Helium-3 MRI: Clinical applications of quantitative measurements of regional lung ventilation

For a variety of lung pathologies, it is crucial to assess lung function in order to quantify the severity of the disease, assess treatments, and predict clinical outcome. Obstructive lung diseases such as chronic obstructive pulmonary disease (COPD) and asthma affect millions of people world-wide. The improvement of therapies for COPD such as lung volume reduction surgery and anti-inflammatory drugs for asthma highlight the continued need for regional assessment of the extent and severity of disease. However, the techniques used to assess regional lung function are limited: -Regional ventilation can be assessed noninvasively with isotopic techniques using radioactive gases such as Xe-133 or Kr-81, but the temporal resolution of these techniques is of several seconds and do not allow real-time investigation of gas dynamics within the lungs. Moreover the subject is exposed to ionizing radiation during the examination which may not be suitable for iterative follow-up, especially in young population. -Traditional pulmonary function tests, such as spirometry evaluate the lung as a whole and this technique is relatively insensitive of early disease particularly during peripheral airways abnormalities. In some cases, bronchoconstrictive drugs such as metacholin can be added to PFT to assess bronchic hyper-responsivness. However, this test is incapable of identifying the magnetitude and distribution of disease on a regional basis. For example, in unilaterally lungtransplanted patients, PFT results may be influenced by both evolution of disease in the native lung and chronic rejection in the graft.