Improved dynamic distortion correction for fMRI using single‐echo EPI and a readout‐reversed first image ( REFILL )

作者：Simon Robinson, Beata Bachrátá, Korbinian Eckstein, Saskia Bollmann, Steffen Bollmann, Barbara Dymerska, Shota Hodono, Martijn A. Cloos, Monique C. Tourell, Jin Jin, Kieran O’Brien, David C. Reutens, Siegfried Trattnig, Christian Enzinger, Markus Barth · 发表于：Human Brain Mapping · 年份：2023 · DOI：10.1002/hbm.26440 · 被引用次数：8 · 研究领域：Advanced MRI Techniques and Applications、Advanced Neuroimaging Techniques and Applications、Functional Brain Connectivity Studies

Abstract The boundaries between tissues with different magnetic susceptibilities generate inhomogeneities in the main magnetic field which change over time due to motion, respiration and system instabilities. The dynamically changing field can be measured from the phase of the fMRI data and corrected. However, methods for doing so need multi‐echo data, time‐consuming reference scans and/or involve error‐prone processing steps, such as phase unwrapping, which are difficult to implement robustly on the MRI host. The improved dynamic distortion correction method we propose is based on the phase of the single‐echo EPI data acquired for fMRI, phase offsets calculated from a triple‐echo, bipolar reference scan of circa 3–10 s duration using a method which avoids the need for phase unwrapping and an additional correction derived from one EPI volume in which the readout direction is reversed. This Reverse‐Encoded First Image and Low resoLution reference scan (REFILL) approach is shown to accurately measure B 0 as it changes due to shim, motion and respiration, even with large dynamic changes to the field at 7 T, where it led to a > 20% increase in time‐series signal to noise ratio compared to data corrected with the classic static approach. fMRI results from REFILL‐corrected data were free of stimulus‐correlated distortion artefacts seen when data were corrected with static field mapping. The method is insensitive to shim changes and eddy current differences between the reference ...