1. Department of Neonatology, Rigshospitalet and University of Copenhagen, Blegdamsvej 9, Copenhagen 2100, Denmark
2. Biomedical Optics Research Laboratory, Department of Medical Physics and Bioengineering, University College London, London, UK
3. Biomedical Optics Research Laboratory, Division of Neonatology, University of Zurich, Zurich, Switzerland