Biomedical Engineering Laboratory, Department of Telecommunications and Control Engineering, Escola Politecnica, University of Sao Paulo, Sao Paulo, Brazil.
Biomed Eng Online. 2014 Mar 10;13(1):25. doi: 10.1186/1475-925X-13-25.
New technologies for data transmission and multi-electrode arrays increased the demand for compressing high-density electromyography (HD EMG) signals. This article aims the compression of HD EMG signals recorded by two-dimensional electrode matrices at different muscle-contraction forces. It also shows methodological aspects of compressing HD EMG signals for non-pinnate (upper trapezius) and pinnate (medial gastrocnemius) muscles, using image compression techniques.
HD EMG signals were placed in image rows, according to two distinct electrode orders: parallel and perpendicular to the muscle longitudinal axis. For the lossless case, the images obtained from single-differential signals as well as their differences in time were compressed. For the lossy algorithm, the images associated to the recorded monopolar or single-differential signals were compressed for different compression levels.
Lossless compression provided up to 59.3% file-size reduction (FSR), with lower contraction forces associated to higher FSR. For lossy compression, a 90.8% reduction on the file size was attained, while keeping the signal-to-noise ratio (SNR) at 21.19 dB. For a similar FSR, higher contraction forces corresponded to higher SNR CONCLUSIONS: The computation of signal differences in time improves the performance of lossless compression while the selection of signals in the transversal order improves the lossy compression of HD EMG, for both pinnate and non-pinnate muscles.
新的数据传输技术和多电极阵列提高了对高密度肌电图（HD EMG）信号压缩的需求。本文旨在压缩在不同肌肉收缩力下由二维电极矩阵记录的 HD EMG 信号。还展示了使用图像压缩技术对非羽状（上斜方肌）和羽状（内侧腓肠肌）肌肉的 HD EMG 信号进行压缩的方法学方面。
根据两种不同的电极顺序（平行和垂直于肌肉长轴），将 HD EMG 信号放置在图像行中。对于无损情况，压缩从单差信号获得的图像以及它们在时间上的差异。对于有损算法，压缩与记录的单极或单差信号相关的图像，用于不同的压缩级别。
无损压缩可将文件大小减少 59.3%（FSR），较低的收缩力与较高的 FSR 相关。对于有损压缩，在保持信噪比（SNR）为 21.19 dB 的情况下，文件大小减少了 90.8%。对于类似的 FSR，较高的收缩力对应较高的 SNR。
信号时间差异的计算可提高无损压缩的性能，而横向顺序信号的选择可提高羽状和非羽状肌肉的 HD EMG 的有损压缩性能。
