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Abstract
ObjectivesTo prospectively estimate the feasibility and reproducibility of dynamic oxygen-enhanced magnetic resonance imaging (OE-MRI) in the assessment of regional oxygen delivery, uptake and washout in asthmatic lungs. Materials and methodsThe study was approved by the National Research Ethics Committee and written informed consent was obtained. Dynamic OE-MRI was performed twice at one month apart on four mild asthmatic patients (23±5 years old, FEV1=96±3% of predicted value) and six severe asthmatic patients (41±12 years old, FEV1=60±14% of predicted value) on a 1.5T MR scanner using a two-dimensional T1-weighted inversion-recovery turbo spin echo sequence. The enhancing fraction (EF), the maximal change in the partial pressure of oxygen in lung tissue (ΔPO2max_l) and arterial blood of the aorta (ΔPO2max_a), and the oxygen wash-in (τup_l, τup_a) and wash-out (τdown_l, τdown_a) time constants were extracted and compared between groups using the independent-samples t-test (two-tailed). Correlations between imaging readouts and clinical measurements were assessed by Pearson's correlation analysis. Bland–Altman analysis was used to estimate the levels of agreement between the repeat scans and the intra-observer agreement in the MR imaging readouts. ResultsThe severe asthmatic group had significantly smaller EF (70±16%) and median ΔPO2max_l (156±52mmHg) and significantly larger interquartile range of τup_l (0.84±0.26min) than the mild asthmatic group (95±3%, P=0.014; 281±40mmHg, P=0.004; 0.20±0.07min, P=0.001, respectively). EF, median ΔPO2max_l and τdown_l and the interquartile range of τup_l and τdown_l were significantly correlated with age and pulmonary function test parameters (r=−0.734 to −0.927, 0.676–0.905; P=0.001–0.045). Median ΔPO2max_l was significantly correlated with ΔPO2max_a (r=0.745, P=0.013). Imaging readouts showed good one-month reproducibility and good intra-observer agreement (mean bias between repeated scans and between two observations did not significantly deviate from zero). ConclusionsDynamic OE-MRI is feasible in asthma and sensitive to the severity of disease. The technique provides indices related to regional oxygen delivery, uptake and washout that show good one month reproducibility and intra-observer agreement.
Highlights
Compared to the mild asthmatic group, the severe asthmatic group was on average older (P = 0.030) with a larger body mass index (BMI, P = 0.020), worse airway obstruction (FEV1%predicted, forced vital capacity (FVC)%predicted, forced expiratory volume in 1 second (FEV1)/FVC and maximum mid-expiratory flow (MMEF)%predicted; P = 0.001, 0.011, 0.005 and 0.001, respectively), air trapping (RV/total lung capacity (TLC), P = 0.003) and airway resistance. 2 out of 4 mild asthmatics and 4 out of 6 severe asthmatics were genuine eosinophilic asthma patients (3-year eosinophil positive)
We have demonstrated that the dynamic oxygen-enhanced magnetic resonance imaging (OE-MRI) technique is able to visualize regional functional abnormalities in patients with asthma
The low value regions in PO2max l, which are more prominent in severe asthmatic lungs, imply reduced ability to deliver O2, as we would expect a low ventilation–perfusion ratio, which can occur even in asymptomatic asthma [27], to lead to low local PO2
Summary
To prospectively estimate the feasibility and reproducibility of dynamic oxygen-enhanced magnetic resonance imaging (OE-MRI) in the assessment of regional oxygen delivery, uptake and washout in asthmatic lungs. Bland–Altman analysis was used to estimate the levels of agreement between the repeat scans and the intra-observer agreement in the MR imaging readouts. EF, median PO2max l and down l and the interquartile range of up l and down l were significantly correlated with age and pulmonary function test parameters (r = −0.734 to −0.927, 0.676–0.905; P = 0.001–0.045). Imaging readouts showed good one-month reproducibility and good intra-observer agreement (mean bias between repeated scans and between two observations did not significantly deviate from zero). The technique provides indices related to regional oxygen delivery, uptake and washout that show good one month reproducibility and intra-observer agreement
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