Zhang Quan, Strangman Gary E, Ganis Giorgio
Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA.
Neuroimage. 2009 Apr 15;45(3):788-94. doi: 10.1016/j.neuroimage.2008.12.048. Epub 2009 Jan 7.
In previous work we introduced a novel method for reducing global interference, based on adaptive filtering, to improve the contrast to noise ratio (CNR) of evoked hemodynamic responses measured non-invasively with near infrared spectroscopy (NIRS). Here, we address the issue of how to generally apply the proposed adaptive filtering method. A total of 156 evoked visual response measurements, collected from 15 individuals, were analyzed. The similarity (correlation) between measurements with far and near source-detector separations collected during the rest period before visual stimulation was used as indicator of global interference dominance. A detailed analysis of CNR improvement in oxy-hemoglobin (O(2)Hb) and deoxy-hemoglobin (HHb), as a function of the rest period correlation coefficient, is presented. Results show that for O(2)Hb measurements, 66% exhibited substantial global interference. For this dataset, dominated by global interference, 71% of the measurements revealed CNR improvements after adaptive filtering, with a mean CNR improvement of 60%. No CNR improvement was observed for HHb. This study corroborates our previous finding that adaptive filtering provides an effective method to increase CNR when there is strong global interference, and also provides a practical way for determining when and where to apply this technique.
在之前的工作中，我们引入了一种基于自适应滤波的减少全局干扰的新方法，以提高用近红外光谱（NIRS）无创测量的诱发血流动力学反应的对比度噪声比（CNR）。在此，我们探讨如何普遍应用所提出的自适应滤波方法。分析了从15名个体收集的总共156次诱发视觉反应测量数据。将视觉刺激前休息期间收集的远源探测器间距和近源探测器间距测量之间的相似性（相关性）用作全局干扰主导性的指标。给出了作为休息期相关系数函数的氧合血红蛋白（O(2)Hb）和脱氧血红蛋白（HHb）中CNR改善的详细分析。结果表明，对于O(2)Hb测量，66%表现出显著的全局干扰。对于这个以全局干扰为主导的数据集，71%的测量在自适应滤波后显示出CNR改善，平均CNR改善为60%。对于HHb未观察到CNR改善。本研究证实了我们之前的发现，即当存在强烈的全局干扰时，自适应滤波提供了一种提高CNR的有效方法，并且还提供了一种确定何时何地应用该技术的实用方法。
