2)
Basics of laser application
The intended effect of the laser application is based on the interaction of the
radiation with the tissue components. The laser radiation is absorbed,
scattered or reflected by the tissue. Air has only little influence on the C-LAS
radiation and therefore the interaction between air and the C-LAS radiation
can be neglected. Reflection plays a major role with metal, glass and other re-
flecting surfaces.
When we apply the C-LAS radiation to tissue the reflection is not dominant.
Nevertheless it is not zero! When the radiation is scattered in the tissue, it
does not influence the absorption. Absorption is mainly responsible for the ef-
ficiency of the laser radiation. Absorption means that the C-LAS laser radiation
is converted mainly into heat, which causes the desired effects (coagulation/
vaporisation).
With low energy density (big laser spot or low power) the heat which is
achieved in the tissue can cause heating of the tissue. The smaller the spot
size is, or the higher the power is set, the warmer it gets. There is a limit,
when the tissue does no longer tolerate the heating, tissue proteins denatur-
ate, coagulation occurs. The next limit is achieved when tissue water (intra-
and extracellular water) suddenly evaporates (> 300°C). Tissue is fragmented
and destroyed. Cutting/ evaporation is achieved.
Temperature effect
Temperature
Effect
> 40° C
45° – 65° C
> 65° C
> 100° C
> 150° C
> 300° C
some 1000° C
enzyme induction, membrane disaggregation, edema
tissue damage, reversible or irreversible, dependent on
the irradiation time
coagulation
dehydration
carbonisation
vaporization, ablation (removal of tissue)
ionisation, immediate burn (shock wave formation)
Tissue cutting always needs high energy densities (high power or small spot
size). At the cutting edges, respectively beside the evaporation zones the tis-
sue is always affected by the heat (coagulation). The positive effect and ad-
vantage of the laser use is that this can stop bleeding from cut vessels (hae-
mostasis). The negative effect is caused directly at the cutting edge where
more than 150°C occur. There is a development of carbonization, created by
burned carbon, which is toxic and prolongs the healing of the wound.
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