On the transient phase of balanced SSFP sequences

Area of Science:

• Magnetic Resonance Imaging
• Biophysics
• Medical Physics

Background:

• Balanced steady-state free precession (SSFP) imaging signal intensity is influenced by proton density, T(1), T(2) relaxation times, flip angle (α), and repetition time (TR).
• The steady-state signal is analytically described after approximately 5*T(1)/TR.
• The transient phase represents the approach to steady-state signal intensity via exponential decay from initial amplitudes after the first excitation pulse.

Purpose of the Study:

• To present an analytical expression for the decay rate of the transient phase in balanced SSFP imaging.
• To demonstrate how this transient phase can be leveraged for optimized image contrast.
• To explore applications in hyperpolarized nucleus imaging.

Main Methods:

• Derivation of an analytical expression for the transient phase decay rate using Bloch equations.
• Analysis of the decay rate as a weighted average of T(1) and T(2) relaxation times.
• Investigation of contrast variations based on flip angle and number of excitation pulses.

Main Results:

• An analytical expression for the transient phase decay rate in balanced SSFP imaging was derived.
• The decay rate is determined by T(1) and T(2) relaxation times, weighted by the flip angle.
• Transient phase imaging offers tunable contrast by adjusting flip angle and pulse number.

Conclusions:

• Balanced SSFP imaging during the transient phase provides versatile contrast mechanisms.
• Optimized contrast can be achieved by manipulating flip angle and excitation pulse count.
• Transient imaging is applicable to hyperpolarized nuclei like (3)He, (129)Xe, and (13)C, allowing optimization based on their specific relaxation properties.