Hyperpolarized Helium 3 MRI in Mild-to-Moderate Asthma: Prediction of Postbronchodilator Reversibility.

Abstract

Background Longitudinal progression to irreversible airflow limitation occurs in approximately 10% of patients with asthma, but it is difficult to identify patients who are at risk for this transition. Purpose To investigate 6-year longitudinal changes in hyperpolarized helium 3 (³He) MRI ventilation defects in study participants with mild-to-moderate asthma and identify predictors of longitudinal changes in postbronchodilator forced expiratory volume in 1 second (FEV₁) reversibility Materials and Methods Spirometry and hyperpolarized ³He MRI were evaluated in participants with mild-to-moderate asthma in two prospectively planned visits approximately 6 years apart. Participants underwent methacholine challenge at baseline (January 2010 to April 2011) and pre- and postbronchodilator evaluations at follow-up (November 2016 to June 2017). FEV₁ and MRI ventilation defects, quantified as ventilation defect volume (VDV), were compared between visits by using paired <i>t</i> tests. Participants were dichotomized by postbronchodilator change in FEV₁ at follow-up, and differences between reversible and not-reversible groups were determined by using unpaired <i>t</i> tests. Multivariable models were generated to explain postbronchodilator FEV₁ reversibility at follow-up. Results Eleven participants with asthma (mean age, 42 years ± 9 [standard deviation]; seven men) were evaluated at baseline and after mean 78 months ± 7. Medications, exacerbations, FEV₁ (76% predicted vs 76% predicted; <i>P</i> = .91), and VDV (240 mL vs 250 mL; <i>P</i> = .92) were not different between visits. In eight of 11 participants (73%), MRI ventilation defects at baseline were at the same location in the lung at follow-up MRI. In the remaining three participants (27%), MRI ventilation defects worsened at the same lung locations as depicted at baseline methacholine-induced ventilation. At follow-up, postbronchodilator FEV₁ was not reversible in six of 11 participants; the concentration of methacholine to decrease FEV₁ by 20% (PC₂₀) was greater in FEV₁-irreversible participants at follow-up (<i>P</i> = .01). In a multivariable model, baseline MRI VDV helped to predict postbronchodilator reversibility at follow-up (<i>R </i>² = 0.80; <i>P</i> < .01), but PC₂₀, age, and FEV₁ did not (<i>R </i>² = 0.63; <i>P</i> = .15). Conclusion MRI-derived, spatially persistent ventilation defects predict postbronchodilator reversibility 78 months ± 7 later for participants with mild-to-moderate asthma in whom there were no changes in lung function, medication, or exacerbations. © RSNA, 2019 <i>Online supplemental material is available for this article.</i> See also the editorial by Stojanovska in this issue.