Bronchial remodeling is a major pathological feature of asthma. Non-invasive assessment of this bronchial remodeling is a crucial issue for asthma patients' follow-up. Currently, computed tomography (CT) is the method of reference to evaluate and quantify bronchial thickness but it remains unable to differentiate bronchial inflammation from remodelling and is a radiation-based technique. Magnetic Resonance Imaging (MRI) with Ultrashort Echo Time (UTE) pulse sequences is a promising non-ionizing alternative for lung imaging. Our objective is to evaluate bronchial thickness in asthma patients using CT and MRI-UTE, and to test the agreement between both techniques.

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.

Inclusion Criteria:

• Male or female aged more than 18 years.
• Patients with diagnosis of asthma according to 2016 "Global Strategy for Asthma Management and Prevention (GINA)" definition
• Pulmonary Function Testings (PFTs) should be available within a maximum of 30 days before inclusion.
• With a written informed consent.

Exclusion Criteria:

• Subjects without any social security or health insurance.
• History of chronic obstructive pulmonary disease, lung fibrosis, pulmonary hypertension, lung cancer or cystic fibrosis.
• Pregnancy or breastfeeding women.
• MRI contraindications: Magnetically activated implanted devices (cardiac pacemakers, insulin pumps, neurostimulators, cochlear implants), metal inside the eye or the brain (aneurysm clip, ocular foreign body), cardiac valvular prosthesis (Starr-Edwards pre-6000), subject with claustrophobia, waistline circumference over 200 cm.