An ECG Acquisition System Prototype Design with Flexible PDMS Dry Electrodes and Variable Transform Length DCT-IV Based Compression Algorithm

Abstract

In this paper, a system is designed using flexible poly-dimethylsiloxane (PDMS) dry electrodes instead of wet electrodes to acquire electrocardiogram (ECG) signals. This flexible PDMS dry electrode (FPDE) is revised from the hard commercial biopotential conductive snap to a flexible electrode using a replica method that provides a reliable attachment for the ECG measurement method. The measurement result shows the proposed FPDE, which has the ability to acquire ECG signals, is comparable with the traditional wet electrodes applied in medicine. In addition, an acquisition circuit design integrated with commercial ICs and an field-programmable gate array (FPGA) platform is built for the development of long-term ECG monitoring. A variable-transform-length DCT-IV-based ECG compression algorithm with a higher quality score (QS) and a better compressing ratio (CR) is further proposed to significantly reduce the large amount of recording data in both storage and transmission. The QS parameter, which denotes a ratio of a CR value to a percent rms difference (PRD) value, is another key index applied to fairly evaluate the performance of various compression algorithms. DCT-IV is used as a unified transform kernel for ECG signal encoding and decoding, because the forward DCT-IV formula is the same as its inverse. It can be easily converted into a compact hardware accelerator with fewer hardware resources. To fairly evaluate the proposed compression algorithm, ECG signals sourced from MIT-BIT arrhythmia database with a sampling rate of 360 Hz are employed as the test patterns. The simulation results show the averages of CR, PRD, and QS to be 6.86, 0.18, 2.60, 1.68, 32.19, and 39.86, respectively, for all 48 lead-II patterns of the MIT-BIH database. Compared with Lee $et al.$ ’s DCT-II based algorithm, the QS value of the proposed method exhibits a 76% improvement. The experimental results clearly show that the proposed system would be a better choice for achieving ECG signal acquisition in the future.