[Mristudio-users] artifact

[susumu mori]

Hmmmm, please check the following;

List up the number of DWIs that are affected (e.g. 4th, 8th, 9th, etc)
Look at the gradient table at the listed number.
Try to find if the identified table lines always contain gradient values of
X, Y, or Z.

Also please show us the color map.

For example, if this artifact shows up every time you apply X, the color map
should become red for the area of the artifact.

If you find this type of correlation between the applied gradient and
artifacts, this is not a typical motion artifacts. You should contact to the
manufacturer.

On Mon, Oct 25, 2010 at 7:58 AM, Katja Doerschner <katja at bilkent.edu.tr>wrote:

> Thank you for your response, Susumu.
>
> I am attaching an example of the artifact.
> If Siemens had issues in the past it sounds as if they must have resolved
> this?
> Thank you very much.
>
>
>
> On Oct 25, 2010, at 2:43 PM, susumu mori wrote:
>
> Hi Katja,
>
> It is difficult to say anything without looking at the images. Usually if
> you find a localized signal drop, that is due to motion. However, they
> appear typically around the 4th ventricle and rarely around the central
> sulcus. Also, 10 out of 30 seem too many. Siemens had some issues in the
> past with signal drop usually in the occipital lobe.
>
> I thought you can attach a small file with some screenshots?
>
>
>> My questions are: 1) what causes these artifacts (I have seen them in
>> other scans/patients at different locations, e.g. posterior tip of the
>> occipital lobe) - could it be the effect of a large blood vessel or other
>> kinds of motion)?
>>
> > I have to see the images.  If you want, you can upload your data to our
> ftp site.
>
> 2) How can I avoid such artifacts?
>>
>  > see above.
>
>> 3) Is there any way of 'saving' the data - other than throwing those
>> images out
>>
> > 10 out of 30 seem too many to save. Usually the artifacts are linked to a
> particular gradient axis; for example, whenever X axis is applied, the
> artifact appears. If so, you lose all X gradient orientations and the data
> can't be saved.
>
>
>> 4) If I have to remove these images - how will that affect the tensor
>> calculation/FA maps/fibertracking?
>>
> > see above
>
>>
>> Thank you very much.
>> Katja
>>
>>
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> --
>
> Katja Doerschner
> Assistant Professor
> Department of Psychology
> & National Center for
> Magnetic Resonance Research (UMRAM)
> Bilkent University
> Bilkent Cyberpark, C-Blok, 2. Kat
> http://www.bilkent.edu.tr/~katja/
> office: +90 (312) 290 3004
> cell: +90 (530) 640 31 33
>
>
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