Short-TR, Coherent, Gradient Echo Imaging

When a spin system is repeatedly disturbed by a fast repetition of RF pulses, the transverse magnetization after each new RF pulse approaches a steady-state value which is smaller than the thermal equilibrium value. The spin system takes a finite number of pulses before this steady-state is reached in a time that depends on both the T1 of the tissue and the flip angle of the RF pulse. The focus of this unit is on understanding the build-up of the magnetization to steady-state and the practical implementation of the simplest forms of imaging in the steady-state. Sequences utilizing a steady-state approach can be broadly classified as steady-state coherent (SSC) and steady-state incoherent (SSI) sequences. The SSC behavior is the subject of this unit.