Accelerated 2D Cartesian MRI with an 8-channel local B₀ coil array combined with parallel imaging.

Area of Science:

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

Background:

• Magnetic Resonance Imaging (MRI) utilizes linear gradients and radiofrequency receiver sensitivity profiles for spatial encoding, leading to long scan times.
• Cartesian MRI, a common clinical technique, can be accelerated using parallel imaging and rapid magnetic field modulation during signal readout.

Purpose of the Study:

• To investigate an optimized modulation scheme for sampling efficiency using an 8-channel local coil array to accelerate 2D Cartesian MRI scans.
• To explore nonlinear encoding for faster MRI acquisition.

Main Methods:

• An 8-channel local coil array was employed to carry sinusoidal currents during signal readout for accelerating 2D Cartesian scans.
• MRI sampling theory based on reproducing kernel Hilbert space was used to analyze nonlinear encoding efficiency.
• A field calibration method with current monitors and the ESPIRiT algorithm facilitated image reconstruction.
• Various modulation field shapes, aliasing control, and frequencies were evaluated for optimization, alongside safety assessments.

Main Results:

• The optimal modulation field for the local coil array approximated a linear gradient field for 2D Cartesian MRI.
• The developed field calibration technique enabled threefold and eightfold acceleration of in vivo scans.
• Accelerated scans were achieved free of visible artifacts, with and without SENSE (Sensitivity Encoding).
• Safety evaluations confirmed the in vivo scans were safe.

Conclusions:

• The study presents a nonlinear encoding analysis tool, a field calibration method, and safety evaluation procedures for accelerating MRI.
• These advancements, demonstrated through in vivo scans, significantly contribute to increasing MRI scan speed using local coil arrays.