Overview of Picosecond Laser

Picosecond laser is a laser with an output pulse width at the picosecond level, mainly with three wavelengths of 755nm, 532nm and 1064nm. Due to its extremely short pulse width, it can instantly reach extremely high peak power, mainly through photoacoustic action (or photomechanical action), finely crushing tattoo dyes or melanin particles, making them easier to remove, and the accompanying inflammatory reaction is relatively mild. Compared with Q-switched laser, picosecond laser is more effective and has fewer adverse reactions in the treatment of tattoos and pigmentary diseases.

Through a honeycomb focusing lens or a holographic diffraction lens, picosecond laser can produce a uniform dot matrix beam. When it exceeds the absorption threshold of the target color base, it produces a laser-induced optical breakdown effect (LIOB) to form cavitation, while the surrounding tissue is not damaged and the inflammation is mild. LIOB can also stimulate the production of new collagen and elastic fibers in the dermis, so fractional picosecond laser has a significant effect in improving photoaging and acne scars, and has a short recovery period and low risk.

Application of picosecond laser

1. Clinical application of picosecond laser-pigmented diseases

01 Treatment effect

• Ideal effect: freckles, solar lentigo, nevus of Ota, etc.

• Effective, with a certain recurrence rate: coffee spots, freckle-like nevus, etc.

• Effect is still uncertain: pigmented hairy epidermal nevus, Reil's melanosis, etc.

02 Epidermal pigmentation diseases

For example, freckles, solar lentigo, coffee spots, etc. can be treated with 532nm Nd:YAG picosecond laser or 755nm alexandrite picosecond laser.

• Treatment parameters: should be set according to the patient's skin type and skin lesion color. Generally, mild white frost reaction is used as the treatment endpoint.

• In the treatment of freckles and solar lentigo, patients with Fitzpatrick I~IVV skin types, skin lesions with obvious contrast and clear boundaries with normal skin have better efficacy; while patients with lighter skin lesions and concurrent chloasma have a higher chance of post-inflammatory pigmentation than the former.

03 Epidermal pigmentation diseases

Such as pigmented piloepidermal nevus and Reil's melanosis, 532nm Nd:YAG picosecond laser, 755nm alexandrite picosecond laser, 1064nm Nd:YAG picosecond laser can be used as one of the treatment methods, but the efficacy is still uncertain.

04 Dermal pigmentation diseases

• Such as Ota nevus and acquired Ota nevus-like spots, 755nm alexandrite picosecond laser and 1064nm Nd:YAG picosecond laser can be used for treatment. The treatment interval is generally 3 to 6 months, and the treatment effect is ideal. Generally, it can be cured after several treatments.

• Children's Ota nevus generally require fewer treatments to achieve cure than adults. In recent years, studies have confirmed that the alexandrite picosecond laser has a higher skin clearance rate than the Q-switched alexandrite nanosecond laser in the treatment of nevus of Ota and acquired nevus of Ota-like spots, and the number of treatments required to achieve recovery is less.

• The incidence of post-inflammatory pigmentation after treatment of acquired nevus of Ota-like spots is high, and the treatment interval can be extended accordingly.

• For patchy blue nevus, some patients are effective in treatment, but the number of treatments is significantly increased. Occasionally, studies have reported that blue nevus can become malignant, and during treatment, attention should be paid to whether the skin lesions increase or ulcerate in a short period of time.

2. Clinical application of picosecond laser-skin rejuvenation

01 Overview

Skin aging refers to the skin aging phenomenon caused by natural or non-natural factors, including endogenous and exogenous aspects.

Clinical manifestations include dry and rough skin, loose and lack of elasticity, increased wrinkles, dull color, enlarged pores, spots and plaques, etc.

02 Treatment

Currently, 755nm and 1064nm picosecond lasers are mainly used for facial rejuvenation treatment.

Weiss et al. used the honeycomb mode of 755nm emerald picosecond laser to improve patients' wrinkles around the mouth and eyes. The study used 6mm spot, 10Hz, 750ps pulse width, and 0.71J/cm2 treatment volume to treat 40 patients with Fitzpatrick wrinkle scores of 4 to 7.

3. Clinical application of picosecond laser - pigmented diseases

01 Overview

Scars are tissues formed by the healing of human skin wounds. They can be divided into physiological scars and pathological scars. The latter can be divided into depressed scars, atrophic scars, hypertrophic scars and keloids.

02 Treatment

The literature reports on the use of different wavelength picosecond pulse width lasers to treat pathological scars are mainly for acne depressed scars. Bernstein et al. used 1064nm or 532nm Nd:YAG picosecond laser to treat facial acne depressed scars. 81% of the subjects believed that their condition improved, and the degree of improvement could reach 60%. The subject satisfaction was as high as 85%. No complications such as pigmentation were observed. There was no significant difference in the treatment effect between the two wavelengths of picosecond lasers.

4. Clinical application of picosecond laser - pigmented diseases

01 Overview

It is currently believed that picosecond laser can be used as an auxiliary means of treating chloasma, but not as a means of maintenance treatment. The complexity of the causes and triggers of chloasma also determines that picosecond laser is not suitable as a single treatment method.

In-depth research and discussion are still needed in terms of the selection of fractional and non-fractional modes of picosecond laser, the setting of optimal treatment parameters, the risk of recurrence, and the combined use with other treatment methods.

02 Treatment

Currently, 1064nm Nd:YAG picosecond laser and 755nm alexandrite picosecond laser have been used to treat chloasma. Clinically, non-fractional mode, fractional mode, and combination of the two are used, but the number of related research cases is limited.

Some studies have shown that:

• Nd:YAG picosecond laser is slightly more effective than 2% or 4% hydroquinone cream for external use on melasma.

• The efficacy of Alexandrite picosecond laser is roughly equivalent to that of triple cream (0.01% fluocinolone acetonide, 4% hydroquinone, 0.05% retinoic acid) and is better than the large-spot, low-energy Q-switched Nd:YAG nanosecond laser, which removes pigments faster and more significantly.

• In the comparison of fractional mode and non-fractional mode in the treatment of melasma, a study showed that the fractional mode of Alexandrite picosecond laser has a higher improvement rate and a lower recurrence rate than the non-fractional mode (flat cap mode); however, the difference in the number of patients in the two groups in this study is quite significant, and the research results need to be verified. Therefore, there is no clear conclusion on which of the two modes, non-lattice and lattice, is better, and further research is needed.

5. Clinical application of picosecond laser - tattoo

01 Overview

The level of evidence for the treatment of tattoos with picosecond laser is 1a, which is the highest level of evidence among all its indications and the gold standard for the treatment of tattoos.

02 Indications

Indications Tattoos can be divided into decorative tattoos, cosmetic tattoos and traumatic tattoos. Decorative tattoos can be divided into professional tattoos and amateur tattoos, and these tattoos can be removed with picosecond lasers.

Based on the theory of selective photothermal therapy, researchers usually use 755 nm and 1064 nm lasers to treat black, blue, and green tattoos. One or two treatments can remove about 75% of the tattoos. Use 532 nm picosecond lasers to treat purple, red, yellow, and orange tattoos. Usually, Q-switched lasers are difficult to remove yellow tattoos, but 532 nm picosecond laser treatment has a good effect, which may be related to the mechanical effect of picosecond lasers.

03 Precautions

For tattoos suspected of containing titanium monoxide or iron oxide dyes (self-color, tan, brown, or rust color in the tattoo), there is a risk of color blackening after pulsed laser treatment.

For patients with dark skin who are getting tattoos, lower energy density and (or longer laser wavelengths (e.g., 1064nm) should be used to reduce the risk of hypopigmentation.

Traumatic tattoos caused by gunpowder should be treated with caution using Q-switched or picosecond lasers, because laser shock can cause micro-explosions of implanted particles, resulting in depressions and atrophic scars.

Patients with active inflammation, infection, or other systemic diseases may experience slow postoperative healing and possible scarring. Patients with photosensitive skin diseases, pregnant women, and breastfeeding women should avoid picosecond laser treatment

Adverse reactions and prevention and treatment strategies

There are three types of pulse output modes of picosecond lasers, which have both commonalities and great differences in causing adverse reactions and their prevention and treatment. Small spot high-energy tissue blasting is mainly used for tattoo removal and the treatment of hyperpigmented skin diseases; large spot low-energy scanning irradiation is mainly used for improving skin color and texture; dot-matrix spot scanning irradiation is mainly used for superficial wrinkle improvement, pore reduction and other skin rejuvenation treatments, which can improve scars and treat capillary dilation.

The characteristics of picosecond lasers are that the photoacoustic effect is greater than the photothermal effect, and the tissue thermal damage is significantly less than that of Q-switched lasers. Therefore, adverse reactions rarely occur after surgery. However, due to its extremely high instantaneous power, erythema, purpura, edema, blisters, pigmentation and even scars may still occur locally after the above-mentioned various modes, especially after small spot high-energy blasting treatment, the above reactions are more likely to occur locally. The most common non-reaction is post-inflammatory pigmentation, which is most common after the treatment of melasma. Some patients are sensitive to pain during treatment.

The cause of adverse reactions is related to excessive energy and repeated exposure to too many spots on the same part. Preventive measures include: fully understanding the patient's skin condition, understanding the equipment condition, and choosing appropriate treatment parameters. For darker skin, the irradiation energy should be reduced, especially the number of irradiation spots. Take necessary repair measures after surgery and strictly protect against the sun.

For intraoperative pain, local anesthetics can be applied before surgery or a mask containing local anesthetics can be applied externally; for large-area blasting treatment, general anesthesia can be performed if necessary. Postoperative erythema and edema are generally mild, and cold spray and cold compress masks can be used. Ice compresses can be used if necessary. For individual small blisters, no special treatment is required. For larger blisters, the blister fluid should be extracted, the wound surface should be protected, and repair products such as epidermal growth factor should be applied externally. If there is scab, the scab should be protected as much as possible, and repair treatment should be continued after the scab falls off. For post-inflammatory pigmentation, repair, anti-inflammatory and depigmentation treatment can be given according to the degree of pigmentation.

Combined treatment

Picosecond laser has less damage due to its treatment , fast recovery, etc., it can be combined with other methods in the treatment of melasma, tattoos, photoaging, facial rejuvenation, acne scars, etc. Specific projects that can be combined include intense pulsed light, laser, radiofrequency, mesotherapy, microneedle, chemical peels, botulinum toxin injections, etc. The recommended treatment sequence is to do non-invasive or minimally invasive treatment first, and then invasive treatment. The treatment interval is usually 1 to 2 weeks depending on the specific project.

Picosecond laser combined with LED blue light can treat freckles, and combined with biophoton treatment can further enhance skin repair. The light modulation effect of biophotons combined with picosecond laser has a strong anti-inflammatory effect and can promote the production of collagen, so that the skin can be restored to health and vitality without being restricted by seasons. Even in summer, it will not cause photosensitivity reactions. Picosecond laser combined with CO₂ and fractional laser treatment of tattoos can significantly reduce the incidence of blisters caused by picosecond laser. Picosecond laser can also be combined with pulsed dye laser to treat melasma and skin photoaging. Combined with intense pulsed light for facial rejuvenation treatment, combined with mesotherapy for chloasma and facial rejuvenation, etc.

 | Original source: Journal of Practical Dermatology, Volume 15, Issue 2, April 2022 

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Foremed Legend

The core founding team of Suzhou Foremed Legend Medical Technology Co., Ltd. comes from well-known universities at home and abroad such as Peking University. Foremed Legend focuses on the design, development and application of high-end medical aesthetic optoelectronic equipment based on compliance and product strength, and is committed to becoming a leading company in the field of high-end medical aesthetic optoelectronic equipment, a provider of integrated intelligent solutions for diagnosis and treatment, and a pioneer of medical aesthetic data integration platform.

Through tackling a series of underlying key technologies, Foremed Legend has independently developed a number of high-end medical equipment such as picosecond laser therapy devices, long pulse laser therapy devices, intense pulsed light therapy devices, photoacoustic imaging skin detection devices and cold air therapy devices, and continues to deepen the research and development of core product technologies, using better technical solutions to benefit the vast number of beauty seekers.

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