Dear On,
As you pointed out, the origin has altered after segmentation and I
don't really know why. Could you elaborate your steps in details so
that someone, or I(very unlikely), may be able to track down what
happened? Posting your Matlab version and spm_preproc version would
also help.
I can come up with one idea for poor segmentataion result. Have you
checked origin of your image using "display" and set position of the
cursor to 0mm,0mm,0mm? It's recommenced to place the origin of the
image near AC that is also in the same plane with PC.
Hope this helps,
Hedok
On Tsang wrote:
> Dear Hedok,
>
> Thank you for your insight. I have tried your suggestion and the results
> confirm my suspicion: that the Native space option does not maintain the
> same coordinate space in the output. In the following screenshots please
> note that the origin has been altered in the segmented output of the gray
> matter image:
>
> http://www.utdallas.edu/~okt061000/anat.png
> http://www.utdallas.edu/~okt061000/gm.png
>
> Would you please verify that for me? Thank you so much! If there is indeed a
> bug, how should I go about escalating the issue? Thanks again, Hedok.
>
> Best Regards,
> On
>
> ===
>
> On Tue, 29 Jan 2008 16:55:03 -0500, Hedok Lee <[log in to unmask]> wrote:
>
>
>> Dear On,
>>
>> Just to add. When I wrote, "These number are typically all the same
>> between segmented images and raw T1W.", I meant segmented images in
>> native space. This is no longer true in warped images(modulated and
>> unmodulated).
>>
>> With regards,
>>
>> Hedok
>>
>>
>> Hedok Lee wrote:
>>
>>> Dear On,
>>>
>>> Somebody who is more knowledgeable about SPM may be able to help you
>>> better, but I give it a try.
>>>
>>> I typically check image tags to ensure raw T1W and native images are
>>> in the same space. If you right click an image in the "checkreg"
>>> function, it pulls out the menu with bunch of nice features. When you
>>> click on the top of the menu, it also displays information such as
>>> Rotations
>>> Origin
>>> Voxel size
>>> Image dimensions.
>>>
>>> These number are typically all the same between segmented images and
>>> raw T1W. Can you check if they are the same? In my experience, they
>>> are always the same. If they are the same, it's possible that
>>> something went wrong during segmentation. See the attached screenshot.
>>>
>>> Hope this helps,
>>>
>>>
>>> Hedok
>>>
>>> On Tsang wrote:
>>>
>>>> Hello SPMers,
>>>>
>>>> I have another question concerning the SPM segmentation algorithm,
>>>> spm_preproc. This question is rather basic and quite fundamental.
>>>> Essentially, I suspect that the algorithm does not actually retain the
>>>> Native space in the output. Can anyone else confirm this? More
>>>> specifically,
>>>> I used the IBSR database which consists of
>>>> positionally-normalized-Talairach
>>>> datasets, and the output of spm_preproc is no longer in
>>>> positionally-normalized-Talairach space. I am attaching a screenshot
>>>> depicting GM segmentation for one such dataset. The image can also be
>>>> found
>>>> at the following location:
>>>>
>>>> http://www.utdallas.edu/~okt061000/native.png
>>>>
>>>> Please can anyone confirm this behavior? I would really appreciate it.
>>>> Thanks in advance!
>>>>
>>>> Best Regards,
>>>> On
>>>>
>>>>
>>> ------------------------------------------------------------------------
>>>
>>>
>
>
>
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