1. Department of Public Health and Clinical Medicine, Umeå University, Universitetstorget 4 , Umeå, 901 87 , Sweden
2. Department of Radiation Sciences, Biomedical Engineering, Umeå University, Universitetstorget 4 , Umeå, 901 87 , Sweden
3. Department of Community Medicine and Rehabilitation, Umeå University, Universitetstorget 4 , Umeå, 901 87 , Sweden