Alternating unbalanced SSFP for 3D mapping of the human brain

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Biophysics

Background:

• T2* relaxation rate mapping is crucial for quantitative tissue microstructure evaluation, including brain oxygenation.
• Current T2* measurement techniques are often time-consuming and may be susceptible to magnetic field variations.

Purpose of the Study:

• To propose a novel alternating unbalanced SSFP pulse sequence for rapid, whole-brain 3D T2* mapping.
• To develop a method for simultaneous T2*, R2, and magnetic susceptibility mapping with improved robustness to magnetic field variations.

Main Methods:

• An alternating SSFP sequence combining SSFP-FID and SSFP-ECHO modes for rapid 3D data acquisition.
• Integration of Z-shimming gradients to mitigate effects of large-scale magnetic field variations (ΔB0).
• Development of signal models accounting for ΔB0-induced modulations for corrected parameter estimation (R2, T2*, T2).
• Quantitative susceptibility mapping (QSM) of phase data to derive relative magnetic susceptibility (Δχ) maps.

Main Results:

• Generated T2* maps exhibited expected contrast across brain regions, consistent with prior studies.
• Derived R2, T2, and Δχ maps showed good agreement with existing literature.
• Strong linear correlations were observed between transverse relaxation parameters (T2*, R2, T2) and Δχ.

Conclusions:

• The proposed alternating SSFP method is feasible for practical and reliable whole-brain T2* mapping.
• The technique enables simultaneous quantification of T2*, R2, T2, and Δχ.
• This approach provides a robust tool for assessing brain tissue microstructure and oxygenation.