Medical laser products for lymphedema

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Home Glossary

Laser Biophysics

This is by no means a comprehensive glossary of laser therapy related terms. However it contains the most commonly seen terms which the reader may come across in the literature.

Mechanism whereby incident light energy is taken up in the target material with a resultant  exchange of energy. Absorption may result in a photothermal reaction, photodestructive reaction, or photoactivative reaction.
A term coined by Professor Endre Mester in the late 1960's to describe the photoactivative effect of low incident levels of laser energy on cells' behaviour. In Mester's publications the reactions resulted in an increased activity, hence his use of biostimulation. In present applications, in addition to purely stimulative effects, retardarive effects are also seen (e.g. reduction of abnormal skin colour or reduction of hypertension), thus photobioactivation or, otphotobiomodulation are preferred terms.
Term describing a beam of light energy which is monochromatic, whose photons are in phase and which may be collimated.
Cold laser
Scientificaily and etymologically incorrect term previously used for 'laser therapy system'. (See also soft-laser and low power laser).
Generation or correction of a light beam to give minimal divergence, i.e. an almost parallel beam.
Contact technique
An LLLT technique whereby the laser probe or fibre is held in contact with the target tissue with or without pressure.
Continuous -wave
Laser output with constant uninterrupted or unmodulated power.
Diode laser
A laser system based on a laser semiconductor as its medium, such as the gallium aluminium arsenide (GaAlAs).
The spreading out of a beam in three dimensions as it leaves the output device, measured in degrees for two-dimensional angles, or steradians for the solid angle.
Electromagnetic spectrum
The wide spectrum of energy which has both an electric and magnetic component, ranging from extremely long wavelengths of kilometres (1000 meters) to ultrashort wavelengths of picometers (1 x 10-12m such as gamma rays). A means of showing schematically the relationship between devices which use some form of electromagnetic energy, such as X-ray systems lasers and microwave cookers.
The power of doing work or incident power of a laser measured over time in seconds expressed in joules (1.0 J =1.0 W x 1.0 sec).
Energy density
The incident energy of a laser per unit irradiated area or spot (expressed in J/cm). Please see power density below.
Exposure time
Time for which a laser beam is incident on target tissue measured in seconds (sec), sometimes also referred to as irradiation time.
Frequency modulated wave
A pattern imposed electronically or mechanically on a continuous wave, often erroneously confused with 'pulsing' and resulting in a series or train of square waveforms.
Grid therapy
A therapeutic method whereby the target area is divided up into equal squares, and the centre of each square or alternate square is irradiated or treated with the laser.
Treatment of a target with incident laser energy. Note that the target is irradiated not the laser.
An SI (Systeme International d'Unites) unit used to express energy.
Laser therapy
The accepted terminology used to describe any use the laser to give a clinical effect in target tissue.
Acronym for Low Level Laser Therapy) which is the term coined by Ohshiro and Calderhead and now well accepted to describe clinical therapeutic applications of a laser system.
Low power laser
Scientifically and etymologically incorrect term previously used for 'laser therapy system'.
Having one single colour or wavelength.
Nanometre (nm)
An accepted derivative of the meter (m) which is the SI (Systeme International d'Unircs) unit used to measure length. Laser wavelengths are usually described in nanometers ( 1 x 10-9 m).
The property of a laser beam to enter tissue and propagate through it for a determined distance, not to be confused with absorption.
Photoactivative reaction
A laser/tissue reaction in which the level of reaction in the target cells is well below their survival threshold, thereby activating them to a different level of activity than before they were irradiated. LLLT is based on photoactivative reactions.
A general term coined by Ohshiro and Calderhead to describe the generalized result of absorption of low incident levels of laser energy by cells.
An alternative and viable suggestion for photobioactivation.
Photodestructive reaction
A laser/tissue reaction in which the level of activity in the target cells is well above their survival threshold so that the cells are irreversibly altered and even destroyed. Laser surgery is based on photodestructive reactions.
A discrete packet or quantum of light energy.
Photothermal reaction
A reaction in target tissue whereby incident light energy is transferred into heat.

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