Adrenal masses: differentiation with chemical shift, fast low-angle shot MR imaging

The purpose of this study was to investigate the efficacy of chemical shift, fast low-angle shot (FLASH) imaging at 1.5 T to differentiate adrenal masses. The materials included patients with adrenocortical adenomas (n = 32), metastatic tumors (n = 17), and pheochromocytomas (n = 4). FLASH images were obtained with breath holding at 100/11 (repetition time msec/echo time msec) (out-of-phase images) and 100/13 (in-phase images) and a flip angle of 20 degrees to differentiate the lipid contents in the adrenal tumors. The signal-intensity (SI) indexes of adrenal masses ([SI on IP - SI on OP]/[SI on IP x 100]), where IP = in-phase image and OP = out-of-phase image, were calculated. All adenomas had SI indexes of more than 5%, while SI indexes of metastatic tumors and pheochromocytomas were less than 5%, with accuracy of 100% in the differentiation between adenoma and nonadenoma. Hyperfunctioning adenoma, however, could not be differentiated from nonhyperfunctioning adenoma. Chemical shift FLASH imaging was superior to the calculated T2 in the characterization of adrenal masses.