Optimal threshold of subtraction method for quantification of air-trapping on coregistered CT in XXXX @entity1 .

@entity1 @entity8431 @entity2415 @entity1030
OBJECTIVES: To investigate the optimal threshold of subtraction method for quantification of air trapping on co-registered CT in @entity1030 @entity1 in correlation with pulmonary function parameters. METHODS: From June 2005 to October 2010, 174 @entity1 were included in our study. Inspiration and expiration CT were performed followed by non-rigid registration using in-house software. The subtraction value per voxel between inspiration and registered expiration CT was obtained, and volume fraction of air trapping (air trapping index, ATI), using variable thresholds was calculated. ATI, expiration/inspiration ratio of mean lung density (E/I @entity8431 ) and the percentage of lung voxels below -856  HU on expiration CT (Exp-856) were correlated with FEF25-75% and RV/TLC. RESULTS: The highest correlation coefficient with FEF25-75% was -0.656, using the threshold of 80  HU. As for RV/TLC, the highest correlation coefficient was 0.664, using the threshold of 30  HU. When plotting the relationship between subtraction thresholds and FEF25-75% and RV/TLC, the threshold of 60  HU was most suitable (r   =   -0.649 and 0.651). Those correlation coefficients were comparable to the results with E/I @entity8431 (r   =   -0.670 and 0.657) and Exp-856 (r   =   -0.604 and 0.565). CONCLUSIONS: The optimal threshold for quantification of air trapping was 60  HU and showed comparable correlations with pulmonary function parameters. KEY POINTS:     The optimal CT threshold of subtraction method for air trapping was 60  HU.     ATI with 60  HU threshold was comparable to E/I @entity8431 and Exp -856 .     @entity2415 may substantially contribute to air trapping with statistical significance (P   <   0.001).
