Hello all,
I have been attempting to apply B0 unwarping using a modified ucsd script
(epidewarp) and B0 unwarping within fugue. We use an 8-channel head coil on
a GE Signa HDX system. After finally obtaining properly scaled phase images
from the scanner (many user CV's later), I re-ran both my modified ucsd
script and fugue within feat, however, I have yet to obtain artifact free
images. I have re-run tests on a single channel coil and the results seem to
work quite well (I have used the fieldmap reconstruction steps as
recommended in
http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0803&L=FSL&P=R70049&D=0&I=-3&X=189EFD2A907E02D552&Y)
Also, I have attached the prestat reports from FEAT for both the single
channel and multi 8-channel acquisitions.
I have a feeling that my method for acquiring the 8-channel scaled phase
images is flawed. For those GE users out there, this is what I have done:
-use two SPGR, TR 50, FA = 45, BW = 31.25, TE 5 and 8 ms, manual prescan
between the two echo times
-same slice locs and FOV as EPI acquisition, however higher resolution
(cannot sample at 64x64 therefore I interpolate to match the EPI)
-User CV's
- rhrcctrl = 15 (output real, imag, phasex1000, magnitude images)
- nofermi and nograd = 1(turn off filters applied to images)
- rhimsize = 128 (recon at 128 x 128)
The next CV's trick GE to use ASSET, as ASSET is not available in the
package to use on a SPGR, however, with ASSET, properly scaled phase maps
can be collected.
- opphaseasset_factor = 1 (do ASSET in the phase direction)
- rhasset_R =1 (turn ASSET on, but collect all the phase information)
Phase maps obtained from this method seem correct, but due to the unwarping
results, I fear they may be innaccurate. Has anyone else had this problem ??
I could output the phase, real, imag, and mag images from each coil and
recombine them, but I am trying to avoid this to decrease reconstruction
time. Also, I am not 100% certain of how to combine either the phase or real
and magnitude images from each coil. Regardless, this process does not seem
trivial.
I would appreciate any input.
Thanks very much
Adrian Koziak
Research Assistant
Brain-Body Insitute,
Imaging Research Centre
St. Joseph's Healthcare
Hamilton, ON
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