Conventional phase-correction algorithms for EPI reconstruction assume constant linear offset in odd-even k-space lines, and so cannot account for dynamically varying offset. The effect of such terms therefore gives rise to Nyquist ghosting. We illustrate this effect with simulated data, and demonstrate the presence of a damped oscillating term in linear phase for ultra-high field (7T) compared to lower field strength (3T). Line-by-line phase correction, using an extended navigator echo train over the full k-space, is able to substantially improve the appearance of ghosting.
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