Hi Rashimi,
1. there can be large differences, often they indicate a problem with the scan (e.g. motion artifacts etc). Or a problem with the processing (you should quality check the aseg and surfaces). 2. you should use FreeSurfer 5.1 and the longitudinal processing stream as is designed exactly for this and reduces variability significantly. A paper about the longitudinal stream has been accepted to NeuroImage, let me know if you want a pre-print. 3. Something is wrong with your table. It is extremely unlikely that both subjects have exactly the same numbers A.T3 and AA.T2. Something got mixed up.
Best, Martin
On Thu, 2012-03-01 at 21:13 +0000, Rashmi Singh wrote:
Hello, I am finding differences in hippocampus voulme of same subject when scanned at different times . Our study requires our subjects to be scanned 3-4 times (T0-T3) within a period of 1 month. We have performed MRI Scanning on all our subjects with same sequence using 3T GE scanner. Please suggest the reason behind this difference and how would I go about correcting it. For example following are the hippocampal values for two subjects ( A and AA ) calculated by freesurfer from different scans. Surprisingly for these two subjects T3 and T2 Hipp-values for A and AA respectively that are differing from the other timepoints are same.
Left-Hippocampus Right-Hippocampus A.T0 3537 3632 A.T1 3629 3796 A.T2 3536 3782 A.T3 3096 3671 AA.T1 4245 4667 AA.T2 3096 3671 AA.T3 4341 4491
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