It looks like this was the study (emphasis added):
Sedentary behavior associated with reduced medial temporal lobe thickness in middle-aged and older adults http://journals.plos.org/plosone/article?id=10.1371/journal....
Sedentary behavior associated with reduced medial temporal lobe thickness in middle-aged and older adults http://journals.plos.org/plosone/article?id=10.1371/journal....
To calculate thickness, for each gray matter voxel we computed the distance to the closest non-gray matter voxel. In 2D-space, for each voxel, we took the maximum distance value of the corresponding 3D voxels across all layers and multiplied by two. Mean thickness in each subregion was calculated by averaging thickness of all 2D voxels within each region of interest.
[0] http://journals.plos.org/plosone/article?id=10.1371/journal....
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.
>"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.
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.
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.
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/
That sounds exactly like what I would expect, nothing to do with density or clumping.