Limitations of rapid myelin water quantification using 3D bSSFP

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Biophysics

Background:

• Conventional myelin water fraction (MWF) imaging uses multi-echo spin-echo sequences, which have long acquisition times and limited volume coverage.
• Developing faster MRI techniques for accurate MWF quantification is crucial for neurological research.

Purpose of the Study:

• To investigate the feasibility of using 3D balanced steady-state free precession (bSSFP) sequences for high-resolution myelin water mapping.
• To assess the potential of bSSFP as an alternative to conventional MWF imaging methods.

Main Methods:

• Derived an approximate bSSFP signal equation based on a two-pool water exchange model.
• Fitted the flip angle dependence of in vivo bSSFP signals to determine MWF and signal amplitude, making assumptions for other parameters.
• Investigated the influence of factors like magnetization transfer and field inhomogeneities on MWF values.

Main Results:

• Acquisition and calculation of quantitative, high-resolution MWF maps from healthy volunteers using bSSFP were demonstrated as feasible.
• Averaged MWF results obtained with bSSFP showed agreement with existing literature values.
• Numerical simulations revealed a significant dependency of derived MWF values on the assumed two-pool model parameters.

Conclusions:

• The proposed bSSFP method for MWF mapping is feasible but requires careful consideration of underlying model parameters.
• The dependence of MWF on two-pool parameters significantly limits the current applicability of this bSSFP-based approach.