Regional Ventilation Changes in the Lung: Treatment Response Mapping by Using Hyperpolarized Gas MR Imaging as a Quantitative Biomarker.

Purpose To assess the magnitude of regional response to respiratory therapeutic agents in the lungs by using treatment response mapping (TRM) with hyperpolarized gas magnetic resonance (MR) imaging. TRM was used to quantify regional physiologic response in adults with asthma who underwent a bronchodilator challenge. Materials and Methods This study was approved by the national research ethics committee and was performed with informed consent. Imaging was performed in 20 adult patients with asthma by using hyperpolarized helium 3 (He) ventilation MR imaging. Two sets of baseline images were acquired before inhalation of a bronchodilating agent (salbutamol 400 μg), and one set was acquired after. All images were registered for voxelwise comparison. Regional treatment response, ΔR(r), was calculated as the difference in regional gas distribution (R[r] = ratio of inhaled gas to total volume of a voxel when normalized for lung inflation volume) before and after intervention. A voxelwise activation threshold from the variability of the baseline images was applied to ΔR(r) maps. The summed global treatment response map (ΔR) was then used as a global lung index for comparison with metrics of bronchodilator response measured by using spirometry and the global imaging metric percentage ventilated volume (%VV). Results ΔR showed significant correlation (P < .01) with changes in forced expiratory volume in 1 second (r = 0.70), forced vital capacity (r = 0.84), and %VV (r = 0.56). A significant (P < .01) positive treatment effect was detected with all metrics; however, ΔR showed a lower intersubject coefficient of variation (64%) than all of the other tests (coefficient of variation, ≥99%). Conclusion TRM provides regional quantitative information on changes in inhaled gas ventilation in response to therapy. This method could be used as a sensitive regional outcome metric for novel respiratory interventions. RSNA, 2017 Online supplemental material is available for this article.