fNIRS provides a measure of cerebral O2 delivery by monitoring concentration changes in oxygenated ∆[HbO2] and deoxigenated ∆[HHb]). Concentration changes in (∆ [oxCCO]) can be derived with NIRS.
Someone knows how? ( I am asking for the mathematical formula)
Tks!
Using the modified Beer-Lambert Law, we separate oxy and deoxyhemoglobin from fNIRS data using at least two wavelengths. This is because of the absorption spectra of tissue to NIR light. In NIR light, the two dominant absorbers are oxy and deoxyhemoglobin, so if we assume that the changes in the concentration of other absobers remains relatively constant, we can attribute all of the light attenuation to oxy and deoxyhemoglobin. Spectroscopy calculations require two wavelengths to calculate these two unknowns. Using a third wavelength, we can add cytochrome c oxidase aa3 to the calculations. This is not usually done for multiple reasons. First, the signal in NIRS is already really noisy and the absorption of light by cytochrome c oxidase aa3 is low in comparison to oxy and deoxyhemoglobin so the resulting signal for cytochrome c oxidase is barely above the noise floor, or not at all. Second, the hardware limitations; you need now a third wavelength which is more expensive and an added expense that may not be worth the effort. Then there are other issues found during modelling. Differential pathlength factors, absorption and scattering coefficients, or geometric models needed for the calculations already have varying sources of error that can introduce noise and/or cross talk between your resulting oxy-deoxy hemoglobin and cytochrome oxidase concentration measurements. These issues compounded on an already noisy and low signal from cytochrome means that meaningful results are really hard to come by for that particular chromophore. If you're looking for the actual math, take a look at the following papers for information.
Article Diffuse Optical Tomography for Brain Imaging: Continuous Wav...
Article In Vivo Near-Infrared Spectroscopy
Yes, using the modified Beer-Lambert law. You can see the math and its easy explanation in the following papers (as I can not type math in the comment). Let me know in case you require further help.
Article Classification of functional near-infrared spectroscopy sign...
Article Online binary decision decoding using functional near-infrar...
Article Classification of prefrontal and motor cortex signals for th...
You just need adequate hardware and optimal wavelength combinations. See here
https://www.osapublishing.org/boe/fulltext.cfm?uri=boe-6-3-933&id=312318
You have probably solved the problem by now?
In the early days of in vivo NIRS back in the 1970s we, and others, built instruments to use 8 wavelengths, for HbO2, HHB and cytaa3. We mostly studied the human fetal brain and the pre-term infant brain, since we could transmit across a diameter of the head (8 cms) without major S/N problems. The early data on cyt aa3 was always questionable and also there was not any clinical enthusiasm for monitoring cyt aa3. We moved on to 4 wavelengths, improved the electronics, the software and the processor speed and started to derive more believable cyt aa3 data. Now most people (users and companies) are, sadly, content to use NIRS just like a simple pulse oximeter, with limited tissue penetration and interest only in the so-called oxygenation index!
I would encourage you to persist with your interest in cytaa3, and other respiratory enzymes. If you do so then I would also encourage the use of at least 4 wavelengths, and 8 if you can.
Good luck!
Tks for your comment Peter, I do completely agree with your view
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