Phase and amplitude correction for multi-echo water-fat separation with bipolar acquisitions.
OBJECTIVE
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.


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.


CONCLUSIONS
For bipolar multi-echo acquisitions, uniform water-fat separation can be achieved by removing high order phase errors with the proposed method.
Yu
Huanzhou
H
Applied Science Laboratory, GE Healthcare, Menlo Park, California, USA. huanzhou.yu@ge.com
Shimakawa
Ann
A
McKenzie
Charles A
CA
Lu
Wenmiao
W
Reeder
Scott B
SB
Hinks
R Scott
RS
Brittain
Jean H
JH
D000273:Adipose Tissue / Q000033:anatomy & histology*; D000465:Algorithms; D016477:Artifacts; D001834:Body Water / Q000166:cytology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique