Slide sem ttulo

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Laser-tissue interaction
Renato Amaro Zângaro - PhD Vale do Paraíba
University São José dos Campos - SP - Brazil
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L A S E R
Light
Amplification by
Stimulated
E mission of
Radiation
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersLaser theory Basics laser light

• Coherence
• Temporal and spatial synchronization of wave
  movement

Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersLaser theory Basics laser light
Laser light
Intensity
Normal light
Wavelength

• Collimation Focusing on a point

Vale do Paraíba University São José dos Campos -
SP - Brazil
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Invisiblethermalradiation
Invisibleionizingradiation
Visible
30.0µ
0.750µ
0.400µ
0.001µ
3.0µ
Ultra-violetrays
Nearinfrared
Midinfrared
Farinfrared
X-rays
ArFexcimer 0.01µ
Argon0.488µ 0.514µ
NdYAG 1.06µ
ErYAG 2.94µ
CO2 10.6µ
Diode .980µ
HoYAG 2.12µ
Heliumneon 0.632µ
XeClexcimer0.308µ
Vale do Paraíba University São José dos Campos -
SP - Brazil
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Vale do Paraíba University São José dos Campos -
SP - Brazil
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The power is defined like the work dispended
by one force in one period of time used to
realise this work. A potência relaciona o
trabalho realizado por uma força, com o tempo
gasto para realizar esse trabalho. P power
(Watts) P t / Dt t energy (Joule) Dt
time (s)
Vale do Paraíba University São José dos Campos -
SP - Brazil
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Power Watts Power Density Watts/cm2 Power
(W) x Irradiation time (s) Energia (J) Energy
Density Joules/cm2
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersLaser operating modes

• Continuous Wave
• Continuous Wave (CW)
• Continuous, uninterrupted laser beam
• Very good power control

Power
Time
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersLaser operating modes

• Chopped mode
• Laser beam interrupted at regular intervals (50
  ON 50 OFF)
• Average power Maximum power / 2
• Advantage Better thermal control
• PULSE MODE

Power
Time
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersLaser operating modes

• Pulsed power output
• Very short treatment time (90 to 300µs)
• Laser beam pulsed gt higher peak (1000 to 20000
  W) and longer cooling time
• Peak Power Pulse energy / pulse width
• Pulse Energy x repetition rate average power

Power
Time
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersCharacteristic data - Terminology

• Pulse frequency (Hz) Number of pulses/second

• Pulse power (W) Power emitted per pulse

Pulse time
Pause time

• Pulse energy( J Ws) Energy emitted / pulse
  time

Pulse power P
Mean CWpower value

• Pulse time (s) Time during which power
  emission takes place

Pulse energy

• Pause time (s) Time between two phases

• CW value (W) Average power value in
  reference to 1 second.

Energy

• Energy (JWs) Power emitted in one sec.

Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersLaser-tissue interaction Beam trajectory
Effects on human tissue
Reflection
Dispersion
Absorption
Transmission
Vale do Paraíba University São José dos Campos -
SP - Brazil
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Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersAbsorption of laser radiation by
biological tissue
Hemoglobin
Water
Melanin
Protein
Hydroxyapatite
Dispersion
Vale do Paraíba University São José dos Campos -
SP - Brazil
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Power density W / cm2
Photodisruption
Photoablation
104
Vaporization
102
100
Nonlinearprocesses
Coagulation
10-2
Thermal effect
Photodynam.therapy
Photochem. reaction
Biostimulation
Exposure time s
Vale do Paraíba University São José dos Campos -
SP - Brazil
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Photochem. reaction 1 W/cm2 x 100 s 100
J/cm2 Thermal effect 103 W/cm2 x 10-1 s 100
J/cm2 Photoablation 108 W/cm2 x 10-6 s
100/Jcm2 Photodisruption 1011 W/cm2 x 10-9 s
100/Jcm2
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersInfluence of temperature and time on
irreversible tissue change
Temperature (C)
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SP - Brazil
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LasersInteractions between laser light and
tissue
37 60C
60 65C
90 100C
Several hundred C
Temperature
Warm-up
Desiccation
Carbonization
Vaporization Combustion
Denaturation of protein
Process
none
Whitish-gray coloration, increased dispersion
Constantdispersion
Black coloration, increased absorption
Formation of smoke and gas
Optical change
none
Decompaction
Shrinkage, dehydration
Strongmechanicaldamage
Ablation
Mechanicalchange
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersEffect of the laser on biological tissue
Laser beam
Vaporization gt 300 0C
Damage
Carbonization gt100 0C
reversible
irreversible
Coagulation gt 65 0C
Hyperemia 37-60 0C
Tissue
Vale do Paraíba University São José dos Campos -
SP - Brazil
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LasersVarious parameters influencing the soft
tissue effectin connection with laser radiation
? Coupling of laser beam to surface of
tissue (absorption of tissue, absorption
of vapor)
Combustion(temp. and flow conditions,absorption
coefficient,focusing properties)
Surrounding medium(air, water, blood)
? Transformation of tissue by irradiated
energy (warm-up, vaporization, ionization,
mechanical destruction)
? Ejection of material removed from tissue
(convection, thermal conduction,
condensation)
Vale do Paraíba University São José dos Campos -
SP - Brazil