Dear Dr. Rorden, Dr Ashburner and SPMīs users:
Thank you for your explanation.
I want to compare postoperative MRI and the statistical results from
preoperative PET from 15 patients with refractary epilepsy.
I want to know, how many cortex of the hipometabolic zone showed in the
preoperative PET were not resected.
But I am not sure, if I need really the normalization or only the
coregistration.
I think, I have understood of the Dr Ashburnerīs answer that the volumetry
would be affected in spite of the masking of the lesion or linear
normalization, isnīt it ?
Iīd apreciate so much to know your opinion.
By the way, I couldnīt download the file coreg.pdf, the page is unavailable.
Best Regards,
Hans
Dr. Hans Carmona
Neurosurgery Department
University of Freiburg
Germany
Tel: 49-761-2705287
Fax: 49-761-2705201
e-mail: [log in to unmask]
[log in to unmask]
----- Original Message -----
From: "Chris Rorden" <[log in to unmask]>
To: "Hans Carmona" <[log in to unmask]>
Sent: Thursday, December 13, 2001 11:07 AM
Subject: Re: Normalization and volume measures
Hans-
Yes, the default normalization routines will most likely compress any focal
lesions. The signal intensity of the lesion will not match the
corresponding region of the template. There are two ways around this:
1.) Only do a linear normalization. The nonlinear functions are
particularly sensitive to lesions. However, this approach will mean that
the overall normalization may not be great.
2.) Mask the lesion and then proceed.
This issue is discussed in:
Brett, M., Leff, A.P., Rorden, C., Ashburner, J. (2001). Spatial
normalization of brain images with focal lesions using cost function
masking. NeuroImage, 14, 486-500.
A step-by-step guide for lesion masking normalizations is at:
http://www.psychology.nottingham.ac.uk/staff/cr1/mritut.html#Normalize
Two PDF presentations also discuss this problem:
http://www.psychology.nottingham.ac.uk/staff/cr1/coreg.pdf
and:
http://www.mrc-cbu.cam.ac.uk/Imaging/JIRMF01/jirmf01_realignment.pdf
At 07:39 AM 12/13/01 +0100, you wrote:
>Dear SPMīs users:
>
>
>Could somebody tell me, if normalization with SPM could influence the
>measures of volume of a focal lesion ?
>
>If the answer is affirmative, could the masking of a focal lesion resolve
>this problem ?
>
>Or there is another solution !!!!
>
>
>Thank you for your help.
>
>
>
>Hans Carmona
>Neurosurgery Department
>University of Freiburg
>Germany
__________________________________________
Dr. Chris Rorden
Department of Psychology
University of Nottingham
Nottingham NG7 2RD, UK
Tel: +44 [0]115-951-5294
Fax: +44 [0]115-951-5324
http://www.psychology.nottingham.ac.uk/staff/cr1/
_________________________________________________________
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