[1] SINTEF, Sect Epidemiol Res, N-7465 Trondheim, Norway
[2] Norwegian Univ Sci & Technol, Fac Med, Dept Neurosci, N-7034 Trondheim, Norway
[3] Norwegian Univ Sci & Technol, Inst Lab Med Children & Womans Dis, N-7034 Trondheim, Norway
[4] Norwegian Univ Sci & Technol, Dept Phys, N-7034 Trondheim, Norway
[5] St Olav Univ Hosp, Canc Clin, Clin Canc Res Unit, N-7465 Trondheim, Norway