The objective of the study is to implement a new method of performing chest CT imaging in young children with cystic fibrosis at Packard Children's Hospital. This technique will be used to evaluate early lung disease comparing quantitative chest CT air trapping and airway measurements with lung function measurements in infants, toddlers, and young children with chronic lung disease.

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.

Young children with cystic fibrosis at Packard Children's Hospital.