Tag contrast in breath-hold CINE cardiac MRI.

Contrast between tagged and nontagged myocardium was investigated using rapid gradient echo segmented k-space CINE MRI. The transient behavior of magnetization was measured in stationary and moving phantoms using gradient recalled acquisition in steady-state GRASS and spoiled GRASS (SPGR) sequences with TR approximately 7 ms and TE approximately 2.5 ms. Bloch equation simulations were used to compute theoretical results. Understanding the transient behavior of magnetization is important because tags only persist in the myocardium during the nonequilibrium transition to steady state. The transition to steady state for both SPGR and GRASS is reproducible after one heartbeat, and including unprocessed data from the first heartbeat leads to image artifacts. In a moving phantom, simulations and experimental results showed that GRASS and SPGR are essentially equivalent. Tag-tissue contrast in SPGR was very sensitive to imaging tip angle. The optimum tip angle for the scanning parameters used in this study was 11 degrees.