Hi Rashmi
what version of FS are you using? And what sequence are you using? There will of course be noise-induced variation across scans, which in the best case is around 2%. But that only occurs if you use multi-echo (high bandwidth sequence) and are careful about subject positioning to minimize differential gradient nonlinearity distortions. You should also make sure that your outlier measurements aren't significantly more motion corrupted than your other scans. Finally, it can also help to control for hydration status and time-of-day.
cheers Bruce
On Thu, 1 Mar 2012, 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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