Reproducibility of Hyperpolarized Xe MRI Ventilation Defect Percent in Severe Asthma to Evaluate Clinical Trial Feasibility.

RATIONALE AND OBJECTIVES

Xe MRI has been developed to noninvasively visualize and quantify the functional consequence of airway obstruction in asthma. Its widespread application requires evidence of intersite reproducibility and agreement. Our objective was to evaluate reproducibility and agreement of Xe ventilation MRI measurements in severe asthmatics at two sites.

MATERIALS AND METHODS

In seven adults with severe asthma, Xe ventilation MRI was acquired pre- and post-bronchodilator at two geographic sites within 24-hours. Xe MRI signal-to-noise ratio (SNR) was calculated and ventilation abnormalities were quantified as the whole-lung and slice-by-slice ventilation defect percent (VDP). Intraclass correlation coefficients (ICC) and Bland-Altman analysis were used to determine intersite Xe VDP reproducibility and agreement.

RESULTS

Whole-lung and slice-by-slice Xe VDP measured at both sites were correlated and reproducible (pre-bronchodilator: whole-lung ICC = 0.90, p = 0.005, slice-by-slice ICC = 0.78, p < 0.0001; post-bronchodilator: whole-lung ICC = 0.94, p < 0.0001, slice-by-slice ICC = 0.83, p < 0.0001) notwithstanding intersite differences in the Xe-dose-equivalent-volume (101 ± 15 mL site 1, 49 ± 6 mL site 2, p < 0.0001), gas-mixture (Xe/He site 1; Xe/N site 2) and SNR (40 ± 19 site 1, 23 ± 5 site 2, p = 0.02). Qualitative Xe gas distribution differences were observed between sites and slice-by-slice Xe VDP, but not whole-lung Xe VDP, was significantly lower at site 1 (pre-bronchodilator VDP: whole-lung bias = -3%, p > 0.99, slice-by-slice bias = -3%, p = 0.0001; post-bronchodilator VDP: whole-lung bias = -2%, p = 0.59, slice-by-slice-bias = -2%, p = 0.0003).

CONCLUSION

Xe MRI VDP at two different sites measured within 24-hours in the same severe asthmatics were correlated. Qualitative and quantitative intersite differences in Xe regional gas distribution and VDP point to site-specific variability that may be due to differences in gas-mixture composition or SNR.