1. From the Department of Radiology (T.N.M., M.C., X.X., F.V.G.) and Oxford Centre for Respiratory Medicine (N.R., A.H.N.), The Churchill Hospital, Oxford University Hospitals NHS Trust, Old Rd, Headington, OX3 7LE, England; Unit of Academic Radiology, Royal Hallamshire Hospital, University of Sheffield, Sheffield, England (N.J.S., J.M.W.); and Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Headington, England (T.D., V.G.).