Farina Darino, Kamavuako Ernest Nlandu, Wu Jian, Naddeo Francesco
Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, DK-9220 Aalborg, Denmark.
IEEE Trans Biomed Eng. 2008 Mar;55(3):914-22. doi: 10.1109/TBME.2007.906509.
A new class of spatial filters for surface electromyographic (EMG) signal detection is proposed. These filters are based on the 2-D spatial wavelet decomposition of the surface EMG recorded with a grid of electrodes and inverse transformation after zeroing a subset of the transformation coefficients. The filter transfer function depends on the selected mother wavelet in the two spatial directions. Wavelet parameterization is proposed with the aim of signal-based optimization of the transfer function of the spatial filter. The optimization criterion was the minimization of the entropy of the time samples of the output signal. The optimized spatial filter is linear and space invariant. In simulated and experimental recordings, the optimized wavelet filter showed increased selectivity with respect to previously proposed filters. For example, in simulation, the ratio between the peak-to-peak amplitude of action potentials generated by motor units 20 degrees apart in the transversal direction was 8.58% (with monopolar recording), 2.47% (double differential), 2.59% (normal double differential), and 0.47% (optimized wavelet filter). In experimental recordings, the duration of the detected action potentials decreased from (mean +/- SD) 6.9 +/- 0.3 ms (monopolar recording), to 4.5 +/- 0.2 ms (normal double differential), 3.7 +/- 0.2 (double differential), and 3.0 +/- 0.1 ms (optimized wavelet filter). In conclusion, the new class of spatial filters with the proposed signal-based optimization of the transfer function allows better discrimination of individual motor unit activities in surface EMG recordings than it was previously possible.
提出了一类用于表面肌电图（EMG）信号检测的新型空间滤波器。这些滤波器基于用电极网格记录的表面EMG的二维空间小波分解，并在将变换系数的一个子集置零后进行逆变换。滤波器传递函数取决于在两个空间方向上选择的母小波。提出了小波参数化，旨在基于信号对空间滤波器的传递函数进行优化。优化标准是使输出信号时间样本的熵最小化。优化后的空间滤波器是线性且空间不变的。在模拟和实验记录中，与先前提出的滤波器相比，优化后的小波滤波器显示出更高的选择性。例如，在模拟中，横向相距20度的运动单位产生的动作电位的峰峰值幅度之比为8.58%（单极记录）、2.47%（双差分）、2.59%（常规双差分）和0.47%（优化后的小波滤波器）。在实验记录中，检测到的动作电位持续时间从（平均值±标准差）6.9±0.3毫秒（单极记录）降至4.5±0.2毫秒（常规双差分）、3.7±0.2毫秒（双差分）和3.0±0.1毫秒（优化后的小波滤波器）。总之，具有所提出的基于信号的传递函数优化的新型空间滤波器，在表面EMG记录中能够比以往更好地辨别单个运动单位的活动。
