Therapeutic Lasers Posted on 21 Aug 22:21 , 0 comments
The wavelengths of surgical lasers (Nd:YAG, CO2, erbium, diode) affect tissues not only through ablation, coagulation, and vaporization, but also through stimulation of natural healing processes in the cells. Other lasers, at much lower power than the surgical lasers, act more as “biostimulators.” This chapter discusses the most useful indications for these lasers, often referred to as “therapeutic lasers.” This therapy is generally called low-level laser therapy (LLLT), although the nomenclature is somewhat controversial. The instruments are generally referred to as “therapeutic lasers” or “cold lasers” versus the “surgical lasers.”
The therapeutic lasers are typically found in the visible red to near-visible infrared (IR) part of the electromagnetic spectrum, from 630 to 980 nanometers (nm). Output powers typically range from 50 to 500 milliwatts (mW) with either pulsed or continuous-wave (CW) emission. The names of therapeutic lasers, as with surgical lasers, are derived from the active medium, such as the gallium-aluminum-arsenide (GaAlAs) laser.
The simplest way to classify therapeutic lasers is by wavelength. Penetration depths vary; lasers in the red part of the spectrum are more superficially absorbed, whereas IR lasers penetrate as much as 3 to 5 cm, depending on wavelength and target tissue. There is an “optical window” at about 820 nm, which has the greatest depth of optical penetration. Mucosa is quite transparent to the wavelengths (does not absorb light well), skin and bone are fairly transparent, and muscles have the greatest absorption of light. Dosage at the target tissue must be calculated accordingly. Another factor in depth of penetration is the distance from the target tissue, which affects the spot size Irradiation out of contact versus irradiation in contact versus irradiation with pressure on the tissue all deliver different dosages to the tissue. Laser irradiation with tissue pressure causes a slight ischemia in the area, which reduces the hemoglobin concentration in the spot.