Thesis defended on the 19th of December 2012 at the faculty of Medicine of the VU University Amsterdam. Promotors: Professor Fedde Scheele MD, PhD, (VUmc Amsterdam) and Professor Albert Scherpbier MD, PhD (University of Maastricht). Copromotors: Pim Teunissen, MD, PhD (University of Maastricht) and Carl Siegert MD, PhD (St. Lucas Andreas Hospital, Amsterdam).