CHARACTERIZATION OF ADRENAL MASSES (LESS-THAN-5 CM) BY USE OF CHEMICAL-SHIFT MR-IMAGING - OBSERVER PERFORMANCE VERSUS QUANTITATIVE MEASURES

OBJECTIVE. The purposes of this study were to evaluate the ability of chemical shift MR imaging to differentiate 1- to 5-cm adrenal adenomas from metastases and to compare subjective interpretation with several different quantitative measures. SUBJECTS AND METHODS. Forty-three pa tients with 46 proved adrenal lesions (28 adenomas and 18 metastases) had MR imaging with a gradient-echo breath-hold technique and echo tim e varied to obtain in-phase and out-of-phase images. Qualitative analy sis of the MR images was done by three experienced observers, who repo rted their confidence in diagnosing the benignity versus the malignanc y of the adrenal masses on the basis of signal loss on out-of-phase im ages. Quantitative analysis was performed by calculating the differenc e in signal intensity between in-phase and out-of-phase images by use of regions of interest (signal intensity index) and by use of adrenal- liver, adrenal-spleen, and adrenal-muscle signal intensity ratios. Res ults between quantitative and qualitative measures were compared by us e of receiver operating characteristic (ROC) analysis. RESULTS. The me an signal intensity was significantly different between adenomas and m etastases on out-of-phase images (64 versus 98) (p < .0005) but not in -phase images (130 versus 122) (p = .47). The adrenal-spleen ratio dis criminated between adenomas and metastases better than did the adrenal -liver ratio, the adrenal-muscle ratio, or the signal intensity index. No significant difference in interpretation among the three observers was evident (areas under the ROC curves, 0.93, 0.95, and 0.96). The p erformance of the observers was comparable to the results obtained wit h the adrenal-spleen ratio measurement (area under the ROC curve, 0.97 ). CONCLUSION. Experienced observers were able to differentiate adrena l adenomas from metastases just as well as quantitative measures. The adrenal-spleen ratio is the best quantitative means of distinguishing benign from malignant adrenal masses. Chemical shift MR imaging is a g ood but imperfect discriminator of adrenal adenomas.