The investigators will apply 129Xenon and/or 3He image acquisition and analysis methods in 200 asthma patient volunteers in order to characterize and probe the relationship between lung structure and function using imaging.

This is an exploratory, longitudinal study with no medication evaluated. 200 asthma patients will visit the Clinical Imaging Research Laboratories at Robarts Research Institute two times over three years: at baseline, and at three years. For the first 60 subjects there will be 3 additional visits - two visits within 4 weeks of baseline (BL+2 weeks; BL+4 weeks; BL+78 weeks) in order to help generate reproducibility data and temporal maps.

For all subjects, the Baseline visit will include 129Xe and/or 3He MRI, chest CT, sputum induction, Pulmonary Function Tests, Airwave Oscillation test, Lung Clearance Index test, BORG Dyspnea Scale, and MRC Dyspnea Scale. All procedures will be before, during and after methacholine challenge (MCh). For V2, all but CT and MCh will be acquired.

Visits 1a and 1b will include MRI, Pulmonary Function Tests including Airwave Oscillation and Lung Clearance Index, and dyspnea questionnaires; Visit 1c will also include sputum induction.

There will be a telephone call at 52+/- 2 weeks, and 104 +/- 2 weeks. to track exacerbations and update medications. Subjects will complete self-assessments in the form of a) the Asthma Quality of Life Questionnaire with Standardized Activities (AQLQ(S)) bi-weekly, and the Asthma Control Diary (weekly) between visits. Self-reported data (the weekly asthma control diary and bi-weekly AQLQ(S)) will be uploaded by each subject monthly to the investigators website using a confidential and password protected upload (www.imaging.robarts.ca/\~gep/ForPatients.htm).

Inclusion Criteria:

• Subjects male and female aged 18-60 with a clinical diagnosis of asthma
• Smoking history ≤ 1 pack/year
• Subject understands the study procedures and is willing to participate in the study as indicated by signature on the informed consent
• Subject is judged to be in otherwise stable health on the basis of medical history
• Subject able to perform reproducible pulmonary function testing (i.e., the 3 best acceptable spirograms have FEV1 values that do not vary more than 5% of the largest value or more than 100 ml, whichever is greater.)
• FEV1 >60% predicted

Exclusion Criteria:

• Patient is, in the opinion of the investigator, mentally or legally incapacitated, preventing informed consent from being obtained, or cannot read or understand the written material
• Patient is unable to perform spirometry or plethysmography maneuvers
• Subject has an implanted mechanically, electrically or magnetically activated device or any metal in their body which cannot be removed, including but not limited to pacemakers, neurostimulators, biostimulators, implanted insulin pumps, aneurysm clips, bioprosthesis, artificial limb, metallic fragment or foreign body, shunt, surgical staples (including clips or metallic sutures and/or ear implants.) (At the discretion of the MRI Technologist/3T Manager)
• In the investigator's opinion, subject suffers from any physical, psychological or other condition(s) that might prevent performance of the MRI, such as severe claustrophobia.
• Patient is pregnant