Patients with COPD have more subtle information in their chest imaging than is generally measured. The severity of COPD in a patient could potentially be determined based on the chest images. It also turns out that there is a COPD imaging threshold that is ideal.
Improving COPD Assessment
Publications
Assessment of lung volume collapsibility in chronic obstructive lung disease patients using CT
To investigate the collapsibility of the lung and individual lobes in patients with COPD during inspiration/expiration and assess the association of whole lung and lobar volume changes with pulmonary function tests (PFTs) and disease severity. PFT measures used were RV/TLC%, FEV1% predicted, FVC, FEV1/FVC%, DLco% predicted and GOLD category. A total of 360 paired inspiratory and expiratory CT examinations acquired in 180 subjects were analysed. Automated computerised algorithms were used to compute individual lobe and total lung volumes. Lung volume collapsibility was assessed quantitatively using the simple difference between CT computed inspiration (I) and expiration (E) volumes (I-E), and a relative measure of volume changes, (I-E)/I. Mean absolute collapsibility (I-E) decreased in all lung lobes with increasing disease severity defined by GOLD classification. Relative collapsibility (I-E)/I showed a similar trend. Upper lobes had lower volume collapsibility across all GOLD categories and lower lobes collectively had the largest volume collapsibility. Whole lung and left lower lobe collapsibility measures tended to have the highest correlations with PFT measures. Collapsibility of lung lobes and whole lung was also negatively correlated with the degree of air trapping between expiration and inspiration, as measured by mean lung density. All measured associations were statistically significant (P < 0.01). Severity of COPD appears associated with increased collapsibility in the upper lobes, but change (decline) in collapsibility is faster in the lower lobes.
Optimal threshold in CT quantification of emphysema
To determine the optimal threshold by quantitatively assessing the extent of emphysema at the level of the entire lung and at the level of individual lobes using a large, diverse dataset of computed tomography (CT) examinations. This study comprises 573 chest CT examinations acquired from subjects with different levels of airway obstruction (222 none, 83 mild, 141 moderate, 63 severe and 64 very severe). The extent of emphysema was quantified using the percentage of the low attenuation area (LAA%) divided by the total lung or lobe volume(s). The correlations between the extent of emphysema, and pulmonary functions and the five-category classification were assessed using Pearson and Spearman’s correlation coefficients, respectively. When quantifying emphysema using a density mask, a wide range of thresholds from −850 to −1,000 HU were used. The highest correlations of LAA% with the five-category classification and PFT measures ranged from −925 to −965 HU for each individual lobe and the entire lung. However, the differences between the highest correlations and those obtained at −950 HU are relatively small. Although there are variations in the optimal cut-off thresholds for individual lobes, the single threshold of −950 HU is still an acceptable threshold for density-based emphysema quantification.