| 1963 - 1967 | Air Intercept Control Officer, United States Marine Corps |
| 1967 - 1970 | Teaching Assistant, Department of Physics, University of California, Berkeley |
| 1970 - 1974 | Research Assistant, Lawrence Berkeley Laboratory (LBL) |
| 1974 - 1975 | Post-Doctoral Fellow, Physics Division, LBL |
| 1975 - 1989 | Physicist, Division of Biology and Medicine, Donner Laboratory, LBL |
| 1989 - 2006 | Senior Staff Physicist, LBL |
| 1989 - 1992 | Deputy Leader, Nuclear Medicine, Research Medicine and Radiation Biophysics Division, LBL |
| 1992 - 1996 | Deputy Head, Center for Functional Imaging, Life Sciences Division, LBL |
| 1994 - 1998 | NIH Diagnostic Radiology Study Section |
| 1998 - present | Associate Editor, IEEE Transactions on Medical Imaging |
| 2002 - present | International Advisory Board, Physics in Medicine & Biology |
| 2002 - 2003 | Visiting Scientist, Max Planck Institute for Neurological Research, Cologne, Germany |
| 2006 - present | Emeritus Senior Scientist, LBL |
| 2007 | NIH Small Business Medical Imaging Study Section |