One of the main advantages of TD-NIRS is that the signal it's imaging is "electrical".
Modalities like PET, BOLD fMRI, and CW-NIRS do depend upon saturation changes. For BOLD and CW-NIRS, it's the change in blood oxygen saturation.
TD-NIRS images the fast optical signal that is correlated with electrical activity in the cortex. MEG images the magnetic fields correlated with electrical activity in the cortex. IMO, they're pretty similar.
> TD-NIRS images the fast optical signal that is correlated with electrical activity in the cortex. MEG images the magnetic fields correlated with electrical activity in the cortex. IMO, they're pretty similar.
So I guess the way I look at it, is that the field is what is augmented in a MEG, that makes the substrate emit an amplified signal naturally there. While a TD-NIRS injects a laser signal into the skull to measure back reflections... both inject energy into the system, but one is a reflection vs. an emission.
Is this the wrong way to look at it?
And anodyne33, yes, it is 100% apples to oranges. I was abreast of their original aims and MEG was on the table at the time - I had hoped that would remain the aim as it to me appears more beneficial, based on how I view the sensing above.
Not a breakthrough. This technique has been known about for at least two decades.
Most fNIRS uses the amplitude-based, continuous-wave modality to compare chromophore concentrations resulting from thermovascular coupling.
This uses time-domain based. What this means more formally is that it uses the impulse response created from a fast optical imaging source to then detect scattering changes in the cortex that ideally correspond to neuronal activation (or lack thereof).
I was actually working on a very similar device a few months ago. I had to give up as the chip shortage made the specialty ICs required to pull this off damn near impossible to buy.
There are a couple of things that make TD-NIRS a bit trickier. First off, it relies upon counting photons. This makes it susceptible to all sorts of noise, coupled with the fact that you need a photodetector with a very fast rise time and at least 10-20% detection of incident photons upon the detector.
Benefits
- Extremely fast (millisecond-range) neuronal activity detection
- Less susceptible to motion artifacts
- Very localized detection, scattering is well-modeled
Drawbacks
- Requires extremely fast sampling rate
- Above sampling rate makes multiplexing difficult
- Still susceptible to all kinds of noise
I don't think kernel has demonstrated fast optical imaging of direct neuronal activity here. The article clearly mentions they detect oxygen activity corresponding, like conventional fNIRS or fMRI.
I've been looking at this field and my conclusion was that non-invasive optical imaging of direct neuronal activity, while possible in theory, it requires several magnitudes of improvement in today's technology. Even Openwater is detecting blood flow (and not individual neurons). Wrote my thoughts here: https://notes.invertedpassion.com/Consciousness/Fast+optical...
Curious to hear what you were building and whether you actually got close to doing fast optical imaging. Happy to chat offline, my email is here: https://invertedpassion.com/about/
Mary Lou Jepsen's Open Water was looking at something similar -
I'm going to say something stupid simple:
Any technique imaging the brain outside the skull is hard. Much of these IR technologies are noble in terms of their general science and engineering learnings, but in terms of practicality, sub-optimal.
Curious to know if you've experimented with other modalities? My base is fNIR and EEG device manufacturing, while just being exposed to (f)MRIs, MEGs and the like.
I'm not entirely sure what you mean about IR technologies. Almost all medical imaging done today is done outside the skull. The only exception is ECoG, which is only medically used for patients with severe epilepsy. This is because open-brain surgery is an extraordinarily risky and expensive proposition.
Every single imaging modality has strengths and weaknesses. It is the goal of the physician, and of the radiologist, to choose the appropriate imaging modality for the patient.
NIRS is not always the best choice, especially not for medical imaging. But it's a good choice if you are looking for a portable modality that can image neuronal activation in the cortex.
EEG is already difficult because you can't just add probes to increase spatial resolution. There is a fundamental limit the information that can be reliably gathered solely based upon the sodium-ion voltage potentials of neurons.
I love these technologies, thanks for engaging with me about them.
IR roughly meant NIRS - was just playing fast and loose with the modality for 'things that suffer from extreme scatter that I believe will prove impossible (for the intended use) for the foreseeable future'
MRIs as I understand it align then flip water molecules that are a super easy signal to read, it comes down to stitching techniques and the hardware affordances to make that easier.
So, now I'm more curious, you believe you solved the scatter issue but were supply chain constrained?
Your assessment is also mine: spatial and temporal resolution requirements drive which sensing techniques one would use.
My aims were consumer based, so much less concerned about precision, more analysis turn around time. EEG was torture, yet rewarding in that realm - though to many techie's dismay, it only offered a single bit of resolution > I still think that's enough.
Edit: If it's still not clear what I mean (I am not a grad student in any respect), I think that anything one has to 'inject' then read the reflection is a suboptimal approach to reading the naturally emitted (albeit amplified) signal.
Why not try a micro approach, 1024 pin sized probes that make an end point connection to the scalp. Most EEGs I have seen have probes the size of a coin. Is there a reason for this? From what I know of electronics the size of the electrode only matters if you are passing high amounts of current through them.
> I believe the "specialized brain regions" idea has been over-debunked. It was the source of so much woo woo in the late 20th century (are you right-brained or left-brained!?) that we've come to think it's complete bunk.
I still see PopSci articles with a title along the lines of; "Scientists have discovered the part of the brain responsible for X". Even in studies or experiments in the literature, I still see color gradient scales used for fMRI. These are known to vastly over exaggerate the discrepancy between functional areas. And yet they allow for a more easily digestible view of what the study is after, which is probably why they're still used.
I think what the author is getting at is that, yes, some parts of the brain are more specialized than others. But there is no specific part of the brain that regulates a specific function and nothing else. Rather, it's an enormously complex system.
edit: Color gradient scales are fine for academic studies and research. However, they can be misleading to laypeople.
And remember that those pictures are themselves the result of lots and lots of clustering and dimension reduction, so are about as useful as cluster analysis of unsupervised data (which is what they are), that is not particularly useful at all.
I mean, the actual problem is that fMRI is expensive, and gives good spatial understanding, but bad temporal understanding (i may be mixing this up, I haven't seriously looked at any brain research in about a decade).
The statistical problems in fMRI are sadly unappreciated, much like the statistical problems in human research more generally.
Most NIRS systems use continuous-wave (CW) systems detecting blood oxygenation/chromophore concentration. I say this because, in the time domain, you're looking at 5-7 seconds to see changes in cerebral oxygenation.
It's also noteworthy that you're dealing with huge amounts of noise, very low resolution, and are limited to the cortical surface. This limits the applications in the BCI-domain.
I'm currently researching the feasability of fast optical imaging. This has to be done in the frequency domain, but may yield temporal resolution in the milliseconds. The downside is finding an incoherent light source that's able to be modulated fast enough to detect the scattering changes.
"Mind Control and EM Wave Polarization Transductions" (1999)
> To engineer the mind and its operations directly, one must perform electrodynamic engineering in the time * domain, not in the 3-space EM energy density domain.*
> Researchers believe that when it is fully understood, TAI can be used to make semiconductors with potential applications in electronic devices, Ma said. The highly unusual properties of Axions will support a new electromagnetic response called the topological magneto-electric effect, paving the way for realizing ultra-sensitive, ultrafast, and dissipationless sensors, detectors and memory devices.
> The new work, reported in a paper published Feb. 25 in the journal Nature Physics, throws wide open the amount of information that can be multiplexed, or simultaneously transmitted, by a coherent light source. A common example of multiplexing is the transmission of multiple telephone calls over a single wire, but there had been fundamental limits to the number of coherent twisted light waves that could be directly multiplexed.
> Army researchers built the quantum sensor, which can sample the radio-frequency spectrum—from zero frequency up to 20 GHz—and detect AM and FM radio, Bluetooth, Wi-Fi and other communication signals.
> The Rydberg sensor uses laser beams to create highly-excited Rydberg atoms directly above a microwave circuit, to boost and hone in on the portion of the spectrum being measured. The Rydberg atoms are sensitive to the circuit's voltage, enabling the device to be used as a sensitive probe for the wide range of signals in the RF spectrum.
> "All previous demonstrations of Rydberg atomic sensors have only been able to sense small and specific regions of the RF spectrum, but our sensor now operates continuously over a wide frequency range for the first time,"
Very interesting implantation method. I never would've thought it possible to use a stent like this. I think the most valuable IP produced from Synchron will be implementing ECoG without an extremely expensive (and risky!) craniotomy.
This is a really hard problem. NIRS is already difficult; very weak signal, limited to <2 cm of cortical surface, and haemodynamic response is 5-7 seconds.
I think it's definitely a useful imaging technique for certain (highly specific) tasks. But to detect language? They would need many, many more source/detector pairs, considering the vast swathes of the brain partially responsible. Language is already very fuzzy within fMRI.
Modalities like PET, BOLD fMRI, and CW-NIRS do depend upon saturation changes. For BOLD and CW-NIRS, it's the change in blood oxygen saturation.
TD-NIRS images the fast optical signal that is correlated with electrical activity in the cortex. MEG images the magnetic fields correlated with electrical activity in the cortex. IMO, they're pretty similar.