Late Breaking Abstract - Use of ultra-low dose CT does not impact structure-function relationships in early Cystic Fibrosis lung disease

Introduction: Impact of ultra-low-dose (ULD) computed tomography (CT) on quantification of structural disease and structure-function relationships in early Cystic Fibrosis (CF) lung disease have not been studied to date. Aim: To quantify structural lung disease and compare same session standard low radiation dose (LD) and ULD CT with pulmonary function measures in early CF lung disease. Methods: 46 CF subjects (age 11(6-17) yrs) with mild lung disease (FEV1≥70%pred) performed multiple breath washout (MBW), and spirometry directed paired inspiratory/expiratory CT with LD (CTDIvol: 1.23 mGy) and ULD (CTDIvol: 0.22 mGy). Quantification was performed automatically by validated institutional CT software. Results: Effective radiation dose was reduced by 78% in ULD vs. LD. Rates of abnormality were highest for CT and MBW and lowest for spirometry. Strong correlations were observed between LD and ULD readouts (gas trapping r=0.91, p<0.001). A consistently positive offset was observed for gas trapping in ULD vs. LD (7.5% greater with ULD, p<0.0001). Values are Pearson9s r unless stated,^ p Conclusions: Excellent correlations, yet significant differences in quantitative metrics were observed between LD and ULD CT. Good and preserved structure-function relationships with ULD support its use for quantitative CT in order to reduce radiation dose in CF populations.