Trapping volumetric measurement by multidetector CT in chronic obstructive pulmonary disease: effect of CT threshold

The purpose of this study was to evaluate the effect of various computed tomography (CT) thresholds on trapping volumetric measurements by multidetector CT in chronic obstructive pulmonary disease (COPD).

Twenty-three COPD patients were scanned with a 64-slice CT scanner in both the inspiratory and expiratory phase. CT thresholds of -950 Hu in inspiration and -950 to -890 Hu in expiration were used, after which trapping volumetric measurements were made using computer software. Trapping volume percentage (Vtrap%) under the different CT thresholds in the expiratory phase and below -950 Hu in the inspiratory phase was compared and correlated with lung function.

Mean Vtrap% was similar under -930 Hu in the expiratory phase and below -950 Hu in the inspiratory phase, being 13.18±9.66 and 13.95±6.72 (both lungs), respectively; this difference was not significant (P=0.240). Vtrap% under -950 Hu in the inspiratory phase and below the -950 to -890 Hu threshold in the expiratory phase was moderately negatively correlated with the ratio of forced expiratory volume in one second to forced vital capacity and the measured value of forced expiratory volume in one second as a percentage of the predicted value.

Trapping volumetric measurement with multidetector CT is a promising method for the quantification of COPD. It is important to know the effect of various CT thresholds on trapping volumetric measurements.