Effects of Tissue Relaxation, Eddy currents, and Acceleration on Velocity-Selective Preparation Pulses

Abstract

Fourier-transform-based velocity-selective (FT-VS) magnetization preparation has shown great promise for unenhanced MR angiography and arterial spin labeling. Although recent technical advances made FT-VS preparation resistant to B-0 and B-1 field inhomogeneity, there remain other non-ideal conditions including tissue relaxation, eddy currents, and accelerated motion, which are often ignored during excitation pulse design. In this study, using a double-refocused VS preparation pulse as a testbed, excitation profiles were numerically simulated taking into account the potential effects of the three non-ideal conditions. The longitudinal magnetization of arterial blood resulting from FT-VS preparation turned out to decrease from the ideal value of M-0 to 0.92M(0), 0.99M(0), and 0.88M(0) due to tissue relaxation, eddy currents, and accelerated motion, respectively. When all three factors were considered simultaneously, the worst-case relative contrast ratio (CR) between arterial blood and muscle tissue was estimated as 0.86, corresponding to a decrease by 14 % from the ideal CR of 1.0.