3 ms·

The authors explained quite carefully what they mean by thickness, as per the quote I provided. They are measuring the average distance between voxels in MRI sc

The authors explained quite carefully what they mean by thickness, as per the quote I provided. They are measuring the average distance between voxels in MRI scans. Since thickness is a measure of average distance in this case, it makes sense to provide it in millimeters like in the figure you mentioned. If you read the article, the authors make distinction between volume, surface area, and thickness under the "Discussion" part [0]. [0] http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0195549#sec010 http://journals.plos.org/plosone/article?id=10.1371/journal....

nonbel 9y ago
Their description sounds like literal thickness. They took the distance to the border (white matter) of all the points in a region. This is like the radius of a circle, and then multiplied by 2, to get a value like the diameter of a circle. It does sound like quite a convoluted process but I don't see where you are getting anything like "density" from that description. Also, reading the methods closer makes me think these are cherry picked results: >"Once segmentation is complete, the original images are interpolated by a factor of 7, resulting in a final voxel size of 0.39 × 0.39 × 0.43 mm. Next, up to 18 connected layers of gray matter are grown out from the boundary of white matter, using a region-expansion algorithm to cover all pixels defined as gray matter." Why 7? Why 18? These magic numbers shouldn't be there without some kind of sensitivity analysis. Finally, you can see the dimensions of the voxels is something determined by their methods, not a property of the brains.
- MikkoFinell 9y ago
  Where in the article did you read anything suggesting that "They took the distance to the border (white matter) of all the points in a region."? I read the article, but didn't find anything like that.
  - nonbel 9y ago
    You quoted it (I guess besides white matter it could also be just to the pia): >"for each gray matter voxel we computed the distance to the closest non-gray matter voxel." I do admit that whatever they did is difficult to follow without seeing images of the transform etc (and figure 1 does not help), but the idea they are somehow measuring density seems impossible to me.
    - MikkoFinell 9y ago
      Within a given region, if there is more gray matter, and it is more clumped together, then the distance to nearest non-gray matter will be larger on average. This is what the authors call thickness.
      - nonbel 9y ago
        The gray/white/pial matter is not randomly distributed in the tissue so that there would be more or less clumping of gray matter. I thought maybe you had some expertise regarding how they processed the data that could somehow make this (extremely strange thing) happen, but you have not demonstrated it. I guess I do not know for sure what they did without seeing the code, but if that is what they measured it is the most bizarre thing I have heard of when it comes to analyzing MRI data.
        MikkoFinell 9y ago
        No one in this thread, or in the article, has claimed that gray matter is randomly distributed. Regarding your comment about how incompetent I am, and how extremely strange this MRI analysis is: Measuring cortical thickness by MRI is a standard technique in neuroanatomy since 15 years ago. And really, a quick search of the literature would have shown you this. But I suppose that's too much to ask.
        nonbel 9y ago
        >"No one in this thread, or in the article, has claimed that gray matter is randomly distributed." I simply cannot imagine what you think is going on in order for them to be looking at "clumping" of gray matter as a proxy for density of the tissue via MRI and calling this "thickness". >"Regarding your comment about how incompetent I am, and how extremely strange this MRI analysis is" I thought perhaps you knew some technical detail about their analysis pipeline, but you still haven't mentioned anything technical... so I just don't have any idea what you are thinking. >"Measuring cortical thickness by MRI is a standard technique in neuroanatomy since 15 years ago." Sure, here is the first article I found regarding "cortical thickness": "The shortest distance between the pial surface and the white/gray junction is the cortical thickness at each point." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561315/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561315/ That sounds exactly like what I would expect, nothing to do with density or clumping.
- MikkoFinell 9y ago
  Regarding your other comments about how the authors cherry picked their results and made up numbers in order to fabricate results, I can not take a stance.

nonbel 9y ago

Their description sounds like literal thickness. They took the distance to the border (white matter) of all the points in a region. This is like the radius of a circle, and then multiplied by 2, to get a value like the diameter of a circle. It does sound like quite a convoluted process but I don't see where you are getting anything like "density" from that description. Also, reading the methods closer makes me think these are cherry picked results: >"Once segmentation is complete, the original images are interpolated by a factor of 7, resulting in a final voxel size of 0.39 × 0.39 × 0.43 mm. Next, up to 18 connected layers of gray matter are grown out from the boundary of white matter, using a region-expansion algorithm to cover all pixels defined as gray matter." Why 7? Why 18? These magic numbers shouldn't be there without some kind of sensitivity analysis. Finally, you can see the dimensions of the voxels is something determined by their methods, not a property of the brains.

MikkoFinell 9y ago
Where in the article did you read anything suggesting that "They took the distance to the border (white matter) of all the points in a region."? I read the article, but didn't find anything like that.
- nonbel 9y ago
  You quoted it (I guess besides white matter it could also be just to the pia): >"for each gray matter voxel we computed the distance to the closest non-gray matter voxel." I do admit that whatever they did is difficult to follow without seeing images of the transform etc (and figure 1 does not help), but the idea they are somehow measuring density seems impossible to me.
  - MikkoFinell 9y ago
    Within a given region, if there is more gray matter, and it is more clumped together, then the distance to nearest non-gray matter will be larger on average. This is what the authors call thickness.
    - nonbel 9y ago
      The gray/white/pial matter is not randomly distributed in the tissue so that there would be more or less clumping of gray matter. I thought maybe you had some expertise regarding how they processed the data that could somehow make this (extremely strange thing) happen, but you have not demonstrated it. I guess I do not know for sure what they did without seeing the code, but if that is what they measured it is the most bizarre thing I have heard of when it comes to analyzing MRI data.
      - MikkoFinell 9y ago
        No one in this thread, or in the article, has claimed that gray matter is randomly distributed. Regarding your comment about how incompetent I am, and how extremely strange this MRI analysis is: Measuring cortical thickness by MRI is a standard technique in neuroanatomy since 15 years ago. And really, a quick search of the literature would have shown you this. But I suppose that's too much to ask.
        nonbel 9y ago
        >"No one in this thread, or in the article, has claimed that gray matter is randomly distributed." I simply cannot imagine what you think is going on in order for them to be looking at "clumping" of gray matter as a proxy for density of the tissue via MRI and calling this "thickness". >"Regarding your comment about how incompetent I am, and how extremely strange this MRI analysis is" I thought perhaps you knew some technical detail about their analysis pipeline, but you still haven't mentioned anything technical... so I just don't have any idea what you are thinking. >"Measuring cortical thickness by MRI is a standard technique in neuroanatomy since 15 years ago." Sure, here is the first article I found regarding "cortical thickness": "The shortest distance between the pial surface and the white/gray junction is the cortical thickness at each point." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561315/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561315/ That sounds exactly like what I would expect, nothing to do with density or clumping.
MikkoFinell 9y ago
Regarding your other comments about how the authors cherry picked their results and made up numbers in order to fabricate results, I can not take a stance.