Hyperpolarized Magnetic Resonance Imaging in Asthma Pre- and Post-Bronchial Thermoplasty

This is a one year, single centre randomized controlled trial. Subjects will be identified through the London Asthma Centre located at St. Joseph's Hospital and from Hamilton at St. Joseph's Healthcare, and will be given a letter of information for the study. The study will only recruit subjects with asthma who are undergoing BT as part of their normal clinical care and asthma treatment plan. Those interested will sign the consent form at the clinic. Bronchial thermoplasty (BT) is a novel FDA approved outpatient asthma treatment procedure which aims to "cure" symptoms by permanently reducing airway smooth muscle mass in the lobar and segmental bronchi. Under local anesthetic, radiofrequency energy is delivered to warm the airway wall to 65 degrees celcius. The effect of this procedure is a reduction in airway smooth muscle mass in the treated airways resulting in a reduced potential for bronchoconstriction. Fourteen asthma patients will be enrolled in the study and each subject will visit the centre on five occasions (three pre-treatment visits and two post-treatment visits). We will evaluate pre-therapy optimization using inflammometry, pre-therapy ventilation defect reproducibility and BT treatment effects (pre-treatment visit 1= 5±2 days pre-optimization, pre-treatment visit 2 = 15±7 days pre-BT, pre-treatment visit 3 = 5±2 days pre-BT, post-treatment visit 4=6 weeks post-BT, post treatment visit 5 = 6 months post-BT). At pre-treatment visit 1, patients will be randomized to image-guided or conventional therapy. For all subjects, at all visits, spirometry, plethysmography and 3He and/or 129Xe MRI will be performed. Methacholine challenge (MCh) will be performed (for those subjects with FEV1 \>60%) at pre-treatment visit 3 and post-treatment visit 4 with spirometry and MRI performed pre- and post-MCh. Pre-treatment visit 3 will include a low-dose thoracic CT that will be used to generate a detailed 3D model of the airway tree. MRI will be co-registered to the CT with 3D airway rendering to enable spatial comparisons between ventilation defects and airways. All subjects will also complete bi-weekly and weekly quality of life questionnaires. Self-reported data will be uploaded by each subject monthly to our website using a confidential and password protected upload. MRI of the lungs will be performed using an inhaled contrast agent: either Hyperpolarized Helium-3 or Hyperpolarized Xenon-129. Participants will inhale the hyperpolarized gas and perform a breathhold for up to 16 seconds. Two different types of images will be acquired in the coronal plain during each visit: 1) 1H thoracic cavity, and 2) 3He and/or 129Xe static ventilation. Respiration and oxygen saturation will be monitored throughout the imaging session.