How is residual transverse magnetisation removed in a steady state sequence?

In a steady state sequence, residual transverse magnetization is primarily removed through the techniques of gradient spoiling and RF spoiling. Gradient spoiling involves the application of gradient pulses that disrupt the coherent transverse magnetization before the next RF pulse is applied. This mechanism helps in dephasing the spins, effectively cancelling out the residual transverse magnetization from the previous excitation, thus preventing it from contributing to the subsequent signals.

RF spoiling works by varying the phase of the RF pulses with each iteration, which prevents the spins from accumulating coherent magnetization. This combination of gradient and RF spoiling is essential in maintaining a steady state where only the new, freshly excited magnetization contributes to the signal, enhancing image quality.

Using a longer repetition time (TR), for instance, may help in allowing the magnetization to relax adequately, but it doesn't specifically target the removal of residual transverse magnetization. Similarly, increasing the flip angle could affect the amount of longitudinal and transverse magnetization created but does not directly address the elimination of residual magnetization from prior sequences. A sufficient time delay between pulses aids relaxation but again does not specifically facilitate the removal of residual transverse magnetization in the same targeted way that gradient and RF spoiling do.