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FSL  December 2007

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Subject:

AW: [FSL] DTI: (NOT A) Vibration Artefacts in Siemens 3T

From:

Andreas Bartsch <[log in to unmask]>

Reply-To:

FSL - FMRIB's Software Library <[log in to unmask]>

Date:

Wed, 19 Dec 2007 16:26:29 +0100

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Hi,
just to follow up on this: The artfact does also occur without angulation - I have tested it.
We have involved Siemens, and as soon as I hear from them I'll keep you posted. Usually, they are pretty dedicated to solve issues like that.
 
Cheers-
Andreas

________________________________

Von: Bartsch, Andreas
Gesendet: Mi 21.11.2007 10:40
An: FSL - FMRIB's Software Library; [log in to unmask]
Betreff: AW: [FSL] DTI: Vibration Artefacts in Siemens 3T


Good thought! Ha someone observed the artefact without any angulation?
Cheers-
Andreas

________________________________

Von: FSL - FMRIB's Software Library im Auftrag von Martin Kavec
Gesendet: Mi 21.11.2007 10:39
An: [log in to unmask]
Betreff: Re: [FSL] DTI: Vibration Artefacts in Siemens 3T



Hi all,

I am guessing here if this could be a coincidence with the slice prescription,
I mean oblicity. If for some cases the slice prescription leaves the TE/2
period after the 180 pulse very packed or the gradients (particularly) the x
is due to the slice rotation too high, the gradients could indeed shake.
Consequently, increasing the TE could change the gradient amplitude/timing to
less demanding mode, and hence the artifact may disappear.

When you see the artifact, I would change the slice prescription to zero
angulation in all directions and see.

Martin

On Wednesday 21 November 2007 09:56:35 Markus Gschwind wrote:
> Hi all there!
>
> @Peter Kochunov <[log in to unmask]>:
>
> I call it a vibration artifact because we thought that this is one
> possibility:
> When I am in the scanner I feel that the vibrations are on my occiput
> exactly at those directions that are affected (remember only x
> gradient!).
> It is a Magnetom Trio TIM system. And we used the 30dir_2x2x2mm
> sequence and the wip_30dir_2x2x2mm sequence from Siemens. There is no
> difference between both sequences. Both of them show the same artifact.
>
> @Andreas Bartsch <[log in to unmask]>:
> @Mikolaj Pawlak <[log in to unmask]>:
>
> Thanks! At least one who saw it!
> In our clinic routine they have it also. But they explained it with
> patients moving...
> I met that artifact because, coming from fMRI, we where constantly
> using the polystyrene-balls-vacuum-cushion and in every of 7 subjects
> I got the same artifact in the same directions (x). Thus I think I
> reproduce it quite constantly ;-)
> Changing the cushion to the Siemens foam cushion made the reproduction
> less reliable, i.e. sometimes it is there, sometimes not.
> My current explanation is that the x direction is the less stables as
> well as for the patient supine as for the scanner bed and that the
> x-gradient vibrations, depending on the subjects weight and size, give
> resonance to the head which might cause this artifact.
> We use a 12-channel receive-only coil.
>
> What would you suggest to do in oder "to go into"?
> Thanks for your help
>
> Markus



--
**********************************
Senior Research Associate in Neuroradiology
MRI Unit of the Department of Radiology
Erasme Hospital
Lennik Street 808
B-1070 Brussels
BELGIUM

tel: +32-2-555-4325
fax: +32-3-555-3994
email: [log in to unmask]
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