Journal
JOURNAL OF MAGNETIC RESONANCE IMAGING
Volume 31, Issue 5, Pages 1264-1271Publisher
JOHN WILEY & SONS INC
DOI: 10.1002/jmri.22111
Keywords
water-fat separation; bipolar gradient; eddy currents; bandpass filter asymmetry; oblique scan; multi-echo
Funding
- Nanyang Technological University [RG 25/08]
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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.
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