[1] Univ Akron, Dept Elect & Comp Engn, Akron, OH 44325 USA
[2] Univ Manchester, Sch Elect Engn & Elect, Manchester M60 1QD, Lancs, England
[3] Univ London Imperial Coll Sci Technol & Med, Dept Elect & Elect Engn, London SW7 2BT, England
[4] Natl Tech Univ Athens, Dept Elect & Comp Engn, GR-15773 Athens, Greece
[5] Univ Genoa, Dipartimento Ingn Biofis & Elettron, I-16145 Genoa, Italy
[6] Democritus Univ Thrace, Dept Prod & Management Engn, Lab Robot & Automat, GR-67100 Xanthi, Greece
[7] Varian Med Syst, Ginzton Technol Ctr, Palo Alto, CA 94304 USA