Dynamic MR imaging of adrenal masses at 0.5 T

The purpose of this study is to determine the clinical efficacy of dynamic MR imaging at 0.5 to diagnose adrenal masses. The series consisted of 19 patients with 20 lesions, including five pheochromocytomas, four adrenocortical adenomas, eight metastatic tumors and three neurinomas of juxtaadrenal regions. We used a superconducting magnet of Toshiba (MRT-50A). Sequential gradient-echo images (TR/TE=100/14 ms, flip angle 60deg) were obtained every two minutes after an intravenous administration of Gd-DTPA. Relative mass-to-fat signal intensity ratios (IM/IF) were calculated on all images. In some cases of pheochromocytomas, the IM/IF values showed signigicant increase immediately after the administration, with faint washout of the contrast material. Some cases of adrenocortical adenomas also showed maximum IM/IF values just after the administration, but the washout was fast. However, other cases of pheochromocytomas and adrenocortical adenomas showed neither strong contrast uptake nor rapid washout. In the cases of neurinomas, highest IM/IF values were noted at five to nine minutes. On the other hand, metastatic tumors showed no definite patterns of time related change of IM/IF values, therefore it was difficult to differentiate metastases from other tumors. In some particular cases, dynamic MR images at 0.5 T may help to specify adrenocortical adenoma, pheochromocytoma, or neurinoma. However, this method does not contribute to differentiate adrenal masses, since metastasis cannot be ruled out in all cases. (author)