Pulmonary hyperpolarized 129Xe 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 129Xe 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 (pAO2) maps by extracting the unrestricted diffusion coefficient (D0) 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/cm2) DW hyperpolarized 129Xe images obtained in four never‐smokers and four COPD ex‐smokers. Morphometric parameters and D0 maps were computed and the latter used to generate [Xe] and pAO2 maps. Xenon concentration phantoms estimating a range of values mimicking those observed in vivo were also investigated. Results Xenon D0 was significantly increased (P = 0.035) in COPD (0.14 ± 0.03 cm2/s) compared with never‐smokers (0.12 ± 0.02 cm2/s). COPD ex‐smokers also had significantly decreased [Xe] (COPD = 8 ± 7% versus never‐smokers = 13 ± 8%, P = 0.012) and increased pAO2 (COPD = 18 ± 3% versus never‐smokers = 15 ± 3%, P = 0.009) compared with never‐smokers. Phantom measurements showed the expected dependence of D0 on [Xe] over the range of concentrations anticipated in vivo. Conclusion DW hyperpolarized 129Xe MRI morphometry can be used to simultaneously map [Xe] and pAO2 in addition to providing micro‐structural biomarkers of emphysematous destruction in COPD. Phantom measurements of D0([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.