Unravelling the mechanisms of CE-SSFP in imaging myocardium at risk: The effect of relaxation times on myocardial contrast

Purpose: The aim of this study was to investigate the contrast mechanisms of Contrast-enhanced steady-state free-precession (CE-SSFP) through the utilization of Bloch simulations in an experimental porcine model and in patients with acute myocardial infarction. Methods: Six pigs and ten patients with myocardial infarction underwent CMR and tissue characterization at 1.5 T whereas a Bloch simulation framework was utilized to simulate the CE-SSFP signal formation and compare it against the actual CE-SSFP signal acquired from the experimental porcine model and the patient population. The relaxation times of remote, salvaged, and infarcted myocardium were calculated after the injection of gadolinium, at the time of CE-SSFP acquisition. Simulations were performed using the same CE-SSFP pulse sequence as used on the scanner on a set of spins with the calculated relaxation times from the CMR scans. Results: The normalized signal intensities of salvaged and infarcted myocardium obtained with simulations were lower than the corresponding normalized signal intensities obtained in vivo in pigs (p < 0.05, 134% vs 153%) and in patients (p < 0.05, 126% vs 145%). The results from simulations showed a linear relationship to the results obtained in the experimental porcine model (r² = 0.61) and in patients (r² = 0.69). Conclusion: The T1 and T2 values of remote, salvaged, and infarcted myocardium only partly explain the signal intensities in CE-SSFP images. Bloch simulations suggest that there may be more elements that contribute to the CE-SSFP contrast. Integration of other aspects of the MR experiment into the simulation model could further help to fully unravel the mechanisms of CE-SSFP.