Introduction to laser dermatology 3
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Transcript of Introduction to laser dermatology 3
Hints laser in dermatology
LASER
• Light• Ampilification• Stimulated • Emission• radiation
Light:
is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight.
Albert Einstein in 1905 in the Swiss patent office in Berne (Lucien Chavan).(Courtesy, The Albert Einstein Archives, The Jewish National and University Library, TheHebrew University of Jerusalem, Israel.)
1919Stimulated emission
Maser (Theodore Schawlow&Charles Townes)
Theodore maiman 1960
Ruby
Leon goldman
Father of laser medicine and surgery
Types of LasersGas Argon , CO2, Excimer laser
Dye Pulsed dye laser
Solid Ruby, Nd YAG and Er Yag
Semiconductor Diode laser
Laser light can be delivered in pulses, continuous wave, or pseudo-continuous wave forms.
Laser components
Optical cavity or the resonating tube: where the amplification of stimulated emission
occurs.
Laser medium: This could be solid, liquid, or gas.
Energy source: which pumps energy to the laser medium to produce
the population inversion.
Wave-guide:as fiber-optic cable.
LASER tissue interactionLASER tissue interaction
When the skin is exposed to LASER, it could be transmitted, or scattered by the skin structures, or absorbed by the chromophores.
Chromophores as oxyhemoglobin, melanin, tattoo ink or water.
Grothus-Draper photobiology law
Light should be absorbed to have a tissue effect if there is no light absorption there will be no effect.
Absorption is controlled by wavelength of laser and the chromophore.
1.Photothermal 2.Photochemical
3.Photomechanical
Theory of selective photothermolysis
In 1983 Drs. R.A. Anderson and J. A. Parrish proposed this theory where a chromophore can be selectively damaged with a light pulse of an appropriate wavelength and suitable pulse duration shorter than the thermal relaxation time of that chromophore.
• Thermal Relaxation Time (TRT)– Time taken for target to dissipate 50% of the energy
absorbed to surrounding tissue– Or time needed for cooling of a given light absorbing
site e’in skin– TRT is roughly equal to the square of the diameter of
target structure– TRT in sec.= ~ d² in mm– Second(S)=
• 10³ millisecons(ms)• 106 microsecond( µs)• 109 nanosecond (ns)• 1012 picosecond(ps)• 1015 femtosecond• 1018 attosecond
TRT
target size TRT
MelanosomeDermal capillary
0.5-1 µm0.1 mm
0.25-1 µs10 ms
1. Exposure time = or < TRT of target lead to selective heating of target without damaging surrounding tissue
2. Exposure time > TRT of target lead to heat diffusion to surrounding tissue
1.2.
Thermal relaxation time
It is time of an object to loose heat energy to the surroundings through thermal diffusion (The time to
disperse the heat absorbed during a laser pulse.)
Pulse duration
It is the time the laser is in contact with the target cell (Chromophore).
Laser parameters
Energy fluence (Energy density) Joules/cm2
= energy delivered to a given unit area for each single pulse.
Irradiance (Power density) (Watt/cm2) = rate of energy delivery = intensity of the energy delivered.
Efficacy of laser depends upon:
The target chromophore Wavelength Pulse duration Energy density