What does a steady state condition imply in MR imaging?

A steady state condition in MRI refers to the equilibrium achieved between the longitudinal (T1) and transverse (T2) relaxation times of the tissue being imaged, influenced primarily by the repetition time (TR) of the imaging sequence. When TR is shorter than both T1 and T2, it allows for a continuous replenishment of the signal, leading to a constant and stable output. This is crucial for producing consistent image contrast and enhancing the quality of dynamic imaging sequences, such as those in fast imaging protocols.

In steady state imaging, the system is designed to reach an equilibrium where the magnetization vectors maintain a consistent orientation and magnitude due to the rapid application of RF pulses. This results in an increased signal intensity because the preceding RF pulse does not allow sufficient time for the spins to fully relax, leading to ongoing contributions to the signal as new pulses are applied. Thus, when TR is shorter than T1 and T2, the signal is continuously updated and becomes stable, fulfilling the condition of a steady state.