Assessment of Emphysema Using 1.5T MRI With UTE Pulse Sequences

Overview

Emphysema is a major pathological feature of Chronic Obstructive Pulmonary Disease (COPD). Non-invasive assessment of emphysema is a crucial issue for the phenotype and follow-up of COPD patients. Currently, CT is the method of reference to evaluate and quantify emphysema but it remains a radiation-based technique. Magnetic Resonance Imagery (MRI) with ultrashort echo time (UTE) pulse sequences is a promising non-ionizing alternative for lung imaging. Our objective is to evaluate emphysema in COPD patients using CT and MR-UTE, and to test the agreement between both techniques.

COPD is a major public health problem and is pathologically characterized by lung emphysema and bronchial remodeling. Emphysema is defined as an irreversible destruction of alveolar walls and subsequent enlargement of air spaces. New targeted therapies against emphysema are currently developed, thereby stressing the need for non-invasive tools aimed at quantifying emphysema. Multi-slice computed tomography (CT) is the method of reference to quantify emphysema but involves ionizing radiation, thus limiting the possibility of long-term follow-up. MRI is a non-ionizing 3D imaging technique; however, lung MRI is technically challenging with the result that it is currently not 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 signal from the lung parenchyma. We aim at using 3D T1-weighted UTE pulse sequences on a 1.5T magnet (Avanto dot, Siemens) in COPD patients in order to distinguish normal lung from emphysematous areas. Thirty COPD patients and 10 volunteers are expected to take part in the study. All will benefit from Pulmonary Functional Testing (PFT), CT and MRI. Our strategy will consist in quantifying pulmonary emphysema using MRI and CT in those subjects, testing for correlations between MR and CT measurements and assessing the reproducibility of emphysema quantification using MRI. Our objective is to demonstrate that MR-UTE pulse sequence at 1.5T is accurate and reproducible in evaluating and quantifying pulmonary emphysema.

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