Noninvasive quantification of airway inflammation following segmental allergen challenge with functional MR imaging: A proof of concept study

Purpose To evaluate oxygen-enhanced T1-mapping magnetic resonance (MR) imaging as a noninvasive method for visualization and quantification of regional inflammation after segmental allergen challenge in asthmatic patients compared with control subjects. Materials and Methods After institutional review board approval, nine asthmatic and four healthy individuals gave written informed consent. MR imaging (1.5 T) was performed by using an inversion-recovery snapshot fast low-angle shot sequence before (0 hours) and 6 hours and 24 hours after segmental allergen challenge by using either normal- or low-dose allergen or saline. The volume of lung tissue with increased relaxation times was determined by using a threshold-based method. As a biomarker for oxygen transfer from the lungs into the blood, the oxygen transfer function (OTF) was calculated. After the third MR imaging examination, eosinophils in bronchoalveolar lavage fluid were counted. Differences between times and segments were analyzed with nonparametric Wilcoxon matched-pairs test and Spearman correlation. Results In lung segments treated with the standard dose of allergen, the OTF was decreased at 6 hours in asthmatic patients, compared with saline-treated segments (P = .0078). In asthmatic patients at 24 hours, the volume over threshold was significantly increased in normal allergen dose-treated segments compared with saline-treated segments (P = .004). In corresponding lung segments, the volume over threshold at 24 hours in the asthmatic group showed a positive correlation (r = 0.65, P = .0001) and the OTF at 6 hours showed an inverse correlation (r = -0.67, P = .0001) with the percentage of eosinophils in the bronchoalveolar lavage fluid. Conclusion OTF and volume over threshold are noninvasive MR imaging-derived parameters to visualize and quantify the regional allergic reaction after segmental endobronchial allergen challenge.