RecruitingPhase 2Drug trial129 Xenon MRI as a Biomarker for Diagnosis and Response to Therapy in Pulmonary Arterial Hypertension (PAH)The overall study objectives outlined in this study are to derive 129Xe MRI pulmonary vascular biomarker signatures that differentiate common subtypes of PAH and to determine the ability of 129Xe MRI to longitudinally monitor disease progression and response to therapy in PAH, with the aid of additional assessments, such as labs, echocardiography, and six-minute walk distance (6MWD).