Assessment of Bronchial Thickness Using MRI in Asthma

Asthma is a major public health problem, pathologically characterized by bronchial remodeling that leads to thickening of the bronchial wall. Computed tomography (CT) is the method of reference to quantify bronchial thickness but involves ionizing radiation, thus limiting the possibility of frequent and long-term follow-up. Magnetic Resonance Imaging (MRI) is a non-ionizing 3D imaging technique. However, lung MRI is technically challenging and is not currently used in routine practice. Indeed, both low proton density and susceptibility effects lead to a very low signal intensity derived from lung parenchyma. Recently, pulse sequences with Ultrashort Echo Time (UTE) have been implemented by the use of half radio-frequency excitations and radial projection reconstruction. These UTE sequences make it theoretically possible to retrieve more signals from the lung parenchyma. We aim at using 3D T1-weighted UTE pulse sequences on a 1.5T magnet (Avanto dot, Siemens) in asthma in order to assess bronchial thickness. Thirty patients with asthma including 10 patients with severe asthma will be enrolled in this study. All participants will benefit from CT and MRI. Our strategy will consist in quantifying bronchial thickness using MRI and CT in those patients, testing for correlations between MRI and CT measurements and assessing the reproducibility of bronchial thickness assessment using MRI. Our objective is to demonstrate that MRI-UTE pulse sequence at 1.5T is accurate and reproducible in evaluating and quantifying bronchial thickness.