A robust protocol for regional evaluation of methacholine challenge in mouse models of allergic asthma using hyperpolarized3He MRI

Hyperpolarized 3He magnetic resonance imaging (MRI) NEED TO INTRODUCE TERM, UNLESS YOU ARE OVER THE WORD COUNThas been recently used to produce high-resolution images of pulmonary ventilation after methacholine challenge in mouse models of allergic inflammation. This capability presents an opportunity to gain new insights about these models and to more sensitively evaluate new drug treatments in the pre-clinical setting. In the current study, we present our initial experience using two-dimensional, time-resolved 3He MRI of methacholine challenge-induced airways hyperreactivity to compare ovalbumin-sensitized and challenged (N=8) mice to controls (N=8). Imaging demonstrated that ovalbumin-sensitized and challenged animals exhibited many large ventilation defects even prior to methacholine challenge (4 out of 8) compared to no defects in the control animals. Additionally, the ovalbumin sensitized and challenged animals experienced a greater number of ventilation defects (4.5±0.4) following methacholine infusion than did controls (3.3±0.6). However, due to variability in methacholine delivery that was specific to the small animal MRI environment, the difference in mean defect number was not statistically significant. These findings are reviewed in detail and a comprehensive solution to the variability problem is presented that has greatly enhanced the magnitude and reproducibility of the methacholine response. This has permitted us to develop a new imaging protocol consisting of a baseline 3D image, a time-resolved 2D series during methacholine challenge, and a post-methacholine 3D image that reveals persistent ventilation defects.