PT 27 LEC: Lasers & Light

Laser

light amplification by stimulated emission of radiation

LED

light-emitting diode

LLLT

low-level laser therapy

Maser

microwave amplification by stimulated emission of radiation; precursor of laser

Chromophores

light-absorbing parts of a molecule that give it color

Monochromatic

light of single frequency, wavelength & color

Coherent

light in which all waves are in phase with each other

Ionizing radiation

any radiation capable of displacing electrons; from atoms, thereby producing ions

Non-ionizing radiation

low-energy radiation that does not have enough energy to remove an electron (negative particle) from an atom or molecule

examples of non-ionizing radiation

- lower frequency & used clinically

- ELF, SWD, MWD, IR, visible light, UV

examples of ionizing radiation

- not used clinically or only for imaging/destroying tissue

- x-rays & gamma rays

intensity of EM radiation

- proportional to energy output

- inverse square of distance from patient

- 90 degrees so angle of incidence is 1 (cosine)

Intensity of ANY type of EM radiation is greatest when?

- energy output is high

- radiation source is close to the patient

- beam is perpendicular to the surface of the skin

Thermal effects

heating superficial or deep tissues

Non-thermal effects

can cause changes at the cellular level by altering cell membrane function & permeability and intracellular organelle functions; promote binding of chemicals to cell membrane to trigger complex sequences of cellular reactions

wavelength of laser vs LED

Laser has a narrower, more concentrated wavelength; more coherent than regular light source

photodiodes

Can be laser diodes, LEDs, or SLDs

laser cavity

gain, feedback

SLD cavity

single-pass; gain in waveguide

LED cavity

no cavity, no gain, no feedbacl

laser diode

- monochromatic

- coherent

- directional

- high intensity light in one area

laser diode application

small, areas; deep focused area of tissue

laser diode power

class 3B; 5mW < x < 500 mW

LED diode

- polychromatic

- not coherent

- spreads widely

- low-output power; needs increased time

LED diode application

larger, superficial areas

LED diode power

- single: 1-5 mW or 30-40 mW

- numerous can be up to 200 mW

SLD diode

- almost monochromatic

- not coherent

- spreads a little

- less light than LED with shorter application time

SLD application

superficial or moderately deep areas; wider area than laser diodes

SLD power

- single: 5-25 mW

- numerous up to 90mW or more

wavelength

600-1300 nm red or IR; penetrates 2 to 4 cm into soft tissue

power

rate of energy flow; mW or W

power density

amount of power per unit area; mW/cm2

laser class 1

no hazard; <0.5 mW

laser class 1M

no hazard; large diameter or divergent beam

laser class 2

- safe for momentary viewing

- blink reflex

- <1 mW

laser class 3A

- laser pointers

- eye hazard if prolonged exposure

- <5 mW

laser class 3B

- most often used for therapy

- permanent eye injury with brief exposure

- <500 mW

laser class 4

- surgical & industrial cutting lasers

- can cause permanent eye injury and burns

- >500 mW

energy density

fluence; J/cm2

Low-energy densities

stimulatory

Too high energy density

suppressive or damaging

For acute & superficial

lower doses of energy density

For chronic & deep conditions

higher doses of energy density

effects of lasers & light

- promote ATP production

- promote collagen production

- modulate inflammation

- inhibit bacterial growth

- promote vasodilaton

- alter nerve conduction & regeneration

clinical indications for lasers & light

- tissue healing

- pain Mx for arthritis

- lymphedema

- neurological conditions

- pain Mx for MSK conditions

contraindications for lasers & light

Direct irradiation of the eyes

Malignancy

Within 4-6 months after radiotherapy

Over hemorrhaging regions

Over the thyroid & other endocrine glands

precautions for lasers & light

Low back or abdomen during pregnancy

Epiphyseal plates in children

Impaired sensation & mentation

Photophobia or abnormally high sensitivity to light

Pretreatment with one or more photosensitizers

Both clinician & patient should wear goggles, marked with intensity that they block

adverse effects of lasers & light

- irradiation to eyes

- burns

- transient tingling

- mild erythema

- skin rash

- inc pain or numbness

Near IR wavelength

700 to 1100 nm; penetrates more deeply up to 30-40 mm

Red wavelength

600 to 800 nm; more superficial up to 5-10 mm

UV A

- long-wave

- fluorescence

- reach earth

- deepest penetration

UV B

- middle-wave

- most skin erythema

- reach earth

- less deep penetration

UV C

- short-wave

- germicidal

- filtered out by ozone

- less deep penetration

factors affecting effects of UV

- wavelength

- intensity

- depth of penetration

- power

- angle of incidence

- distance

factors affecting depth of penetration of UV

- intensity

- wavelength & power

- size of area

- color of skin

- duration of tx

effects of UV radiation

- erythema production

- tanning

- epidermal hyperplasia

- vitamin D synthesis

- bactericidal effects

erythema production

Redness of the skin resulting from dilation of superficial blood vessels caused by the release of histamines

tanning

Delayed pigmentation of the skin

Result from increased production and upward migration of melanin granules & oxidation of premelanin in the skin

epidermal hyperplasia

Thickening of the superficial layer of the skin

Occurs ~72 hours after exposure to UV radiation

vitamin D synthesis

- happens most in first 2 years of life

- controls Ca+ absorption & exchange

- essential for bone formation

pathway for vitamin D synthesis

Skin absorbs vitamin D → liver & kidney convert vitamin D to calcium → stored in bone

Low doses of UV

immune response is suppressed

Higher doses of UV

immune response is activated

contraindications to UV

Irradiation of the eyes

Skin cancer

Pulmonary tuberculosis

Cardiac, kidney, or liver disease

SLE

Fever

precautions to UV

Photosensitizing medications & dietary supplements

Photosensitivity

Recent x-ray therapy

No dose of UV radiation should be repeated until effects of previous dose have disappeared

adverse effects of UV

- burning

- premature aging of skin

- actinic damage

- carcinogenesis

- eye damage

Actinic damage

causes skin to have a dry, coarse, leathery appearance with wrinkling & pigment abnormalities

application technique

DOSE-RESPONSE ASSESSMENT FIRST

The same lamp that will be used for treatment should be used to assess a person's UV sensitivity

Cover area with paper & expose each area with UV radiation after a certain amount of time (30-120 seconds)

Check which area has the least amount of change within 24 hours

Observe for the next 3 days

Suberythemal dose (SED)

no change in skin redness occurs in the 24 hours after UV exposure

Minimal erythemal dose (MED)

the smallest dose producing erythema within 8 hours after exposure that disappears within 24 hours after exposure.

First-degree erythema (E1)

definite redness with some mild desquamation appears within 6 hours after exposure and lasts for 1 to 3 days. This dose is generally about 2½ times the MED.

Second-degree erythema (E2)

intense erythema with edema, peeling, and pigmentation appears within 2 hours after treatment and is like a severe sunburn. This dose is generally about 5 times the MED.

Third-degree erythema (E3)

erythema with severe blistering, peeling, and exudation; generally about 10 times the MED

clinical indications for UV

- psoriasis

- wound healing

psoriasis tx using UV B

Initial dose: 50% of MED to E1 dose

With increases of 10% to 40% at each treatment depending on skin response

psoriasis tx using UV B duration

3-5x weekly

psoriasis tx using UV A

- applied after oral or topical psoralen

Initial dose: 40% to 70% of the MED

Increased by 10% to 40% each week to maintain response

psoriasis tx using UV A duration

2-3x/weekly

erythema in response to PUVA

usually appears 24 to 48 hours after exposure, peaks at 72 hours