Zhang, W-J; Niven, RM; Young, SS; Liu, Y-Z; Parker, GJM; Naish, JH; (2015) Dynamic oxygen-enhanced magnetic resonance imaging of the lung in asthma—Initial experience. European Journal of Radiology , 84 (2) pp. 318-326. 10.1016/j.ejrad.2014.10.021.

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Abstract

OBJECTIVES: 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. MATERIALS AND METHODS: The 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, FEV_{1} = 96 ± 3% of predicted value) and six severe asthmatic patients (41 ± 12 years old, FEV_{1} = 60 ± 14% of predicted value) on a 1.5 T MR scanner using a two-dimensional T_{1} -weighted inversion-recovery turbo spin echo sequence. The enhancing fraction (EF), the maximal change in the partial pressure of oxygen in lung tissue (ΔPO_{2MAX_1}) and arterial blood of the aorta (ΔPO_{2max_a}), and the oxygen wash-in (τ_{up_l}, τ_{up_a}) and wash-out (τ_{down_l}, τ_{down_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. RESULTS: The severe asthmatic group had significantly smaller EF (70 ± 16%) and median ΔPO_{2max_1} (156 ± 52 mmHg) and significantly larger interquartile range of τ_{up_1} (0.84 ± 0.26 min) than the mild asthmatic group (95 ± 3%, P = 0.014; 281 ± 40 mmHg, P = 0.004; 0.20 ± 0.07 min, P = 0.001, respectively). EF, median ΔPO_{2max_1} and τ_{down_l} and the interquartile range of τ_{up_1} and τ_{down_1} 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 ΔPO_{2max_1} was significantly correlated with ΔPO_{2max_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). CONCLUSIONS:Dynamic 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.

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