Simultaneous quantification of hyperpolarized xenon-129 ventilation and gas exchange with multi-breath xenon-polarization transfer contrast (XTC) MRI
Faraz Amzajerdian, Hooman Hamedani, Ryan Baron, Luis Loza, Ian Duncan, Kai Ruppert, Stephen Kadlecek, Rahim Rizi
Abstract
Purpose
To demonstrate the feasibility of a multi-breath xenon-polarization transfer contrast (XTC) MR imaging approach for simultaneously evaluating regional ventilation and gas exchange parameters.
Methods
Imaging was performed in five healthy volunteers and six chronic obstructive pulmonary disease (COPD) patients. The multi-breath XTC protocol consisted of three repeated schemes of six wash-in breaths of a xenon mixture and four normoxic wash-out breaths, with and without selective saturation of either the tissue membrane or red blood cell (RBC) resonances. Acquisitions were performed at end-exhalation while subjects maintained tidal breathing throughout the session. The no-saturation, membrane-saturation, and RBC-saturation images were fit to a per-breath gas replacement model for extracting voxelwise tidal volume (TV), functional residual capacity (FRC), and fractional ventilation (FV), as well as tissue- and RBC-gas exchange (f Mem and f RBC, respectively). The sensitivity of the derived model was also evaluated via simulations.
Results
With the exception of FRC, whole-lung averages for all metrics were decreased in the COPD subjects compared to the healthy cohort, significantly so for FV, f RBC, and f Mem. Heterogeneity was higher overall in the COPD subjects, particularly for f RBC, f Mem, and f RBC:Mem. The anterior-to-posterior gradient associated with the gravity-dependence of lung function in supine imaging was also evident for FV, f RBC, and f Mem values in the healthy subjects, but noticeably absent in the COPD cohort.
Conclusion
Multi-breath XTC imaging generated high-resolution, co-registered maps of ventilation and gas exchange parameters acquired during tidal breathing and with low per-breath xenon doses. Clear differences between healthy and COPD subjects were apparent and consistent with spirometry.