Characterization of Subjects with Severe Asthma – SARP 2

MR imaging of the lungs will be used to define the number and size of ventilation defects seen in asthma patients with varying degrees of disease severity. During the imaging session, subjects will inhale the contents of a bag containing a small sip of hyperpolarized Helium-3 for the calibration of the scanner, followed by three 1.0 L doses of hyperpolarized Helium-3 with a net activity of 4.5 mmol. The first dose of hyperpolarized Helium-3 will be used for static imaging, where subjects will take a breath of hyperpolarized Helium-3 and hold their breath for 10 seconds while MR imaging is performed. This will allow investigators to determine the distribution of airflow into all areas of the lung. The second dose of hyperpolarized Helium-3 will be used for dynamic imaging, where subjects will take a breath of hyperpolarized Helium-3 and then do a forced exhalation so that imaging information on residual volume may be obtained. The third dose will be used to either repeat the previously acquired dynamic scan (to validate the reproducibility of regional lung function), or to repeat a previous imaging sequence if technical failures were encountered.