Hi,
I have performed a longitudinal analysis using the lme module in FreeSurfer, with this model:
*intercept(random effect) + centered age + group + group x centered age + sex*
I tested the effect of time with this contrast vector [ 0 1 0 0 0 ]. Dependent variable is area.
Here, mapping the second beta means mapping the effect size for (change over) time. In the beta map, I find values from 0 to 0.004. I would interpret that to mean that local area shrinks by at most 0.004 mm² per year in the reference group. But I'm not 100% sure about the biological (or geometrical) meaning of that.
Can I interpret this literally as the mean yearly shrinkage of the three triangles surrounding a given vertex, the average of whose area comprises the area score of the vertex, being 4/1000 mm? Of course, these maps are smoothed with 30mm, so the real spatial resolution is nowhere near this....
Thank you!
Hi Lars
which surface are you using? If it's the white surface you might try looking at white matter volume to see if it is decreasing
cheers Bruce
On Sat, 6 Sep 2014, Lars M. Rimol wrote:
Hi,
I have performed a longitudinal analysis using the lme module in FreeSurfer, with this model:
intercept(random effect) + centered age + group + group x centered age + sex
I tested the effect of time with this contrast vector [ 0 1 0 0 0 ]. Dependent variable is area.
Here, mapping the second beta means mapping the effect size for (change over) time. In the beta map, I find values from 0 to 0.004. I would interpret that to mean that local area shrinks by at most 0.004 mm² per year in the reference group. But I'm not 100% sure about the biological (or geometrical) meaning of that.
Can I interpret this literally as the mean yearly shrinkage of the three triangles surrounding a given vertex, the average of whose area comprises the area score of the vertex, being 4/1000 mm? Of course, these maps are smoothed with 30mm, so the real spatial resolution is nowhere near this....
Thank you!
-- yours, Lars M. Rimol, PhD St. Olavs Hospital Trondheim, Norway
This is tough to interpret, but basically, yes it would be 0-.004mm2/year. It is not quite right to say that it is at that vertex because of smoothing, but in that area. It is also hard to say what the total change would be for a cluster. One could sum the changes over the cluster vertices, but that would probably over-estimate the change. doug
On 09/06/2014 09:51 AM, Lars M. Rimol wrote:
Hi,
I have performed a longitudinal analysis using the lme module in FreeSurfer, with this model:
*intercept(random effect) + centered age + group + group x centered age + sex*
I tested the effect of time with this contrast vector [ 0 1 0 0 0 ]. Dependent variable is area.
Here, mapping the second beta means mapping the effect size for (change over) time. In the beta map, I find values from 0 to 0.004. I would interpret that to mean that local area shrinks by at most 0.004 mm² per year in the reference group. But I'm not 100% sure about the biological (or geometrical) meaning of that.
Can I interpret this literally as the mean yearly shrinkage of the three triangles surrounding a given vertex, the average of whose area comprises the area score of the vertex, being 4/1000 mm? Of course, these maps are smoothed with 30mm, so the real spatial resolution is nowhere near this....
Thank you!
-- yours,
Lars M. Rimol, PhD St. Olavs Hospital Trondheim, Norway
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Bruce Fischl -
Douglas N Greve -
Lars M. Rimol