[1] MIT, George R Harrison Spect Lab, Cambridge, MA 02139 USA
[2] MIT, Harvard Mit Div Hlth Sci & Technol, Cambridge, MA 02139 USA
[3] Univ Illinois, Coll Med, Urbana, IL 61801 USA
[4] Univ Illinois, Beckman Inst Adv Sci & Technol, Dept Elect & Comp Engn, Urbana, IL 61801 USA