Magn Reson Med 2019 Apr 16. Epub 2019 Apr 16.
Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada.
Purpose: To demonstrate the feasibility of mapping gas exchange with single breath-hold hyperpolarized (HP) Xe in humans, acquiring parametric maps of lung physiology. The potential benefit of acceleration using parallel imaging for this application is also explored.
Methods: Six healthy volunteers were scanned with a modified spiral-IDEAL sequence to acquire gas exchange-weighted images using a single dose of Xe. These images were fit with the model of xenon exchange (MOXE) on a voxel-wise basis calculating parametric maps of lung physiology, specifically: air-capillary barrier thickness (δ), alveolar septal thickness (d), capillary transit time (t ), pulmonary hematocrit (HCT), and alveolar surface area-to-volume ratio (SVR). An accelerated version of the sequence was also tested in subset of 4 volunteers and compared to the fully sampled (FS) results.
Results: Mean image-wide values calculated from MOXE parametric maps derived from FS dissolved Xe spiral-IDEAL images were: δ = 0.89 ± 0.17 μm, d = 7.5 ± 0.5 μm, t = 1.1 ± 0.2s, HCT = 28.8 ± 2.3%, and SVR = 140 ± 16 cm , in good agreement with previously published values based on whole-lung spectroscopy of healthy human subjects. Parallel imaging sufficiently reduces artifacting in accelerated images, but increases disagreement with MOXE parameters derived from FS data with mean voxel-wise unsigned relative differences of: δ = 39 ± 9%, d = 22 ± 3%, t = 117 ± 43%, HCT = 11 ± 2%, and SVR = 31 ± 12%.
Conclusion: Dissolved HP Xe spiral-IDEAL imaging for gas exchange mapping is feasible in humans using a single breath-hold. Accelerated gas exchange mapping is also shown to be feasible but requires further improvements to increase quantitative accuracy.