Controlled Ventilation CT in CF Infants

Inclusion Criteria: 1. Infants and young children (age \~ 2/3 months to \< 5 years) 2. Diagnosed with cystic fibrosis with either 2 identified CFTR gene mutations, or a positive sweat chloride 3. Informed consent by parent or legal guardian. 4. Ability to comply with study visit procedures as judged by the investigator. Exclusion Criteria: 1. Acute wheezing and/or respiratory distress at either study visit. 2. Acute intercurrent respiratory infection, defined as an increase in cough, wheezing, or respiratory rate with onset in 1 week preceding Study visit. 3. Oxygen saturation \< 90% on room air at study visit. 4. Any medical condition that in the opinion of the investigator precludes subject participation.