Related Experiment Video
Updated: Apr 20, 2026
Magnetic Resonance Imaging of Multiple Sclerosis at 7.0 Tesla
Published on: February 19, 2021
Phase-corrected bipolar gradients in multi-echo gradient-echo sequences for quantitative susceptibility mapping
Jianqi Li1, Shixin Chang, Tian Liu
1Shanghai Key Laboratory of Magnetic Resonance and Department of Physics, East China Normal University, 3663 North Zhongshan Road, Shanghai, 200062, China, jqli@phy.ecnu.edu.cn.
Objective:
Large echo spacing of unipolar readout gradients in current multi-echo gradient-echo (GRE) sequences for mapping fields in quantitative susceptibility mapping (QSM) can be reduced using bipolar readout gradients thereby improving acquisition efficiency.
Materials And Methods:
Phase discrepancies between odd and even echoes in the bipolar readout gradients caused by non-ideal gradient behaviors were measured, modeled as polynomials in space and corrected for accordingly in field mapping. The bipolar approach for multi-echo GRE field mapping was compared with the unipolar approach for QSM.
Results:
The odd-even-echo phase discrepancies were approximately constant along the phase encoding direction and linear along the readout and slice-selection directions. A simple linear phase correction in all three spatial directions was shown to enable accurate QSM of the human brain using a bipolar multi-echo GRE sequence. Bipolar multi-echo acquisition provides QSM in good quantitative agreement with unipolar acquisition while also reducing noise.
Conclusion:
With a linear phase correction between odd-even echoes, bipolar readout gradients can be used in multi-echo GRE sequences for QSM.
