Developing Hyperpolarized 129Xe MRI Biomarkers for Evaluation of Pulmonary Arterial Hypertension

Inclusion Criteria: * Age ≥ 18 years of age * Documented diagnostic right heart catheterization (RHC) at any time prior to screening confirming the diagnosis of WHO PAH Group 1 in any of the following subtypes: * Idiopathic PAH * Heritable PAH * Drug/toxin-induced PAH * PAH associated with CTD * Symptomatic PAH classified as WHO FC I, II, or III. * Documented Historical RHC with a mPAP ≥ 20 mmHg, PCWP ≤15 mmHg, and PVR ≥ 3 Wood Units (WU) * Ability to adhere to the study visit schedule, adhere, and comply with all protocol requirements. * Ability to understand and provide written informed consent. For patients in the Initiating Therapy Arm: * Initiation of pulmonary vasodilator therapy within ±3 weeks of baseline imaging timepoint. For patients in the Stable Arm: * On stable doses of background PAH therapy and diuretics (i.e., patient-specific dose goal for each therapy already achieved) for at least 90 days prior to screening; for infusion prostacyclins, dose adjustment within 10% of optimal dose is allowed per medical practice Exclusion Criteria: * Subject unable to undergo MRI based on MRI safety screening * Diagnosis of pulmonary hypertension WHO Groups 2, 3, 4, or 5 * Pregnant or breastfeeding female subjects * Prisoners or incarcerated individuals * Any major surgical procedure within 90 days prior to study enrollment or planned surgical procedure during the study period. * Concomitant medical disorder, condition, or history, that in the opinion of the I…