Abstract: Obstructive sleep apnea diagnosis based on peripheral arterial tone (PAT) and real-time magnetic resonance imaging (MRI) is provided. PAT and other physiological data are used to identify respiratory events experienced by a subject with obstructive sleep apnea. MRI images are recorded at least during the respiratory events to identify airway obstructions responsible for the sleep apnea events. The MRI images are recorded in real-time at a high frame rate during the sleep apnea events. The PAT signals and MRI images are collected while the subject is in a sleep state. PAT signals can also be used to identify sleep apnea events and trigger an MRI device to begin recording, thereby reducing the costs associated with recording extraneous and large amounts of MRI data.