Comparison of nephrographic with excretory phase helical computed tomography for detecting and characterizing renal masses

Objective: A retrospective study was performed to compare nephrogaphic phas e (NP) with excretory phase (EP) renal belied computed tomographic (CT) ima ges with respect to detection of renal masses 10 mm or more in diameter, an d reviewer confidence in mass characterization. Methods: Two reviewers eval uated 39 rend helical CT examinations. All masses measuring 10 mm or more i n maximal diameter were classified as simple cysts, complex cysts, solid le sions, or indeterminate lesions. Reviewers graded their confidence in the c haracterization of the masses and decided whether the NP or EP contrast-enh anced images were superior. Results: The 2 reviewers confidently characteri zed 71 (reviewer 1) and 65 (reviewer 2) of 72 detected masses 10 mm or more in diameter on NP images and 70 (reviewer 1) and 67 (reviewer 2) of 71 det ected masses on EP images. There was strong agreement between the 2 sets of images in respect to the characterization of renal masses (kappa = 1.00 an d 0.86). Only one mass (a focus of acute pyelonephritis) was not detected b y either reviewer on EP images. Collecting system artifact degraded the qua lity of the EP image in images from only 1 patient. Conclusion: Although EP images are often aesthetically inferior to NP images, use of EP images res ults in a similar rate of detection and confidence in characterization of r enal masses measuring 10 mm or more in diameter.