Previously, when using the UCSF/NIST breast phantom, we discovered an x-direction distortion in DW-EPI and the resulting ADC maps that was dependent on spatial location within the scanner and was also present in patient images. The distortion was unaffected by switching the phase encode direction and did not change with increasing b-value, and thus was most likely not due to gradient nonlinearity nor eddy currents. Here, we demonstrate that the distortions decrease when using multi-shot EPI, which is less sensitive to off-resonance distortion, and change direction when reversing the gradient polarity.
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