Bronchial Thermoplasty for Severe Asthmatics Guided by HXe MRI

Inclusion Criteria (bronchial thermoplasty): * Males or females age 18 or greater and less than 65. * Subject has asthma and is taking regular maintenance medication for past 12 months that includes: * Inhaled corticosteroid (ICS) at a dosage greater than 1000μg beclomethasone per day or equivalent, AND long acting ß2-agonist (LABA) at a dosage of ≥100μg per day Salmeterol or equivalent. * Other asthma medications such as leukotriene modifiers, or anti-immunoglobulin E (IgE), are acceptable (Subjects on Xolair® must have been on Xolair for greater than 1 year). * Asthma confirmed by: (a) b-agonist reversibility of FEV1 ≥ 12 % following 360mcg albuterol OR (b) 20% fall in forced expiratory volume in 1 second (PC20-FEV1) after a challenge with methacholine ≤ 8 mg/ml if not receiving an inhaled corticosteroid (ICS) or ≤ 16 mg/ml if receiving an ICS. * FEV1 ≥ 50% predicted pre-bronchodilator. * Asthma symptoms on at least two days or one night per week over the last 2 weeks. * Subject is a non-smoker for 1 year or greater (if former smoker, less than 10 pack-years total smoking history). * Patient has a clinical indication for bronchial thermoplasty as decided by their treating physician. * Ability to undergo bronchoscopy in the opinion of the investigator. Exclusion Criteria (bronchial thermoplasty): * Asthma exacerbation (ED visit, hospitalization, course of increased systemic steroids, or urgent health care visit for asthma) during the prior four weeks. * Asthma exacerbation requiring hospitalization during the prior six weeks. * Chronic oral steroid therapy greater than 30 mg per day. * Respiratory tract infection within past 4 weeks * Subject has a known sensitivity to medications required to perform bronchoscopy (such as lidocaine, atropine and benzodiazepines). * Subject is undergoing immunosuppressant therapy (e.g., methotrexate). * Subject is on anticoagulant medication. * Subject has bleeding diathesis, platelet dysfunction, and thrombocytopenia with platelet count less than 125,000/mm2 or known coagulopathy (INR \> 1.5). * Subject has other respiratory diseases including interstitial lung disease, emphysema, cystic fibrosis, vocal cord dysfunction, mechanical upper airway obstruction, untreated obstructive sleep apnea, Churg-Strauss syndrome, cardiac dysfunction, and allergic bronchopulmonary aspergillosis (total IgE of \>1000 Units/mL with positive specific IgE to aspergillus and evidence of central bronchiectasis). * Subject has segmental atelectasis, lobar consolidation, significant or unstable pulmonary infiltrate, or pneumothorax, confirmed on x-ray. * Subject has clinically significant cardiovascular disease, including myocardial infarction, angina, cardiac dysrhythmia, conduction defect, cardiomyopathy, aortic aneurysm, or stroke. * Subject has uncontrolled hypertension (\>200mm Hg systolic or \>100mm Hg diastolic pressure). * Subject uses an internal or external pacemaker or cardiac defibrillator. * Chronic diseases (other than asthma) that in the opinion of the investigator would prevent participation in the trial or put the participant at risk by participation, e.g. chronic diseases of the lung (other than asthma), heart, liver, kidney, or nervous system, or immunodeficiency * History of cigarette smoking with \> 10 pack years total * Use of investigative drugs or intervention trials in the 30 days prior to enrollment or during the duration of the study * Any condition or compliance issue which in the opinion of the investigator might interfere with participation in the study Exclusion Criteria (Magnetic Resonance Imaging): * Obesity exceeding the scanner capability * Metal implants or non-removable metal piercings * Inability to tolerate MRI scanning due to claustrophobia Exclusion Criteria (HXe inhalation): * Pregnancy or intention to become pregnant * Neurological or cardiac comorbidities * Hemoglobin level below 10 g/dl as determined in a recent (within 12 months) measurement