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. 2011 Nov 2;4(11):1941–1955. doi: 10.3390/ma4111941

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© 2011 by the authors;

licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).

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Suitable echo-planar imaging (EPI) sampling schemes for high-field fMRI. Panel (A) top: Conventional 2D EPI where every slice is excited and acquired separately; middle: in multiplexed EPI several slices are excited simultaneously (colors indicate slice groups), allowing an acquisition speed-up given by the multiplexing factor; bottom: in 3D EPI the slice direction is replaced by a secondary phase encoding direction and the entire volume is continuously excited. With full sampling the speed is identical to 2D EPI, but parallel undersampling along k_z is now possible and allows substantial repetition time (TR) reductions. Panel (B) illustrates full (left) and factor-two accelerated (right) in-plane k-space sampling with 2D EPI. Panel (C) shows 3D EPI sampling schemes with factor 2 × 1 (left) and factor 2 along both primary (k_y) and secondary (k_z) phase encoding direction (right).