Clinical Research Directory

Inclusion Criteria: 1. Enrolled and randomized in BREATHE-3 to the Treatment arm or enrolled as a Control arm participant who has elected crossover treatment following BREATHE-3 Month 12. 2. Separate written BREATHE-Xe informed consent obtained prior to any sub-study procedures. 3. Able to perform coached breath-hold maneuvers of ≥10 seconds, as assessed by the site investigator. 4. Willing and able to travel to KUMC or UAB for all scheduled Xe-MRI sessions. 5. Eligible for MRI per local MRI safety screening, with no contraindications to MRI. Exclusion Criteria: 1. Any absolute contraindication to MRI, including ferromagnetic implants not approved for MRI, cardiac pacemaker or ICD not MRI-conditional, cochlear implants, severe claustrophobia, or any condition judged incompatible with safe MRI by the investigator. 2. Known allergy or hypersensitivity to xenon gas or components of the HP ¹²⁹Xe formulation. 3. SpO₂ \<88% at rest on the day of planned Xe-MRI, measured on the participant's usual oxygen (room air or standard supplemental oxygen per BREATHE-3 protocol or site standard of care). Supplemental oxygen is removed only for the preparation breaths and xenon inhalation, then resumed. 4\. Any medical condition that, in the investigator's opinion, would preclude safe participation or compromise imaging data integrity.