[1] Royal Perth Hosp, Dept Neurosurg, Perth, WA, Australia
[2] Sir Charles Gairdner Hosp, Dept Neurosurg, Perth, WA, Australia
[3] Royal Perth Hosp, Dept Med Engn & Phys, Perth, WA, Australia
[4] Royal Perth Hosp, Dept Intens Care, Perth, WA, Australia
[5] Univ Western Australia, Sch Populat Hlth, Perth, WA 6009, Australia