Evaluation method of CT number linearity

Objective To explorethemethodfor computedtomography(CT)numberlinearityevaluation.Methods The modelCTP401of Catphan500phantomwas adoptedto test43setsof CT scannersunderthesamescanningconditions.1-and2-ordercurvefittingof thetestingresultsof eachscannerwereperformed,withthebendingof the2-orderfittedcurve definedas thedegreeof CT numbernon-linearityandtheslopeof thelinearfittingas contrastscale.The2-normsof thefitting coefficientswerecalculatedfor thepurposeof fittingqualityevaluation.MATLAB6.1was employedfor programming.Results The2-normof thefittingcoefficientsof the2-orderfittingcurvewas approximately1/10of thatof corresponding linearfitting,indicatingthat2-orderfittingaccordedbetterto theparentpopulationdistributionpattern.Thedegreeof the non-linearitywas manifestedby thebendingof the2-orderfittingcurvethatincreasedmonotonouslywiththe2-normof the correspondinglinearfitting.Conclusion It is statisticallyvalidto defineCT numbernon-linearityandcontrastscaleon the basisof1and2-orderfittingsof thetestingresults,whichwellservesthepurposeof quantitativeanalysis.