Manuscript received September 26;
1996. This work was supported in part by the National Science Foundation under Grant BCS-9 157 202 and the Center for High Performance Computing at the University of Texas. The authors are with the Biomedical Engineering Program;
Department of Electrical and Computer Engineering;
University of Texas;
Austin;
TX 78731 USA. Publisher Item Identifier S 1077-260X(96)09666-9;