PAO2 Mapping Using HP Gas MRI

Hyperpolarized gas MRI is uniquely capable of noninvasively measuring regional alveolar oxygen tension ( P AO 2 ). As P AO 2 reflects both the intake of oxygen to the parenchyma and its uptake into the blood, it has substantial promise as a marker of both restrictive and obstructive lung diseases. Many of these disorders progress in a heterogeneous fashion such that global markers of lung function—e.g., alveolar blood gas testing, spirometry—are unable to detect their earliest manifestations. In contrast, imaged P AO 2 can reveal localized physiologic alterations caused by nascent pathology. In this chapter, we describe the series of technical advancements achieved over roughly the last two decades of P AO 2 imaging research, including the development of a theory of oxygen-induced depolarization, sophisticated acquisition techniques, and multibreath protocols. We then turn to the latest findings in clinical P AO 2 imaging, focusing particularly on a series of experiments carried out to assess the validity, reliability, pathologic relevance, and sensitivity/specificity of this parameter in the detection of smoking-related pathophysiology and chronic obstructive pulmonary disease.