[1] Stavanger Univ Hosp, Norwegian Ctr Movement Disorders, NO-4005 Stavanger, Norway
[2] Stavanger Univ Hosp, Dept Radiol, Stavanger, Norway
[3] Univ Bergen, Inst Clin Med, N-5020 Bergen, Norway
[4] Haraldsplass Deaconess Univ Hosp, Geriatr Sect, Bergen, Norway
[5] Kings Coll London, Wolfson Ctr Age Related Dis, London WC2R 2LS, England