Purpose: Chronic Obstructive Pulmonary Disease (COPD) is a heterogeneous disease but is currently measured holistically by spirometry. This project aims to begin to describe the heterogeneous nature of COPD through ventilation and elasticity by characterizing these parameters for individual lobes.
Methods: Eight patients with varying degrees of COPD and two patients without COPD were scanned 25 times using a free-breathing fast helical CT protocol. The 5DCT motion model was used to simulate end-exhalation and end-inhalation images from the 25 images and recorded breathing amplitudes. The DVFs between these pseudo-images were used to guide a biomechanical model to estimate elasticity and to calculate the Jacobian, which represents ventilation. The Pulmonary Toolkit was used to segment the lobes semi-automatically. The resulting lobe masks were used to analyze the Jacobian and elasticity distributions in each lobe, separately. A Ventilation Heterogeneity Index (VHI) was defined as the ratio of the minimum lobe Jacobian divided by the mean of the other lobe Jacobians. The relative volume of low-elasticity values (1-3 kPa), an elasticity range that is reflective of diseased lung tissue, was determined for each lobe. An Elasticity Heterogeneity Index (EHI) was also defined to describe the ratio of the lobe with the maximum relative volume of low elasticity to the mean values of the other lobes.
Results: Patients with severe COPD had a mean VHI of 0.00230 while patients with mild or no COPD had a mean VHI of 0.104 The EHI for patients with severe COPD was 1.69, denoting further heterogeneity than the 3.13 calculated for mild/non-COPD patients.
Conclusion: We have measured a marked increase in heterogeneity in tissue elasticity and ventilation in patients with severe COPD. This work is one step towards personalizing treatment for patients with COPD to better spare the healthy tissue and maintain lung functionality.