Single‐shot echo‐planar imaging with Nyquist ghost compensation: Interleaved dual echo with acceleration (IDEA) echo‐planar imaging (EPI)

Echo planar imaging (EPI) is most commonly used for blood oxygen level‐dependent fMRI, owing to its sensitivity and acquisition speed. A major problem with EPI is Nyquist (N/2) ghosting, most notably at high field. EPI data are acquired under an oscillating readout gradient and hence vulnerable to gradient imperfections such as eddy current delays and off‐resonance effects, as these cause inconsistencies between odd and even k‐space lines after time reversal. We propose a straightforward and pragmatic method herein termed “interleaved dual echo with acceleration (IDEA) EPI”: two k‐spaces (echoes) are acquired under the positive and negative readout lobes, respectively, by performing phase encoding blips only before alternate readout gradients. From these two k‐spaces, two almost entirely ghost free images per shot can be constructed, without need for phase correction. The doubled echo train length can be compensated by parallel imaging and/or partial Fourier acquisition. The two k‐spaces can either be complex averaged during reconstruction, which results in near‐perfect cancellation of residual phase errors, or reconstructed into separate images. We demonstrate the efficacy of IDEA EPI and show phantom and in vivo images at both 3 T and 7 T. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.