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Keywords:

  • water–fat separation;
  • bipolar gradient;
  • eddy currents;
  • bandpass filter asymmetry;
  • oblique scan;
  • multi-echo

Abstract

Purpose:

To address phase and amplitude errors for multi-point water–fat separation with “bipolar” acquisitions, which efficiently collect all echoes with alternating read-out gradient polarities in one repetition.

Materials and Methods:

With the bipolar acquisitions, eddy currents and other system nonidealities can induce inconsistent phase errors between echoes, disrupting water–fat separation. Previous studies have addressed phase correction in the read-out direction. However, the bipolar acquisitions may be subject to spatially high order phase errors as well as an amplitude modulation in the read-out direction. A method to correct for the 2D phase and amplitude errors is introduced. Low resolution reference data with reversed gradient polarities are collected. From the pair of low-resolution data collected with opposite gradient polarities, the two-dimensional phase errors are estimated and corrected. The pair of data are then combined for water–fat separation.

Results:

We demonstrate that the proposed method can effectively remove the high order errors with phantom and in vivo experiments, including obliquely oriented scans.

Conclusion:

For bipolar multi-echo acquisitions, uniform water–fat separation can be achieved by removing high order phase errors with the proposed method. J. Magn. Reson. Imaging 2010;31:1264–1271. © 2010 Wiley-Liss, Inc.