Hyperpolarized-gas MRI has seen a steadily increasing, albeit tortuous, path toward relevance in pulmonary medicine. During the last 10 years, the field has seen an increased focus on 129Xe, which can be used to measure regional ventilation, to characterize the size of alveolar spaces (diffusion MRI), and to measure gas exchange between the airspaces, red blood cells, and interstitium/plasma. This presentation will focus on ventilation imaging and the relevance of ventilation imaging to sensitive detection of early, regional lung obstruction. Application to well-characterized patient populations has allowed detailed comparisons of hyperpolarized-gas MRI to clinically-accepted techniques, demonstrating high sensitivity.
Hyperpolarized-gas MRI began in earnest over 20 years ago, and has seen a steadily increasing, albeit tortuous, path toward relevance in pulmonary physiology, pathophysiology, and medicine. During the last 10 years, the field has seen a decreased focus on 3He and increased focus on 129Xe, for reasons relating to decreasing supplies of 3He and improvements in engineering and our understanding of the physics of spin-exchange optical pumping of 129Xe and alkali metals.
129Xe MRI can be used to measure regional spin density after various types of inhalation or exhalation (often called ventilation imaging), to measure the restricted diffusion and characterize the size of alveolar spaces (diffusion MRI), and to measure the direct exchange of Xe between the airspaces, red blood cells, and interstitial tissue and plasma. As our ability to create high-quality, diagnostic images has consistently improved, so has our understanding of the relationship of spatial abnormalities to underlying lung disease.
This talk will focus on simple ventilation imaging (the most well-developed of the techniques above), and the relevance of ventilation imaging to sensitive detection of early, regional lung obstruction. While applicable to nearly all pulmonary diseases with obstruction, including COPD, asthma, bronchiolitis obliterans, and rare-lung conditions, application to a well-characterized population of patients with cystic fibrosis has allowed detailed comparisons of hyperpolarized-gas MRI to clinically-accepted techniques such as pulmonary function testing and multiple-breath inert gas washout. These straightforward studies demonstrate not only the sensitivity of the technique, but its ability to be combined with structural modalities, such as proton MRI or CT, to provide a rich dataset with clinically-relevant information for future translation to the clinic.
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