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Purpose:To compare the influence betweenconventional polychromatic CT(quality control QC) imaging andvirtualmonochromaticspectral(VMS)imagingbyfast-switchkVpdual-energyCTonrenalcystpseudo-enhancement. Methods: Thestudycollected15patientswithatotal26cystfrom38renalsbyultrasound,MRandCTmulti-phaseabdominal gemstonespectralimaging(GSI)ofrenalcystdisease(BosniakⅠtype).RetrospectiveanalysisoftheCTvaluesobtainedfrom QCimagingand70keVvirtualmonochromaticspectral(VMS)images,theywerereconstructedfromDECTdata,thenassessthe influenceofVMSonpseudo-enhancementofcystsinclinicalstudy.AfterplainCTscanning,bolus60-90ml(About1millilitersper kilogramofbodyweight,rateof3.0ml/s)ofnon-ioniccontrastagentwasinjectedviaelbowvein,thedelayedtimewere25-30s(corticalphase),60-70s(cortico-medullaryphase),withthethicklayerfor5mm.ViaGSIviewer,Scandatawerereconstructionand obtainpolychromaticimagesand70keVmonochromaticimageslayerfor5mmand1mm,respectively.Analyzedthedifferenceof CT values between preconstrast images and enhancement images by measuring CT values of cysts in different periods and reconstructionslices,andexpressedbymeansofCT±SD.Withthedefinitionofthefalseaggrandizementas10Hubethecritical value. Results: 38casesofcystweremeasured,theminimumdiameteris5.0mm,42.5mmmaximum.QCimagingandVMSimagingsets showedpseudoenhancement(postcontrastattenuationincrease> 10HU)inallinvestigatedconditions.IntheQCimageslayer for 5mm,12 cysts exist pseudo-enhancement in arterial phase,and 14 in cortico-medullary phase;In the QC images layer for 1.25mm,6and8casesexistpseudoenhancement;6and7casesexistin70keVimageslayerfor5mm,2and3casesexistin70keV imageslayerfor1.25mm.Thenumberofpseudoenhancementin5mmslicethickness(18and21)weremarkedlymorethanthat reconstructed on 1.25mm slice thickness(8 and 11)(X2=4.64,P=0.031;X2=3.96,P=0.047).The number of pseudo enhancement in QCimages((18and22)morethan70keVimages(8and11)(X2=4.64,P=0.031;X2=5.70,P=0.017). Conclusion: The pseudo enhancement of renal cyst was objectively existed.Compared with conventional polychromatic and thicklayermode,virtualmonochromaticspectral(VMS)andthinlayerimagingcanconsiderablyreducethephenomenonofrenal cystpseudo-enhancement. Clinical Application/ Relevance: Virtualmonochromaticspectral(VMS) and thin layer imaging can considerably eliminate the phenomenonofPseudoreinforcement.Theyhaveroletorealenhancementcharacteristicsofthelesion.