4 ms·

I don't understand the breakthrough here, they miniaturized fNIRS?

anonymouse008 5y ago
'Tis also my read on the technology. They originally intended to miniaturize MEGs, which would have been remarkable, but diverted to the more immediately feasible. With $100m in personal funding, I felt MEG was absolutely the right route. I'm let down a bit by the recent marketing as well - when thinking optical sensing for neurology, you really think optogenetics like applications.
- anodyne33 5y ago
  Isn't that a bit apples v oranges? I've had a MEG and I'm floored by the technology but would a better analog be a PET? We're looking for two different things, metabolism v saturation but it seems like they're both in the physical or structural realm than the electrical.
  - cknizek 5y ago
    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.
    - anonymouse008 5y ago
      > 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.
cknizek 5y ago
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
- anonymouse008 5y ago
  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.
  - cknizek 5y ago
    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.

'Tis also my read on the technology. They originally intended to miniaturize MEGs, which would have been remarkable, but diverted to the more immediately feasible. With $100m in personal funding, I felt MEG was absolutely the right route. I'm let down a bit by the recent marketing as well - when thinking optical sensing for neurology, you really think optogenetics like applications.

anodyne33 5y ago
Isn't that a bit apples v oranges? I've had a MEG and I'm floored by the technology but would a better analog be a PET? We're looking for two different things, metabolism v saturation but it seems like they're both in the physical or structural realm than the electrical.
- cknizek 5y ago
  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.
  - anonymouse008 5y ago
    > 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.

cknizek 5y ago

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

anonymouse008 5y ago
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.
- cknizek 5y ago
  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.