The aim of this study is to compare a new Magnetic Resonance Imaging (MRI)protocol, including a new MRI sequence for visualization of lung parenchyma, to computed tomography as the gold standard for the evaluation of thoracic region in children.

The potential effects of ionizing radiation are of particular concern in children. Exposure to ionizing radiation of medical origin is responsible for an increased risk of brain tumors and hematopoietic lineage in children. It is therefore necessary to find alternative to the use of irradiating imaging examinations. Currently, computed tomography (CT) is the gold standard in the study of lung diseases and is used in children deepening of standard radiography in acute or chronic situations, sometimes requiring iterative controls. Chest CT delivers a radiation dose equivalent to up to 500 days of natural exposure. Moreover, for the analysis of mediastinal and vascular structures it requires an intravenous injection of iodinated contrast, potentially source of nephrotoxicity and anaphylactic reactions. Recently, new developments in Magnetic Resonance Imaging (MRI) have shown interest in the study of lung diseases when they are responsible for filling of aeric structures (mucoid impaction in cystic fibrosis, alveolar filling in infectious process and tumor) and in the analysis of vascular and mediastinal structures and heart. However, the aerated lung presenting a very low density of protons, and MRI being particularly sensitive to artifacts from cardiac and respiratory movements, sequences currently used in MRI remain insufficient in the analysis of pulmonary structures and pathologic conditions not filling aeric spaces (bronchial, cystic, emphysematous or interstitial diseases). The aim of this study is to test in clinical practice, a new MRI sequence for visualizing lung parenchyma, 3D zero Time Echo (Advanced ZTE) and to propose a protocol combining several MRI sequences without injection as an alternative to chest CT with or without contrast medium injection in childhood.

The proposed hypotheses are :

1. MRI sequence Advanced ZTE allows visualization of normal and pathological lung parenchymal structures.
2. A complete MRI protocol, without injection, including this sequence to those already used in clinical practice could replace the enhanced CT in most pediatric indications.

The principal objective of the study is to evaluate the Advanced ZTE sequence in the visualization of lung parenchyma structures in comparison to CT scan in lung window as gold standard.

Inclusion Criteria:

• Children, aged 6-16 years,
• Introducing one or more clinical indications for performing a chest CT with and without contrast injection within 1 day to 3 months.
• Monitoring at the Necker Hospital.
• Signature of consent by a holder of parental authority.
• Patient affiliated or beneficiary of a social security

Exclusion Criteria:

• Contraindication to performing MRI: claustrophobia, cochlear implant, nerve stimulator, pacemaker implant or intra-cardiac metallic foreign body, chest or eye.
• Need for MRI under sedation or general anesthesia.
• Indication of an emergency CT within less than 12 hours (especially suspected pulmonary embolism).