锥形束ct图像重建若干关键技术研究

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1、万方数据硕士学位论叉range，theanalyticalreconstructionalgorithmcanreconstructtheimageswiththehighquality．Butiftheprojectiondataaresampledsparsely，thequalityofthereconstructionimagesignificantlydecreasedbyusingtheanalyticalreconstructionalgorithm．IntheCBCTscanning，thescan

2、fieldofview(SFOV)isdeterminedbytheXraysourceandtheflatpaneldetectorarray．Becausethecostoftheflatpaneldetectorarrayishigher，atthesametime，inordertoreducetheradiationdoseofpatient，SOthesizeofthedetectorislimited．Becausethetraditionalscanninggeometrystructureisli

3、mited．Sosometimesthedetectorcannotcompletelycovertheareaofscanning．Whenthereisaobesitypatientandthesmallsizeofdetectororthepatientcannotbeplacedaccurately，theXraysbeamsarenotsufficienttocoverthepatient’Sscanningarea，whichismeaningbeyondtheSFOV．Sothepartofthear

4、eawhichisnotcoveredbytheXraysbeamswillnothavetheprojectiondate．Ifitusethetraditionalanalyticalreconstructionalgorithmdirectlytoreconstruct，thereconstructionimageswillappearthetruncationartifactswhichismanifestedasthebrightringartifactandthebrightspeckartifact．

5、Thetruncationartifactswilldeclinethereconstructionimage’Squalitysignificantlyandgiverisetothereconstruction’Serror．Itwillaffectthedoctortochecktheinterestingareas．Thebrightringartifactmainlybecausethedetector’Swidthistooshort，whichwillresultinthemissingofboths

6、idesintheprojectiondata．ThereisabrightringaroundtheSFOVinthereconstructionofimagebecausethedatadeviation．Tosolvetheproblemofthetruncation，Ohnesorgeandotherpeopleproposedaimageprojectionalgorithmwhichnameisthesymmetricmirroringalgorithm．Thealgorithm’Simplementa

7、tionprocessincludesthat．Thefirststep，tofindthevaluewhichistwotimesascomparedwiththeboundaryvalueofthetruncateddata．Thesecondstep，tousethesymmetricmirroringalgorithmtoaddthedeviatedvalues．Thethirdstep，tomodifythedatabythesineorcosinefunction．Thefourthstep，torec

8、onstructtheimagebytheFDKalgorithm．Thisalgorithmcanremovethebrightringartifact，butthepositionofthevaluewhichistwotimesascomparedwiththeboundaryvalueofthetruncateddataisuncertain．Sot