Interaction of Light & Matter

Interaction of Light & Matter - Transcript

Now when we start looking at light there is a lot to understand about light. The most complex part, and this is what kind of gets overshadowed by the ease of application, is the complexity of light. What I mean by that it seems pretty easy to go “beep”, wait 10 minutes and then something happens. But the complexity of it, the richness of it, is really understood in its complexity. So whenever we have photons hit matter, and we’ll call this tissue matter, at this point in time, there’s a couple of things that happen. The first thing that could potentially happen is the light is reflected. This is what you see when you shine aser. So anything that you see when you’re doing laser or photobiomodulation is energy that’s not getting into the tissue. If it was getting absorbed into the tissue you wouldn’t see it because 100 percent is getting absorbed. So the first thing we look at is reflection. As it starts penetrating and transmitted through the surface, one of the other things you’ll have is refraction. So you think you’re pointing it there, but just like with x-ray it can scatter and go in a different direction. An important part of refraction is internal reflection. So you can see that that reflects at a 90 degree angle to the vector and what does it go back towards? Your target tissue. So we actually use some of the scatter when we’re looking at a photobiomodulation. Other things that we have on the right side of the screen there, you see diffraction and scatter. This is energy that becomes wasted or absorbed by other tissue other than your target tissue. And then we also have back scatter. So when these light waves or these photons get in, they just go all over the place and a small percentage of them go right to where you are you’re trying to target them. So we always have collateral influence on our tissue with photobiomodulation.

When you start looking at penetration, only light that is absorbed by the chromophore is actually utilized. So chromophore reflect or absorb certain wavelengths. What happens with sunlight, because a lot of people say “ What if I just stand outside in the sun? I’ll get tons of infrared, visible and UV.” When you have tons of light, especially non-coherent light, it scatters all over the place, and reflects all over the place. You don’t get a concentrated dose of any one wavelength. When focusing on transcranial photobiomodulation we also have to consider impedance by both hair and skin. Different colors of skin, darker skin doesn’t transmit light as well as lighter skin. We have to consider the lack of transmission through bone, meninges, blood, water and tissue. Different tissues also have different impedances.  As a matter of fact, when you look at grey matter vs. white matter they have totally different impedances for this photoenergy. When you start looking at some of your different devices, wavelength has the greatest impact on penetration, not power. Everybody’s always trying to buy a powerful laser. It’s not always the right thing depending on what you’re trying to accomplish. So your target tissue should be the determining factor on what type of light you’re purchasing or what type of illumination source.

But penetrating the skull.. does it really happen? So we’ve talked in the beginning about how we were going to come back Jagdeo. He used human cadaver heads with the skull intact as well as soft tissue to measure penetration of 830 nanometre light. He found that the penetration depended on the anatomical region they were trying to shine the light through. So different skull bones or cranial bones have different transmissions of light. So less than 1 percent in the temporal region, 2 percent of the frontal region, 11 almost 12 percent at the occipital region. It’s said specifically in this report that 633 nanometre wavelength had hardly any penetration through the skull at all. Does that mean that 633 or in that spectrum doesn’t work for photobiomodulation? No it doesn’t mean that. It just means that maybe your intended target is different than the actual target being treated and we’ll talk about that in just a moment. Tedord in 2015 also used the human cadaver heads, compared penetration between three different wavelengths 660, 808, and 940.  They found that 808 was the best and it could reach a depth of up to 40 to 50 millimeters into the brain tissue. When we started looking at the cerebral cortex, some layers of the cerebral cortex are only 10 millimeters thick. So you start seeing some significant penetration into the brain tissue if you’re using the right wavelength and if you consider the impedance from other tissues.

So we know that about 2 to 12 percent of energy delivered trans-cranially will actually even reach the cortex. A twenty-fold higher efficiency of light is delivered through the sphenoid, so instranassalar. So you’ll see some applications of intranasal light. Twenty times more gets through the sphenoid because the sphenoid is not as big. We know what lives behind that spheroid and how beautiful and important it is, right? This is where you have structures like your nigra. This is where you have structures like your brain stem and oculomotor nuclei and all those things that sit right behind there; the thalamus, the basal ganglia. All of these different beautiful areas that allow us to interact with the world and you have a great pathway right through your nose. We also understand that when considering a tissue impedance it will really help you understand how to pick your instrument and target your tissue.