Consistent non-cartesian off-axis MRI quality: calibrating and removing multiple sources of demodulation phase...

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging (MRI)
• Biophysics

Background:

• Off-axis MRI using non-Cartesian sequences exhibits significant performance variability across scanners.
• Improper timing alignment of gradient fields and data acquisition systems is a key factor contributing to this variability.
• Eddy currents and anisotropic gradient delays further complicate k-space trajectories and demodulation accuracy.

Purpose of the Study:

• To develop a method for measuring timing errors in the frequency demodulation reference signal.
• To differentiate timing errors from anisotropic gradient delays.
• To improve the consistency and quality of off-axis MRI, particularly for non-Cartesian sequences.

Main Methods:

• A novel technique to rapidly measure timing errors in the frequency demodulation reference signal.
• Separation of timing errors from anisotropic gradient delays.
• Application of retrospective phase correction using measured timing delays and k-space deviations before data regridding.
• Partial prospective correction for spiral imaging.

Main Results:

• Measured timing delays on four MRI scanners ranged from 4.2 to 7.5 microseconds below manufacturer specifications.
• Significant retrospective correction of image degradation in 3D radial (3D projection reconstruction (PR)) knee and breast imaging.
• Demonstrated improvement in image quality for non-Cartesian sequences.

Conclusions:

• The developed method effectively measures and corrects timing errors and k-space deviations in off-axis MRI.
• This approach enhances the consistency of non-Cartesian MRI sequences across diverse scanner hardware.
• The technique offers a pathway to more reliable and operator-independent off-axis MRI performance.