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Wiley, Magnetic Resonance in Medicine, 5(76), p. 1388-1399, 2015

DOI: 10.1002/mrm.26018

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Correcting dynamic distortions in 7T echo planar imaging using a jittered echo time sequence

Journal article published in 2015 by Barbara Dymerska, Benedikt A. Poser, Wolfgang Bogner, Eelke Visser, Korbinian Eckstein, Pedro Cardoso ORCID, Markus Barth, Siegfried Trattnig ORCID, Simon D. Robinson ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Purpose: To develop a distortion correction method for echo planar imaging (EPI) that is able to measure dynamic changes in B0. Theory and Methods: The approach we propose is based on single-echo EPI with a jittering of the echo time between two values for alternate time points. Field maps are calculated between phase images from adjacent volumes and are used to remove distortion from corresponding magnitude images. The performance of our approach was optimized using an analytical model and by comparison with field maps from dual-echo EPI. The method was tested in functional MRI experiments at 7T with motor tasks and compared with the conventional static approach. Results: Unwarping using our method was accurate even for head rotations up to 8.2°, where the static approach introduced errors up to 8.2 mm. Jittering the echo time between 19 and 25 ms had no measurable effect on blood oxygenation level–dependent (BOLD) sensitivity. Our approach reduced the distortions in activated regions to