The effect of concomitant gradient fields on diffusion tensor imaging | JoVE Visualize

Area of Science:

Physics
Medical Imaging
Biophysics

Background:

Concomitant gradient fields are inherent transverse magnetic fields in MRI, arising from Maxwell's equations during gradient use.
These fields can negatively impact image quality, particularly at lower static magnetic field strengths and higher gradient amplitudes.
In diffusion tensor imaging (DTI), asymmetric gradient schemes can lead to phase accrual, potentially corrupting diffusion measurements.

Purpose of the Study:

To theoretically predict and experimentally validate the errors caused by concomitant gradient fields in diffusion tensor imaging.
To investigate the factors influencing the magnitude of these errors, such as distance from isocenter and gradient asymmetry.
To develop and verify a prospective correction scheme to mitigate these concomitant field-induced errors.

Main Methods:

Developed theoretical models to predict phase accrual and diffusion measurement bias due to concomitant fields.
Experimentally validated the theoretical predictions using both Reese twice-refocused and split gradient single spin-echo diffusion gradient schemes.
Evaluated the impact of gradient asymmetry and distance from isocenter on apparent diffusion coefficient (ADC) bias in phantom and brain imaging.
Proposed and tested a prospective correction method for concomitant gradient errors.

Main Results:

Experimental validation confirmed theoretical predictions of phase accrual and bias in diffusion measurements.
Apparent diffusion coefficient bias was observed to increase with distance from the isocenter and gradient asymmetry duration.
The magnitude of error was found to be dependent on various factors including gradient pattern, timing, field strength, and voxel size.
The proposed correction scheme successfully reduced errors caused by concomitant gradient fields.

Conclusions:

Concomitant gradient fields introduce significant errors in diffusion tensor imaging, particularly with asymmetric gradient designs.
Understanding and correcting for these errors is crucial for accurate diffusion measurements in MRI.
The developed prospective correction scheme offers an effective solution for mitigating concomitant gradient field artifacts in diffusion imaging.