Hi,
I have two questions regarding ICV correction for total hippocampal volume (from aseg.stats) and for hippocampal subfield volumes.
1) Total hippocampal volume: I am using the mri_label_volume script that uses the atlas normalization factor as an estimate for total ICV two T1-weighted scans (T1 = 1100ms, TE = 3.39ms, TR = 2530 ms, FOV = 256) and a third T1-weighted (T1 = 1100ms, TE = 1.54ms, TR = 2200ms, FOV = 192) conducted in the same session. The pearson's correlation coefficient between the left hippocampal volume of the 3 scans and their corrected volumes (35 healthy subjects) are .998, .662 and .997.For the right hippocampal volumes, the coefficients are .678, .995 and .893.
If the eTIV accounts for variances in head, are the r-values too high (especially .998, .995)?
2) As for hippocampal subfield volume correction for head size, can I similarly apply the same method, or would you recommend just using total ICV (from aseg.stats) as a covariate?
Thanks, New Fei