Medical Physics Seminar – Monday, October 22, 2012
Fast MRI for Non-Invasive Assessment of Lung Structure and Function
Sean Fain, PhD.
Associate Professor of Medical Physics, UW-School of Medicine & Public Health, Madison, WI USA
Both hyperpolarized 3He and 129Xe MRI have been safely applied in a range of obstructive lung diseases to demonstrate areas of ventilation defect and structural abnormalities at the scale of the small airways and alveoli. These noble gas nuclei provide extremely high MRI signal because they are optically pumped using spin exchange laser polarization to levels 100,000 times their equilibrium polarization. This non-equilibrium magnetization requires rapid imaging with high data acquisition efficiency to achieve multi-dimensional imaging during a fixed breath-hold or during free breathing. Several methods using radial trajectories and constrained reconstruction have been implemented by my group to allow 4D (3D plus time) and high resolution diffusion weighted imaging under conditions of free breathing or short breath-holds. Application to investigation of pediatric asthma have demonstrated ventilation heterogeneity and microstructural abnormalities that are associated with asthma risk factors in early life and are similar to ventilation heterogeneity observed in adult asthma. The safe non-invasive nature of these techniques for pulmonary imaging without ionizing radiation dose make them particularly valuable for applications in pediatric lung diseases generally, and for longitudinal evaluation of disease especially. Cystic fibrosis is a lung disease with obstructive physiology caused by a set of limited mutations affecting function of the cystic fibrosis transmembrane regulator (CFTR) protein with targeted therapies in late phase testing or on the horizon. MRI with polarized gases may be useful for early assessment of CF disease severity and treatment response using these emerging therapies.