Adrenal masses: Quantification of pat content with double-echo chemical shift in-phase and opposed-phase FLASH MR images for differentiation of adrenal adenomas

PURPOSE: To quantify fat content in adrenal lesions with double-echo chemic al shift magnetic resonance (MR) imaging in a phantom study and to differen tiate adrenal adenomas from other adrenal masses by assessing fat content i n a clinical study. MATERIALS AND METHODS: The study consisted of two parts: a phantom study an d a clinical study. To explore the effect of the T1 value on in- and oppose d-phase MR images of fat-containing tissues, phantom models with various pr oportions of fat and gadopentetate dimeglumine concentrations were implemen ted. Signal intensity (SI) indexes ([SI in-phase - SI opposed-phase]/SI in- phase) were calculated with double-echo fast low-angle shot (FLASH) MR imag ing. In the clinical study, 23 patients with 28 adrenal masses (16 adrenal adenomas, nine adrenal metastases, and three pheochromocytomas) underwent d ouble-echo FLASH MR imaging, and SI indexes were calculated. RESULTS: SI index reached a maximum of 0.87 at 53% fat fraction for gadopen tetate dimeglumine concentration at 0.5 mmol/L as the simulated T1 of the a drenal mass. The SI indexes of the adrenal adenomas, adrenal metastases, an d pheochromocytomas, respectively, were 0.36, -0.15, and -0.07, and estimat ed fat fraction from the phantom study was 26.5%, 0%, and 0%. All adrenal a denomas contained fat on double-echo FLASH images. There was no overlap in SI index between adenomas and other tumors. CONCLUSION: Preliminary experience indicates that quantitative measurement of the fat fraction of adrenal masses is possible with the double-echo chem ical shift FLASH technique and allows for differentiating adrenal adenomas from other adrenal masses.