[1] Univ Hosp Bristol NHS Fdn Trust, Bristol Royal Infirm, Bristol Adult Cyst Fibrosis Ctr, Bristol BS2 8HW, Avon, England
[2] Bristol Royal Infirm & Gen Hosp, Dept Clin Radiol, Bristol, Avon, England
[3] Southmead Hosp, Med Sch Unit, Bristol, Avon, England
[4] Univ Bristol, Dept Cellular & Mol Med, Bristol BS8 1TH, Avon, England