1. Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milano 20133, Italy e-mail:
2. Department of Biomedical Engineering, The Pennsylvania State University, State College, PA 16802 e-mail:
3. Mem. ASME Department of Biomedical Engineering, The Pennsylvania State University, University Park, PA 16802 e-mail:
4. Mem. ASME Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milano 20133, Italy e-mail: