MR imaging of the hilum and mediastinum: effects of cardiac gating.

The effect of cardiac gating (CG) on the diagnostic quality of magnetic resonance images of the hilum and mediastinum was evaluated by comparing gated with nongated scans in 20 patients. The advantages of CG varied depending on the regions and structures under study and the presence and extent of disease. In general, CG was more advantageous in normal subjects and patients with small or subtle lesions than in patients with advanced disease. In the posterior and superior portions of the thorax there was no clear-cut advantage of CG. Normal structures were usually seen slightly better on gated images, but lung and mediastinal masses were usually visualized equally well with or without CG. From the level of the pulmonary arteries to the diaphragm, gated images were superior for visualizing normal and abnormal structures in the hilum, mediastinum, and to a lesser extent, the lungs. Both hilar and mediastinal lymphadenopathy and mediastinal invasion at the level of the lung root were consistently better visualized with CG. Large masses were usually well demonstrated without CG, but the relationship of the mass to adjacent structures was better delineated with CG.