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Original Research |
1 Department of Medical Imaging, University Health Network and Mount Sinai
Hospital, Princess Margaret Hospital, 610 University Ave., Toronto, ON M5G
2M9, Canada.
2 Department of Diagnostic Radiology, Christie Hospital NHS Trust, Withington,
Manchester M20 4BX, United Kingdom.
3 Main X-ray Department, City General Hospital, Stoke-on-Trent ST4 6QG, United
Kingdom.
OBJECTIVE. Adrenal nodules having an attenuation of more than 10 H on unenhanced CT are considered indeterminate. The purpose of this study was to compare CT histogram analysis and chemical shift MRI in the characterization of indeterminate adrenal nodules.
MATERIALS AND METHODS. Thirty-nine adrenal masses that were indeterminate on CT were identified in 37 patients. Histogram analysis was performed on unenhanced CT from a region of interest (ROI) that recorded mean attenuation, number of pixels, and percentage of negative pixels. MR signal intensity drop between the in- and opposed-phase images was measured for the masses. Analyses to determine whether correlations existed among the mean CT attenuation, percentage of negative pixels, and MR signal intensity drop were performed. A final diagnosis was obtained by pathology results, follow-up of more than 6 months, or adrenal washout CT findings.
RESULTS. Negative pixels were present in 25 of 28 adenomas and nine
of 11 nonadenomas. A threshold of more than 10% negative pixels for the
diagnosis of adenoma provided a sensitivity of 46% and specificity of 100%. A
threshold of more than 20% MR signal intensity drop yielded a sensitivity of
71% and specificity of 100%. An increase in the percentage of negative pixels
was correlated with a decrease in mean CT attenuation. Using MRI, observers
characterized seven additional nodules as adenomas compared with CT histogram
analysis (McNemar test, 
2 = 5.1429; p = 0.023).
CONCLUSION. CT histogram analysis with a threshold of a 10% negative pixel presence increases sensitivity for the characterization of adenomas compared with analysis of the mean CT attenuation alone. The use of chemical shift MRI with a threshold of 20% signal intensity drop results in a higher sensitivity than CT histogram analysis.
Keywords: adenoma • adrenal nodules • chemical shift MRI • CT histogram analysis
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