Selective photothermolysis is a physical principle of action that is used in the application of laser therapy and is often used in the field of cosmetic dermatology (the study of skin diseases). A laser acts on tissue in the following ways:
- Selective photothermolysis – selective destruction of a target structure by heat generation without damaging the surrounding area.
- Vaporization/ablation – vaporization and detachment of tissue.
- Nonspecific coagulation – obliteration of tissue structures.
The aim of selective photothermolysis is the targeted treatment of different tissue structures mostly from an aesthetic point of view. This is due to the accessibility usually pigment disorders (eg hyperpigmentation – increased coloring of the skin) and vascular anomalies (vascular changes, eg spider veins) in the skin area.
Indications (areas of application)
- Spider veins – This refers to small reddish-bluish veins or varicose veins, which are usually the first sign of venous disease.
- Blue nevi
- Cafè-au-lait spots – milk coffee colored circumscribed spot in the epidermis.
- Granuloma teleangiectaticum – mushroom-shaped, pedunculated hemangioma located on the skin.
- Infantile hemangioma (blood sponge).
- Laser epilation (depilation by laser).
- Lentigines (moles)
- Nevus flammeus (port-wine stain)
- Naevus Ota (Mongolian spot)
- Spider nevi (nevus araneus) – star-shaped vascular neoplasm with central vascular nodule.
- Teleangiectasia – dilation of small superficial skin vessels that are permanent.
- Tattoos
Before treatment
Before starting treatment, an educational and counseling discussion should be held between the doctor and the patient. Content of the conversation should be the goals, expectations and the possibilities of treatment, as well as side effects and risks.Anticoagulants such as acetylsalicylic acid (ASA) should be discontinued as far as possible 14 days before treatment.
The procedure
As mentioned earlier, the goal of selective photothermolysis is the targeted thermal destruction of specific tissue structures without affecting the immediate, surrounding tissue. This effect is achieved by precisely matching the laser parameters with the effect on the target structure. The laser must meet the following requirements:
- Wavelength – The light from the laser must be optimally absorbed (taken up) by the so-called target chromophore so that sufficient heat is generated for its destruction. In the case of a blood vessel, the target chromophore is hemoglobin (red blood pigment), for example. The goal is to select a wavelength that is absorbed exclusively by hemoglobin and not by other chromophores such as water or melanin (skin pigment) and destroy them.
- Energy density – In order for the heat generation to be sufficient, the energy density, i.e. the intensity of the energy acting on a given area, must be adapted to the size of the target structure. The larger it is, the greater the energy density must be.
- Pulse duration – Pulse duration refers to the short period of time in which the target tissue is heated. It is of particular importance for the selectivity of the laser: the pulse duration must be below the so-called thermal relaxation time. This is the time required by the target tissue to conduct the generated heat back to the environment. Only if the heat conduction can not take place due to the short pulse duration, the tissue is selectively destroyed.
The laser light can thus penetrate the epidermis (top layer of skin) without damaging it when treating deeper structures. However, to counteract the heat generated, the skin must be cooled during treatment. To prevent pain, a local anesthetic can be applied. There are a variety of laser devices or light treatment methods that can cause selective photothermolysis:
- Flashlamp-pulsed dye laser; FPDL (wavelength: 585 nm; energy density: 10 joules/cm²; pulse duration: 450 μs) – A dye solution is excited to fluoresce (glow by reflection of colored light) by flashes of light. A specific wavelength of light can now be amplified and then used primarily to treat superficial vascular lesions.
- Ruby laser (wavelength: 694 nm; energy density: 4-12 joules/cm²; pulse duration: 20-40 ns) – The ruby laser is primarily used for the treatment of melanin-containing target structures, e.g. for the destruction of hair follicles (permanent hair removal/ laser epilation).
- Q-switched Nd:Yag laser (wavelength: 1064 nm and frequency-doubled at 532 nm; energy density: 400 mJ; pulse duration: nanosecond range) – This laser is used to treat melanin-containing structures as well as to remove tattoos.
- Alexandrite laser (wavelength: 755 nm; pulse duration: nanosecond range) – This laser is also used for tattoo removal and laser epilation.
- High-energy flash lamps (IPL – intensed pulsed light).
Benefits
Selective photothermolysis provides you with an effective method of removing troublesome skin lesions that is effective from an aesthetic point of view.
