129-Xe MRI Study of Single Triple Therapy Inhaler Effects in COPD Patients With Moderate-severe Dyspnea and/or Poor Health Status With High or Low Risk of Exacerbation

The goal of this study is to study how 12-weeks daily (and optional 48-weeks) single inhaler triple therapy (fluticasone furoate (FF)-an inhaled corticosteroid; umeclidinium (UMEC)-a long-acting muscarinic antagonist; vilanterol (VI)-a long-acting β2-adrenergic agonist) works to treat adults with COPD. The investigators will compare the effects of this medication on adults with COPD who are at low risk of a flare-up and adults with COPD who are at high risk of a flare-up. The main questions it aims to answer are: * Does FF/UMEC/VI improve ventilation defect percent as measured on 129-Xenon MRI in adults with moderate-severe COPD * Evaluate the relationships between the ventilation defect percent and lung function test results Participants will: * Take the inhaler FF/UMEC/VI once daily for 12-weeks (optional 48-weeks) * visit Robarts 2 times (with optional 3rd visit) for tests and imaging