cknizek

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.

I currently do research in MRI.

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.

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 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.

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.

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.