Characterization of adrenal tumors by chemical shift fast low-angle shot MR imaging: Comparison of four methods of quantitative evaluation

OBJECTIVE. The aim of our study was to assess quantitative methods of distinguishing adenomas from malignant adrenal lesions using chemical shift fast low-angle shot MR imaging. MATERIALS AND METHODS. We assessed 102 adrenal tumors in 88 patients (27 hyperfunctioning and 44 nonhyperfunctioning adenomas, 19 metastases, nine pheochromocytomas, and three other adrenal tumors) using chemical shift MR imaging. On the chemical shift imaging, signal intensity index, calculated as [(signal intensity on in-phase imaging - signal intensity on opposed-phase imaging) / (signal intensity on in-phase imaging)] x 100%, was compared with the adrenal-to-spleen ratio, adrenal-to-muscle ratio, and adrenal-to-liver ratio for signal change on opposed-phase fast low-angle shot MR imaging. The tissues in the spleen, paraspinal muscle, and liver were reference tissues. RESULTS. The signal intensity index had several advantages over the other three parameters calculated. We found no overlap in indexes between adenomas and metastatic tumors. The accuracy in distinguishing adenomas from metastatic tumors was 100% if the cutoff value of the signal intensity index selected was 11.2-16.5%. CONCLUSION. The signal intensity index is the most reliable evaluation method for differentiating adrenal adenomas from metastatic adrenal tumors.