Fourier Decomposition MRI is a recent development in functional lung MRI (1). This non-contrast-enhanced ventilation-perfusion imaging is based on lung signal changes during respiration and cardiac cycle. Periodic signal alterations in lung parenchyma can be transformed in ventilation and perfusion-weighted maps by means of Fourier decomposition allowing for site-resolved assessment of lung function. Fourier Decomposition MRI has been successfully validated against V/Q scintigraphy, contrast-enhanced perfusion MRI and ventilation MRI using hyperpolarized gases (2-4). The purpose of the present study is to evaluate the feasibility of Fourier Decomposition MRI for lung ventilation imaging in patients with cystic fibrosis.Fischer et al. (5) recently updated the classic approach by adding cardiac and respiratory self-navigation of quasi randomly sampled data and using a 2D FLASH sequence with DC signal acquisition for self navigation. Further technical details of data acquisition and image reconstruction have been described before (5). This approach named SENCEFUL (Self-gated Non-Contrast-Enhanced Functional Lung imaging) was used for the present work. SENCEFUL ventilation MRI was performed on 7 cystic fibrosis patients and 7 age-matched healthy controls using a 1.5T system (Magnetom Aera, Siemens Healthcare, Erlangen, Germany). Ventilation measurements were quantified based on the method proposed by Zapke et al., providing quantification in ml gas exchange per ml lung volume (6). Measurements of tidal breathing and of ventilation in deep breathing were performed. Quantitative lung ventilation maps were reconstructed and ventilation values were recorded for the entire lung, as well as for both upper and lower quadrants. Thus, each coronal map provided 5 quantitative ventilation measurements. Results for patients with cystic fibrosis and healthy controls were consecutively compared using a t-test for independent samples.Fourier Decomposition MRI using the SENCEFUL approach was successfully performed in all patients and volunteers without periprocedural complications. Under tidal breathing, mean quantitative ventilation of the entire lung was significantly lower for patients with cystic fibrosis when compared to the healthy controls (0.09±0.02 vs. 0.13±0.02 ml/ml, p=0.005). Comparable results were found under deep breathing conditions (0.17±0.04 vs. 0.25±0.05 ml/ml, p=0.016). Minimum and maximum values were also lower for patients with cystic fibrosis under tidal (min. 0.07 vs. 0.09 ml/ml; max. 0.12 vs. 0.15 ml/ml) and deep breathing (min. 0.11 vs. 0.17 ml/ml; max. 0.23 vs. 0.34 ml/ml). Measurements in the single lung quadrants provided similar results. Table 1 and Figure 1 give detailed information regarding the quantitative measurements. The reconstructed functional ventilation maps were of diagnostic quality and indicated mostly lower ventilation values and increased inhomogeneity in patients with cystic fibrosis (Figure 2).First measurements using SENCEFUL demonstrate that quantitative ventilation values of patients with cystic fibrosis significantly differ from those of healthy subjects. Lower ventilation values are supposed to be caused by static hyperinflation, which is well known in cystic fibrosis and leads to an increase of the intrathoracic gas volume. In consequence, higher residual volumes lead to a decrease of the inspiratory reserve in cystic fibrosis patients. Beside static hyperinflation, bronchial wall thickening, obstruction or mucus plugging might also contribute to the ventilation inhomogeneities observed in the functional maps. These maps allow for site-resolved assessment of the ventilation without application of any contrast or radiation being of special interest in follow-up examinations or for planning of interventional procedures such as bronchoscopy and/or bronchial lavage e.g. in case of atelectasis resulting from mucus plugging. However, the technique does currently not allow to safely distinguish between patients and healthy persons as the phenotype of the disease is variable and ventilation can be nearly unimpaired in mild courses or due to effective therapy. Further research is necessary to evaluate the prognostic value of the observed alterations in ventilation and for correlation of the quantitative measurements to clinical parameters used for disease monitoring.