Hi Asaf,
it may be due to the shift of the bold effect to the venous
compartment. The area where your out-of-brain effect is most
conspicuous is where the superior sagittal sinus and the sinus rectus
join.
The bold may be shifted to the venous compartment also in other cases,
but only in the vicinity of large venous structures may this shift
result in a recognizable anatomical structure. I see it often in my
data in that position with visual activations, but occasionally also
for medial activations close to the outer edge, i.e. elsewhere in the
vicinity of the sup. sag. sinus. I initially thought it to be an
artefact, but since it keeps appearing I think otherwise now. The
effect also tends to peak in the sinus when it is present.
Anecdotally, I have yet to find it in perfusion studies -- where in
fact there should be no such spatial shift.
My advice is to mask the image explicitly. Your finding will certainly
be misrepresented by reviewers as an artefact.
Best wishes,
Roberto Viviani
Dept. of Psychiatry, Univ. of Ulm, Germany
Quoting Asaf Kaftory <[log in to unmask]>:
> Hello Michael and other list members.
> my answers:
> 1. I'm not sure the problem lies in the glass-brain. I've attached a
> photo of activations overlaid on mni T1 (SPM8's template), and as
> you can see, the curser clearly indicates to activity in a no-brain
> area (you can further look at the coordinates i've inserted in WFU
> atlas).
> 2. We're naturally normalizing all the EPI images, not just the
> first or the mean. what do you mean?
> 3. We're no using fieldmaps.
>
> any other thoughts?
>
> thanks again,
> Asaf.
>
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