扰”，源自心脏活动、呼吸及其他稳态过程。我们提出了一种基于多分离探头配置与自适应滤波相结合的减少全局干扰及实时恢复诱发脑活动的新方法。蒙特卡罗模拟表明，该方法能有效减少全局干扰并恢复原本被掩盖的诱发脑活动。我们还证明，表层的生理干扰是全局干扰的主要组成部分。因此，对表层血流动力学的测量（例如使用短源 - 探测器间距）在自适应干扰消除中可作为良好的参考。基于自适应滤波的算法显示出对源 - 探测器位置信息误差以及差分程长因子（DPF）误差具有抗性。该技术可实时执行，这是脑活动定位、生物反馈及潜在神经假体装置等应用所需的一个重要特性。
