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Renal Masses: Quantitative Assessment of Enhancement with Dynamic MR Imaging¹

¹ From the MR Research Division, Department of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Rd, Bethesda, MD 20814-4799 (V.B.H., M.N.H., P.L.C.); and Department of Diagnostic Radiology, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Md (V.B.H., S.F.A., M.N.H., P.L.C.). Received June 14, 2001; revision requested July 6; final revision received February 14, 2002; accepted March 12. Address correspondence to V.B.H. (e-mail: vho@usuhs.mil or vho@nih.gov).

PURPOSE: To establish a quantitative magnetic resonance (MR) imaging contrast enhancement criterion for distinguishing cysts from solid renal lesions.

MATERIALS AND METHODS: Regions of interest were measured in 74 patients with renal lesions evaluated by means of dynamic contrast material–enhanced MR imaging with serial breath-hold spoiled gradient-echo acquisitions. Sensitivity for renal tumors and specificity for renal cysts were established by using percentage of enhancement thresholds that varied between 5% and 35%.

RESULTS: The mean percentage of enhancement at MR imaging for the 50 renal cysts was less than 5%; for the 50 renal tumors, it was 97% or higher. With use of a threshold percentage of enhancement of 15% and results obtained between 2 and 4 minutes after administration of contrast material, all malignancies (sensitivity for tumor, 100%) were diagnosed, and there were 6% or fewer false-positive tumor diagnoses. Lower thresholds resulted in unacceptably high false-positive rates (ie, cysts that appeared to enhance—pseudoenhancement), whereas higher threshold values (>20%) resulted in an unacceptably lower sensitivity for tumors.

CONCLUSION: The optimal percentage of enhancement threshold for distinguishing cysts from malignancies with the imaging technique prescribed was 15%, and the optimal timing for measurement was 2–4 minutes after administration of contrast material.

© RSNA, 2002

Index terms: Kidney, cysts, 81.311 • Kidney, MR, 81.121411, 81.121412, 81.121415, 81.121416, 81.12143 • Kidney neoplasms, 81.311, 81.32 • Magnetic resonance (MR), contrast enhancement, 81.12143

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