Compressed sensing reconstruction for high-SNR, rapid dissolved ¹²⁹Xe gas exchange MRI

Three-dimensional hyperpolarized ¹²⁹Xe gas exchange imaging suffers from low SNR and long breath-holds, which could be improved using compressed sensing (CS). The purpose of this work was to assess whether gas exchange ratio maps are quantitatively preserved in CS-accelerated dissolved-phase ¹²⁹Xe imaging and to investigate the feasibility of CS-dissolved ¹²⁹Xe imaging with reduced-cost natural abundance (NA) xenon.

¹²⁹Xe gas exchange imaging was performed at 1.5 T with a multi-echo spectroscopic imaging sequence. A CS reconstruction with an acceleration factor of 2 was compared retrospectively with conventional gridding reconstruction in a cohort of 16 healthy volunteers, 5 chronic obstructive pulmonary disease patients, and 23 patients who were hospitalized following COVID-19 infection. Metrics of comparison included normalized mean absolute error, mean gas exchange ratio, and red blood cell (RBC) image SNR. Dissolved ¹²⁹Xe CS imaging with NA xenon was assessed in 4 healthy volunteers.

CS reconstruction enabled acquisition time to be halved, and it reduced background noise. Median RBC SNR increased from 6 (2-18) to 11 (2-100) with CS, and there was strong agreement between CS and gridding mean ratio map values (R² = 0.99). Image fidelity was maintained for gridding RBC SNR > 5, but below this, normalized mean absolute error increased nonlinearly with decreasing SNR. CS increased the mean SNR of NA ¹²⁹Xe images 3-fold.

CS reconstruction of dissolved ¹²⁹Xe imaging improved image quality with decreased scan time, while preserving key gas exchange metrics. This will benefit patients with breathlessness and/or low gas transfer and shows promise for NA-dissolved ¹²⁹Xe imaging.