Overview of Picosecond Laser:

Picosecond laser refers to a laser with an output pulse width at the picosecond level, mainly including 755nm, 532nm and 1064nm 3 working wavelengths. Due to the extremely short pulse width, the picosecond laser can achieve extremely high peak power in an instant, thereby producing a photoacoustic effect (or photomechanical effect) on the target color base, crushing the tattoo dye particles or melanin particles into smaller particles, making them easier to be cleared by chromatin cells such as macrophages, and the inflammatory response is lighter. Therefore, picosecond laser is more effective and has less adverse reactions than Q-switched laser in the treatment of tattoos and most pigmentation diseases. In addition, through honeycomb focusing lens or holographic diffraction lens, picosecond laser can be focused into uniformly spaced dot beams. Since each micro beam has extremely high peak power, when the photolysis threshold of the target color base (melanin or hemoglobin) is exceeded, the target color base absorbs energy nonlinearly to produce photolysis effect, forming plasma. The plasma continues to absorb laser energy efficiently and expands continuously, and finally produces a burst phenomenon in the epidermis or dermis, leading to the formation of cavitation bubbles, which is laser-induced optical breakdown (LIOB). There is no damage to the tissues around LIOB, and the inflammatory reaction is also very mild. With the occurrence of LIOB, new collagen and elastic fibers may appear in the dermis. The LIOB effect enables the dotted picosecond laser to improve photoaging and acne pitting scars. Compared with ablative dotted laser and near-infrared non-ablative dotted laser, it has less adverse reactions and almost no downtime.

Indications, parameter selection and contraindications:

1. Pigmented diseases

Picosecond laser can be used to treat a variety of epidermal and dermal pigmented diseases. It has an ideal effect on freckles, solar lentigo, nevus of Ota and other diseases; it is effective for diseases such as coffee spots and freckles, but there is still a certain recurrence rate; the effect on pigmented hair epidermal nevus and Reil's melanosis is still uncertain, and it can be used as one of the means of improvement.
Epidermal pigmented diseases such as freckles, solar lentigo, coffee spots, etc. can be treated with 532nm Nd:YAG picosecond laser or 755nm alexandrite picosecond laser. The treatment parameters should be set according to the patient's skin type and skin lesion color, and generally a mild white frost reaction is used as the treatment endpoint.

In the treatment of freckles and solar lentigo, patients with Fitzpatrick type III-IV skin, skin lesions with obvious contrast and clear boundaries with normal skin have better effects; while patients with lighter skin lesions and concurrent chloasma have a higher chance of post-inflammatory pigmentation than the former. For the treatment of coffee spots, freckles, etc., some patients can have obvious effects, but the recurrence rate is high.

For epidermal pigmentation diseases such as pigmented piloepidermal nevus and Reil's melanosis, 532nm Nd:YAG picosecond laser, 755nm alexandrite picosecond laser, and 1064nm Nd:YAG picosecond laser can be used as one of the treatment methods.

For dermal pigmentation diseases such as nevus of Ota and acquired nevus of Ota-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, recovery can be achieved after several treatments. The number of treatments required to achieve recovery for children with Ota nevus is generally less than that for adults. In recent years, studies have confirmed that the alexandrite picosecond laser treatment of Ota nevus and acquired Ota nevus-like spots has a higher skin lesion clearance rate than Q-switched alexandrite nanosecond laser single-time treatment, and the number of treatments required to achieve recovery is less. The incidence of post-inflammatory pigmentation after treatment of acquired Ota nevus-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 have increased or ulcerated in a short period of time.

2. Skin rejuvenation

Skin aging refers to the skin aging phenomenon caused by natural or non-natural factors, including endogenous and exogenous aspects. Skin aging is often accompanied by a series of pathological and physiological changes, such as thinning of the epidermis, reduction of dermal collagen, decreased tightness of the epidermis, atrophy or reduction of dermal papillae, capillaries and skin appendages. Clinical manifestations include dry and rough skin, loose and lack of elasticity, increased wrinkles, dull color, enlarged pores, spots and plaques, etc.
Currently, 755nm and 1064nm picosecond lasers are mainly used for facial rejuvenation treatment.

Weiss et al. used 755nm emerald picosecond laser honeycomb mode 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. Six of the subjects underwent skin biopsy observation: 1 month after treatment, the basal layer keratinocytes were slightly vacuolated, the volume and density of dermal collagen increased, and the elastin fibers increased with mild inflammatory cell infiltration; 3 months after treatment, there was no inflammatory cell infiltration, the collagen structure continued to maintain a trend of increasing density, and the elastic fibers increased significantly; 6 months after treatment, histology showed that the dermal collagen increased significantly, especially in the middle and lower dermis, and the elastic fibers in the upper dermis increased significantly. Two other clinical studies using picosecond lasers to improve wrinkles showed that picosecond lasers have a positive therapeutic effect on improving wrinkles and achieving facial rejuvenation.

3. Scars

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. The application of photoelectric technology to treat pathological scars has always been one of the important clinical practices of scar treatment, and has achieved satisfactory results. Literature reports on the use of different wavelength picosecond pulse width lasers to treat pathological scars are mainly for acne depressed scars.

Bemstein et al. used 1064nm or 532nm Nd:YAG picosecond lasers to treat facial acne depressed scars. 81% of the subjects believed that their condition had improved, and the degree of improvement could reach 60%. The subject satisfaction was as high as 85%. No complications such as pigmentation were observed, and there was no significant difference in the treatment effect between the two wavelengths of picosecond lasers.

4. Chloasma

Currently, 1064nm Nd:YAG picosecond laser and 755nm alexandrite picosecond laser have been used to treat chloasma. Clinically, some use non-fractional mode, some use fractional mode, and some use a combination of the two, but the number of related research cases is limited. Some studies have shown that the efficacy of Nd:YAG picosecond laser on chloasma is slightly better than 2% or 4% hydroquinone cream for external use, while 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 better than 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 alexandrite picosecond laser fractional mode had 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 was significant, and the research results need to be verified. Therefore, there is no clear conclusion as to which of the two modes, non-fractional and fractional, is better, and further research is needed.

There is no uniform treatment parameter and course of treatment for picosecond laser in the treatment of melasma. Most treatments are 3 to 6 times, with intervals of 1 to 4 weeks, with 4 weeks being the most common. Like the large spot and low energy Q-switched Nd:YAG nanosecond laser, the energy of picosecond laser in the treatment of melasma should be low, and generally mild erythema, with or without edema, and no purpura are the treatment endpoints.

Currently, the quality of clinical studies on the treatment of chloasma with picosecond laser varies, and the follow-up time is also short. Some clinical research results show limited efficacy. Therefore, 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.

5. Tattoos

The evidence level for the treatment of tattoos with picosecond laser is level la, which is the highest level of evidence among all its indications and the gold standard for the treatment of tattoos. Picosecond laser has a good effect on tattoo removal of almost all colors, and many observations have shown that the treatment effect of picosecond laser tattoo is better than that of Q-switched nanosecond laser, and the number of treatments is less, the energy density is lower, and the adverse reactions are less.
The reason why picosecond laser is effective in tattoo removal may be related to the fact that the tattoo dye particles of different sizes from 40 to 300nm just correspond to the thermal relaxation time of picosecond laser (about 12 to 1060ps). A computer simulation study believes that picosecond laser can generate a high temperature of 900℃, resulting in a strong pressure wave. This strong mechanical effect can cause carbon particles to break, which is also one of the mechanisms of high efficiency of picosecond laser treatment. Picosecond laser can also change the optical properties of tattoo dye and reduce the visibility of dye.

Tattoos can be divided into decorative tattoos, cosmetic tattoos and traumatic tattoos. Among them, decorative tattoos can be divided into professional tattoos and amateur tattoos, and these tattoos can be removed with picosecond laser. There is no research comparing the efficacy of various wavelengths of picosecond lasers, but according to the theory of selective photothermal therapy, researchers usually use 755nm and 1064nm lasers to treat black, blue, and green tattoos. One to two treatments can remove about 75% of tattoos; 532nm picosecond lasers are used to treat purple, red, yellow, and orange tattoos. Usually, Q-switched lasers are difficult to remove yellow tattoos, but 532nm picosecond laser treatment has a good effect, which may be related to the mechanical effect of picosecond lasers.

The following points need to be considered in the evaluation of tattoo efficacy: Professional tattoos are less effective than amateur tattoos because the former have a higher dye density and are located deeper. It is also necessary to understand the scar situation because scars can cause laser scattering and immune disorders, thereby affecting the effect. The location of the tattoo is also a factor that affects the efficacy. The head and neck have rich regional lymph nodes and blood vessels, which help to remove pigments, while the distal limbs are just the opposite.

Picosecond laser operation process and precautions:

·Operation process·

①Clean the patient's face; ②Take photos before treatment for archiving; ③Doctors and patients wear protective glasses; ④Select hand tools, energy, frequency, and spot size according to indications for treatment; ⑤Pay attention to observe the intraoperative spot reaction and treatment endpoint reaction (the appearance of erythema or white film, etc.); ⑥Apply cold compress after surgery; ⑦Explain the postoperative precautions and skin moisturizing care measures, etc.

·Precautions·

①Avoid sun exposure for 1 month before and after picosecond laser treatment. It is recommended to continue to use sunscreen after treatment; ②The skin of the treatment area must be thoroughly cleaned before surgery; ③It is recommended to apply cold compress or cold spray after surgery to relieve reactions such as erythema; ④Pay attention to moisturizing after surgery and avoid using irritating skin care products; ⑤For some indications, scabs after surgery are normal and can generally fall off on their own in about 7 days. Do not forcibly remove scabs; ⑥For different indications, perform the next treatment according to the interval period prescribed by the doctor.

·Adverse reactions and prevention strategies of picosecond laser treatment·

The characteristics of picosecond laser are that the photoacoustic effect is greater than the photothermal effect, and the thermal damage to tissue is significantly less than that of Q-switched laser. 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 adverse reaction is post-inflammatory pigmentation, which is most common after the treatment of melasma. Some patients are more 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 irradiated spots. Take necessary repair measures after surgery and strictly protect against the sun.

For intraoperative pain, local anesthetics can be applied locally before surgery or masks 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. No special treatment is required for individual small blisters. Larger blisters should be drained of blister fluid, 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 with picosecond laser

Picosecond laser can be combined with other methods in the treatment of melasma, tattoos, photoaging, facial rejuvenation, acne scars, etc. due to its characteristics of small treatment damage and fast recovery. Specific combined projects include intense pulsed light, laser, radio frequency, mesotherapy, microneedle, chemical peel, botulinum toxin injection, 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 according to 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, restore the skin to health and vitality, and is not restricted by seasons, and will not cause photosensitivity even in summer. Picosecond laser combined with CO₂ and fractional laser for tattoo treatment 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, combined with mesotherapy to treat melasma and facial rejuvenation, etc.

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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 beauty optoelectronic equipment based on compliance and product strength, and is committed to becoming a leading enterprise in the field of high-end medical beauty optoelectronic equipment, a provider of integrated intelligent solutions for diagnosis and treatment, and a pioneer of medical beauty data integration platform.

Through tackling a series of underlying key technologies, Foremed Legend has now independently developed a number of high-end medical equipment, including 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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