Biomechanical CT metrics are associated with patient outcomes in COPD

Abstract

Background: Traditional metrics of lung disease such as those derived from spirometry and static single-volume CT images are used to explain respiratory morbidity in patients with COPD, but are insufficient. We hypothesised that the mean Jacobian determinant, a measure of local lung expansion and contraction with respiration, would contribute independently to clinically relevant functional outcomes.

Methods: We applied image registration techniques to paired inspiratory-expiratory CT scans and derived the Jacobian determinant of the deformation field between the two lung volumes to map local volume change with respiration. We analysed 490 participants with COPD with multivariable regression models to assess strengths of association between traditional CT metrics of disease and the Jacobian determinant with respiratory morbidity including dyspnoea (modified Medical Research Council), St Georges Respiratory Questionnaire (SGRQ) score, 6-min walk distance (6MWD) and the Body Mass Index, Airflow Obstruction, Dyspnoea and Exercise Capacity (BODE) index, as well as all-cause mortality.

Results: The Jacobian determinant was significantly associated with SGRQ (adjusted regression coefficient β=-11.75,95% CI -21.6 to -1.7; p=0.020), and with 6MWD (β=321.15, 95% CI 134.1 to 508.1; p<0.001), independent of age, sex, race, body mass index, FEV1, smoking pack-years, CT emphysema, CT gas trapping, airway wall thickness and CT scanner type. The mean Jacobian determinant was also independently associated with the BODE index (β=-0.41, 95% CI -0.80 to -0.02; p=0.039) and mortality on follow-up (adjusted HR=4.26, 95% CI 0.93 to 19.23; p=0.064).

Conclusions: Biomechanical metrics representing local lung expansion and contraction improve prediction of respiratory morbidity and mortality and offer additional prognostic information beyond traditional measures of lung function and static single-volume CT metrics.

Trial registration number: NCT00608764; Post-results.

Keywords: COPD ÀÜ Mechanisms; Imaging/CT MRI etc.

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Figures

Figure 1

Panels a and b show axial CT section and the corresponding deformation map respectively for a representative participant with GOLD 1 with low BODE index. Panels c and d show similar images for a representative participant with GOLD 4 COPD and high BODE index. The colors depict the Jacobian deformation map from full inspiration to end expiration and show the variability in regional tissue expansion patterns across both subjects. Jacobian determinant = 1 represents no deformation; >1 = local expansion; and