Accelerated silent echo-planar imaging

Liebig, P., Heidemann, R. M., Hensel, B. and Porter, D. A. (2019) Accelerated silent echo-planar imaging. Magnetic Resonance Imaging, 55, pp. 81-85. (doi: 10.1016/j.mri.2018.09.016) (PMID:30236603)

Abstract

Purpose: The standard approach to Echo-Planar Imaging (EPI) is to use trapezoidal readout (RO) gradients with blipped phase-encoding (PE) gradients. Sinusoidal RO gradients with constant PE gradients can reduce acoustic noise. However, this sequence, originally introduced by Mansfield et al., constitutes major challenges for Cartesian parallel imaging techniques. In this study two alternatives to reconstruct a non-blipped EPI are proposed and evaluated. Theory and methods: The first method separates the acquired k-space data into odd and even echoes and applies Cartesian GRAPPA separately to each partial data set. Afterwards, the resulting reconstructed data sets for each echo are summed in image space. In the second method, an iterative parallel-imaging algorithm is used to reconstruct images from the highly non-Cartesian data samples. Results: Compared to blipped-EPI, the first method reduces image SNR depending on the acceleration factor between 11% and 60%. For an acceleration factor of 3 folding artefacts appear. The second method produces slight fold-over artefacts although image SNR is on the same level as the blipped approach. Conclusion: In this study, we have introduced two new approaches to EPI that allow the use of Cartesian parallel imaging in conjunction with continuous data sampling. In addition to providing a reduction in acoustic noise compared to the standard blipped PE EPI sequence, the proposed techniques improve sampling efficiency, resulting in a reduction of the echo-spacing. Of the two methods, the second approach, based on an iterative image reconstruction, provides higher SNR, but requires a longer reconstruction time.

• Item Type: Articles
• Additional Information: The Imaging Centre of Excellence at the University of Glasgow is supported by a gift from the Sackler Trust and the Dr. Mortimer and Theresa Sackler Foundation and also received financial support from the Wolfson Foundation.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Porter, Professor David
• Authors: Liebig, P., Heidemann, R. M., Hensel, B., and Porter, D. A.
• College/School: College of Medical Veterinary and Life Sciences > School of Psychology & Neuroscience
• Journal Name: Magnetic Resonance Imaging
• Publisher: Elsevier
• ISSN: 0730-725X
• ISSN (Online): 1873-5894
• Published Online: 18 September 2018