if you work on a study comparing groups or age effects, that analyzes hippocampal volume, then you would usually normalize that volume. People have different head sizes and therefore differently sized hippocampi. To remove headsize differences researchers often normalize voumes by ICV.

If you are interested in comparing the hippocampal volume between methods (manual and different automatic methods) and not between subjects, you do not need to normalize. ICV will be computed differently by different packages so you would just add more noise. Furthermore for your manual hippocampus labels you probably won't have manual ICV.

On Oct 6, 2012, at 1:25 PM, Ana Arruda wrote:

Thanks a lot Martin.

I really get confused about normalization. I've already done the comparisons and the values between methods, as you said, are different. Although I haven't understood why, in this case, I don't have to normalize. My advisor told me to normalize all the brain values from the patients. Do you have any idea what did he mean with that? I thought that this suggestion would be related to hippocampus volume.

Ana Arruda

---------------------------------

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
Email:

mreuter@nmr.mgh.harvard.edu

reuter@mit.edu

Web : http://reuter.mit.edu