SHIP-CT is a parallel study to SHIP001 (ClinicalTrials.gov Identifier NCT02378467). The primary hypothesis of SHIP001, which runs in North America, is that compared to IS, HS will improve the LCI, a measure of ventilation heterogeneity, during the 48-week treatment period among preschool children with CF. The SHIP-CT study (SHIP002) will use a nearly identical study design as the SHIP001 study, with similar eligibility criteria and treatment arms, to determine whether HS reduces structural lung disease as measured by chest computed tomography (CT), in addition to stabilizing or improving functional outcomes as measured by LCI.