[1] Univ Oxford, Nuffield Dept Clin Neurosci, Oxford, England
[2] Aneurin Bevan Univ Hlth Board, Dept Anaesthesia, Newport, England
[3] Intelligent Ultrasound, Cardiff, Wales
[4] Univ Oxford, Inst Biomed Engn, Oxford, England
[5] Oxford Univ Hosp NHS Fdn Trust, Nuffield Dept Anaesthet, Oxford, England