Page 60 - Demo
P. 60
58Chapter3variations such as artefactsin the 3Dphotographs causedbyhair The directions oftheisolatedvariationsarecalledprincipalcomponents(PCs) Themostprominentvariationinthepopulationisdescribedbyprincipalcomponent1(PC1)followedbyprincipalcomponent2(PC2)etc The valueofaPCdescribes thedeviation fromthemeanshapeinstandarddeviations(SD) TheeffectofaPCcanbe visualizedbysimulatingavalueof-2and2standarddeviationsInthisstudyPCAwasappliedtothemodified3DphotographsofthecontrolpopulationThisresultedinasetofPCslabellingthedirectionsofvariationinthecontrolpopulationThecranialshapeofeveryindividualcanbereconstructedbythesePCsandthefoundvalues(describingthemagnitudeofeveryPC) ThemorphologicaleffectofthefirsttwoPCsisshowninFigure2ThePCscalculatedfromthecontrolpopulationwerethenappliedtothescaphocephalypatientsandthetrigonocephalypatients Thiswasdonetodetermineif,andinwhichdirectionthepatientsweredifferentfromthecontrolsAmathematicaldescriptionisgivenintheAppendixAsignificantdifferenceinvaluesofthePCswasusedtodistinguishascaphocephalyortrigonocephalyshapefromanormalcranialshapeFourPCsthatexposedthemostprominentdifferencesbetweenthecontrolsandscaphocephalypatientswereselectedLikewisefourPCsthatrevealedadifferencebetweenthecontrolsandtrigonocephalypatientswereselected14Figure2Overviewof theeffectofprincipalcomponent1(upper)andprincipalcomponent2(lower)of thecontrolpopulationA+2and-2SDwasappliedtoillustratetheeffectGreenindicatesvolumeincreaseandredavolumedecrease
