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There is a growing motivation for imaging regional lung ventilation. Global measures of lung function such as spirometry are not able to distinguish patterns of obstruction and regional reversibility in response to intervention. Advantages of MRI for lung imaging include use of nonionizing radiation and flexibility for acquiring dynamic, multidimensional signal changes in response to changes in lung function. For these reasons, MRI is particularly attractive for longitudinal studies of chronic lung disease, especially in pediatric populations. There are two broad classes of ventilation imaging methods using MRI, which have matured over the past decade: proton-based methods and direct imaging of exogenous gases using multinuclear MRI and spectroscopy. This chapter will provide a review of the theory and rationale of ventilation imaging with MRI, results of clinical research in ventilation MRI, and emerging methods of ventilation imaging. Proton MRI ventilation imaging techniques covered in this chapter include deformable image registration, Fourier decomposition, and oxygen-enhanced methods. This chapter also covers ventilation techniques utilizing MRI of visible gas nuclei, including hyperpolarized gas MRI and perfluorinated gas MRI.

Background There is an unmet need for an objective biomarker to predict asthma exacerbations. Objective Our aim was to assess the ventilation defect percent (VDP) on hyperpolarized helium-3 magnetic resonance imaging as a predictor of exacerbation frequency following imaging. Methods Subjects underwent hyperpolarized helium-3 and conventional clinical measurements, including pulmonary function tests, during a period of disease stability, and exacerbations were recorded prospectively over the following 2 years. We used a Poisson regression tree model to estimate an optimal VDP threshold for classifying subjects into high- versus low-exacerbation groups and then used statistical regression to compare this VDP threshold against conventional clinical measures as predictors of exacerbations. Results A total of 67 individuals with asthma (27 males and 40 females, 28 with mild-to-moderate asthma and 39 with severe asthma) had a median VDP of 3.75% (1.2% [first quartile]-7.9% [third quartile]). An optimal VDP threshold of 4.28% was selected on the basis of the maximum likelihood estimation of the regression tree model. Subjects with a VDP greater than 4.28% (n = 32) had a median of 1.5 exacerbations versus 0.0 for subjects with a VDP less than 4.28% (n = 35). In a stepwise multivariate regression model, a VDP greater than 4.28% was associated with an exacerbation incidence rate ratio of 2.5 (95% CI = 1.3-4.7) versus a VDP less than or equal to 4.28%. However, once individual medical history was included in the model, VDP was no longer significant. Nonetheless, VDP may provide an objective and complementary quantitative marker of individual exacerbation risk that is useful for monitoring individual change in disease status, selecting patients for therapy, and assessing treatment response. Conclusion VDP measured with magnetic resonance imaging shows promise as a biomarker of prospective asthma exacerbations.