Hi Ana,
when comparing to manual labels or other segmentation methods you do not need to normalize. But other methods and even manual segmentations may follow a different protocol, so it can be expected that some method gives consistently different (e.g. smaller) values.
ICV in FreeSurfer is computed via the scaling needed to map a scan into Talairach space, where ICV values are known. The Talairach ICV values were established using a protocol that included CSF. Take a look at the Buckner paper (should be on the wiki, there is also a page about eTIV (estimated total intacranial volume).
Best, Martin
On Oct 6, 2012, at 12:35 PM, Ana Arruda wrote:
Hello,
I'm working on hippocampus segmentations obtained by Freesurfer to compare with manual and FSL segmentations. Do I have to normalize to make these comparisons more accurate?If so, what volume do I have to use? I've read about eTIV but I would like to confirm if there is any value for normalization purpose in the aseg.stats file.
What does ICV include? Does it include the CSF between the brain and the skull?
Best regards,
Ana Arruda
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---------------------------------
Dr. Martin Reuter
Assistant in Neuroscience - Massachusetts General Hospital
Instructor in Neurology - Harvard Medical School
MGH / HMS / MIT
A.A.Martinos Center for Biomedical Imaging
149 Thirteenth Street, Suite 2301
Charlestown, MA 02129
Phone: +1-617-724-5652
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