Introduction:Visual CT emphysema scoringhasbeen shown to improve the prediction of lung cancer mortality and COPD death, but optimal Hounsfield unit (HU) threshold for emphysema detection hasnotbeen determined for lung cancer screening (LCS) subjects.

Objectives:To find the optimal HU threshold forthe early detection of emphysema in a low dose CT (LDCT) LCS dataset.

Methods:352participantswere selectedfrom aLCS dataset with LDCTusing Definition AS, at inspiration in spiral mode at 120 kVp and 35 mAs. Images were reconstructed with B30fkernel at 2.0/1.0 mm thickness. Emphysema was quantified below a range of HUthresholds from ?900 to ?1,024HU, while excluding the vessels and bronchus. One radiologist (reader A) and two trainees (reader BandC) visually scored emphysema according to the Fleischner criteria. Kappa statistics, Spearman analysis and ROC(Receiver operating characteristic) are used to assess the correlation between quantified emphysemaunder different HU thresholds and visual emphysema.

Results:High agreement in the detection of emphysema was found (Kappa: 0.728 ? 0.835).The spearman analysis demonstrated that emphysema volume under different thresholdsis significantly correlated to the visual classification(P<0,05). ROC showed -1000 HUto be optimal for discrimination between normal and emphysematous lung parenchyma when correlated to visual scoring for all readers, by excluding all influence of noise on voxel quantification.Despite of noise correction, the emphysema voxel counting suffers from this threshold.

Conclusions:The optimal threshold for noise cancelation in emphysema quantification was established to be -1000 HUin a LDCT LCS dataset.