In a series of experiments we investigated the extent to which coherence is preserved in tissue. We
investigated whether the decrease in coherence length is dependent upon the coherence length of
the illuminating light and possibly also if the light is polarized. We compared highly coherent light
from a HeNe laser, and less coherent light from a semiconductor laser, in scattering media such as
raw ground beef. We studied the laser speckle contrast after passing through 1 - 2 cm of meat.
The conclusion is that the laser light is still coherent enough to form laser speckles after passing
through a 2 cm thickness of meat.
Laser immunotherapy is a promising cancer treatment method that induces antitumor immunity and appears to be
effective both locally and systemically. In this context, an important factor is the overall state of the immune system,
both locally and systemically. The success of any immunotherapy treatment depends on the balance between the local
immunosuppressive forces induced by the tumor and the immune response of the host organism. Factors that influence
this balance include heat-shock proteins (for example HSP70), transforming growth factor β (TGF-β), tumor necrosis
factor α (TNF-α), interleukins, and more.
Laser phototherapy, which is based on non-thermal photobiological processes, has been shown to modulate the body's
own immune response, both locally and systemically, with a strong influence on for example cytokine production and
heat-shock protein synthesis. Laser phototherapy may therefore be an important component in the overall efficacy of
laser immunotherapy, and may tip the balance between the immunosuppressive and immunostimulatory forces in favor
The importance of coherence in phototherapy has been questioned over the last two decades, with the arguments largely being based on; 1) Lasers are just convenient machines that produce radiation, 2) It is the radiation that produces the photobiological and/or photophysical effects and therapeutic gains, not the machines, and 3) Radiation must be absorbed to produce a chemical or physical change, which results in a biological response.
Whilst these conclusions are, in essence, true, they neglect to account for the effects of laser speckle in vivo. In a proportion of individual laser speckles the intensity is higher than the surrounding environment, and the light is partially linearly polarized. This is important because the probability for a photon absorption event to occur largely depends on intensity and the photon absorption cross section of the molecule (which in turn is influenced by polarization and several other factors).
In superficial tissue, where the photon flux is high (less absorption has taken place), it is easy to reach necessary power density thresholds without the benefits of laser speckle. However, in deep tissue where the photon flux is extremely low, the increased probability of photon absorption from individual laser speckles increases the probability of reaching the necessary power density thresholds. Because of the non-coherent nature of radiation from light/IR emitting diodes speckle does not occur in the tissue with LED therapy, which may explain why head-to-head comparisons between lasers and LEDs in deep tissue seem to be in favor of lasers, and super-pulsed lasers in particular.
One of the most important factors in laser therapy is the dose. In the literature we find that the dose usually is defined as
the amount of energy applied to 1 cm2 of skin. In this presentation we will look closer on what we mean with "dose" and
what happens to the energy brought into the tissue. What is the dose 1 cm down in tissue? Should the unit instead be
joules per cm3, or, would it be better using joules per mm3. In a blood vessel under an illuminated square centimeter of
skin, we might perhaps use joules per ml. The light gives both local effects on cells and tissue and systemic effects -
which is the most dominating? The energy that we feed into the tissue will cause a three dimensional light intensity
distribution with different values in different points. In a static situation we will have the same dose distribution growing
linearly with exposure time. In the case of coherent light illumination, a three dimensional speckle field is created and
locally the energy density is varying a lot from point to point, causing field gradients. In some points of the illuminated
volume, the dose might be so high that retarding effects may occur while in other, the dose may be close to zero. The
situation is different for in vitro situation, for treatment of open wounds, for entering the light via a fiber in a syringe, for
using super pulsed light sources etc. For wavelengths with very low tissue penetration the situation is different.
A major argument among the opponents of laser therapy has been the absence of scientific documentation. This was a valid position in the 80s and partly in the 90s. But today, is this still a sound argument. There are more than 2,000 published studies in the field, including meeting abstracts and anecdotal reports. The vast majority of these papers reports positive effects of LLLT in vitro and in vivo. It is fair to argue that negative results are less prone to be published, but certainly more than 80 percent of the published studies are positive. In the field of dentistry, for instance, the positive percentage is well above 90 percent. The present literature study will look at the heart of the positive documentation: the positive double blind studies. It may come as a surprise to many critics that there are more than 100 positive double blind studies in the field laser therapy. This is a god base for a further understanding of the effects of low level laser in the clinical setting. We must, however, be as critical as the sceptics themselves in order to obtain a constructive dialogue between 'attorneys' and sceptics. In this paper, a critical review of 100 positive double blind studies will be presented.
The article aims to make a comparison, starting form a review of the available literature data, between the low level laser therapy and the light emitting diode therapy (LEDT) applied on human patients. The main conclusion is that too little research efforts have been devoted on the effects specific to LEDT. More than that, it is the authors opinion that every device claiming to heat has to prove the effectiveness in controlled studies.
In the literature, the given parameters are seldom well enough specified. Because of that, it is not possible to repeat a study - even if the intensities to repeat it, it will always be a new and different one. The dose, for instance, is usually given as a single value and this is not unambiguous. As a matter of fact, no matter how a treatment is carried out, the dose is never a single constant factor. Our intensities is to shed some light on the complexity of the dose distribution in treated tissue and to give some recommendations in the specification of the dose in future reports on laser treatment.