The modern skin cosmetic laser works according to the theory of selective photothermal action, so that laser light of a certain intensity and specific wavelength is specifically absorbed by the target color base (such as melanin, hemoglobin, water, etc.) in the tissue, thereby destroying the target; The control of the laser emission pulse concentrates the energy on the target tissue, reduces damage to the surroundings, and reduces adverse reactions. In recent years, picosecond lasers with extremely short pulse widths have been used in dermatology clinics, providing new means of treatment.
The effects of laser action on skin tissue are the basis of its treatment, including biostimulation, photochemical reactions, and photothermal effects. It has been found that when the pulse width reaches the picosecond level, it mainly manifests as a photomechanical effect rather than a pure photothermal effect. The photomechanical effect produced by the picosecond laser is that when the target chromophore absorbs the laser energy, if the energy density exceeds a certain threshold, a plasma effect occurs, and the instantaneous pressure wave causes the target tissue to blast and pulverize, forming gas. Holes and bubbles. Therefore, some researchers believe that compared with the Q-switched laser, the picosecond laser, which is mainly based on the photomechanical effect, can decompose the target tissue into finer particles, which is more conducive to macrophage phagocytosis. In addition, the picosecond laser disintegrates the target chromophore through a lower energy density, and its pulse width is much lower than the thermal relaxation time of the melanin body, thereby further limiting thermal damage to surrounding tissues, reducing the number of treatments, and reducing the number of defects. reaction.
2.Dermatological clinical application
At present, the picosecond laser used in dermatology mainly includes the emerald laser with a wavelength of 755 nm and the Nd:YAG laser with a wavelength of 532/1064 nm. It is mainly used for the treatment of tattoos, and has obvious advantages over the Q-switched laser. As the indications continue to expand, picosecond lasers are increasingly being used to treat pigmented skin diseases as well as other cosmetic dermatological related problems.
The Q-switched laser is capable of selectively acting on dye particles and is the primary device for removing tattoos. When it comes to color tattoos, clinicians need to choose different treatment wavelengths for specific color dye particles, but some colors do not have specific therapeutic wavelengths, such as yellow. In addition, when the red, orange, and yellow tattoos are removed, the preferred wavelength is 532 nm, but in the dark-skinned population, adverse reactions such as pigmentation and pigmentation are increased due to competitive absorption of epidermal melanin. On the other hand, laser-clearing tattoos often require multiple treatments. How to improve the efficacy and reduce the number of treatments is also of great significance. These issues have driven the development of laser technology. Some researchers have found that the effect of picosecond laser treatment on tattoos is better than that of nanosecond lasers. The former has lower adverse reactions at lower energy than the latter. In addition, a number of clinical observations show that the picosecond laser has better advantages in removing black, brown, and blue-black tattoos than the Q-switched laser, and has higher safety. For color tattoos, clinical studies have confirmed that picosecond lasers can more effectively remove yellow, green, purple and red tattoos.
2.2 Pigmented skin disease
Q-switched lasers are currently the primary treatment for a variety of benign pigmented skin diseases, but for patients with skin type III-V, there is still a risk of pigmentation and scarring. Existing studies have shown that picosecond lasers are safe and effective for the treatment of solar sunspots, coffee spots, and cyan brown cyanosis. For the treatment of Ota, some studies have found that compared with Q-switched laser, picosecond laser can reduce the number of treatments and reduce the occurrence of adverse reactions such as post-inflammatory hyperpigmentation. Another study found that patients who had received multiple Q-switched laser treatments but had poor efficacy had significant improvement after 2-3 treatments with picosecond lasers, and no adverse reactions occurred.
Photoaging of the skin is currently mainly improved by intense pulsed light, exfoliation or non-stripping lattice laser, chemical stripping, and the like. The 755nm picosecond laser can achieve non-stripping lattice mode through diffractive lens array (DLA). Through 120 diffractive lenses, evenly distributed energy can be focused on the center of each lens, and more than 90% of the area is exposed. 30% of the energy, and less than 10% of the region focus on 70% of the high energy, forming epidermal cavity, through the mechanical vibration wave and the role of cytokines, promote the regeneration of dermal collagen fibers. The Department of Laser Medicine, Dermatology Hospital of Chinese Academy of Medical Sciences has completed a clinical study on the efficacy and safety of picosecond laser DLA technology in the treatment of facial photoaging. Ten subjects were enrolled and received 4 treatments at intervals of 2 weeks. During the follow-up to 2 months after treatment, the average photoaging of the subjects decreased from 2.67 to 1.44. Compared with the improvement of pigmentation spots, the improvement of wrinkles was more obvious. The main adverse reaction was transient erythema. In addition, the 532/1064nm dual-wavelength picosecond laser can generate laser-induced breakdown lattices by holographic diffracting beam splitting, focusing on the epidermis (532nm) or the dermal papilla layer (1064nm), which has been shown to improve by this technique. Photoaging problems such as wrinkles, skin texture, and pigmentation spots.
2.4 Acne scars
Common treatments for acne scars include grinding, exfoliation, and non-stripping lattice lasers, radio frequency, and the like. With the development of technology and the daily work needs of people, the treatment methods with small trauma and quick recovery are gradually favored by patients. Some researchers have observed the safety and efficacy of picosecond laser DLA mode in the treatment of facial acne scars. Seventeen patients received a total of 6 treatments, with an interval of 1-2 months, followed by 1 month and 3 months after treatment, which improved 24% and 27.3%, respectively, and improved pigmentation and skin texture around the scar. Histopathology showed an increase in intradermal elastic fibers and collagen fibers. Other researchers have observed the efficacy and safety of dual-wavelength picosecond lasers for acne scars using holographic diffractometry. 19 patients were treated at 1064 nm and 8 were treated at 532 nm. Both were found to be safe and effective for acne scars. And the difference was not statistically significant.
In clinical work, we also found that picosecond lasers have a certain degree of improvement in chloasma, post-inflammatory hyperpigmentation, enlarged pores, post-operative scars, and poroke keratosis.
3.The side effects of picosecond laser
Mild and transient side effects usually occur after picosecond laser treatment, mainly characterized by erythema, mild edema, scarring, hyperpigmentation/reduction, and no serious adverse reactions.
4.The outlook of picosecond laser
At present, the application of picosecond laser in dermatology is still in its infancy, so we need more large-scale clinical research to confirm its efficacy and safety. On the other hand, studying more indications of picosecond laser helps to enrich Clinical protocols that provide patients and physicians with more treatment options.