1. Respiratory Division, University Hospital UZ Brussel, Vrije Universiteit Brussel, Brussels, Belgium.
2. Research Group Fluid Mechanics and Thermodynamics, Department of Mechanical Engineering, Vrije Universiteit Brussel, Brussels, Belgium.
3. Airway Disease Section, National Heart and Lung Institute, Imperial College London and Royal Brompton Hospital, London, United Kingdom.
4. Nuclear Medicine Department, Royal Brompton Hospital, London, United Kingdom.
5. Radiology Department, University Hospital UZ Brussel, Vrije Universiteit Brussel, Brussels, Belgium.