Clinical utility of Gd-DTPA-enhanced magnetic resonance imaging in lung cancer.

Magnetic resonance (MR) imaging has both advantages and disadvantages in its application in lung cancer staging. Because of its ability to provide superior contrast resolution and to display structures in many planes, MR imaging is better than computed tomography (CT) for the detection of mediastinal and chest wall invasion. MR imaging also is more sensitive than CT for detection of hilar and mediastinal lymph node enlargement. Multiplanar T1- and T2-weighted images are optimal for differentiating lymph nodes from large vessels without the need for contrast enhancement; in these cases administration of Gd-DTPA provides no more information than plain MR images. MR studies should be used for examining patients with suspected mediastinal or chest wall invasion and those who have equivocal hilar or mediastinal adenopathy. The shortening effect of Gd-DTPA on the T1 value results in a high signal. This effect is dependent upon both the perfusion and diffusion of the contrast agent and the amount of extracellular fluid. The distribution of Gd-DTPA is similar to that of iodinated water-soluble contrast media. Gd-DTPA examination should be tailored to provide information regarding blood flow, vascularity, and permeability, none of which is easily appreciated on CT or plain MR images. Applications for which Gd-DTPA enhancement may be helpful include differentiating between malignant and benign pulmonary masses, differentiating between hilar lung cancer and peripheral postobstructive atlectasis or pneumonia, determining therapeutic effect after radiation therapy, and differentiating between recurrent or residual tumor and radiation pneumonitis.