Assessment of pulmonary function in COPD patients using dynamic digital radiography: A novel approach utilizing lung signal intensity changes during forced breathing.

Objectives: To investigate the association of lung signal intensity changes during forced breathing using dynamic digital radiography (DDR) with pulmonary function and disease severity in patients with chronic obstructive pulmonary disease (COPD). Methods: This retrospective study included 46 healthy subjects and 33 COPD patients who underwent posteroanterior chest DDR examination. We collected raw signal intensity and gray-scale image data. The lung contour was extracted on the gray-scale images using our previously developed automated lung field tracking system and calculated the average of signal intensity values within the extracted lung contour on gray-scale images. Lung signal intensity changes were quantified as SImax/SImin, representing the maximum ratio of the average signal intensity in the inspiratory phase to that in the expiratory phase. We investigated the correlation between SImax/SImin and pulmonary function parameters, and differences in SImax/SImin by disease severity. Results: SImax/SImin showed the highest correlation with VC (rs = 0.54, P < 0.0001), followed by FEV1 (rs = 0.44, P < 0.0001), both of which are key indicators of COPD pathophysiology. In a multivariate linear regression analysis adjusted for confounding factors, SImax/SImin was significantly lower in the severe COPD group compared to the normal group (P = 0.0004) and mild COPD group (P=0.0022), suggesting its potential usefulness in assessing COPD severity. Conclusion: This study suggests that the signal intensity changes of lung fields during forced breathing using DDR reflect the pathophysiology of COPD and can be a useful index in assessing pulmonary function in COPD patients, potentially improving COPD diagnosis and management.

Projected lung area using dynamic X-ray (DXR) with a flat-panel detector system and automated tracking in patients with chronic obstructive pulmonary disease (COPD).

OBJECTIVES: To assess the association of projected lung area (PLA) measured by DXR with demographic data, pulmonary function, and COPD severity, and to generate PLA over time curves using automated tracking. METHODS: This retrospective study recruited healthy volunteers and COPD patients. Participants were classified into three groups: normal, COPD mild and COPD severe. PLA was calculated from the manually traced bilateral lung contours. PLA over time curves were produced using automated tracking, which was used to calculate slope and intercept by approximate line during forced expiration. The correlation of PLA, difference of PLA between end-inspiration and end-expiration (ΔPLA), slope, and intercept with demographic data and pulmonary function tests were investigated. The difference of PLA, ΔPLA, intercept, and slope among three groups were also evaluated. RESULTS: This study enrolled 45 healthy volunteers and 32 COPD patients. COPD severe group had larger PLA in both lungs at tidal/forced end-inspiration/expiration, smaller slope, and larger intercept than normal group (p < 0.001). PLA was correlated with % forced expiratory volume in one second (%FEV1) (rs from -0.42 to -0.31, p ≤ 0.01). ΔPLA in forced breathing showed moderate correlation with vital capacity (VC) (rs = 0.58, p < 0.001), while ΔPLA in tidal breathing showed moderate correlation with %FEV1 (rs = -0.52, p < 0.001) as well as mild correlation with tidal volume (rs = 0.24, p = 0.032). Intercept was slightly underestimated compared with manually contoured PLA (p < 0.001). CONCLUSION: COPD patients had larger PLA than healthy volunteers. PLA and ΔPLA in tidal breathing showed mild to moderate correlation with %FEV1.

Vector-field dynamic x-ray (VF-DXR) using optical flow method in patients with chronic obstructive pulmonary disease.

BACKGROUND: We assessed the difference in lung motion during inspiration/expiration between chronic obstructive pulmonary disease (COPD) patients and healthy volunteers using vector-field dynamic x-ray (VF-DXR) with optical flow method (OFM). METHODS: We enrolled 36 COPD patients and 47 healthy volunteers, classified according to pulmonary function into: normal, COPD mild, and COPD severe. Contrast gradient was obtained from sequential dynamic x-ray (DXR) and converted to motion vector using OFM. VF-DXR images were created by projection of the vertical component of lung motion vectors onto DXR images. The maximum magnitude of lung motion vectors in tidal inspiration/expiration, forced inspiration/expiration were selected and defined as lung motion velocity (LMV). Correlations between LMV with demographics and pulmonary function and differences in LMV between COPD patients and healthy volunteers were investigated. RESULTS: Negative correlations were confirmed between LMV and % forced expiratory volume in one second (%FEV1) in the tidal inspiration in the right lung (Spearman's rank correlation coefficient, rs = -0.47, p < 0.001) and the left lung (rs = -0.32, p = 0.033). A positive correlation between LMV and %FEV1 in the tidal expiration was observed only in the right lung (rs = 0.25, p = 0.024). LMVs among normal, COPD mild and COPD severe groups were different in the tidal respiration. COPD mild group showed a significantly larger magnitude of LMV compared with the normal group. CONCLUSIONS: In the tidal inspiration, the lung parenchyma moved faster in COPD patients compared with healthy volunteers. VF-DXR was feasible for the assessment of lung parenchyma using LMV.

Vector-Field dynamic X-ray (VF-DXR) using Optical Flow Method.

OBJECTIVES: To explore the feasibility of Vector-Field DXR (VF-DXR) using optical flow method (OFM). METHODS: Five healthy volunteers and five COPD patients were studied. DXR was performed in the standing position using a prototype X-ray system (Konica Minolta Inc., Tokyo, Japan). During the examination, participants took several tidal breaths and one forced breath. DXR image file was converted to the videos with different frames per second (fps): 15 fps, 7.5 fps, five fps, three fps, and 1.5 fps. Pixel-value gradient was calculated by the serial change of pixel value, which was subsequently converted mathematically to motion vector using OFM. Color-coding map and vector projection into horizontal and vertical components were also tested. RESULTS: Dynamic motion of lung and thorax was clearly visualized using VF-DXR with an optimal frame rate of 5 fps. Color-coding map and vector projection into horizontal and vertical components were also presented. VF-DXR technique was also applied in COPD patients. CONCLUSION: The feasibility of VF-DXR was demonstrated with small number of healthy subjects and COPD patients. ADVANCES IN KNOWLEDGE: A new Vector-Field Dynamic X-ray (VF-DXR) technique is feasible for dynamic visualization of lung, diaphragms, thoracic cage, and cardiac contour.