Myelin water imaging from accelerated 3D-GRASE acquisitions using subspace constrained reconstruction

Area of Science:

• Neuroimaging
• Quantitative MRI
• Biomarker Development

Background:

• Quantitative MRI markers like myelin water fraction (MWF) and intra-/extra-cellular water T2 (IET2) are crucial for diagnosing brain disorders.
• Current methods for acquiring these markers involve lengthy scan times due to multi-echo spin-echo sequences.
• Accelerated imaging techniques, such as undersampled 3D-GRASE with parallel imaging, are needed to reduce scan duration.

Purpose of the Study:

• To investigate the potential of subspace constrained reconstruction (SCR) for further accelerating 3D-GRAdient Echo and Spin Echo (3D-GRASE) MRI scans.
• To assess the feasibility of using SCR to generate artifact-free myelin water fraction (MWF) and intra-/extra-cellular water T2 (IET2) maps at higher acceleration factors.
• To evaluate the performance of SCR compared to state-of-the-art and reference multi-spin-echo techniques for quantitative MRI marker mapping.

Main Methods:

• Two novel undersampling techniques for 3D-GRASE acquisition were developed, exploiting redundancy across echoes.
• Retrospective undersampling of fully sampled phantom and in-vivo data was performed to test the proposed techniques.
• Comparisons included MWF and IET2 mapping against a reference multi-spin-echo technique and prospective undersampled in-vivo acquisitions.

Main Results:

• Retrospective analysis showed worse Root Mean Square Deviation (RMSD) for MWF with proposed techniques compared to state-of-the-art.
• For IET2, retrospective RMSD was similar or slightly improved using the proposed techniques.
• Prospective scans revealed that undersampling artifacts degraded MWF maps, but IET2 maps remained accurate within 10 ms of the reference.

Conclusions:

• Exploiting echo redundancy with SCR does not yield additional acceleration benefits beyond the current state-of-the-art for myelin water fraction (MWF) mapping.
• However, SCR enables acceleration beyond the state-of-the-art for intra-/extra-cellular water T2 (IET2) mapping.
• These findings highlight the potential of SCR for specific quantitative MRI biomarkers, improving scan efficiency.