Thanks Donald & David for your kind replies. As per your suggestions, I
checked the T1 images corresponding to the artifact scans, and they are
artifact free in all the cases. Also, we performed a diagnostic software
and hardware check on the scanner which revealed no non-uniformity in
magnetic fields.
Adding to that, I reduced the slice thickness to 3.5 mm (without
interslice gap), TE to 40, 35 and then 30 ms and matrix size of 64x64.
With these parameters, comparing different EPI scans, the overall image
quality seems to increase several fold with reduced artifacts, but the
signal dropout (in the form of similar artifacts) is still persistent in
EPI scans(although it is reduced greatly).
What are your thoughts about the solution to the artifact problem apart
from optimizing the scanning parameters (TE = 30 ms, Flip over angle = 90
and slice thickness 3.5 mm give the optimized images).
Vaibhav Tyagi
National Brain Research Centre
Gurgaon, India
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