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Abstract
Introduction and objectives To derive quantitative regional imaging lung function parameters using hyperpolarised xenon MRI (Xe-MRI) and computed tomography (QCT), and compare these to pulmonary function tests (PFTs) in subjects with chronic pulmonary obstructive disease (COPD).
Methods Twenty patients with COPD (stage II – IV GOLD criteria classification) underwent Xe-MRI at 1.5T, QCT, and PFTs.
Whole lung and lobar percentage ventilated volumes were obtained using automated segmentation of multi-slice Xe-MRI ventilation images acquired at a breath hold of FRC + 1L using in-house software. Average whole lung apparent diffusion coefficients (ADCs) were calculated from multi-slice Xe-MRI diffusion-weighted images (b=20.855 sec/cm2). Percentage predicted PFT results were established for each participant.
Whole lung and lobar QCT-derived metrics for emphysema and bronchial wall thickness were calculated from percentage of lung tissue with density of <-950 HU and Pi10 (the square root of wall area for an airway with lumen perimeter of 10 mm), respectively.
Pearson’s correlation coefficients were used to evaluate the relationship between whole lung and lobar imaging measures and PFTs.
Results Xe-MRI whole lung average ADC showed significant correlation with: whole lung QCT percentage emphysema (r = 0.79, p = 0.001), whole lung Pi10 (r = 0.68, p < 0.05), percentage predicted functional residual capacity (FRC) (r = 0.635, p < 0.05) and demonstrated significant negative correlation with percentage predicted TLCO (r= -0.81, p < 0.001). Whole lung QCT percentage emphysema showed a similar significant negative correlation with percentage predicted TLCO (r= -0.80, p < 0.001). Xe-MRI lobar percentage ventilated volume showed significant correlation with lobar QCT percentage emphysema (r= -0.51, p < <0.001). The QCT-derived metrics, percentage emphysema and Pi10 demonstrated significant correlation on a whole lung (r = 0.75, p < 0.015) and lobar basis (r = 0.29, p < 0.015).
Conclusion This study demonstrates excellent correlation between Xe-MRI, QCT-derived metrics and PFTs in COPD. New quantitative whole lung and lobar functional imaging parameters have been derived that may be of value when assessing patients with COPD for regional treatment and in trialling new therapies. Although further investigation is required, this may represent the first integrated regional lung imaging technique linked to pulmonary functional outcomes.
