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SPM  February 2011

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Subject:

Re: VBM8 - What to do after sample homogeneity check

From:

John Ashburner <[log in to unmask]>

Reply-To:

John Ashburner <[log in to unmask]>

Date:

Fri, 4 Feb 2011 17:42:01 +0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (60 lines)

Most demographic information about these subjects is available from
http://www.brain-development.org/ . Age is not explicitly provided,
although date of birth is there (but not the date of the scans).

Best regards,
-John

On 4 February 2011 15:05, michel grothe <[log in to unmask]> wrote:
> If you didnīt change the default settings of the toolbox, then all of your
> images are warped independently to the IXI-template provided by the toolbox.
> This is a DARTEL-compatible average template of healthy adult subjects in
> MNI space (see also the VBM8-manual). Thus, outliers wonīt affect the
> template and it should be safe to go for option 1 (given that you have good
> reasons to exclude these images, i.e. your definition of "poor" quality).
>
> BTW, it would be of interest to know the average age of the IXI-template
> sample, but as far as I know this information is not provided by the
> VBM8-manual. Maybe the author, Christian Gaser, can comment on this.
>
> Best regards,
> Michel
>
>> Date: Fri, 4 Feb 2011 11:52:04 +0000
>> From: [log in to unmask]
>> Subject: [SPM] VBM8 - What to do after sample homogeneity check
>> To: [log in to unmask]
>>
>> Dear SPM experts,
>>
>> I've run VBM8 using a customized DARTEL-template. Then, I did sample
>> homogeneity check and identified some poor images (i.e. images with severe
>> motion artefacts, enlarged ventricles, etc.). Among 296 images in total, I
>> found 11 "poor" images so far, but there seem to be some more of them.
>>
>> Now, my question is which option I should choose between the following.
>>
>> (-----1-----) Start statistical analysis without those outliers
>> (-----2-----) Start again from the beginning (i.e. re-run VBM8) without
>> those outliers
>>
>> I was originally going to go for option 2 because, to my understanding, a
>> customized DARTEL-template is made from my own images, and therefore
>> outliers would cause bias in the template. However, I'm not sure whether
>> this reasoning is correct.
>>
>> So, could anyone who understands how VBM8 works please advise me on this?
>> I would really appreciate your help.
>>
>> Best wishes,
>>
>> Kie Woo Nam
>>
>> ___________________________
>> Kie Woo Nam, PhD student
>> Division of Psychological Medicine
>> Institute of Psychiatry, King's College London
>> 16 De Crespigny Park, Denmark Hill
>> London, SE5 8AF, UK
>

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