1. Medical Physics Group, Department of Cardiovascular Science, University of Sheffield, Beech Hill Road, Sheffield S10 2RX, UK
2. The Rotherham NHS Foundation Trust, Rotherham Hospital, Moorgate Road, Rotherham S60 2UD, UK
3. Radboud University Medical Centre, Department of Surgery, P.O. Box 9101, 6500 HB Nijmegen, Netherlands