Compression of ECG signals by optimized quantization of discrete cosine transform coefficients

This paper presents an ECG compressor based on optimized quantization of Di screte Cosine Transform (DCT) coefficients. The ECG to be compressed is par titioned in blocks of fixed size, and each DCT block is quantized using a q uantization vector and a threshold vector that are specifically defined for each signal. These vectors are defined, via Lagrange multipliers, so that the estimated entropy is minimized for a given distortion in the reconstruc ted signal. The optimization method presented in this paper is an adaptatio n for ECG of a technique previously used for image compression. In the last step of the compressor here proposed, the quantized coefficients are coded by an arithmetic coder. The Percent Root-Mean-Square Difference (PRD) was adopted as a measure of the distortion introduced by the compressor. To ass ess the performance of the proposed compressor, 2-minute sections of all 96 records of the MIT-BIH Arrhythmia Database were compressed at different PR D values, and the corresponding compression ratios were computed. We also p resent traces of test signals before and after the compression/decompressio n process. The results show that the proposed method achieves good compress ion ratios (CR) with excellent reconstruction quality. An average CR of 9.3 :1 is achieved for PRD equal to 2.5%. Experiments with ECG records used in other results from the literature revealed that the proposed method compare s favorably with various classical and state-of-the-art ECG compressors. (C ) 2001 IPEM. Published by Elsevier Science Ltd. All rights reserved.