Use of dynamic chest radiographic measurements to estimate total lung capacity in patients with respiratory disease

Introduction: Pulmonary Function Tests (PFTs) are key in diagnosing numerous conditions, but require experienced operators and are expensive to obtain. Studies demonstrate correlation between projected lung area (PLA) at maximal inspiration measured using Dynamic Chest Radiography (DCR) and spirometric measurements, e.g. total lung capacity (TLC) (Hino et al. EJR Open. 2020;7:100263). DCR is an imaging modality in which sequential radiographs are used to form a moving image, providing functional/structural information. We describe use of DCR to estimate TLC in respiratory patients. Methods: 42 patients with underlying respiratory conditions (asthma n=12, COPD n=10, recent history CoVid-19 n=12, ILD n=9) underwent DCR during which they were instructed to take a deep breath in and out. PLA at maximal inspiration was measured by automated proprietary software, and then used to estimate TLC (DCR-TLC). DCR-TLC was compared to TLC measured with whole body plethysmography (WBP-TLC) and Pearson’s correlation coefficient derived. Results: Results are outlined in Table 1. Correlation between DCR-TLC and WBP-TLC was 0.86, and >0.8 across all subgroups. Conclusion: DCR-TLC had a good degree of correlation with WBP-TLC across a range of different respiratory conditions, suggesting potential future use as a clinical surrogate. Further research is needed to correlate PFT results with DCR-derived measurements.