33 Lung function tests are commonly used to monitor lung disease in cystic fibrosis (CF). While 34 practical, they cannot locate the exact origin of functional impairment. Contemporary magnetic 35 resonance imaging (MRI) techniques provide information on the location of disease but need of 36 contrast agents constrains their repeated application. We examined the correlation between functional 37 MRI, performed without administration of contrast agent, and lung clearance index (LCI) from 38

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... gen-multiple breath washout (N 2 -MBW). 39 40 Forty children with CF (median age 12.0 years, range 6-18) and twelve age-matched controls (HC) 41 underwent functional and structural MRI, and lung function tests on the same day. Functional MRI 42 provided semi-quantitative measures of perfusion (R Q ) and ventilation (R FV ) impairment as 43 percentages of affected lung volume. Morphological MRI was evaluated using CF-specific scores. LCI 44 measured global ventilation inhomogeneity. 45 46 MRI detected functional impairment in CF: R FV ranged from 19% to 38% and R Q from 16% to 35%. 47 R FV and R Q correlated strongly with LCI (r=0.76, p<0.0001; r=0.85, p<0.0001, respectively), as did 48 total morphology score (r=0.81, p<0.0001). All indices differed significantly between patients with CF 49 and HC, p<0.001. 50 51 Non-invasive functional MRI is a promising method to detect and visualize perfusion and ventilation 52 impairment in CF without need of contrast agents. 53 54 Keywords 55 Magnetic resonance imaging, lung function, nitrogen multiple breath washout, cystic fibrosis 56 57