- Poster presentation
- Open Access
Through-slice dephasing for eddy current artifact reduction in bSSFP
© Sayin et al; licensee BioMed Central Ltd. 2012
- Published: 1 February 2012
- Artifact Reduction
- Degrade Image Quality
- Eddy Current Effect
- Induce Eddy Current
- bSSFP Imaging
Eddy current effects can severely degrade image quality when using balanced steady-state free precession imaging with rapidly varying phase encode ordering schemes, which have common use in cardiac cine MRI. In this work, we explore and characterize a previously-proposed technique, through-slice dephasing, as the sole technique for eddy current artifact removal. We demonstrate that artifacts vary for different slice orientations yet they can be removed using the herein investigated technique.
Gd-doped water bottles were imaged on a 1.5T system (Avanto, Siemens Medical Systems, Erlangen, Germany) using the standard cardiac phased-array and spine coils. Max gradient amplitudes and slew rates were 33 mT/m and 130 mT/m/ms respectively. 2D bSSFP imaging was implemented using a hardware optimized gradient sequence design  (TR=3.0-3.5 msec). In addition to linear, centric and random PE orderings, a Cartesianized golden-ratio (Cart-GR) step ordering was tested. With Cart-GR, the resolution in the phase encode direction is a Fibonacci number (e.g. 377) and the step over the ky-grid between consecutively acquired PE lines is the previous one (e.g. 233). Cart-GR is guaranteed to sample exactly all the Cartesian grid without repetitions or missing lines for an arbitrary scan window . All PE orderings were acquired using identical parameters (e.g. TE: TR/2, matrix: 377x384, FOV: 450 mm, flip angle: 35°). Through-slice dephasing was achieved by modifying the 0th moment of the slice-selection dephasing gradient (Fig 1), creating symmetrical phase accrual at the end of each TR. Dephasing angles ranged between 0° and ±180° per TR. SNR and root-mean-square error (RMSE) values were computed using planimetry.
Through-slice dephasing is highly effective in suppressing eddy current induced artifacts in bSSFP imaging. Considering these artifacts appear substantial in Cart-GR and random PE scans, they are most likely caused by the zero order (spatially independent) EC field yielding an off-resonance shift over time. We propose that dephasing angles smaller than ±60°/TR provide sufficient suppression of EC artifacts with little SNR loss . More work is needed to determine effects of TSD on moving spins.
This work was funded in part by Siemens Medical Solutions USA, Inc. and the American Heart Association, 11SDG5280025.
This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.