Chapter 14 - Hyperpolarized Gas MRI of the Lung in Asthma

Abstract

This chapter explores the application of magnetic resonance imaging (MRI) to the study of asthma with an emphasis on the role of hyperpolarized (HP) gases. Asthma affects millions of people worldwide and trends indicate increasing incidence particularly among children. In the first three sections of the chapter we focus on a general overview of asthma as a disease, characterize the obstructive physiology involved in asthma, and describe its clinical presentation. These sections include the rationale for imaging in asthma specifically as a useful tool to advance our understanding of the basic phenotypes of this disease and of its regional heterogeneity in the lungs. Subsequent sections are dedicated more specifically to the role of HP gas MRI for breath-held and dynamic imaging of airway obstruction in asthma and the physiologic meaning of the observed “ventilation defects.” Different approaches to the analysis and quantification of the observed ventilation defects in asthma are also briefly addressed. Specific clinical research applications of HP 3He MRI in the study of the spatial and temporal ventilation patterns in asthma phenotypes are described, including exercise-induced asthma, childhood asthma, and severe asthma. Images of ventilation are being used to explore mechanisms of airway closure and disease progression, and to target and evaluate regional disease and response to therapy. The use of diffusion-weighted MRI of HP gases to investigate lung microstructure in asthma is given a brief treatment, since the technique has shown promise in preliminary investigations of childhood asthma but is still in its early stages. The final sections are dedicated to emerging techniques as they apply to the study of asthma, especially the ongoing transition to HP 129Xe MRI with its added potential to study gas exchange. Finally, there is a brief discussion of what has been learned about asthma thus far, what remains to be studied, and the possible future role of HP gas MRI in this important area.