Pure balanced steady-state free precession imaging (pure bSSFP)

Area of Science:

• Magnetic Resonance Imaging
• Biophysics
• Medical Physics

Background:

• Balanced steady-state free precession (bSSFP) imaging is widely used in MRI.
• Tissue microstructure can cause conspicuous asymmetries in the bSSFP frequency response function.
• Configuration theory predicts that bSSFP approaches a symmetric profile with very short repetition times (TR).

Purpose of the Study:

• To demonstrate that reducing the repetition time (TR) in bSSFP can mitigate asymmetries in the frequency response function for tissues.
• To validate theoretical predictions regarding bSSFP behavior in the limit of short TR.

Main Methods:

• Measured the bSSFP frequency profile of a manganese-doped aqueous phantom and ex vivo brain tissue across a TR range of 1.5-8 ms.
• Acquired data at 1.5 T and 3 T using 2.0 mm isotropic resolution.
• Employed linear radiofrequency phase increments for sampling the frequency response function.

Main Results:

• Pure substances exhibited a TR-independent symmetric frequency profile.
• Brain tissue showed a pronounced asymmetry that decreased with shorter TR.
• The results support the theory that bSSFP becomes symmetric in the limit of short TR, particularly evident at 1.5 T.

Conclusions:

• Tissues exhibit apparently pure bSSFP characteristics when sufficiently short TR values are employed.
• Achieving this limit for brain tissue is feasible at 1.5 T with TR values around 1-2 ms at clinically relevant resolutions.
• Residual asymmetry may persist at higher field strengths like 3 T even with short TR.