1 Grey versus white matter segmentation of the human conus medullaris: reliability and variability in healthy volunteers Marios C. Yiannakas 1,a , Martina D. Liechti 1,2,a , Nuttakarn Budtarad 1 , Patrick Cullinane 1 , Xixi Yang 1,2 , Ahmed T. Toosy 1 , Jalesh N. Panicker 2,b , Claudia A. M. Gandini Wheeler-Kingshott 1, 3,b ¹NMR Research Unit, Queen Square MS Centre, Department of Neuroinflammation, UCL Institute of Neurology, University College London, London, United Kingdom. 2 Department of Uro-Neurology, The National Hospital for Neurology and Neurosurgery and UCL Institute of Neurology, London, United Kingdom. 3 Department of Brain and Behavioral Sciences, University of Pavia, Pavia, PV, Italy. a Joint first authors. b Joint senior authors. Running title: MRI assessment of the neurologically intact conus medullaris