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Comment by GistNoesis | Hacker News Reader

I'm no expert, but what about seeing the brain using radio-waves diffraction pattern.

You take an emitting antenna in-front of the person, 1 meter behind him you make a grid array of Software Defined Radios (like 10x10=100 SDR (SDR are so cheap that it will be ~ the price of an OpenBCI set) ), and you record the diffraction/interference pattern, then you software analyze it to produce a 3d image via solving the inverse scattering problem, to get the fluids flows and densities (you should even get the speeds through Doppler)).

My simple back of the envelope calculations, says that at 5Ghz we should rather easily get a spatial resolution of lambda/4=1.5 cm, maybe more using super resolution techniques. Going to 60Ghz, we should soon be able to reach millimeters spatial resolution.

It obviously won't reach the quality levels of FMRIs.

Can someone from the field tell what kind of bandwidth we should expect from such a setup?

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EEG noise to signal ratio is so ridiculously low that you really need to be as close to the brain as possible. Any muscular activity produces electrical currents an order of magnitude higher.

As a side note: what an FMRI sees and what an EEG measures is fundamentally different. EEG can reliably only detect the Pyramidal neurons in the cortex an MRI can see below that.

I'm not suggesting that we measure the signal emitted by the brain like EEG do. I'm suggesting that we look at the fluids movements like FMRI do but using diffraction like xray-imaging with bigger wavelengths.

>I'm suggesting that we look at the fluids movements like FMRI do but using diffraction like xray-imaging with bigger wavelengths.

What would we gain from using RF-diffraction as opposed to MR?

The major advantage of fMRI is that you're measuring a so-called Blood-Oxygen-Level-Dependent (BOLD) signal. That is, you're looking at a contrast between oxygenated and de-oxygenated blood, which is more interesting than just looking at where blood (of all types) is going.

The underlying assumption is that brain volumes consume oxygen at a rate roughly proportional to the level neuronal activity. As such, a BOLD signal is really what you want.

>BOLD signal is really what you want

Thank you so much (I have no medical knowledge and that is some key domain-knowledge I've missed). How much correlation with blood flow is there ? Maybe the BOLD signal can be reconstructed from the graphs of all mixed blood flow.

>What would we gain from using RF-diffraction as opposed to MR?

Main gain is practicality. Main usage would be for brain interface. This is phase contrast tomography, so you can get the refractive index of the materials inside, and their speed.

It won't be as precise as MRI, but it will be more practical. More portable. It doesn't use magnets so not limited by maximum magnetic fields. It is more scalable if you have compute power, meaning you can add some SDR to increase the resolution and bandwidth if necessary. Time resolution would probably be better as it doesn't need moving parts (if beam forming). It's cheaper. It's non invasive and usable 24/7.

We already have wifi imaging, so this is just putting it in favorable condition so as to extract more info from the brain. Basically until we can get the full connectome activation real time, we are just side-channel attacking the brain to extract some info. I'm just trying to grasp how much and how useful is the info we can get using existing techniques.

For example you put this device inside every monitor screen (for 60Ghz or in a TV sized box for 5Ghz) and a software controlled radio emitter behind the back of your head. And if the useful info bandwidth is sufficient we could have vastly better interface to the computer.

This can probably be adapted for room-sized continuous body health monitoring if the resolution is not sufficient or if the info extracted is not relevant enough.

>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] is a good starting point. I'll see if I can dig up the PDF for you.

Does de-oxygenated blood have a measurably different refractive index w.r.t. radio waves than oxygenated blood?

No, 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).

I see, so you are proposing a way to infer capillary expansion/contraction as a way to measure blood flow.

No, 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/...

You 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)%20ne...]

>wexler.free.fr

Holy shit, I am laughing my ass off. That domain belongs to a guy in my former lab :'D

And in an ideal world you want an even more direct measure than BOLD, which is why folks are examining perfusion imaging.

What you want is better temporal resolution, better spacial resolution, a less restrictive environment and a more direct measure of activity. The indirect BOLD signal has a long delay and is hard to accurately separate from noise. The spatial resolution of fMRI is a fraction of that achievable by clinical imaging and the MR environment is very expensive, restrictive and generally unhelpful for many experiments.

It’s always great to have informed responses here so thank you for contributing.

I gotta say though regarding the other comments on data quality, if a lay person read through the wiki pages on common brain imaging techniques (as I did) including fMRI, it seems easy to come away, rightly or wrongly, thinking, that’s all we have? That’s the state of the art spatial/temporal resolution? No wonder we can’t model the brain from first principles.

The amount of innovation, effort, and complexity that was needed to get imaging where it is today seems amazing to me, just glossing over the major achievements, it’s nobel prize level stuff. Yet you guys seem to have to still work in so much darkness with so little light. It seems rather than imaging one day simply revealing fundamental secrets, it’s just providing clues that will continue to require great insights and experiments to change the world.

But again, full admission of popcorn eating ignorance in these assumptions.

You hit the nail on the head. Cognitive neuroscience -- especially WRT functional imagery -- reminds of the fable of the blind men and the Elephant.

(Very) roughly speaking, you have the choice between:

- Excellent temporal resolution & crappy spatial resolution (EEG / MEG)

- Pretty good spatial resolution & crappy temporal resolution (fMRI)

Other techniques (NIRS, TMS, etc) fall somewhere along the spectrum and have their own quirks. We're peering into brain function with a super-low-res "camera" and attempting to draw only the roughest contours of the thing we're exploring.

The eye blinks... oh the eye blinks! Many a datapoint has been rendered useless by a dry contact lens.

Maybe try infrared?

https://en.wikipedia.org/wiki/Functional_near-infrared_spect...

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