The goal of this study is to evaluate the diagnostic agreement between, on the one hand, ultra-low dose CT and MRI with UTE pulse sequences, and on the other hand, standard CT scan, to quantify lung parenchyma patterns in thoracic sarcoidosis.

Sarcoidosis is a chronic disease involving lung and mediastinum in more than 90% of cases. Five to 25% of thoracic sarcoidosis are complicated by a severe fibrotic lung disease. Computed tomography (CT) is critical for the diagnosis of thoracic sarcoidosis as well as for therapeutic management. Repeated CT examinations, sometimes all life long, raise the issue of the cumulative radiation dose and subsequent risk of cancer, thus pushing the need for imaging techniques using low or no radiation dose. Based upon tube voltage and current reduction as well as iterative recontsruction, ultra-low dose CT (ULD CT) allows to lower the dose up to that of a traditional chest X-ray. Magnetic resonance imaging (MRI) using Ultrashort echo time (UTE) enables lung parenchyma imaging with high signal-to-noise and spatial resolution.

Inclusion Criteria:

• Patients aged 18 years or more
• Diagnosed with thoracic sarcoidosis according to ATS/ERS/WASOG 1999 criteria, with stages 2, 3 or 4, or lung function significantly impaired
• For whom a chest CT examination without contrast medium is indicated in the normal follow-up of the disease
• covered by social security
• having received information about the study and having given written informed consent

Exclusion Criteria:

• Pregnant woman
• Adult person unable to give consent
• Patient in exclusion period du to another protocol