IMPAHCT: Inhaled iMatinib Pulmonary Arterial Hypertension Clinical Trial is a Phase 2b/Phase 3 study to evaluate the safety and efficacy of AV-101 (dry powder inhaled imatinib) in patients with Pulmonary Arterial Hypertension (PAH). The Phase 2b part of the study will assess three doses to establish an optimal dose for the Phase 3 part of the study. The Phase 2b primary endpoint will be the placebo corrected change in pulmonary vascular resistance (PVR). The Phase 3 primary endpoint will be the placebo corrected change in 6-minute walk distance (6MWD) after 24 weeks of treatment.