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

Abstract

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.

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

“…Healthy volunteers took several tidal breaths followed by one forced breath, while COPD patients took tidal breaths and a forced breath separately. Imaging parameters for DDR were almost the same as the previous reports [16] , [18] : tube voltage, 100 kV; tube current, 50 mA; pulse duration of pulsed X-ray, 1.6 ms; source-to-image distance, 2 m; additional filter, 0.5 mm Al plus 0.1 mm Cu. The additional filter was used to remove soft X-rays.…”

“…The multivariate linear regression analysis revealed significant differences in the SImax/SImin between the severe COPD and the normal groups, as well as between the severe COPD and the mild groups. While multiple studies to date have demonstrated the utility of quantitative DDR markers in assessing pulmonary function in COPD patients [10] , [12] , [14] , [16] , [17] , [18] , [20] , [23] , this is the first report to focus on the signal intensity changes of the entire lung fields on DDR images in COPD patients and investigate the correlation with PFT parameters and the differences by disease severity.…”

“…Of note, these methods represent a novel approach to pulmonary function imaging in COPD patients in that they can detect physiological information more specific to structures within the lungs, and are different from the methods using respiratory kinetics of the diaphragm and the thorax on DDR images discussed in previous studies [10] , [12] , [14] , [16] , [17] , [18] , [20] . The unique approach-derived indices, particularly in the evaluation of localized areas of the lung, have shown to correlate with ventilation metrics from nuclear medicine imaging [21] , [22] and could detect ventilation abnormalities such as air trapping and airflow restriction [28] .…”

“…COPD patients were recruited from June 2009 to August 2011, and healthy volunteers were recruited from May 2013 to February 2014. The inclusion criteria were the same as in previous studies [14] , [16] . The common inclusion criteria for both groups were: (1) ≥ 20-year-old adults with informed consent; (2) scheduled for conventional chest radiograph; (3) ability to follow instructions for forced breathing; (4) no status of pregnancy, potential pregnancy, or lactation.…”

“…Dynamic digital radiography (DDR) is a novel functional imaging technique that utilizes sequential images obtained by a pulsed X-ray generator and a flat panel detector (FPD) with a large field of view and can be used in routine clinical practice [8] , [9] , [10] . DDR can not only quantitatively assess pulmonary ventilation and perfusion but also offer a non-invasive and comprehensive evaluation of pulmonary function, potentially impacting clinical practice significantly [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] . Previous studies have focused on the dynamic changes in X-ray translucency of the lung fields during respiration, which mainly reflect the changes of air volume inside the alveoli.…”