1. Hospital Sao Lucas, Porto Alegre, Brazil
2. Hospital Mae de Deus, Porto Alegre, Brazil
3. Department of Neurology, Harvard Medical School, Boston, MA, USA
4. Department of Radiology, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
5. Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil