Hyperpolarized Xenon-129 gas-exchange imaging of lung microstructure: First case studies in subjects with obstructive lung disease

Purpose: To develop and test a method to noninvasively assess the functional lung microstructure. Materials and Methods: The Multiple exchange time Xenon polarization Transfer Contrast technique (MXTC) encodes xenon gas‐exchange contrast at multiple delay times permitting two lung‐function parameters to be derived: (i) MXTC‐F, the long exchange‐time depolarization value, which is proportional to the tissue to alveolar‐volume ratio and (ii) MXTC‐S, the square root of the xenon exchange‐time constant, which characterizes thickness and composition of alveolar septa. Three healthy volunteers, one asthmatic, and two chronic obstructive pulmonary disease (COPD) (GOLD stage I and II) subjects were imaged with MXTC MRI. In a subset of subjects, hyperpolarized xenon‐129 ADC MRI and CT imaging were also performed. Results: The MXTC‐S parameter was found to be elevated in subjects with lung disease (P‐value = 0.018). In the MXTC‐F parameter map it was feasible to identify regional loss of functional tissue in a COPD patient. MXTC‐F maps showed excellent regional correlation with CT and ADC (P ≥ 0.90) in one COPD subject. Conclusion: The functional tissue‐density parameter MXTC‐F showed regional agreement with other imaging techniques. The newly developed parameter MXTC‐S, which characterizes the functional thickness of alveolar septa, has potential as a novel biomarker for regional parenchymal inflammation or thickening. J. Magn. Reson. Imaging 2011;33:1052–1062. © 2011 Wiley‐Liss, Inc.