Hi Bruce,

Thank you for your quick reply!

The decrease in percent difference vary. I  have listed the range here for each region:

Left Lateral Ventricle: -26 to -0.06
Left inferior ventricles: -67 to -0.2
Third ventricle: -23 to -0.06
Fourth ventricle: -7 to -0.142
Right lateral ventricle: -21 to -0.04
Right inferior ventricle: -59 to -0.68

I had a chance to examine one brain that showed -16% difference score in the left lateral ventricles between the longitudinal and baseline scan. The scans seemed to show a smaller left lateral ventricle at time 2. Do you know whether the variability of Freesurfer (version 5.1) may contribute to some of the decreases I am seeing?

Thank you in advance for your help.

Best,
Tamara


Message: 32
Date: Tue, 5 Sep 2017 21:43:23 -0400 (EDT)
From: Bruce Fischl <fischl@nmr.mgh.harvard.edu>
Subject: Re: [Freesurfer] Ventricle Volumes Decreasing over time?
To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
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        <alpine.LRH.2.20.1709052142520.4038@gate.nmr.mgh.harvard.edu>
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Hi Tamara

have you visualized the multiple time points of a subject whose ventricular
volume is decreasing? How big a decrease are you seeing?

cheers
Bruce


On Tue, 5
Sep 2017, Tamara Tavares wrote:

> Hello,
> I used the default longitudinal stream to calculate ventricular volumes over time. When I examined
> the difference score (longitudinal-baseline) I noticed that for some participants ventricular
> volumes decreased. The same site, scanner and scanning protocol was used for both baseline and
> longitudinal scans. I processed the cross, template and longitudinal time points on the same
> computer using the same Freesurfer version (v 5.1). Furthermore, this decrease in ventricular volume
> is evident before and after manual corrects were made to the aseg file. Is it common to see an
> decrease in ventricular volume over time? Can this be due to Freesurfer variability or slight
> differences in the scanner over the two time points?
>
> Thank you in advance for your help.
>
> Best,
> Tamara