Comparison of Chest-MRI to Chest-CT to Monitor Cystic Fibrosis (CF) Lung Disease

PURPOSE: The most important components of CF lung disease are bronchiectasis (BE) and trapped air (TA). Chest-CT is the current gold standard to diagnose and monitor BE and TA. Chest-MRI has been suggested as a radiation free alternative for CT but its spatial resolution is inferior to CT. The purpose of our study was to do a head to head comparison to assess the sensitivity of chest-CT and chest-MRI to monitor BE and TA air in CF. METHOD AND MATERIALS: This 2 center study was approved by the institutional review boards. 39 stable CF patients (20 female; mean age 16.7 years) had a chest-CT and -MRI performed on the same day. MRI (Siemens Avanto): BLADE proton density (PD) transversal (TR/TE/alpha: ∞/28 ms/180º), perfusion-weighted MRI (PWI) and Diffusion-weighted imaging (DWI). CT (Siemens Somatom): low dose; volumetric; end inspiration and end expiration: 120 kV, dose modulation. CTs and MRIs were anonymized and scored in random order by 2 independent observers using the validated CF-CT score and an equivalent CF-MRI scoring system. BE, TA and other structural components were scored. Scores are expressed as % of the maximal score. Mean scores of both observers were used for comparisons between CT and MRI scores. Statistics: Pearson; Intra class coefficient (ICC); Bland-Altman plots. Results mean (range). RESULTS: Interobserver variability (ICC): CT-BE (0,931); MRI-BE (0,892); CT-TA (0,917); MRI-TA (0,677) Correlation between CT-BE score and MRI-BE score (R=0,940, p=0,0001); between CT-TA and MRI-TA (r=0,511, p=0,005). Bland-Altman plots showed that MRI systematically underestimated severity of BE relative to CT. Moreover the Intraobserver variability was greater for MRI than CT (CT-BE vs.MRI-BE, 0,925 vs. 0,838). This head to head comparison between CT and MRI shows that there is good agreement between observers to identify structural abnormalities both on CT as on MRI and that CT-BE and MRI-BE correlated well. However the sensitivity of MRI to detect BE is still inferior to that of CT. The measurement of TA by MRI was not reliable. CONCLUSION: MRI is less sensitive compared to CT to detect BE and TA. We are currently testing alternative image analysis techniques to improve the sensitivity of MRI to monitor CF lung disease. CLINICAL RELEVANCE/APPLICATION: MRI shows to be less accurate compared to CT in the evaluation of CF lung disease, especially for AT. Further studies are needed to define the role of lung MR in CF follow-up.