Some stripe-like artifact

[wy issac]

Hello!

I found that in the QSM image reconstructed from a 5-echo 3D GRE sequence acquired on 7.0T Siemens scanner, there was always a continuous stripe-like artifact that go through the whole brain, from below the basal ganglia to the cerebral cortex. It happened in almost every image collected from different volunteers, so that I guess it's a reconstruction problem. Below are some representative images with arrow showing the position of artifact.

Also, I found that a corresponding stripe artifact with the same shape and position on the field/phase image after phase-unwrapping. It appears like a stripe with sharp phase transition caused from uncorrected phase aliasing.

Can anyone give some advice about how to avoid this artifact or why this happens. Thank you very much!

P.S. I use 'unwrapLaplacian' function to do the unwrapping. But I also try the method based on region growth, yet it still had the artefact.

[Steffen Bollmann]

Dear Wy Issac,

Is this data from a Magnetom 7T or a Terra 7T? The artifacts originate from phase-offsets between different channels and they lead to these open-ended fringe lines. One way of avoiding these is to use the ASPIRE C2P from Simon Robinson, which is a modified GRE sequence and ICE program that corrects the phase offsets before coil combination (It is available for VB and VE). If this is data from a 7T Terra you could try to switch the coil combine mode from Sum-of-Squares to adaptive combine (+ activate prescan normalize) and with a recent software version this problem might also be fixed :)

Cheers

Steffen

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