Quantitative Ventilation Imaging Using Hyperpolarized Gas and Multibreath Imaging Sequences

Abstract Ventilation, or the ability to exchange air with the outside environment, is an essential feature of the healthy lung. During tidal breathing, regions of poor ventilation (or less well-appreciated, overdistension) are characteristic of many lung disorders. Quantitative assessment of these regions is perhaps the most important means of evaluating the organ for signs of early disease or progression. In this chapter, we introduce quantitative metrics that have been used for this purpose and discuss the several modalities that have been employed. Although no current technique corresponds exactly to the idealized measurement, we summarize each along with its well-understood ambiguities. We then focus on quantitative methods that employ hyperpolarized (HP) gas, covering the successful methods of agent administration, the theoretical basis of image analysis, and several example applications in healthy subjects, animal models, and human disease. Finally, we detail an analytical method by which the acquisition of several functional maps simultaneously can improve the validity of the entire set (i.e., each serves as a small but important correction to the others). This set can then be used to derive an additional measure of local oxygen uptake. HP gas imaging is thus a very powerful tool, capable of measuring local lung function from a uniquely diverse variety of perspectives. As with all imaging methods, however, it may be impractical or subject to inaccuracy in specific circumstances; its place is therefore best appreciated in light of these potential difficulties, as well as the strengths and weaknesses of the other options available.