Gradient Response Harvesting for Continuous System Characterization During MR Sequences.

Area of Science:

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

Background:

• MRI gradient systems demand high-fidelity magnetic field generation.
• Calibration and pre-emphasis are standard but fail to address time-varying gradient responses.
• Thermal variations and other factors degrade gradient performance over time.

Purpose of the Study:

• To introduce and validate a novel method, gradient response harvesting, for continuous characterization of MRI gradient systems.
• To address limitations of traditional calibration methods by monitoring gradient response in real-time.
• To improve MRI image quality by compensating for dynamic changes in gradient performance.

Main Methods:

• Gradient response harvesting continuously acquires field measurements during normal MRI sequences.
• Model-based and model-free variants calculate gradient response and offsets from acquired data.
• The method was demonstrated using Echo Planar Imaging (EPI) with high gradient duty-cycle.
• K-space trajectory estimates were derived from continuous gradient characterization for image reconstruction.

Main Results:

• Observed real-time changes in the envelope and phase of gradient response functions, including mechanical resonance shifts.
• Detected gradient response variations were reflected in calculated gradient waveforms and k-space trajectories.
• Utilizing updated encoding information in image reconstruction successfully eliminated ghosting artifacts.
• Demonstrated the feasibility and effectiveness of gradient response harvesting.

Conclusions:

• Gradient response harvesting offers a feasible approach for continuous MRI gradient characterization.
• The method enables real-time adaptation of gradient pre-emphasis and calculation of uninterrupted gradient waveforms.
• Obtained gradient response functions can be used for quality assurance and preventive maintenance.
• This technique significantly enhances MRI image quality by mitigating artifacts caused by gradient instability.