ELECTRONIC POSTER - ismrm

15:30 5058. Reducing Ghosting in EPI Using Trajectory Based Reconstruction with Dixon
Method Fat Suppressed Navigator Echoes at 7T
Oliver Josephs 1 , Chloe Hutton 1 , Joerg Stadler 2 , Johannes Bernarding 3 , Oliver Speck 3 ,
Nikolaus Weiskopf 1
1 Wellcome Trust Centre for Neuroimaging, University College London, London, United Kingdom; 2 Leibniz
Institute for Neurobiology, Magdeburg; 3 Otto-von-Guericke University, Magdeburg
At 7T, navigator echoes, acquired at short TE, and used in EPI to reduce Nyquist ghosting, can be significantly compromised by fat
signal. Usually, in EPI, fat is suppressed by applying a fat saturation pulse before slice selective excitation but at 7T this significantly
increases the required SAR. We present a two point Dixon technique for suppressing the fat signal in the navigator echoes and
demonstrate its effectiveness in human brain imaging. The new technique is an efficient alternative for improving phase navigators
and can be used in additon to fat saturation and other artifact suppression methods.
Tuesday 13:30-15:30 Computer 123
13:30 5059. Navigator-Free Dynamic Phase Correction for Echo-Planar Imaging Based
Functional MRI
Dan Xu 1 , R. Scott Hinks 1 , Bruce D. Collick
1 Applied Science Laboratory, GE Healthcare, Waukesha, WI, United States
In echo-planar imaging based functional MRI, non-phase-encoded navigator echoes are sometimes collected to enable correction of
temporal frame dependent even-odd-echo phase modulation. However, the navigator-based method assumes that the additional
modulation that the center echoes experience is the same as that predicted by navigator echoes, which is not true when there is
additional modulation building up across echoes. Therefore, the modulation of the center echoes would not be well corrected, leading
to ghost drift. We propose a method to use scan data itself to more faithfully estimate the per-temporal-frame modulation than the
navigator-based method, which significantly reduces ghost drift.
14:00 5060. Robust 2D Phase Correction for Echo-Planar Imaging Under a Tight Field-Of-View
Dan Xu 1 , Kevin F. King 1 , Yuval Zur 2 , R. Scott Hinks 1
1 Applied Science Laboratory, GE Healthcare, Waukesha, WI, United States; 2 GE Healthcare, Haifa, Israel
The existing 2D phase correction methods to reduce Nyquist ghost in echo-planar imaging (EPI) have several unaddressed issues that
largely affect their practicality. These issues include uncharacterized noise behavior, image artifact due to unoptimized phase
estimation, and most seriously a new image artifact under tight FOV. We propose a modified, more robust method that addresses all
the abovementioned issues. Various EPI results show that the proposed method can robustly generate images free of Nyquist ghost
and some other image artifacts even in oblique scans or when cross-term eddy current terms are significant.
14:30 5061. Comparison of Applying 1D Phase and 2D Phase N/2 Ghost Correction Prior to
PROPELLER-EPI Reconstruction
Hing-Chiu Chang 1,2 , Chun-Jung Juan 3 , Tzu-Chao Chuang 4 , Yi-Jui Liu 5 , Chao-Chun
Lin 2,6 , Hsiao-Wen Chung 2
1 Applied Science Laboratory, GE Healthcare Taiwan, Taipei, Taiwan; 2 Institute of Biomedical Electronics and
Bioinformatics, National Taiwan University, Taipei, Taiwan; 3 Department of Radiology, Tri-Service General
Hospital, Taipei, Taiwan; 4 Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan;
5 Department of Automatic Control Engineering, Feng Chia University, Taichung, Taiwan; 6 Department of
Radiology, China Medical University Hospital, Taichung, Taiwan
PROPELLER-EPI consists of EPI signal readout with alternative echoes, thereby the phase inconsistencies between odd and even
echoes generate N/2 ghost artifact in each rotating blade as well as conventional EPI imaging. The 1D correction method fails in
oblique scan (rotating blades) because the phase inconsistencies along both readout and phase direction. A 2D phase correction
method can overcome this problem by modifying the reference scan manner. In this work, we compare the quality of reconstructed
PROPELLER-EPI images by applying 1D phase and 2D phase N/2 ghost correction prior to PROPELLER-EPI reconstruction.
15:00 5062. In FMRI a Dual Echo Time EPI Pulse Sequence Can Induce Sources of Error in
Dynamic Magnetic Field Maps
Andrew Hahn 1 , Andrew Nencka 1 , Daniel Rowe, 1,2
1 Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States; 2 Mathematics, Statistics, and
Computer Science, Marquette University, Milwaukee, WI
Estimations of main magnetic field inhomogeneity are often acquired for correction of image warping in echo planar images (EPI)
resulting from vulnerability to off-resonance effects of EPI. Many established methods exist for field estimation, one of which
involves two EPI acquisitions with different echo times. The method is fast, easily implemented and can be performed in-line with
fMRI experiments. However, inconsistencies in the MRI scanner hardware, specifically with the RF pulse, as well as physiologic
phenomena that alter the off-resonance characteristics between image acquisitions such as motion or respiration can induce errors in
field maps estimated in this manner.