Evaluation of magnetic resonance sequences in imaging mediastinal tumors.

Ten patients having a mediastinal tumor were studied with magnetic resonance imaging (MRI) using from two to four imaging sequences. Seven had bronchial carcinoma and three had benign lesions. The sequences included the spin-echo technique with repetition time (TR) values of 0.5, 1.0, and 2.0 sec and echo time (TE) values of 28 and 56 msec, and the inversion-recovery technique. The signal-intensity ratios of the mediastinal mass and mediastinal fat, which are a measure of image contrast, were compared for the different imaging sequences. Also signal-to-noise ratios were measured relative to both mediastinal fat and mediastinal mass. With spin-echo imaging, decreasing the TR value resulted in an increase in mass/fat contrast in all patients, making the masses easier to detect, but this also resulted in decreased signal-to-noise ratios. Inversion-recovery imaging with the sequence used resulted in a greatly increased mass/fat contrast, because of a relative decrease in signal from the mass. However, in two of four patients studied with this technique, the mass was so low in intensity that it could not be distinguished from the trachea or mediastinal vessels, and in one of these four, a lung nodule was also invisible. Spin-echo imaging with both short and long TR values provides good tissue contrast and good signal-to-noise ratios.