Transcript PET 4995: Therapeutic Modalities

Low-Power Lasers
Jennifer L. Doherty-Restrepo, MS, ATC, LAT
Entry-Level Master Athletic Training Education Program
PET 4995: Therapeutic Modalities
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Light
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Amplification of
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Stimulated
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Emission of
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Radiation
Physics of the Laser
• Light energy transmitted through space
as waves that contain tiny "energy
packets" called photons
• Each photon contains a definite amount
of energy depending on its wavelength
(color)
Physics of the Laser
• If a photon collides with an electron of
an atom, it causes the atom to be in an
excited state
• Atom stays in excited state only
momentarily
• Atom quickly releases an identical
photon to return to its ground state
– Process is called spontaneous emission
Stimulated Emissions
• A photon released from an excited atom
will stimulate another atom to return to
its ground state
• For this to occur, an environment must
exist with unlimited excited atoms
• This is termed population inversion
Stimulated Emissions
• Population inversion occurs when there are
more atoms in an excited state than in a
ground state
– May be stimulated by an external power source
• Photons may be contained in a chamber
Stimulated Emissions
• Mirrors are placed at either end of the chamber
• Photons are reflected within chamber, which
amplifies the light and stimulates the emission
of other photons from excited atoms
Stimulated Emissions
• Eventually so many photons are stimulated
that the chamber cannot contain the energy
• Photons of a particular wavelength are
ejected through the semipermeable mirror
producing amplified light through stimulated
emissions
Types of Lasers
• Classified according to the nature of
material between two reflecting surfaces
– Crystal lasers
• Synthetic ruby (aluminum oxide and chromium)
• Neodymium, Yttrium, Aluminum, Garnet
– Gas lasers (under investigation in the U.S.)
• Helium neon (HeNe)
• Argon
• Carbon dioxide (CO2)
Types of Lasers
• Classified according to the nature of
material between two reflecting surfaces
– Semiconductor or Diode lasers (under
investigation in the U.S.)
• Gallium-arsenide (GaAs)
– Liquid lasers
• Organic dyes = lasing medium
– Chemical lasers
• Used for military purposes
Laser Classification
• Laser equipment is grouped into four
FDA classes with simplified and welldifferentiated safety procedures for
each
• Low power lasers used in treating
sports injuries are categorized as Class
I and II laser devices
Laser Classification
• High power lasers = "hot" lasers
– Thermal effects
– Surgical cutting and coagulation,
ophthalmological, dermatological,
oncological, and vascular specialties
• Low power lasers = “cold” lasers
– Cause photo-chemical rather than thermal
effects
Laser Generators
• Power Supply
• Lasing Medium
– Gas, solid or liquid
• Pumping Device
– Creates population inversion
• Optical Resonant Cavity
– Chamber where population inversion occurs
– Contains reflecting surfaces
Helium-Neon Lasers
• Gas lasers
• Deliver a red beam
– Wavelength = 632.8nm
• Laser delivered in a continuous wave
• Direct penetration of 2 to 5 mm
• Indirect penetration of 10 to 15 mm
Gallium-Arsenide Lasers
• Semiconductor lasers
• Invisible beam
– Wavelength = 904nm
• Direct penetration of 1 to 2 cm
• Indirect penetration to 5 cm
Techniques of Application
• Laser energy emitted from hand held
remote applicator
• Tip should be in light contact with the
skin
• Applicator should be directed
perpendicularly to the skin
Dosage
• Dosage reported in Joules per square
centimeter (J/cm2)
• One Joule is equal to one watt per
second
• Dosage is dependent on
– Output of the laser in mWatts
– Time of exposure in seconds
– Beam surface area of laser in cm2
Dosage
• Dosage should be accurately calculated
to standardize treatments and to
establish treatment guidelines for
specific injuries.
• Intention is to deliver a specific number
of J/cm2 or mJ/cm2
Pulsed vs. Continuous Laser
• With pulsed laser treatment, times may be
exceedingly long to deliver same energy
density as compared to a continuous wave
laser
Depth of Penetration
• Depends on type of laser
energy delivered
• “Direct effect”
– Response that occurs from
absorption of laser energy
• “Indirect effect”
– Lessened response that
occurs deeper in the tissues
Depth of Penetration
• HeNe lasers
– Direct effect = 2-5 mm
– Indirect effect = 8-10 mm
• GaAs lasers (longer
wavelength)
– Direct effect = 1-2 cm
– Indirect effect = 5 cm
– Better for treating deeper
tissues
Clinical Applications
Wound healing
Immunological responses
Inflammation
Scar tissue
Pain
Bone healing
Indications for Laser
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Facilitate wound healing
Pain reduction
Increasing the tensile strength of a scar
Decreasing scar tissue
Decreasing inflammation
Bone healing and fracture consolidation
Contraindications for Laser
• Cancerous tumors
• Directly over eyes
• Pregnancy