[Agreement of Virtual Non-contrast CT Numbers for Renal Cysts on Dual-source CT: Comparison with True Non-contrast Images].
PURPOSE Virtual non-contrast (VNC) imaging may reduce the need for additional true non-contrast (TNC) acquisition in the evaluation of incidental renal cysts. The purpose of this study was to evaluate the agreement of computed tomography (CT) numbers for renal cysts between VNC images derived from dual-source CT (DSCT) and TNC images. METHODS This study included 144 patients with renal cysts larger than 10 mm. All patients underwent unenhanced and contrast-enhanced parenchymal-phase imaging using a DSCT system. VNC images were generated from the parenchymal-phase data. CT numbers of renal cysts were measured on both TNC and VNC images. The difference (ΔHU=TNC-VNC) and the absolute difference (|ΔHU|) were calculated. Agreement was categorized as follows: substitutable (|ΔHU|≤10 HU), indeterminate (10<|ΔHU|<20 HU), and risk of misclassification (|ΔHU|≥20 HU). RESULTS The mean CT numbers were 11.8±7.3 HU for TNC and 5.8±6.4 HU for VNC. ΔHU (TNC-VNC) was 6.0±6.3 HU, indicating that VNC CT numbers were significantly lower than TNC CT numbers (p<0.001). Regarding agreement, 85.4% of cysts showed |ΔHU|≤10 HU, 13.9% showed 10<|ΔHU|<20 HU, and 0.7% showed |ΔHU|≥20 HU. CONCLUSION Although VNC images demonstrated systematically lower CT numbers compared with TNC images, the difference was within 10 HU in more than 85% of cases. VNC images obtained from DSCT may serve as a clinical alternative to TNC images for evaluating morphologically simple renal cysts.