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>Thank you so much My pleasure :) >This is phase contrast tomography, so you can get the refractive index of the materials inside, and their speed. This is w
by omginternets 9y ago
>Thank you so much
My pleasure :)
>This is phase contrast tomography, so you can get the refractive index of the materials inside, and their speed.
This is way outside of my domain of competence, but if I understand correctly, this would not constitute a BOLD signal?
I'm skeptical of the idea that blood diffusion alone correlates with cerebral activity. With fMRI, you're looking at temporary gradients of de-oxygenated hemoglobin rather than a net direction of blood movement. This is sometimes confused with "blood flow", and I've been guilty of interchanging the two terms myself :/ I suspect the fluid dynamics of blood in the head is outrageously noisy and difficult to contrast out or filter though statistical means (because it's roughly random).
Concerning the relationship between neural activity and BOLD signal this paper [https://www.nature.com/articles/35084005 https://www.nature.com/articles/35084005] is a good starting point. I'll see if I can dig up the PDF for you.
- ericjang 9y agoDoes de-oxygenated blood have a measurably different refractive index w.r.t. radio waves than oxygenated blood?
- GistNoesis 9y agoNo, that's why MRI has an undeniable advantage if it's what's important. What I was hoping, was that if the brain is somehow "opening" the various valves to bring more juice to certain area then that would be useful info (regardless of whether or not there is O2 in the blood, and where this O2 is consumed).
- ericjang 9y agoI see, so you are proposing a way to infer capillary expansion/contraction as a way to measure blood flow.
- omginternets 9y agoNo, but de-oxygenated hemoglobin is paramagnetic, and therefore detectable using what's called T2*-weignted scan sequences. http://casemed.case.edu/clerkships/neurology/Web%20Neurorad/MRI%20Basics.htm http://casemed.case.edu/clerkships/neurology/Web%20Neurorad/...
- GistNoesis 9y agoYou are right this is not a BOLD signal. I was hoping the brain was able somehow to vaso-constrict to direct its oxygen supply toward some region and that we could observe that. But from what I'm picking from you is that it's more like there is fluid everywhere, and cells are just consuming more or less kind of an open-buffet (versus cells waiting at the table and asking for more or less food). ^^found your paper without paywall but haven't read it yet [http://wexler.free.fr/library/files/logothetis%20(2001)%20neurophysiological%20investigation%20of%20the%20basis%20of%20the%20fmri%20signal.pdf http://wexler.free.fr/library/files/logothetis%20(2001)%20ne...]
- omginternets 9y ago>wexler.free.fr Holy shit, I am laughing my ass off. That domain belongs to a guy in my former lab :'D