Mapping the amplitude and phase of dissolved 129Xe red blood cell signal oscillations with keyhole spectroscopic lung imaging

Motivation: Cardiogenic oscillations in dissolved 129Xe red blood cell (RBC) signal are sensitive to cardiopulmonary disease. Current methods to map the amplitude of these oscillations do not consider oscillation phase, leading to physiologically unrealistic amplitude values. Goal(s): To map the amplitude and phase of 129Xe RBC oscillations in the lung vasculature. Approach: Multiple phases of the cardiac cycle were reconstructed from multi-echo dissolved 129Xe spectroscopic imaging data using a sliding window keyhole method, to map both oscillation amplitude and phase in healthy volunteers and post-COVID-19 patients. Results: Both oscillation amplitude and phase were mapped regionally. Phase-adjustment improved oscillation amplitude inter-scan repeatability in healthy volunteers. Impact: Sliding-window keyhole 129Xe RBC oscillation amplitude and phase mapping corrects for physiologically unrealistic negative amplitudes. This approach allows regional mapping of RBC oscillation phase, which may represent the cardiac pulse wave in the pulmonary microvasculature, and its alteration in disease.