Dear experts, SPMers, colleagues & friends-
I am bothered by artifact lines in phase encoding direction of our
mosaic EPIs (Siemens product sequence: ep2d_fid_60b2080_62_64.ekc). They
look very much like hf-artifacts, and first I assumed they are due to my
trigger signal. However, that is NOT the case: There are no artifacts
neither in untriggered nor in triggered images taken from a homogenous
phantom. Irrespective of triggering, they set in as soon as a proband is
inside the headcoil and, thus, are object-dependent. However, the
positioning does not really matter since they occur quite strictly at
the phase encoding vector.
By now, I suspect that they are due to unsuccesful offset compensations
for the coil, i.e. some offset artifacts. My consulting physicists told
me they have seen offset artifacts in their cardiac imaging which looked
very much alike mine but they never really got rid of them.
Well, the sequence itself runs quite stable and gives very good and
reliable results on our paradigms. Thus, I regard the artifacts as ugly
but not totally obsolete. Since they remain stable over the shots in
extent (overlayed onto the image pixels) and coil-centered topography,
they do not seem to affect the statistics a lot as long as there is not
a lot of movement. In any case, in some individuals they are quite
strong but in others they are weak. After reconstruction of the volume,
they are often barely noticeable ( at least, in favorable contrast
windows).
I would appreciate any comments on the following questions:
1. Could these in fact be offset artifacts? (I can provide images to
those willing to look at them.)
2. What can I do about it? Will Siemens care and provide help? (My
consulting physicists told me they are probably intractable and a known
Vision problem.)
3. In Numaris, I find no gradient overdrive option applicable. Could
pargen editing on the sequence to get some gradient overdrive be a
remedy?
4. Will such aritfacts discredit our results and lead to rejection of
manuscripts? (e.g., by some "fMRI- Data Centers"...)
TIA-
Andreas J. Bartsch, MD
currently @
Neuroradiology, BJMU Wuerzburg
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|