Hello Gabor,
a few quick comments:
i) Although we typically aim for maximizing both, accuracy and
reproducibility are different things. In a longitudinal study you are
often particularly interested in the reproducibility of the findings, in
the sense of their repeatability across different time points if there
are no significant biological changes in your sample. T
ii) Ideally you would have included in your experimental design a group
of controls that you expect to not show longitudinal effects, and used
them to measure and estimate the test-retest reproducibility error of
your experimental setup (i.e., acquisition + analyses pipeline). This
information can then be used to estimate a lower limit of the effect
size you may be able to measure with your setup.
iii) We have looked at reproducibility errors of the longitudinal
Freesurfer cortex in healthy elderly volunteers from standard 3T MPRAGE
and found that it was generally above 2% in the structures we looked at
(https://www.ncbi.nlm.nih.gov/pubmed/23668971, Table 7). We did not look
at the cerebellum, but I imagine its reproducibility will not be higher.
However, if your acquisition protocol and subject population are very
different then these results might not apply well as reference for you.
Cheers,
jorge
On 13/12/2016 11:41, Gabor Perlaki wrote:
I've found the article "Within-subject template estimation for
unbiased longitudinal image analysis" by Reuter et al. It only
examines a limited number of structures for the reproducibility of
longitudinal Freesurfer. Are there any other paper that examines the
cerebellum as well? Any suggestion from the authors of Freesurfer
about accuracy of longitudinal Freesurfer for the cerebellum in
healthy subjects?
Best,
Gabor
2016-12-06 11:44 GMT+01:00 Gabor Perlaki <[email protected]
<mailto:[email protected]>>:
Dear all,
We've run longitudinal Freesurfer on 30 healthy subjects. We have
two subgroups (n=15) and we found a significant longitudinal
change in the left and right cerebellar cortex in one of our
subgroups. However, this change is very small: mean=0.67% range:
-1.61-2.3% for the right cerebellar cortex; mean=0.86% range:
-1.64-3.7% for the left cerebellar cortex. Although statistics
indicate significant cerebellar cortex increase, we are sceptical
that Freesurfer's accuracy allows reliable detection of such small
differences. Is there any article on how accurate the longitudinal
Freesurfer for cerebellum segmentation or any suggestion on how to
decide whether our results are reliable?
Best,
Gabor
--
Gabor Perlaki
research associate
Diagnostic Center of Pécs
H-7623 Pécs, Rét str. 2.
Tel.: 0036-30-2084367
E-mail: [email protected] <mailto:[email protected]>
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Jorge Jovicich, Ph.D.
MR Lab Head
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