Dynamic oxygen-enhanced magnetic resonance imaging of the lung in asthma—Initial experience

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, 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 (?PO2max_l) and arterial blood of the aorta (?PO2max_a), and the oxygen wash-in (?up_l, ?up_a) and wash-out (?down_l, ?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 ?PO2max_l (156�52mmHg) and significantly larger interquartile range of ?up_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 ?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). Median ?PO2max_l was significantly correlated with ?PO2max_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.