LASER
Laser
Acronym: Light Amplification of the Stimulated
Emission of Radiation.
Einstein – postulated the theory that developed Laser
in 1916.
Townes and Schawlow (1955) – worked with MASERs
i.e. Microwave Amplification of Stimulated Emission of Radiation.
In 1965 the term laser was substituted for optical
masers after the work of Theodore Maiman in 1960.
Important Terminology
LASER
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PHYSICS:
A laser generates a beam of EM radiation within
the IR; visible; or UV range
Wavelengths between 100nm – 1mm
Difference between laser and other light is that
MONOCHROMATIC
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All photons have a single wavelength & a single
color
Advantage is that it can target specific wavelength
dependent chromophores
Laser produces amplified light through stimulated emissions
LASER - PHYSICS
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Laser light is produced when an electron of an
active medium undergoes a stimulated quantum
leap from a higher to a lower erg state, causing the emission of photons.
The frequency of the laser light is characteristic of
LASER - PHYSICS
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The frequency of the laser, as well as the tissue type
being irradiated, determines the depth of penetration
The higher the frequency the more superf the
penetration.
The HeNe & the GaAs lasers are the 2 principal
PHYSICS
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Helium Neon Laser:
It is a gas laser producing red light in the 633nm
waveband.
The power typically runs from 1.0-10.0mW
If fibre-optics are used, the laser output can over
a number of working hours, rough handling. It
PHYSICS
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Gallium Arsenide Lasers:
This laser utilizes a diode to produce an invisible
infrared light(904nm).
The 904nm laser is produced in a pulsed mode
because of the heat produced at the junction of the diode chips.
It produces a power of 2W, but because it is pulsed,
PHYSICS
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The body consists of 70% water & 30% organic
molecules.
Water mol = transparent to LLL
The absorption characteristics of the organic mol
PHYSICS
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Chromophore specificity for LLL:
Is the optical window (600-1200nm) that allows
PHYSICS
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The respiratory chain enzymes (ie cytochromes)
within the mitochondria & other chromophones
PHYSICS
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A short wavelength (400-700nm) is highly
pigment-specific with its photons absorbed by melanin; hemoglobin; & myoglobin
Longer wavelengths are absorbed by other organic
PHYSICS
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Photo-bio-modulation (PBM):
Is the manifestation of photochemical reactions as opposed to photo thermal reactions
PBM implies:
1. Photo-bio-stimulation
DOSAGE
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Laser can be expressed in terms of power(W);
power density(W/cm²); energy density(J/cm²).
Power density(w/cm²) = power(W)
area of irrad(cm²)
Energy density(J/cm²) = power(W)x time(s)
DOSAGE
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The GaAs lasers are pulsed and the pulse rate is
variable. The pulse modes drastically reduces the amount of energy emitted, eg:
DOSAGE
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Dosage should be accurately calculated to
standarise Rx to establish guidelines for specific injuries. After setting the pulse rate, which
determines the average power (Pav), the Rx time can be calculated.
Ta = (E/Pav)x A
DOSAGE
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Eg: to deliver 1 J/cm² with a 0.004mW average
power GaAs laser with a 0,07cm² beam area: Ta = (1 J/cm²/0.004 mW)x 0.07cm²
= 17.5 sec
PHYSICS
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Cold Lasers with an erg density <35J/cm² have been
studied and recommended for the use in rehab for its biostimulative and healing effect.
In general, low I are recommended for acute
conditions (1-5 J/cm²) and high I for chronic, up to 40J/cm².
Some studies have found that the effects are more
DOSAGE
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Although higher output is recommended to Rx
times over stimulation should be avoided.
Therefore laser should be administered of once
daily per Rx area.
If the effects reaches a plateau, a break in Rx of 1
EFFECTS OF COLD LASERS
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1. Cellular effects:
ATP production
Stim of macrophages
Stim of fibroblasts to collagen production
EFFECTS (Clinical)
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4. Wound healing 5. Fracture healing
6. Musculoskeletal disorders 7. Pain management
PHYSIOLOGICAL EFFECTS
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Cellular Effects:
In vitro studies have demonstrated short-term
activation of the electron transport chain; ATP
synthesis; cellular pH; initiate reaction on the
PHYSIOLOGICAL EFFECTS
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Nerve Conducton & regeneration:
Conflicting results were found in different studies on
PHYSIOLOGICAL EFFECTS
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Vasodilation:
It has been proposed that laser causes vasodilation,
THERAPEUTIC EFFECTS
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Wound Healing:
Ten studies reported acceleration of wound healing,
tensile strength and collagen content of the
wound.
Significanly greater tensile strength most commonly
THERAPEUTIC EFFECTS
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Also, hypertrophic scars did not occur in that period
Doses from 1.1 – 2.2J/cm², elicited positive results
THERAPEUTIC EFFECTS
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Six studies have failed to show the above
mentioned effects.
Systematic, well documented clinical trails are still
THERAPEUTIC EFFECTS
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Scar tissue:
Macroscopic examination of healed wounds was
subjectively described after laser radiation in most studies.
In general, the wounds had less scar tissue and a
THERAPEUTIC EFFECTS
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Fracture Healing:
Studies on bone healing yielded mixed results.
Some showing acceleration of # healing, others delayed ossificaton.
A study conducted on animals showed a faster bone
THERAPEUTIC EFFECTS
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Musculoskeletal Disorders:
A recent meta-analysis showed that laser was more
effective than placebo for the Rx of musculoskeletal disorders.
Studies have focused on arthritic conditions and soft
tissue conditions.
On Rh arthritis, they reported handgrip strength
THEARPEUTIC EFFECTS
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Contrasting results were found in other studies
Different outcomes may be due to different doses
used and different methods of application
Clear documentation on the type of laser used,
THERAPEUTIC EFFECTS
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Pain Management:
Mixed results on pain management of disorders such
as arthritis; LBP; neck pain; trigger points and chronic pain were reported
Snyder-Mackler & Bork investigated the effect on
pain by irradiating the superficial radial nerve with a HeNe laser which showed a pos decrease in
THERAPEUTIC EFFECTS
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Pos results have also been demonstrated in a
double blind study to investigate the effect of laser on chronic pain with a HeNe laser.
Lymph Oedema
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Studies have shown that LLL (IR) helps to reduce
post-mastectomy lymph oedema.
Dose: 1.5J/cm 2; to a total area of 3cm2 x 3 times
THERAPEUTIC EFFECTS
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CONTRAINDICATIONS
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Direct irradiation of the eyes
Within 6-12 months after radiotherapy
Haemorrhaging regions
APPLICATION
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Scanning technique
