Oral Abstract Session
SCMR 22nd Annual Scientific Sessions
Coronary vasodilation and the ensuing myocardial hyperemia following the administration of a provocative stressor is a dynamic process. Noninvasive assessment of this process may provide important insights into pathological conditions that affect the heart. Cardiac BOLD MRI is an emerging method with the capacity to report on changes in myocardial oxygenation. However, current BOLD CMR techniques are relatively slow to rapidly sample the oxygenation changes in response to a vasodilatory stimulus, susceptible to motion and unreliable in the presence of heartbeat variations. To overcome these limitations and to enable highly time-resolved assessment of myocardial oxygenation, we developed a non-ECG-gated, free breathing, respiratory and cardiac phase-resolved, T2-based BOLD CMR sequence which can report on myocardial T2 changes every heart beat using a low rank tensor (LRT) formulation. Specifically, we tested whether myocardial oxygenation dynamics can be captured using the proposed method in clinically relevant large animal models with and without disease in the setting of regadenoson stress.
The proposed cardiac BOLD MRI approach was developed based on a LRT formalism (acquisition and reconstruction) that has been recently described for cardiac applications. It is composed of (i) adiabatic T2 preparation that is repeated at a fixed interval; (ii) repeat acquisition of a set of central k-space lines every other repetition time (TR) to serve as respiratory and cardiac navigators; and (iii) interleaving of a set of golden-ratio radial gradient-echo readout lines for LRT training. We tested the technique in dogs (intact, n=4; and with chronic myocardial infarction, n=4) in a 3T MRI system (Siemens, Verio) during regadenoson stress. The data acquisition and reconstruction schemes are illustrated in Figure 1.
Results: Figure 2 shows a representative time-series of normalized BOLD Response at rest and following regadenoson delivery from an intact animal and an animal with chronic MI. Under the resting condition, BOLD Response was relatively constant in both groups (Fig.2 A and D). Following regadenoson delivery, BOLD Response in healthy and remote myocardial territories steadily increased over a period of 2-3 minutes and plateaued to a level that is greater than 10% of the baseline values (Fig.2 B and E). BOLD Response was blunted in the affected (infarcted) myocardium, which is consistent with the minimal vascularization of the infarcted myocardium. Results were consistent across the two groups of animals.
Conclusion: The proposed BOLD CMR approach is the first to enable noninvasive, highly time-resolved, interrogation of vasomotor differences in vascular beds of myocardium in health and disease. We envision that this approach has the capacity to open the door for exploring novel insights into coronary circulation in health and disease.