TOWARDS UNDERSTANDING THE BALANCED STEADY-STATE FREE PRECESSION SIGNAL INTENSITY CHANGES IN CINE CARDIAC MAGNETIC RESONANCE IMAGING: A PRELIMINARY EVALUATION IN HEALTHY SUBJECTS PRE- AND POSTCONTRAST.

Background: Balanced steady-state free-precession (bSSFP) cines provide excellent contrast for morpho-functional cardiac evaluation. The myocardial cine signal intensity (mcSI) fluctuation during the cardiac cycle has not yet been considered diagnostically relevant, in part because the impact of through-plane motion on the mcSI remains unclear.

Purpose: We aim to characterize the mid ventricular pre- and postcontrast bSSFP cyclic mcSI fluctuations in healthy subjects and compare these to Bloch simulations incorporating through-plane motion and to acquisitions in a moving phantom.

Methods: Retrospectively-gated mid-ventricular short-axis cine bSSFP images from healthy subjects (n=49) acquired at 1.5 Tesla pre- and early postcontrast were analyzed. First, the mcSI fluctuations during the heart cycle were determined and their timing compared to the radial myocardial motion. Next, pre- versus postcontrast differences were determined during systole, early-diastole and late-diastole. Finally, Bloch simulations and acquisitions in a moving T1 phantom were performed to analyze the through-plane motion effect on the bSSFP and spoiled gradient echo (SGRE) mcSI.

Results: The bSSFP mcSI showed a three peak pattern both pre- and postcontrast, corresponding to the contraction and relaxation phases. However, the mcSI peaks showed a time lag versus the times of maximum radial velocity that was larger for the systolic contraction than for the early or late-diastolic relaxation phases. In addition, the shape and amplitude of the systolic and early diastolic mcSI peaks changed significantly post- versus precontrast. Bloch simulations showed an in-vivo-like (regional) three-peak signal profile and similar changes for post- versus precontrast T1 levels. Finally, results in the moving phantom and accompanying simulations confirmed a slice-thickness dependent time lag between the motion and mcSI profile in both bSSFP and SGRE.

Conclusions: In healthy subjects before and after contrast, the bSSFP mcSI variation during the heart cycle is characterized by a three-peak pattern associated with the contraction and relaxation phases. However, the delays in timing of these peaks versus the myocardial motion, as well as the differences between pre- and postcontrast, vary with the stage of the heart cycle. Bloch simulations suggest that these mcSI fluctuations are largely determined by the regional through-slice motion. A better understanding of these motion-induced contrast mechanisms may be beneficial to methods exploiting bSSFP myocardial cine SI.