Asthma Exacerbation and Helium-3 MRI

Inclusion Criteria * At least 18 years old * Able to speak and read English * Acute asthma exacerbation, defined as requirement for hospitalization or emergent outpatient visit, and treatment with high dose corticosteroids ( 40mg prednisone or equivalent) * FEV1 \< 80% predicted on the day of MRI * Attending physician agrees that patient is safe to participate on the day of the MRI scan Exclusion Criteria * Evidence of pneumonia, based on chest radiograph obtained within 24 hours of enrollment (if performed) * Documented fever or requirement for antibiotics * Unable to hold breath for 10 seconds * Active smoker or history of at least 10 pack years cigarette smoking * Chest radiograph with active pulmonary disease, except for changes expected with asthma (hyperinflation, subsegmental atelectasis) * Admission to ICU * For inpatients: contraindication to leaving hospital room for MRI as determined by Attending physician and RN on day of MRI * Any other concurrent active pulmonary disease or other unstable or active medical condition (including suspected active coronary ischemia, acute bleeding), as determined by Attending physician * Pregnancy as self reported * Need for cardiac monitoring * Need supplemental oxygen at an amount of 4L/min or a facemask