Pulmonary hyperpolarized 129 Xe morphometry for mapping xenon gas concentrations and alveolar oxygen partial pressure: Proof‐of‐concept demonstration in healthy and COPD subjects

Purpose Diffusion‐weighted (DW) hyperpolarized 129 Xe morphometry magnetic resonance imaging (MRI) can be used to map regional differences in lung tissue micro‐structure. We aimed to generate absolute xenon concentration ([Xe]) and alveolar oxygen partial pressure (p A O 2 ) maps by extracting the unrestricted diffusion coefficient ( D 0 ) of xenon as a morphometric parameter. Methods In this proof‐of‐concept demonstration, morphometry was performed using multi b‐value (0, 12, 20, 30 s/cm 2 ) DW hyperpolarized 129 Xe images obtained in four never‐smokers and four COPD ex‐smokers. Morphometric parameters and D 0 maps were computed and the latter used to generate [Xe] and p A O 2 maps. Xenon concentration phantoms estimating a range of values mimicking those observed in vivo were also investigated. Results Xenon D 0 was significantly increased ( P  = 0.035) in COPD (0.14 ± 0.03 cm 2 /s) compared with never‐smokers (0.12 ± 0.02 cm 2 /s). COPD ex‐smokers also had significantly decreased [Xe] (COPD = 8 ± 7% versus never‐smokers = 13 ± 8%, P  = 0.012) and increased p A O 2 (COPD = 18 ± 3% versus never‐smokers = 15 ± 3%, P  = 0.009) compared with never‐smokers. Phantom measurements showed the expected dependence of D 0 on [Xe] over the range of concentrations anticipated in vivo. Conclusion DW hyperpolarized 129 Xe MRI morphometry can be used to simultaneously map [Xe] and p A O 2 in addition to providing micro‐structural biomarkers of emphysematous destruction in COPD. Phantom measurements of D 0 ([Xe]) supported the hypotheses that differences in subjects may reflect differences in functional residual capacity. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc. Magn Reson Med 74:1726–1732, 2015. © 2014 Wiley Periodicals, Inc.