Department of Mathematics & Statistics, McGill University, 805 Sherbrooke Street West, Montreal, H3A 0B9, Canada. irene.vrbik@mcgill.ca.|Department of Mathematics & Statistics, McGill University, 805 Sherbrooke Street West, Montreal, H3A 0B9, Canada. d.stephens@math.mcgill.ca.|Centre de recherche du CHUM, 900 rue Saint-Denis Tour Viger, H2X 0A9, Montreal, Canada. michel.roger.chum@ssss.gouv.qc.ca.|Faculty of Surgery (Medicine), McGill University, 1010 Sherbrooke Street West, Montreal, H3A 2R7, Canada. bluma.brenner@mcgill.ca.