ANGY: A Rule-BasedExpertSystemforAutomatic SegmentationofCoronaryVesselsFrom Digital Subtracted Angiograms

This paperdetails thedesign andimplementation of ANGY,a rule-based expert systenm inthedomainofmedical image processing. Givenasubtracted digital angiogram ofthechest, ANGY identifies andisolates thecoronary vessels, while ignoring anynonves- selstructures whichmayhavearisen fromnoise, variations inback- groundcontrast, imperfect subtraction, andirrelevent anatomical de- tail. The overall systemismodularized intothreestages: the preprocessing stage andthetwostages embodied intheexpert itself. Inthepreprocessing stage, low-level imageprocessing routines written inCareusedtocreate asegmented representation oftheinput image. Theseroutines areapplied sequentially. Theexpert system isrule-based andiswritten inOPS5andLISP.Itisseparated intotwostages: The low-level imageprocessing stageembodiesa domain-independent knowledge ofsegmentation, grouping, andshapeanalysis. Working withbothedgesandregions, itdetermines suchrelations asparallel andadjacent andattempts torefine thesegmentation begunbythepre- processing. Thehigh-level medical stage embodies adomain-dependent knowledge ofcardiac anatomyandphysiology. Applying thisknowl- edgetotheobjects anid relations determinied inthepreceding twostages, itidentifies thoseobjects whicharevessels andeliminates allothers.