Fractional laser technology is the newest and hottest technology in the United States and the most talked about technology in the global skin industry, and is a minimally invasive treatment between invasive and non-invasive. The theory of fractional laser treatment, called Fractional Photothermolysis, was first published in 2004 by Dr. Rox Anderson, an expert in laser medicine at Harvard University, and was immediately recognized by experts around the world and rapidly applied to clinical treatment.
I. Overview of fractional laser
(A) Fractional laser
Fractional laser is called Fractional laser in English, and there are many different names in China. One of the more popular applications is fractional laser or pixel laser, which is also called bridge laser, bridge treatment, fractional laser and perforated laser.
Conventional laser treatment produces a surface treatment in the treatment area, while fractional laser produces a fractional, a very small damage with a lot of normal skin around it.
(II) Exfoliative laser technology and its advantages and disadvantages
The representative devices of exfoliative laser technology are CO2 laser and ER-YAG laser, which can be used independently or in combination. Their color bases are both water, which is vaporized tissue, removing the epidermal and dermal papillary layers and regenerating the skin. The energy of the laser is used to selectively heat and contract the dermal collagen, activating fibroblasts and synthesizing new collagen to tighten the skin. The advantage is that it produces very good skin rejuvenation results and is the gold standard for skin rejuvenation treatments. The disadvantage is that it produces extensive exfoliation symptoms during the treatment, requiring a 1-2 week trauma repair period and experiencing a prolonged erythema period (usually lasting around 6 months). Complications are higher for people of color, such as yellow people, and the more common ones are infection, scarring, hyperpigmentation or depigmentation.
(iii) Concept of non-ablative laser technology and its advantages and disadvantages
Non-ablative laser technology is to produce a controlled damage to specific target tissues in the dermis, without producing damage to the epidermis. It uses laser energy to selectively heat the dermis, stimulate collagen remodeling, form new collagen, tighten the skin, and remove abnormal skin pigments and dilated blood vessels. The advantage is that there is no damage to the epidermis, no peeling symptoms, no recovery time, very few complications from peeling, and it can be performed on almost any part of the body. Its disadvantage is that it can only produce a certain degree of skin rejuvenation.
(D) The concept of fractional laser technology and its advantages and disadvantages
Fractional laser technology is a relatively new technology. Its representative devices are CO2 laser, Er:YAG laser, Erbium fiber, Erbium glass and Nd:YAG laser. It treats only part of the skin in the treatment area, producing many tiny wounds or coagulated necrotic columns, with most of the surrounding skin left intact and undamaged to provide a source of skin regeneration, so that the tiny wounds or necrotic columns are rapidly repaired in a short period of time and the barrier function of the skin is more completely preserved. It uses laser energy to selectively heat and contract dermal collagen, activate fibroblasts, synthesize new collagen, and tighten the skin.
Advantages of fractional laser: It is between exfoliative and non-exfoliative, gathering the effectiveness of the exfoliative technique and the safety of the non-exfoliative technique, bridging the gap between exfoliative and non-exfoliative treatments, producing fast and dramatic results of exfoliative treatment, but also having the advantage of non-exfoliative treatment with few side effects and rapid recovery, combining the advantages of both into one, with few permanent complications. Its disadvantages are that it can produce crusting, requires about a week for wound repair, requires multiple treatments, and has some incidence of hyperpigmentation, but it is relatively rare.
After the first treatment, many tiny columnar skin lesions are produced in the skin layer, then the skin is repaired, the epidermis is shed, and collagen is stimulated for remodeling. After the recovery is over, I perform the next fractional laser treatment to make up for the untreated areas left by the last treatment, so that after repeated treatments a traditional laser skin resurfacing treatment can be achieved.
Second, the classification of fractional laser
Fractional lasers are divided into two categories: the first category is non-ablative fractional lasers and the second category is ablative fractional lasers. Non-exfoliative fractional lasers include 1550 nm diode-pumped erbium fiber laser, 1540 nm flash lamp-pumped erbium glass laser, 1320 nm and 1440 nm Nd:YAG two lasers. The exfoliative fractional lasers are represented by CO2 laser and Er:YAG laser and Er:YSGG laser.
(i) Non-ablative fractional laser
Non-exfoliative fractional laser is the first and most reported class of laser used in clinical practice. Its wavelength is between 1400 and 1600 nm. It only produces tissue coagulation during the treatment, and does not produce tissue vaporization. The epidermis is intact, while the dermal collagen shrinks and undergoes denaturation, which can stimulate the proliferation of collagen and the formation of new collagen tissue.
(ii) Exfoliative fractional laser
Although the clinical application of exfoliative fractional laser is relatively short, it has been fully demonstrated that the effect of this type of laser is superior to that of non-exfoliative laser and also has good safety. Its chromophore is mainly water in the tissue, and the target tissues are epidermal cells, collagen and blood vessels. It creates a series of columnar vaporization and exfoliation of the epidermis and part of the dermis during the treatment, and its depth depends on the wavelength of the laser, the amount of energy and the state of the skin (hydration state of the skin and surface temperature). Compared to non-exfoliative lasers, exfoliative treatments are less frequent and more effective, but the treatment is more painful, often requires the cooperation of anesthesia, and the recovery time is relatively long.
The laser irradiation creates a micro treatment zone, which consists of three parts, with a central micro-exfoliation zone (MTZ), a thin carbonized layer in the middle, and an outer micro-coagulation layer. The three zones formed by each of the three types of lasers are different due to the difference in laser wavelength and water absorption rate. For Er:YAG laser, the formation of carbonized layer is not visible in tissue biopsy under narrow pulses, even if two pulses are superimposed consecutively, while CO2 laser pulses are difficult to make narrow, and only one pulse will form a distinct carbonized layer around the micro-exfoliation zone. It induces a specific repair response after treatment, leading to re-epithelialization and remodeling of collagen, increasing hyaluronic acid and collagen production.
(iii) Microbeam generation technology
Microbeam generation is formed by a special technique. The first type is a scanner, commonly used for CO2 lasers, the second type is an optical sieve or lens array, generally used for Er lasers, and the third type is a prism, which can divide a laser into many tiny laser beams. The laser that applies the scanner can adjust the density of the micro treatment area, and the laser that uses sieves, lenses and prisms, this density is generally more fixed, and it can only change its density by replacing the lenses.
Third, the factors affecting the role of fractional laser
(A) Wavelength
As the laser wavelength increases, the scattering of the laser in the dermis decreases and the penetration depth has increased. As can be seen from the figure below, the penetration depth of the laser deepens as the wavelength increases. However, when it exceeds 1200 nm, the chromophore becomes water, which absorbs a large amount of energy and makes the penetration depth of the laser shallow.
The reaction of different wavelengths of laser on the tissue is different. CO2 laser produces a more obvious carbonized layer, while 2790nm ER laser only produces a slight carbonized layer in the underlying layer, while 2940nm Er laser is without the presence of carbonized layer, so blood will be oozing after treatment.
(ii) Spot density
Multivariable treatment at a fixed position can increase its spot density. Initially starting with a spot density of 5%, it can become 15% after 3 Passes, i.e. 3 times of treatment, 10% can become 27% and 15% can become 39%. The treatment process should be fully considered, and the number of repetitions is a certain relationship with the area treated.
(iii) Light spot size
It is generally believed that the light spot less than 200μm has a deeper penetration depth and can be used for deeper treatment, such as scar and wrinkle treatment. The penetration depth is shallower than 300μm, such as ActveFX mode, whose spot diameter is 1.3mm, which can reach the dermal papillae layer, and can be used for superficial treatments such as skin pigmentation diseases, which can be treated with larger spots.
(iv) Light spot type
There are two types of light spots, one is raster and the other is random. In the raster, there is one kind of low density and one kind of high density. Random density, because the distance between each spot is more distant, so the chance of tissue heat dissipation, time is longer, while the raster type, especially the high-density treatment, often forms a treatment similar to the full peeling of carbon dioxide peeling, which should be avoided in clinical practice.
(E) Light spot scanning mode
The light spot scanning mode is either sequential or non-sequential, which has an effect on the distribution of heat in the tissue. Sequential scanning affects the heat dissipation during the treatment. The distance between each spot of non-sequential scanning is farther, and there is time to reorganize to dissipate the heat, so it is not easy to produce a situation of overheating and overall heating.
(vi) Energy density
The depth of the microtherapy area has a linear relationship with the diameter and energy density, and the energy setting should reach the area where the patient’s problem is located, i.e. the energy is located where the target base is. Superficial wrinkles and thin skin should be set at a lower energy density, and deep scarring should necessarily be applied at a high energy density. Insufficient energy density will not achieve sufficient depth even with multiple treatments.
With some non-ablative fractional laser treatments, high energy density can lead to subepidermal separation, resulting in swelling of melanocytes, which can easily produce post-inflammatory hyperpigmentation.
(vii) Pulse width
In general, the longer the pulse width, the more heat energy is generated. The diameter of the micro treatment area is positively correlated with the pulse width, and the morphology is transformed from columnar to triangular as the pulse width increases. To prevent undue damage to the epidermis, the pulse width should be chosen as short as possible. For super pulse mode laser, the pulse width is generally in the range of 200-500 μs, which is within the range of the thermal duration of the skin and is relatively safe.
(H) Pulse characteristics
The pulse can be a single pulse or a pulse string, and the two pulse wavelengths can be different from the pulse width, or the energy level can be different. The balance between vaporization and solidification can be optimized by the adjustment of sub-pulses. If we use a double pulse, the second pulse has a reduced energy density and increases its pulse width below a kind of exfoliation range, it produces coagulation in the surrounding tissue. And the longer the pulse width, the thicker the coagulation layer.
Four, the indications of fractional laser
The indications for fractional laser in clinical practice include
1.Improve wrinkles on face and neck, whiten and tighten skin, shrink pores and improve skin roughness.
2, removal of skin pigmented lesions, including freckles, sun spots, age spots, hyperpigmentation, chloasma, etc. Fractional laser is the only feasible treatment for melasma approved by FDA.
3.It can treat rosacea, capillary dilation and other vascular diseases of the skin.
4. It can reduce or remove acne scars, various traumatic scars including depressed, proliferative scars or keloids and the treatment of swelling lines.
V. Complications of fractional laser
Fractional laser does not have many complications. The blue in the figure below indicates a conventional CO2 laser, the red is a conventional erbium laser, and the yellow is a fractional laser. You can see that the incidence of HSV infections, viral infections, acne, and post-inflammatory hyperpigmentation with fractional laser is much less than with traditional peel lasers.
Acne, melanin infections, vesicles, post-inflammatory hyperpigmentation, erythema, edema and dermatitis, with the exception of post-inflammatory hyperpigmentation, have a relatively early incidence and do not last long, usually fading on their own within 10 days. Only post-inflammatory hyperpigmentation occurs later, usually after debridement, and lasts longer, but most patients will slowly fade away in about two months.