Magnetic resonance imaging of mediastinal vessels

MRI complements echocardiography and cineangiography in the evaluation of the great vessels. Advantages of echocardiography are its low cost, ready availability, and portability. Similar to echocardiography, MRI is noninvasive and lacks ionizing radiation, but it also has the advantages of multiplanar imaging and large field of view. This article reviews the indications for MRI of the great vessels of the chest and the magnetic resonance (MR) appearance of some of the more common anomalies of the pulmonary arteries, aorta, and systemic and pulmonary veins. MRI techniques The thoracic vessels can usually be completely imaged with a T1-weighted spin-echo sequence followed by three-dimensional (3D) gadoliniumenhanced MR angiography. These sequences can be supplemented with a cine gradient-echo technique, using segmented k-space acquisition (Fastcard or Fastcine). Spin-echo and cine gradient echo techniques including segmented k-space acquisition, safety considerations, and sedation requirements have been previously described Contrast-enhanced MR angiography takes advantage of the T1 shortening property of paramagnetic agents (such as gadolinium chelates) and 3D imaging. The advantages of 3D gadoliniumenhanced MR angiography over other MRI techniques for the evaluation of the thoracic vessels include (a) rapid acquisition, (b) ability to image vessels in any plane, and (c) absence of a dephasing artifact. 3D gadolinium-enhanced MR angiography of the thoracic vessels in infants and young children is performed with a nonbreath-hold technique; in older children and adolescents, a breathhold technique can be used. A double dose (0.2 mmol/kg body weight) of gadolinium suffices for optimal visualization of the mediastinal vessels Multiplanar volume reconstructions, as well as maximum intensity projections (MIP) and subvolume MIPs, are obtained in orthogonal and oblique plains to optimally display the vessel of interest. Pulmonary arteries Abnormalities of the pulmonary arteries often occur in association with obstructive lesions of the right ventricular outflow tract (eg, pulmonary artery atresia, stenosis, and hypoplasia), truncus arteriosus and its variants, and pulmonary sling