Laser Therapy Terminology, Definitions
The following laser therapy (photomedicine) terms are provided in alphabetical order:
- Ablation: Removal of a segment of tissue using thermal energy; also termed vaporization or thermal decomposition
- Absorption: The transfer of radiant beam energy into the target tissue resulting in a change in the targeted tissue
- Active Medium: Any material within the optical cavity of a laser that, when energized, emits photons (radiant energy)
- Attenuation: The decline in the energy or power as a beam passes through an absorbing or scattering medium
- Average Power: An expression of the average power emission over time expressed in Watts; total amount of laser energy delivered divided by the duration of the laser exposure. For a pulsed laser, the product of the energy per pulse (Joule) and the pulse frequency (Hertz)
- Beam: Radiant electromagnetic rays that may be divergent, convergent, or collimated (parallel)
- Chopped Pulse: See Gated Pulse Mode
- Collimation: A collimated laser beam propagates in a homogeneous medium (e.g. in air) with a low beam divergence, so that the beam radius does not undergo significant changes within moderate propagation distances (the beam is the same size whether one inch or one foot or more away from the target
- Chromophore: A substance or molecule exhibiting selective light-absorbing qualities, often to specific wavelengths
- Class IV Laser: A surgical laser that requires safety personnel to monitor the nominal hazard zone, eye protection, and training. This class of laser poses significant risk of damage to eyes, any nontarget tissue, and can produce plume hazards
- Coagulation: An observed denaturation of soft tissue proteins that occurs at 60˚C.
- Contact Mode: The direct touching/contact of the laser delivery system to the target tissue
- Continuous Mode: A manner of applying the laser energy in an uninterrupted (non-pulsed) fashion, in which beam power density remains constant over time; also termed continuous wave, and abbreviated as ‘CW.’ Contrast with ‘Pulsed Mode’, or ‘Phased Mode’
- Energy: The ability to perform work, expressed in Joules. The product of power (Watts) and duration (seconds). One Watt second = one Joule; 1 J = 1 Watt x 1 second
- Energy Density: The measurement of energy per area of spot size, usually expressed as Joules per square centimeter; also known as fluence
- Fluence: See Energy Density
- Free-Running Pulse Mode: A laser operating mode where the emission is truly pulsed or phased and not gated. A light-emitting diode (LED) is used as the external energy source so that noticeably short pulse durations and peak powers of thousands of Watts are possible; a laser operated in continuous wave
- Gated Pulse Mode: A laser operating mode where the emission is a repetitive on-and-off cycle. The laser beam is actually emitted continuously, but a mechanical shutter or electronic control ‘chops’ the laser beam into pulses. This term is synonymous with chopped pulse mode, phase mode, or multi-phasic mode
- Intensity: See Power Density
- Irradiance: See Power Density
- Joule(J): See Energy(E) or Watt(W). A unit of energy or work equal to an exposure of one Watt of power for one second
- Low-Level Laser Therapy (LLLT): See Photobiomodulation (PBM); simply stated, a therapy laser device producing extraordinarily little power output, or therapeutic doses of extraordinary little energy. In most cases, LLLT is inadequate when attempting to stimulate tissue in an in-vivo environment; often used to describe devices that are super-luminous but not stimulated (i.e., not a laser)
- Non-contact Mode: A laser technique in which the delivery system is used without touching the target tissue; light radiation made be defocused or focused, depending on operator’s technique and procedure. NOTE: this technique is not as efficient as Contact-Mode
- Photobiomodulation (PBM): The use of stimulated light radiant energy to elicit biological responses in living cells, typically in a Petri dish in vitro; NOTE: radiation output power and volume can be adjusted to any level that is not harmful to the patient – PBM is used to describe laser therapy at extraordinarily low dosage, often inadequate to produce a tissue response in most situations.
- Photomedicine Therapy: Laser Therapy with knowledge
- Peak Power: The highest power achieved in each pulse
- Plume: The smoke produced for aerosolization of by-products due to laser tissue interaction; composed of particulate matter, cellular debris, carbonaceous and inorganic materials, and potentially biohazardous products
- Power(P): The amount of energy delivered per unit time, expressed in Watts (Joules per second). 1 Watt = 1 Joule x 1 Second
- Power Density: The measurement of power per area of spot size, usually expressed as Watts per square centimeter; also known as intensity, irradiance, and radiance
- Pulse Duration: A measurement of the total amount of time that a pulse is emitted; also known as pulse width
- Pulse Width: see Pulse Duration
- Pulsed Mode (or phased mode): Laser radiation that is emitted intermittently as short bursts or pulses of energy rather than in a continuous fashion. Contrast with ‘Continuous Mode.’
- Repetition Rate: Number of pulses per second, also known as pulse rate; usually expressed in Hertz (Hz) or pulses per second (PPS)
- Scattering: An interaction as the laser beam disperses in a non-uniform manner throughout targeted tissue
- Super-pulse (intense-pulsed light): A variation of gated pulsed mode in which the pulse durations are noticeably short, producing high peak power w/LOW-ENERGY transfer; also termed very short pulse
- Thermal Effect: Increased temperature in targeted tissues; for lasers, the absorption of radiant beam energy by tissue producing an increase in temperature (see First Law of thermodynamics)
- First Law of Thermodynamics The First Law of Thermodynamics as it applies to photomedicine states that heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy. This means that heat energy cannot be created or destroyed. It can, however, be transferred from one location to another and converted to and from other forms of energy. In Photomedicine, this means that when stimulated light energy is transferred from the laser to targeted tissues, some energy will be absorbed by the surrounding atmosphere. The corresponding loss of energy by the targeted tissues is converted to heat energy. For every Joule of light energy absorbed by the atmosphere, a thermal increase equal to the same will occur in targeted tissues ΔU=Q−W
- Thermal Relaxation Time: The amount of time required for temperature of the tissue that was raised by absorbed laser irradiation to cool down to one half of that value after the laser pulse
- Vaporization: The physical process of converting a solid or liquid into a gas; for laser procedures, it describes conversion of fluids in tissue into vapor
- Watt(W): See Power(P) and Joules(J)