[Mristudio-users] Eddy currents interact with fat shift ?

[Dorian P.]

As a matter of fact the images above are already coregistered with mutual
information, rigid body. Maybe there has been a shift that moved the rings
in other slices. Yet I don't understand why fat could be sometimes dark and
sometimes bright (noticed this in more than one subject). The only
explanation out of my head is that fat is subject to eddy currents, and
maybe its signal swaps because one acquisition was clean, the other had
eddy currents. Still don't know whether this is plausible though.

Thank you.
Dorian


2013/6/18 susumu mori <smoriw at gmail.com>

> Hi Dorian,
>
> This is interesting. If the band is really a fat shift and its appearance
> is sensitive to gradient application, you should get reproducible effects.
> I mean, the three repetitions should be the same within each column, while
> they look different in the row. The fat bands look different both in the
> row and column directions. So something is happening randomly, it seems.
>
>
> On Sun, Jun 16, 2013 at 11:22 AM, Dorian P. <alb.net at gmail.com> wrote:
>
>> Dear experts,
>>
>> Below is a picture from 3 DTI sequences during the same MRI acquisition
>> on a subject As you can see the fat shift didn't work properly, showing fat
>> rings. This ring seem to alternate for some slices, clearly visible in DWI
>> fitting error. Does this mean that fat shift problems interact with eddy
>> currents to produce alternating rings or is it just normal that fat ring
>> alternates between diffusion directions?
>>
>> Second, this is somehow a naive and unrelated question. Given that I
>> obtain always 2+ datasets from each subject, isn't there a way to invert
>> fat suppression technique in the scanner such that one time I have a fat
>> ring showing as dark, but in the next dataset the same volume have the ring
>> brighter? This way the average of the fat ring will cancel out. Is there a
>> way to invert, not the position, but the values from the fat so that the
>> artifact would average theoretically to zero?
>>
>> Thank you
>>
>>
>> Figure with fat ring problem. Lower lines are the DWI fitting error
>> images:
>>
>> [image: Immagine in linea 1]
>>
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>
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