Describing the Nonstationarity Level of Neurological Signals Based on Quantifications of Time–Frequency Representation
Describing the Nonstationarity Level of Neurological Signals Based on Quantifications of Time–Frequency Representation
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DOI：
10.1109/tbme.2007.893497
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发表时间：
2007-09
影响因子：
4.6
通讯作者：
S. Tong;Zhengjun Li;Yisheng Zhu;N. Thakor
中科院分区：
文献类型：
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作者：
S. Tong;Zhengjun Li;Yisheng Zhu;N. Thakor
众所周知，大多数神经信号（包括脑电图（EEG）、诱发电位（EP）和局部场电位（LFP））都是时变和非平稳的，尤其是在某些病理条件下。目前，对这种非平稳信号最广泛使用的定量工具是时频表示（TFR），它展示了不同频率分量的时间演化。然而，TFR并不直接提供非平稳性水平的定量测量，例如，过程偏离平稳性的程度。在这项研究中，我们引入了三种不同的量化TFR（qTFR）来表征涉及信号的非平稳性水平：1）平稳度（DS）; 2）边缘谱的香农熵（SE）; 3）TFR和均匀分布之间的Kullback-Leibler距离（KLD）。这些描述符提供信号的平稳性的定量分析，使得可以比较不同信号的平稳性。在本研究中，我们获得了缺氧缺血性脑损伤（HI）前后脑电信号的时频响应，并检测了脑电信号的平稳性。DS、SE和KLD可指示HI损伤后各频率EEG的非平稳性变化，尤其是在上δ和下θ频带（例如，[2 Hz，8 Hz]）以及β 2频带（例如，[22 Hz-26 Hz）。此外，它表明，脑电的平稳性改变不同的频率后，HI损伤。
Most neurological signals including electroencephalogram (EEG), evoked potential (EP) and local field potential (LFP) have been known to be time varying and nonstationary, especially in some pathological conditions. Currently, the most widely used quantitative tool for such nonstationary signals is time-frequency representation (TFR) which demonstrates the temporal evolution of different frequency components. However, TFR does not directly provide a quantitative measure of nonstationarity level, e.g., how far the process deviates from stationarity. In this study, we introduced three different quantifications of TFR (qTFR) to characterize the nonstationarity level of the involving signals: 1) degree of stationarity (DS); 2) Shannon entropy (SE) of the marginal spectrum; and 3) Kullback-Leibler distance (KLD) between a TFR and a uniform distribution. These descriptors provide quantitative analysis of stationarity of a signal such that the stationarity of different signals could be compared. In this study, we obtained the TFRs of the EEG signals before and after the hypoxic-ischemic (HI) brain injury and examined the stationarity of the EEG. DS, SE, and KLD can indicate the nonstationarity change of EEG at each frequency following the HI injury, especially in the upperdelta-and lower thetas-band (e.g., [2 Hz, 8 Hzi) as well as in the beta2 band (e.g., [22 Hz-26 Hzi). Moreover, it is shown that the stationarity of the EEG changes differently in different frequencies following the HI injury.