1. Department of Neuroradiology (LD, CM), Imperial College Healthcare NHS Trust, London, UK; National Centre for Human Retrovirology (DD, GPT, ND), Imperial College Healthcare NHS Trust, London, UK; Section of Virology, Department of Infectious Disease (GPT), Imperial College London, UK; Department of Neurology (GPT), Imperial College Healthcare NHS Trust, London, UK; Department of Neurology (GPT), Chelsea and Westminster Hospital NHS Trust, London, UK.