Chapter 10 - PAO2 Mapping Using HP Gas MRI

Abstract

Hyperpolarized gas MRI is uniquely capable of noninvasively measuring regional alveolar oxygen tension (PAO2). As PAO2 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 PAO2 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 PAO2 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 PAO2 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.