PULSE AGAIN BEFORE EVERYTHING RECOVERS
Steady state reuses magnetization from earlier repetitions.
With a very short TR, the next RF pulse arrives before longitudinal magnetization has fully recovered and before all transverse magnetization has disappeared. After several repetitions, the magnetization settles into a repeating pattern called steady state.
The signal now depends on how each new RF pulse interacts with magnetization left from earlier TR periods.
BUILD THE RHYTHM
Repeated RF pulses lead to a stable, repeating signal.
Magnetization is tipped and a transverse signal begins.
The next pulse arrives while residual magnetization remains.
The signal changes during the first several repetitions.
The amount and phase of magnetization repeat predictably from one TR to the next.
“Steady” does not mean the magnetization stops moving. It means the same dynamic pattern repeats each TR.
WHAT HAPPENS TO THE LEFTOVER SIGNAL?
Sequence families differ in whether transverse coherence is removed or preserved.
RF or gradient spoiling disrupts residual transverse coherence so the next repetition relies mainly on longitudinal magnetization. These methods commonly support T1-weighted imaging.
Refocused steady-state families keep or refocus part of the residual transverse magnetization, producing different mixtures of FID and echo signal.
In bSSFP, the net gradient area is balanced along slice, phase, and frequency directions during each TR, helping preserve phase coherence.
With short TR under common conditions, bSSFP contrast is strongly related to the tissue T2/T1 ratio. Fluids and blood often appear bright, and the sequence offers high signal efficiency.
Balanced SSFP may be labeled TrueFISP, FIESTA, or balanced FFE depending on the manufacturer. It is widely used for cardiac cine imaging and high-resolution imaging around fluid-filled spaces. Exact contrast and use depend on the implementation.
Off-resonance can create dark bands.
When local field differences disrupt the repeating phase relationship, bSSFP signal can drop into dark banding artifacts. Short TR, careful shimming, frequency adjustment, and phase-cycling methods may help according to the scanner and protocol.
THE SWING ANALOGY
Push at the right rhythm and the motion builds.
Imagine pushing a swing before it stops. Each well-timed push adds to motion already present. A steady-state sequence does something similar with repeated RF pulses and residual magnetization.
The next pulse arrives while magnetization remains.
All three axes finish with zero net gradient area.
The dynamic signal pattern becomes predictable.
Remember: Steady state reuses the signal; balanced SSFP keeps it in step.
CHECK YOUR UNDERSTANDING
Separate steady state from balanced steady state.
What creates a steady state?
Rapid repeated RF pulses with short TR interact with residual longitudinal and transverse magnetization until a predictable pattern repeats from one TR to the next.
What is balanced in bSSFP?
The gradient areas along all three spatial axes are balanced so their net area is zero over each TR, helping preserve phase coherence.
What common artifact affects bSSFP?
Off-resonance and field inhomogeneity can disrupt the phase relationship and create dark banding artifacts.
LESSON 20 COMPLETE
You understand how steady-state families preserve or remove residual transverse signal.Educational references
Steady-state terminology and acronyms vary by manufacturer. This lesson introduces broad sequence families; signal behavior depends on TR, TE, flip angle, phase cycling, spoiling, field uniformity, and the exact implementation.