Assessment of Emphysema Using 1.5T MRI With UTE Pulse Sequences

Assessment of Emphysema in COPD Patients Using 1.5T MR Imaging With Ultrashort Echo Time (UTE) Pulse Sequences

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.

Inclusion Criteria:

• Male or female aged more than 40 years.
• COPD group: patients with diagnosis of COPD at distance (minimum 4 weeks) from any acute exacerbation; staging 1-4 according to 2010 GOLD guidelines. PFTs and chest CT-scan should be available within a maximum of 30 days before inclusion.
• Control group: subjects without any chronic symptoms such as cough or expectoration (St-Georges symptoms scoring < 5%), with normal chest CT-scans performed in the pretherapeutic work-up of extrapulmonary cancers within a maximum of 30 days before inclusion. These subjects will be age- and sex-matched with COPD patients.
• With a written informed consent and health insurance.

Exclusion Criteria:

• Subjects without any social security or health insurance.
• History of asthma, lung fibrosis, pulmonary hypertension or cystic fibrosis.
• Pregnancy.
• Any respiratory treatment for control subjects.
• 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.