MAGNIFY - Pulmonary Magnetic Resonance Imaging for Cystic Fibrosis

General Inclusion criteria For eligibility into MAGNIFY, subjects should meet all of the following criteria: 1. A confirmed clinical diagnosis of CF, consisting of 2 confirmed disease-causing CFTR mutations along with either positive sweat chloride (\>60mmol/L, measured before starting CFTR modulator therapy) or a clinical picture consistent with CF as judged by a senior CF physician. Patients will be under one of named regional CF centres above. 2. Be able to attend the local facility for scans (Royal Hallamshire Hospital, Sheffield). For eligibility into 129Xe-MRI and lung function (cohort 1,2 and 3) 1. Aged 5 years and above 2. FEV1 \>30% predicted (best in the previous 6 months) For eligibility for cohort 1 1\. Previous participation in the MMAVIC study, with at least one prior visit where lung ventilation MRI was successfully measured. For eligibility into cohort 4 for 1H MRI only: 1\. Aged between 1 and 5 years of age General Exclusion criteria Patients who meet any of the following criteria will be excluded from the study. Further exclusions may be applied at the discretion of the principal investigators. 1. Previous lung transplant. 2. Infection with organisms of the Burkholderia cepacia complex, MRSA or Mycobacterium abscessus. 3. Pregnancy. 4. Resting SpO2 \< 90% in room air. 5. Inability to comfortably lie supine for more than 60 minutes. 6. Any contraindication(s) to MRI scanning as per the MRI questionnaire used in clinical practice by the University of Sheffield MRI unit, Royal Hallamshire Hospital. Research visit (temporary) exclusion criteria 1. Pulmonary exacerbation within 4 weeks as defined by no new treatments in that time, no clinically significant change in their symptoms or spirometry (as judged by attending physician). 2. Pregnancy. Patients who become pregnant prior to consent or during the study can remain in the study. However, no research visits will take place during pregnancy.