EDUCATION & TRAINING
3D Photon Distribution inside the Tissue
Photobiomodulation phenomena induced by Low Level (Cold) Lasers and LEDs and resulting therapeutic effects strongly depend on their optical parameters: power (mW), fluence (dose, J/cm2), fluence rate (irradiance, intensity, mW/cm2) and others. Current approaches to dosimetry of photobiomodualtion phenomena induced by Low Level (Cold) Lasers and LEDs in basic and clinical studies centered primarily around incident optical parameters and in particular on fluence (dose, J/cm2). Other optical parameters are often neglected and not taken into consideration.
However, it is important to understand that cellular response to Low Level (Cold) Lasers and LEDs in reality depends on what optical parameters cells actually "see" within the tissue. As a result of photon scattering, absorption, reflectance, the incident photon fluence (dose, J/cm2) on the skin surface and the photon fluence inside the tissue are very different. Photon fluence values differ by orders of magnitude depending on the depth of the tissue (epidermis, dermis and other layers). Because of significant photon absorption in epidermis, there is significant decline of fluence within epidermis, and dermis.
Cells at various tissue layers "see" substantially different pictures of photon emission. The "lion share" of incident emission from Low Level (Cold) Lasers and LEDs is actually absorbed by cells of epidermis (melanocytes, keratinocytes, Langerhans, and Mekkel cells) with a smaller portion of emission left for dermis cells (fibroblasts, macrophages, mast cells, endothelial cells, Schwann cells, and others). Only a very small portion (tale) of incident emission is left for the cells of underlying skin tissues.
Because of this difference in the dose received by various tissue layers in many cases, there could be a mismatch between the response to photon emission between the upper tissue cell layers and lower tissue layers. This mismatch is usually resulting in reducing of therapeutic efficacy. Excessive increase of power for CW lasers or peak power of laser pulse may also result in photothermal (not photochemical) interactions of photons with the tissue which also may result in diminished therapeutic efficacy, if any.
Cells of epidermis and dermis individually and collectively react to photon emission with changes in their metabolism, proliferation, secretion, and motility. Photon emission can substantially modulate release of various cytokines, growth factors, prostaglandins, etc., that regulate tissue response to photon emission. Scientific studies suggest that response of skin cells to photon emission may be one of the most important factors that define tissue response to incident photon emission.
For example, it is known that photons can modulate release of pro-inflammatory (IL-6, IL-8, IL-1alpha) and anti-inflammatory (IL-10) cytokines by keratinocytes in a dose-dependent manner. Therefore, it is very important to know what photon parameters these cells receive.
It is very difficult and expensive to measure photon distributions within the tissue. Below are presented 3D photon distributions for single and multiple optical sources used in IMI Healing Technologies. These 3D photon distributions were computed and controlled using Monte-Carlo and Neural-Network software specially designed for specific configuration of photon sources.
These calculations allow determining the ranges of fluences "seen" by various cells at different depths, the fluence space gradients, and distributions within the tissue. Furthermore, these calculations help to compare cell culture dosimetry with animal and clinical studies dosimetry and envision possible tissue responses to particular incident photon irradiation patterns. Knowledge of 3D light distribution helped us to filter out the ranges of optical parameters not useful for clinical applications. Also, from the analysis of 3D dosimetry, the reasons of failed or low efficacy basic and clinical studies became transparent. 3D photon dosimetry was a basis for the development of LEP2000T technology. Consistent high efficacy of LEP2000T is directly related to the understanding of 3D dosimetry.
As a result of photon scattering, reflections, transmission and so on, the photons fluence which is approaching skin surface and the photon fluence (dose J/cm2) inside the tissue are very different. Photons fluence values will be different for fixed incoming fluences at different depth of the skin (epidermis, dermis and so on) by orders of magnitude.
Below are presented 3D photon distribution for single and multiple optical sources used in IMI Healing Technologies. These 3D photon distributions are computed and controlled using Monte-Carlo and Neural-Network software specially designed for specific configuration of photon sources.
1. Optical head with a single photon source
Relative position of the single photon source and the skin, r is the distance from the photon source, d is the skin depth.
Fig. 1a and 2a fluence distributions from parallel and unparallel beams on the skin surface
Fig. 1a and 2a represent one quadrant of the skin surface.
The abscissa shows the distance on the skin surface from the center of the beam and below the abscissa is shown the color scale for fluence (red - 1.00, dark blue - 0.001).
Fig. 1b and 2 b represent 3D distributions of photons in the tissue; and below the figures is shown the color scale of relative fluence values.
Fig. 3 shows integral fluence in the centre of the beam as a function of skin depth. It is interesting to mention that the maximum fluence is not on the surface of the skin.
2. Optical heads with 7 photon sources
Figures 4-7 show the photon distributions from an LED matrix with 7 photon sources for different tissue depths 0, 100, 220 and 400 microns.
The horizontal line below the pictures reflects the color scale for fluence.
3. Optical heads with 22 photon sources
Fluences at the depth 0.2 mm under the skin surface are presented for 22 optical sources as a function of selected parameters for Monte-Carlo and Neural Network presentation.
Fig. 8 -13 show changes of 3D photon distribution controllable by the microprocressor. h is a parameter of Monte-Carlo and Neural Network calculations.