Estimation oflung volumes fromchest radiographs using shape information

Thecross-sectional shapes ofthechest anditscontained structures havebeenassessed inpost-mortem anatomical sections andfromcomputerised tomographic scansinliving subjects. Theseshapes aredescribed bysimple equations that canbeusedtoincrease the accuracyofmeasuring lungvolumes fromchest radiographs. Radiographic estimates oftotal lungcapacity, using theequations, werecompared withplethysmographic andsingle-breath helium dilution measurements in35normalsubjects. Thepostures commonly usedfortaking chest radiographs werefound, on average,todecrease total lungcapacity (TLC)andtoincrease residual volume byabout 200mlwhencompared withthesitting positions usedfortheother twomeasurements (studies madein18ofthesubjects). After correction forthis effect, the radiographic estimates ofTLC,which measurethedisplacement volume ofthelung, exceeded theplethysmographic estimates ofcontained gasvolumebya mean of720ml,which was taken asthevolume oftissue, blood, andwaterinthelungs. Thesingle-breath dilution estimates ofTLCfell short oftheplethysmographic values bya mean of480ml,taken asthevolumeof contained gasthat was inaccessible tohelium in10seconds. Thetomographic studies suggested thattheradiographic technique ofmeasuring lungdisplacement volumes hasan accuracyof +210ml.Themethodisrapid andsimple touseandhasintra- andinter-observer variabilities of<1% and<5% respectively.