This is a prospective, longitudinal observational study conducted at The Hospital for Sick Children (SickKids). The purpose of this study is to evaluate the ability of MRI to detect changes in lung structure and function in CF patients receiving CFTR-modulator therapy. Participants who meet eligibility criteria and consent to the study will undergo study procedures which include spirometry and body plethysmography (optional), multiple breath washout testing, MRI and measurement of quality of life. The study will consist of three to six study visits for Group 1, 2 and 3: baseline, one month (±1 week) and 6 month (±2 week) and if they re-consent then 3 additional visits of 1 year (±6 months). (2 years (±6 months) and 3 years (±6 months) follow-up. Some participants in Group 2 may transition to Group 3. This study includes three populations of interest: Group 1: 25 healthy volunteers, Group 2: 25 patients with stable CF lung disease , Group 3: 20 patients with CF lung disease anticipated to receive treatment with CFTR-modulator therapy and Group 4: 18 patients with CF who are between 4-8 years old and are starting triple combination modulator therapy using the rapid lung and abdominal imaging methods.