Myelin water imaging at 0.55 T using a multigradient-echo sequence

Area of Science:

• Neuroimaging
• Biophysics

Background:

• Myelin water imaging (MWI) is crucial for assessing white matter integrity.
• Higher magnetic field strengths (e.g., 3 T) are commonly used for MWI.
• Challenges exist in MWI at higher field strengths, including signal-to-noise ratio and susceptibility artifacts.

Purpose of the Study:

• To evaluate the feasibility and potential of a 3D multigradient-echo (mGRE) sequence for in vivo myelin water imaging at 0.55 T.
• To compare the quality of myelin water fraction (MWF) maps generated at 0.55 T with those acquired at 3 T.

Main Methods:

• A 3D mGRE sequence was employed to scan the brains of four healthy volunteers at both 0.55 T and 3 T.
• Myelin water fraction (MWF) was calculated using a nonnegative least squares (NNLS) algorithm within the qMRLab software.
• Visual comparison of MWF map quality and single-voxel fitting accuracy was performed between the two field strengths.

Main Results:

• Myelin water fraction values obtained at 0.55 T align with previously reported findings at higher field strengths.
• The MWF maps generated at 0.55 T demonstrated a significant improvement in quality compared to those from 3 T.
• Data acquired at 0.55 T were better represented by an exponential model, enhancing the accuracy of the NNLS algorithm's multi-exponential assumption.

Conclusions:

• Myelin water imaging using mGRE at 0.55 T is feasible.
• This lower field strength shows potential for yielding superior results compared to higher field strengths.
• The findings suggest 0.55 T mGRE is a viable and potentially advantageous approach for in vivo myelin water imaging.