Gradient Echo Sequences - Balanced sequences

 
A steady state will also be established without any (gradient induced) dephasing between excitations. This sequence is called balanced SSFP (or TrueFISP, FIESTA, balanced FFE). In some publications and presentations this sequence is just called SSFP. This is misleading since each gradient echo sequence (including RF-spoiled types) is a SSFP sequence (they exhibit a steady state of the transverse and longitudinal magnetization). For balanced SSFP all gradients areas between excitations pulses are zero. For SSFP the gradient areas are constant, but not zero (this requires a refocused phase encode gradient). To minimize banding artifacts balanced SSFP is used with alternating excitation pulses, and a repetition time that should be as short as possible. The balanced SSFP steady state describes an oscillation of the magnetization around z axis. This steady state can be approached very fast with the use of an α/2-TR/2-preparation, as shown below. This simulation includes some small dephasing between excitations (±0.3π), and T1=20TR, T2=10TR, α=±70°.

Strong initial oscillations can be observed without α/2-TR/2-preparation, as shown below. As before, this simulation includes some small dephasing between excitations (±0.3π), and T1=20TR, T2=10TR, α=±70°.

Last updated: Montag, 18.04.2011