This study, funded by a Project Grant from the Canadian Institutes of Health Research (CIHR), aims to better understand the underlying causes of breathlessness in patients in the initial stages of chronic obstrucitve pulmonary disease (COPD). These patients experience intense breathlessness during exercise that appears to be out-of-proportion to the degree of impairment that is measured on standard lung function tests. We are using functional imaging techniques, most notably phase-revolved functional lung MRI (PREFUL-MRI, the imaging technique from where this project derives it's name) during exercise to better understand the structural and functional contributors to breathlessness in these patients. The goal of this project is to better understand the contributors to breathlessness in this population so that we may find better ways of managing this debilitating symptom.