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Abstract: Objective: We developed a semi-automated tool to quantify emphysema from thoracic X-ray multi-detector (64-slice) computed tomography (CT) for training purposes and multi-reader studies. Materials and Methods: Thoracic X-ray CT was acquired in 93 ex-smokers, who were evaluated by six trainees with little or no expertise (trainees) and a single experienced thoracic radiologist (expert). A graphic user interface (GUI) was developed for emphysema quantification based on the percentile of lung where a score of 0=no abnormalities, 1=1–25%, 2=26–50%, 3=51–75% and 4=76–100% for each lung side/slice. Trainees blinded to subject characteristics scored randomized images twice; accuracy was determined by comparison to expert scores, density histogram 15th percentile (HU15), relative area at −950HU (RA950), low attenuation clusters at −950HU (LAC950), −856HU (LAC856) and the diffusing capacity for carbon monoxide (DLCO%pred). Intra- and inter-observer reproducibility was evaluated using coefficients-of-variation (COV), intra-class (ICC) and Pearson correlations. Results: Trainee–expert correlations were significant (r =0.85–0.97, p <0.0001) and a significant trainee bias (0.15±0.22) was observed. Emphysema score was correlated with RA950 (r =0.88, p <0.0001), HU15 (r =−0.77, p <0.0001), LAC950 (r =0.76, p <0.0001), LAC856 (r =0.74, p =0.0001) and DLCO%pred (r =−0.71, p <0.0001). Intra-observer reproducibility (COV=4–27%; ICC=0.75–0.94) was moderate to high for trainees; intra- and inter-observer COV were negatively and non-linearly correlated with emphysema score. Conclusion: We developed a GUI for rapid and interactive emphysema scoring that allows for comparison of multiple readers with clinical and radiological standards. [Copyright &y& Elsevier]