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



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.


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


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.