Usefulness of the Virtual Monochromatic Image in Dual-Energy Spectral CT for Decreasing Renal Cyst Pseudoenhancement: A Phantom Study

OBJECTIVE: The purpose of this study was to determine the effect that dual-energy spectral CT has on renal cyst pseudoenhancement with a renal cyst phantom. MATERIALS AND METHODS: Two renal compartments within a CT phantom were filled with 40- and 240-HU solutions of diluted contrast material, mimicking the nonenhanced phase and nephrographic phase of MDCT, respectively. A saline-filled tapering cylindric cyst model was used, simulating cysts of varying diameters (range, 0.7-3.0 cm) suspended in the renal compartments. The phantom was scanned using dual-energy CT (DECT) (80 and 140 kVp) and conventional, single-energy CT (120 kVp) with the same 64-MDCT scanner. Attenuation increase was measured for a cyst model within 40- and 240-HU dilutions. We compared the attenuation increase obtained on virtual monochromatic images from DECT with conventional, single-energy MDCT images using a paired Student t test. RESULTS: Pseudoenhancement occurred in the conventional single-energy CT acquisitions, with water attenuation increase of 42.44 ± 4.03 HU measured at 120 kVp. In virtual monochromatic images of DECT, we observed less pseudoenhancement with water attenuation increase of 21.51 ± 6.18 HU at 70 keV. Both acquisitions yielded a p value less than 0.0001. CONCLUSION: We achieved less pseudoenhancement of renal cysts with virtual monochromatic images of DECT compared with conventional single-energy CT. This method may be useful when an accurate differentiation between small renal cysts and solid masses is critical.