Monitoring myocardial oxygenation response to respiratory maneuvers using real-time magnetic resonance imaging

Oxygenation-sensitive (OS) cardiovascular magnetic resonance (CMR), using breathing maneuver-induced stress and blood oxygen level-dependent contrast, is a well-tolerated, non-invasive approach for assessing myocardial oxygenation. This study evaluated two real-time CMR sequences and a semi-automated analysis workflow to enable continuous, motion-robust assessment of myocardial oxygenation dynamics, aiming to overcome limitations of electrocardiogram (ECG)-triggered acquisitions and reduce manual evaluation requirements.

Signal intensity dynamics of ten young healthy female volunteers were analyzed from images acquired on a 3T scanner using an ECG-triggered balanced steady-state free precession (bSSFP) sequence, a real-time (RT) bSSFP sequence, and a RT fast low-angle short (FLASH) sequence. Images were obtained in a mid-ventricular slice while participants performed a breathing maneuver consisting of normal breathing, paced hyperventilation, and a prolonged breath hold. A semi-automated processing pipeline was implemented to generate motion-resolved oxygenation maps using retrospective cardiac phase binning, deformable image registration, and automated segmentation.

The RT sequences captured end-systolic global myocardial signal intensity change (ΔSI, relative to reference frames at breath-hold start) with dynamics comparable to those of the ECG-triggered bSSFP sequence. As expected in healthy volunteers, ΔSI decreased during hyperventilation and recovered during the prolonged breath-hold. At 20-30s, oxygenation responses at end-systole were 3.95%[3.36, 7.50] for ECG-triggered bSSFP, 5.47%[3.31, 9.08] for RT bSSFP, and 3.24%[1.99, 4.80] for RT FLASH. RT FLASH showed fewer artifacts but lower contrast and smaller ΔSI than the bSSFP sequences, with inter-sequence differences appearing modest in mixed-effects analysis.

This exploratory study demonstrates the feasibility of combining real-time MR sequences with a semi-automated processing pipeline for continuous assessment of T2∕T2*-related myocardial oxygenation dynamics. Potential confounders, including through-plane motion and physiological drift, warrant further investigation.