Characterization of adrenal lesions using chemical shift MRI: Comparison between 1.5 tesla and two echo time pair selection at 3.0 tesla MRI

Purpose: To compare chemical shift MRI obtained at 1.5 Tesla (T) and two pairs of echo time (TE) in-phase and opposed-phase 3.0T MRI to assess their usefulness for the differentiation between adrenal adenomas and non-adenomas. Materials and Methods: We evaluated 91 adrenal masses (75 adenomas, 16 non-adenomas) in 85 patients. The MR imaging parameters were: T1-dual-gradient-echo(GRE) [echo times (TEs) = 1.1/2.3 ms (first-echo-pair) or 3.5/4.6 ms (second-echo-pair)] at 3.0T, and T1-dual-GRE (TEs = 2.4/4.8 ms) at 1.5T. Scans were quantitatively assessed for the signal intensity (SI) index, calculated as [(SIin-phase-SIopposed-phase)/(SIin-phase)] x 100(%). To test for differences between adenomas and non-adenomas, we performed quantitative analysis and analysis of variance. Results: For all images, the SI index differed significantly between adenomas and non-adenomas. The sensitivity / specificity of SI index at the first-echo-pair of 3.0T was 100%/ 100%, that of 95.6%/ 100% at the second-echo-pair of 3.0T, and 91.7%/ 88.9% at 1.5T, respectively. At intra-individual comparisons, the SI indices obtained with the second-echo-pair at 3.0T were significantly lower than on the first-echo-pair at 3.0T and 1.5T. Conclusion: Chemical shift MRI at 3.0T provides more accurate differentiation between adenomas and non-adenomas than at 1.5T. The SI index of the first-echo-pair at 3.0T is the most reliable evaluation method for differentiating adrenal adenomas from non-adenomas.