A child presents with respiratory distress. A vascular ring is suspected. Investigation of choice is:

MRI Sabiston writes-"Initially, diagnosis is made by a high index of suspicion, and the barium swallow is the first investigation. Echocardiography can document an abnormal head and neck vessel branching pattern, excluding intracardiac abnormalities. MRI provides complete anatomic detail." A vascular ring is a condition in which an anomalous configuration of the arch and/or its associated vessels completely or incompletely surrounds the trachea and oesophagus causing compression of these structures. Neonates present with respiratory distress, older children present with stridor or dysphagia. The two most common types of complete vascular rings, which account for 85-95% of cases, are double aoic arch and right aoic arch with left ligamentum aeriosum. Tracheomalacia results from compression of the trachea by vascular rings. Surgical division of a vascular ring is the only definitive treatment.