Body Surface Potential Maps Compression by Two-Level Thresholding

Abstract

Body Surface Potential Mapping (BSPM), is a technique used t o improve the spatial resolution of measurement of bioelectrical information originating from myocardial sources, which is poorly represented in standard ECG. The BSPM are represented as a series of 3-D maps, which are time consuming t o process and expensive t o store. Fine spatial details, which are usually extracted from low level surface potentials, were reported t o be significant in diagnostic electrocardiography. In spite of the growing interest in the technique, its use has not become common in clinics. This is due to the overwhelming amount of data recorded and lack of quantitative methods t o analyze them. A technique is presented which concurrently compresses the data and preserves fine but significant details. By accurately chosen two low positive levels thresholding of each map, a sequence of annula is generated which is shown t o describe the dynamic nature of the process and t o preserve the spatial details. This sequence of annula are further characterized by a set of parameters which quantify its dynamic behaviour. The parameters are: Time of annula sequence appearance, its duration, 3-D loci of centers of mass of the annula, distances between successive centers of mass, and cross-correlation coefficients between successive annula. Maps from 20 subjects have been studied (normals and various pathologies). It has been found that these indices, which vary in time, well represent the changes in location of the annula and their dynamic variations of shape.The indices have also been found t o be grouped together for the maps of the normals and each pathology.