Adrenal masses: Correlation between CT attenuation value and chemical shift ratio at MR imaging with in-phase and opposed-phase sequences

PURPOSE: To correlate attenuation values at computed tomography (CT) with signal intensity at chemical-shift magnetic resonance (MR) imaging in adrenal masses. MATERIALS AND METHODS: Thirty-eight patients with 47 adrenal lesions underwent MR imaging and unenhanced CT examinations. MR examinations, performed at 1.5 T, included T1-weighted imaging with fat and water in phase and gradient-echo imaging with fat and water out of phase (repetition time, 45-180 msec; echo time, 1.4-3.1 msec). Lesion-to-spleen signal intensity ratios were calculated for the in-phase and opposed-phase images. The chemical-shift ratio, a measure of signal intensity loss between in-phase and opposed-phase images, and the CT attenuation value (in Hounsfield units) were determined for each lesion. RESULTS: A statistically significant correlation (0.85) was found between attenuation and chemical-shift-ratio values (P < .000001). Attenuation in six benign lesions was within 2 standard deviations of the mean attenuation in malignant lesions, and the chemical-shift ratio in eight benign lesions was within 2 standard deviations of the mean chemical-shift ratio in malignant lesions. Six of these eight lesions were misclassified on the basis of both attenuation and chemical-shift-ratio values. CONCLUSION: CT attenuation values are highly correlated with chemical-shift ratios. Both values were indeterminate for a similar subset of benign lesions.