Simplified model and stabilization of SSFP sequences.
Steady-state free precession (SSFP) is used today in a form similar to other rapid sequences like fast spin echo (FSE) where a large longitudinal magnetization is present at the beginning of the train of excitations. This results in a transient behavior which impedes any measurement before the steady state is established. Several solutions have been proposed to stabilize the signals more quickly. Starting from a simplified model of signal generation, and by a suitable change of reference frame, this paper justifies theoretically the linear ramp-up proposed by Nishimura and Vasanawala (p. 301, 8th Annual Proceedings of ISMRM, 2000, Denver). This linear ramp-up can be generalized into a one giving less oscillatory residues. The solution is efficient in the sense that it does not require nutation angles larger than the one used during the stabilized period. Also, this solution is robust because it scales up or down nicely and is thus insensitive to B(1) variations.
Le Roux
Patrick
P
GE Medical Systems, Applied Science Lab Europe, 283 rue de la Miniere, 78530 Buc Cedex, France. Patrick.LeRoux@med.ge.com