Fast measurement of the gradient system transfer function at 7 T

Area of Science:

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

Background:

• Gradient System Transfer Function (GSTF) is crucial for MRI hardware characterization and calibration.
• Accurate GSTF determination corrects gradient distortions and enhances gradient fidelity.
• Existing methods may lack the necessary frequency resolution or signal-to-noise ratio (SNR).

Purpose of the Study:

• To present a novel method for determining the GSTF with high frequency resolution and high SNR.
• To enable fast and simple phantom measurements for GSTF acquisition.
• To characterize gradient field fluctuations effectively, especially at ultrahigh field strengths.

Main Methods:

• Expanded the thin-slice approach for phantom-based GSTF measurements.
• Incorporated shifted excitations post-gradient application to capture field fluctuations.
• Implemented physics-informed regularization for high-quality transfer functions from minimal data.
• Evaluated GSTFs via gradient time-course estimation and pre-emphasis on a 7T scanner.

Main Results:

• The proposed method accurately captures sharp mechanical resonances with high detail.
• GSTF estimations faithfully reproduced measured trapezoidal gradient progressions across all axes.
• GSTF-based pre-emphasis significantly improved gradient fidelity and reduced field oscillations.

Conclusions:

• The developed approach enables rapid and straightforward characterization of gradient field fluctuations.
• Eddy current and vibration effects, prominent at ultrahigh fields, can be effectively identified.
• This method enhances MRI system performance through precise gradient characterization.