Hyperpolarized ¹²⁹Xe Lung MRI and Spectroscopy in Mechanically Ventilated Mice

Abstract

Hyperpolarized (HP) xenon-129 (¹²⁹Xe) is an inhaled magnetic resonance imaging (MRI) contrast agent possessing unique spectral and physical properties that can be exploited to quantify key aspects of pulmonary physiology, including ventilation, restricted diffusion (alveolar-airspace size) and gas exchange dynamics. In humans, it has been used to evaluate disease severity and progression in a diverse set of pulmonary disorders (e.g., chronic obstructive pulmonary disease, cystic fibrosis, and pulmonary fibrosis) and is now approved for clinical use in the United States, United Kingdom, and Denmark. Beyond its clinical and translational applications, the ability of ¹²⁹Xe MRI to noninvasively assess pulmonary pathophysiology and provide spatially resolved information is also of interest in preclinical research. Among animal models, mice are the most widely used due to the accessibility of genetically modified disease models. Here, ¹²⁹Xe MRI is uniquely promising as a minimally invasive, ionizing radiation-free, and sensitive technique to longitudinally monitor lung disease progression and therapy response (e.g., in the context of drug discovery). Like ¹²⁹Xe imaging in human studies, it is necessary to have a gas hyperpolarization device and MRI hardware with multi-nuclear capabilities. This technique can be extended to preclinical applications by incorporating an MRI-triggered, free-breathing apparatus or mechanical ventilator to deliver gas. Here, we describe the steps and provide checklists to ensure robust data collection and analysis, including creating a thermally polarized xenon gas phantom for quality control, optimizing polarization, animal handling (sedation, intubation, ventilation, and care for mice), and protocols for obtaining and quantifying ventilation, restricted diffusion, and gas exchange data. While preclinical ¹²⁹Xe MRI can be applied in a variety of animal models (e.g., rats, pigs, sheep), this protocol is tailored to mice due to the unique challenges posed by the small anatomy of mice, which are balanced by their affordability and the availability of many disease models.