Frequency-modulated SSFP with radial sampling and subspace reconstruction: A time-efficient alternative to...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Medical Physics
• Biomedical Engineering

Background:

• Balanced steady-state free precession (bSSFP) MRI is widely used but suffers from banding artifacts.
• Frequency-modulated bSSFP (fmSSFP) offers potential improvements but requires efficient reconstruction methods.

Purpose of the Study:

• To develop and investigate a novel subspace-based reconstruction method for fmSSFP MRI.
• To optimize data acquisition schemes, subspace sizes, and banding removal efficiencies.
• To evaluate the proposed technique as a time-efficient alternative to existing methods.

Main Methods:

• Combined fmSSFP MRI with a 3D stack-of-stars trajectory for maximized scan efficiency.
• Implemented a memory-efficient reconstruction using the low-frequency Fourier transform as a subspace.
• Investigated banding artifact removal by comparing with phase-cycled bSSFP MRI.
• Analyzed aliasing properties of undersampling schemes and demonstrated water/fat separation via post-processing reweighting.

Main Results:

• Achieved high signal-to-noise ratio (SNR) images with bSSFP contrast and no banding artifacts using a simple root-of-sum-of-squares combination.
• Turn-based sampling schemes outperformed Golden-Angle trajectories in minimizing aliasing.
• Successfully generated water/fat separated images of the human knee.

Conclusions:

• The subspace-based fmSSFP MRI technique is a time-efficient alternative to phase-cycled bSSFP.
• The method provides high SNR, avoids banding artifacts, and eliminates the need for intermediate preparation phases.
• Reweighting reconstructed subspace coefficients enables virtual spectral responses for applications like water/fat separation.