Re: [Freesurfer] volume, surface area, and thickness

[Anderson M. Winkler]

Hi Woo-Suk

Just adding to Bruce's reply: area isn't a "technically more noisy and
usually thus less sensitive" as the reviewer suggests. Area isn't noisier
on its own right, and it's measured from the very same surfaces from which
thickness is measured. However, there is a much larger variability of area
across subjects than of thickness, even within the normal range, such that
the variance of volume, that can be explained by or associated with other
indices, is largely explained by the variance in area. The first paper that
(as far as I know) showed this is Voets et al. (Neuroimage, 2008), and we
keep observing this repeatedly in different datasets, published or not.

About the Schmaal et al. paper (Molecular Psychiatry, 2016): it is an
excellent paper in which the authors didn't spend time (or space)
discussing volume, going instead straight to the more interesting bits:
area and thickness.

All the best,

Anderson


On 29 August 2016 at 13:56, Bruce Fischl  wrote:

> Hi Woo-Suk
>
> why not just do the surface analysis that they are requesting? I'm not
> sure what you are asking, but certainly volume = surface area * thickness
> in general, and so a volumetric effect can be driven by one or both of
> surface area and thickness
>
> cheers
> Bruce
>
>
>
> On Sat, 27 Aug 2016, Woo-Suk Tae wrote:
>
> Dear FreeSurfer experts and developers
>>
>> I am confronted with some technical question of a reviewer.
>> I am not sure about "volume = thickness-by-surface area" and the review's
>> opinion (attached below) about volume, surface area, and thickness was
>> correct.
>> Any comments from FreeSurfer's experts would help me.
>>
>> Sincerely yours
>>
>> Woo-Suk Tae
>> Seoul, Korea
>>
>> I added the reviewer's comments.
>> -
>> 1. Volume/thickness: The authors cite many papers that show volume and
>> thickness differences in MDD. The unresolved part here, however, is the
>> RELATION between cortical thickness and cortical volume: There is no
>> doubt,
>> that both measures are found affected in MDD. This is, because cortical
>> thickess multiplied by the surface area of a gyrus results in its volume,
>> so
>> volumse = thickness-by-surface area. Surface area values themselves are
>> technically more noisy and usually thus less sensitive (due to the problem
>> of false attributions to an area).
>>
>> So, volume is influenced by thickness and surface and is the less specific
>> measure. If a volume effect is detected in a study, it is unclear, if it
>> is
>> driven by thickness, or surface area, or both. In this respect, the study
>> of
>> Schmaal et al. is telling, as it analyzed BOTH measures, finding only
>> thickness effects of MDD, and (practically) no surface area changes except
>> for adolescent MDD. In the adolescent MDD samples gross surface area
>> differences were detected.
>>
>> This means, that the question of "superiority" is rather a question of
>> "specificity": (Cortical) volume findings in adult MDD are mostly driven
>> by
>> thickness differences and are in on way independent from thickness
>> differences. In this respect, the authors should follow the basic
>> geometric
>> principles of morphometry and point out the relatedness of the two. They
>> can
>> simply check this in their FreeSurfer variables (e. g. for total grey
>> matter
>> volume). Not reporting surface area is leaving an interpretational gap as
>> surface area differences could in addition drive volume differences. The
>> authors may want to decide not to present surface area results, but then
>> they should discuss this as limitation to disentangle the origin of
>> volumetric (cortical) effects. This seems important as methylation effects
>> and FKBP5 interact with early life time stress, so effects on surface area
>> as seen in adolescent MDD highlight that surface area effects could play
>> in.
>>
>>
>>
>>
>>
>>
>>
>> 
>> ---
>> -
>> Woo-Suk, Tae  Ph.D.  Research Professor
>> Brain Convergence Research Center, Medical Research Center
>> Anam Hospital, Korea University Medical Center, Seoul, Korea
>> mobile: 82-10-9120-4629
>> office: 82-2-920-6831
>> email: woosuk@gmail.com, woos...@gmail.com
>> 
>> ---
>> -
>>
>>
>>
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> dispose of 

Re: [Freesurfer] volume, surface area, and thickness

[Bruce Fischl]

Hi Woo-Suk

why not just do the surface analysis that they are requesting? I'm not
sure what you are asking, but certainly volume = surface area * thickness 
in general, and so a volumetric effect can be driven by one or both of 
surface area and thickness


cheers
Bruce


On 
Sat, 27 Aug 2016, Woo-Suk Tae wrote:



Dear FreeSurfer experts and developers

I am confronted with some technical question of a reviewer.
I am not sure about "volume = thickness-by-surface area" and the review's
opinion (attached below) about volume, surface area, and thickness was
correct.
Any comments from FreeSurfer's experts would help me.

Sincerely yours

Woo-Suk Tae
Seoul, Korea

I added the reviewer's comments.  
-
1. Volume/thickness: The authors cite many papers that show volume and
thickness differences in MDD. The unresolved part here, however, is the
RELATION between cortical thickness and cortical volume: There is no doubt,
that both measures are found affected in MDD. This is, because cortical
thickess multiplied by the surface area of a gyrus results in its volume, so
volumse = thickness-by-surface area. Surface area values themselves are
technically more noisy and usually thus less sensitive (due to the problem
of false attributions to an area). 

So, volume is influenced by thickness and surface and is the less specific
measure. If a volume effect is detected in a study, it is unclear, if it is
driven by thickness, or surface area, or both. In this respect, the study of
Schmaal et al. is telling, as it analyzed BOTH measures, finding only
thickness effects of MDD, and (practically) no surface area changes except
for adolescent MDD. In the adolescent MDD samples gross surface area
differences were detected.

This means, that the question of "superiority" is rather a question of
"specificity": (Cortical) volume findings in adult MDD are mostly driven by
thickness differences and are in on way independent from thickness
differences. In this respect, the authors should follow the basic geometric
principles of morphometry and point out the relatedness of the two. They can
simply check this in their FreeSurfer variables (e. g. for total grey matter
volume). Not reporting surface area is leaving an interpretational gap as
surface area differences could in addition drive volume differences. The
authors may want to decide not to present surface area results, but then
they should discuss this as limitation to disentangle the origin of
volumetric (cortical) effects. This seems important as methylation effects
and FKBP5 interact with early life time stress, so effects on surface area
as seen in adolescent MDD highlight that surface area effects could play
in. 





 

---
-
Woo-Suk, Tae  Ph.D.  Research Professor
Brain Convergence Research Center, Medical Research Center
Anam Hospital, Korea University Medical Center, Seoul, Korea
mobile: 82-10-9120-4629
office: 82-2-920-6831
email: woosuk@gmail.com, woos...@gmail.com
---
-


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[Freesurfer] volume, surface area, and thickness

[Woo-Suk Tae]

Dear FreeSurfer experts and developers

I am confronted with some technical question of a reviewer.
I am not sure about "volume = thickness-by-surface area" and the review's
opinion (attached below) about volume, surface area, and thickness was
correct.
Any comments from FreeSurfer's experts would help me.

Sincerely yours

Woo-Suk Tae
Seoul, Korea

I added the reviewer's comments.
-
1. Volume/thickness: The authors cite many papers that show volume and
thickness differences in MDD. The unresolved part here, however, is the
RELATION between cortical thickness and cortical volume: There is no doubt,
that both measures are found affected in MDD. This is, because cortical
thickess multiplied by the surface area of a gyrus results in its volume,
so volumse = thickness-by-surface area. Surface area values themselves are
technically more noisy and usually thus less sensitive (due to the problem
of false attributions to an area).

So, volume is influenced by thickness and surface and is the less specific
measure. If a volume effect is detected in a study, it is unclear, if it is
driven by thickness, or surface area, or both. In this respect, the study
of Schmaal et al. is telling, as it analyzed BOTH measures, finding only
thickness effects of MDD, and (practically) no surface area changes except
for adolescent MDD. In the adolescent MDD samples gross surface area
differences were detected.

This means, that the question of "superiority" is rather a question of
"specificity": (Cortical) volume findings in adult MDD are mostly driven by
thickness differences and are in on way independent from thickness
differences. In this respect, the authors should follow the basic geometric
principles of morphometry and point out the relatedness of the two. They
can simply check this in their FreeSurfer variables (e. g. for total grey
matter volume). Not reporting surface area is leaving an interpretational
gap as surface area differences could in addition drive volume differences.
The authors may want to decide not to present surface area results, but
then they should discuss this as limitation to disentangle the origin of
volumetric (cortical) effects. This seems important as methylation effects
and FKBP5 interact with early life time stress, so effects on surface area
as seen in adolescent MDD highlight that surface area effects could play
in.








Woo-Suk, Tae  Ph.D.  Research Professor
Brain Convergence Research Center, Medical Research Center
Anam Hospital, Korea University Medical Center, Seoul, Korea
mobile: 82-10-9120-4629
office: 82-2-920-6831
email: woosuk@gmail.com, woos...@gmail.com 

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Freesurfer mailing list
Freesurfer@nmr.mgh.harvard.edu
https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer


The information in this e-mail is intended only for the person to whom it is
addressed. If you believe this e-mail was sent to you in error and the e-mail
contains patient information, please contact the Partners Compliance HelpLine at
http://www.partners.org/complianceline . If the e-mail was sent to you in error
but does not contain patient information, please contact the sender and properly
dispose of the e-mail.