Renal cyst pseudoenhancement: Evaluation with an anthropomorphic body CT phantom

PURPOSE: To determine the effects of cyst diameter and location (intrarenal, exophytic), renal attenuation, section collimation, and computed tomographic (CT) interscanner variability on renal cyst pseudoenhancement in a phantom model. MATERIALS AND METHODS: A customized anthropomorphic phantom was designed to accept 40-, 140-, and 240-HU renal inserts containing intrarenal and exophytic 7-, 10-, and 15-mm cysts. Each phantom and insert were scanned with five different helical CT scanners by,using 1.0-1.5-mm, 2.50-3.75-mm, 5.0-mm, 7.0-8.0-mm, and 10.0-mm section, collimation. Means and SDs of CT number measurements were obtained for each cyst within each variably "enhanced" renal insert. Mixed-model analysis of variance accommodating heteroscedasticity of data was used to assess the type, section, collimation, and cyst diameter on cyst attenuation. effect of scanner RESULTS: Pseudoenhancement (range, 10.3-28.3 HU), observed by using effective section collimation equal to or less than 50% of cyst diameter, occurred in 34 (38%) of 90 intrarenal cyst Measurements. Pseudoenhancement was observed with all five CT scanners, though the magnitude of the effect was nonuniform. Significant interactions were noted between renal cyst diameter, background renal attenuation, and CT scanner type in terms of their effects on cyst attenuation. No appreciable pseudoenhancement was observed with exophytic cysts. CONCLUSION: Pseudoenhancement is maximal when small (less than or equal to1.5-cm) intrarenal cysts are scanned during Maximal levels of renal parenchymal enhancement. The magnitude of this effect varies with scanner type but may be large enough, to prevent accurate lesion characterization, despite use of a thin-section helical CT data acquisition technique. (C) RSNA, 2002.