Is Nd:YAG good for tattoo removal?

Abstract

Introduction: Although tattoos are ancient and very popular among young people, it is also a reason for regret, and many people today have a desire to remove them. Among the possibilities for this, laser removal is the most successful procedure with the highest degree of pigment removal and the lowest risk of complications.

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Methods: This study was recorded on three patients with tattoos, and only the black pigments were removed. None of the patients involved had a history of skin allergies, skin cancer, and/or keloid formation. Case 1 had a professional tattoo removed in the right calf region in two sessions. Case 2 had an amateur tattoo that was removed on the scalp in three sessions. Finally, Case 3 had two professional tattoos, which were removed from the face in a total of eleven sessions. The following equipment was used: Spectra XT Q-Switched Nd:YAG nm with a pulse width of 5 ns; Pico Ultra 300 Nd:YAG nm with a pulse width of 300 ps; and SoftLight Q-Switched Nd:YAG nm with a pulse width of 17 ns.

Results: In general, satisfactory results were obtained, but hypopigmentation was present in Cases 1 and 3. This was probably due to sun exposure at the laser removal site, the short interval between the sessions, and/or higher radiant exposure combined with a smaller spot size, respectively.

Conclusion: To achieve a successful tattoo removal in the higher phototypes and reduce unwanted effects, the professionals must know the best parameters to be used, as well as the adequate foundation on the individual characteristics of each patient and the tattoos. Furthermore, patient compliance with the pre/post session care and a suitable interval between the laser sessions are essential to avoid undesirable complications.

Keywords: Q-Switched laser, Nd:YAG laser, Laser tattoo removal, Tattoo removal

Introduction

Tattoos are present on the skin in a large part of the population.1,2 However, there is a significant percentage of regret and desire for the removal of the tattoo in individuals from several countries.1,3,4 According to the American Society for Dermatologic Surgery, more than 160'000 tattoo removal procedures were performed in in the USA for a variety of reasons.5

Several techniques such as salabrasion, dermabrasion, electrocautery, cryosurgery, and chemical peeling have been developed to remove pigments from the skin since then, although they are accompanied by unsatisfactory results and adverse events, such as scar formation and skin dyspigmentation. Nowadays, tattoo removal with the Q-Switched Laser has become the method of choice, given the availability of different wavelengths, which allows for reaching the various pigments with a less risk of complications.1,2,6

The use of laser for tattoo removal is based on selective photothermolysis, which occurs from the absorption of energy that is emitted from the equipment to the ink that is present in the skin.7 Additionally, light absorption may also generate any photoacoustic effect, whose mechanical stress might destroy the pigment particle.1 In this way, the ink particles that are present within the lysosomes of the resident dermal cells are released into the extracellular space and phagocytosed, with the subsequent transfer through the lymphatic system and elimination.1,4,8

Although safe and effective, Nd:YAG laser tattoo removal in patients with ethnic skin, for instance, with Fitzpatrick skin phototypes from IV to VI, is still challenging since dyspigmentation and scarring are of greater risk. These effects may be due to existing biological characteristics in the darkly pigmented populations, namely an increased epidermal melanin content, especially enriched in DHI-eumelanin (black)9 together with larger melanosomes that are more singly dispersed (non-aggregated) and widely distributed throughout the entire epidermis. Additionally, naturally more reactive fibroblasts due to genetic factors that are present in this type of population, favor the development of keloids and hypertrophic scars as a consequence of dermal injuries.10,11 In addition, in patients with higher phototypes, it is common for results to take longer to appear, and they are often unsatisfactory, given that epidermal melanin acts as a competitor for the ink pigment that is present in the tattoo,10 making these subjects more prone to hypopigmentation after the laser procedure.1 Thus, this study aimed to describe and evaluate a case series, in which protocols were used to enable effective laser tattoo removal in patients with darker skin types.

Presentation of the Cases

This case series reports on three clinical cases of patients with Fitzpatrick phototypes between IV and VI, who sought a laser removal service because they were dissatisfied and regretful about instigating their tattoos. These patients were informed about the interest of the researchers to publish the information regarding their treatments, and they signed a consent form, which was approved by the Ethics Committee of Nove de Julho University, Brazil, No. 5.598.427. All of the participants also filled and signed the image use permission term.

All of the removed figures contained black ink pigment, and the patients that were involved in this study had no history of skin allergies, skin cancer, and/or keloid formation. All of the patients that have been described received asepsis with 70% ethanol, followed by 2% lidocaine, plus epinephrine 5 mcg/mL injections at the treatment site. All of these patients received skin cooling when using a cold air device (SIBERIAN-FIT®, VYDENCE Medical, São Carlos, Brazil) during the laser application. The devices used in this study were SOFTLIGHT® Q-Switched Nd:YAG nm ThermoLase with a 17 ns pulse width, SPECTRA XTTM Q-Switched Nd:YAG nm Lutronic with a 5ns pulse width, and PICO ULTRA® 300 Nd:YAG nm with a 300 ps pulse width, and their details are presented in Table 1. The interval between the sessions, the equipment models, and the parameters that were used for cases 1, 2, and 3 are shown in Tables 2, 3, and 4, respectively.

Table 1. Laser System Parameters .

SoftLight Spectra XT Pico Ultra 300 System type Nd:YAG Nd:YAG Nd:YAG Wavelength (nm) (532, 585, and 650) Pulse width (ps) 300 Spot size range (mm) 4-7 2-10 2-10 Energy range (mJ) 100- 100-500 Radiant exposure range (J/cm2) 2-9 0.13-38 0.13-16.7 Repetition rate range (Hz) 1-10 1-10 1-10 Open in a new tab

Table 2. Treatment Protocol for the Tattoo Removal in Case 1 .

Session Date (M/D/Y) Equipment Repetition Rate (Hz) Spot Diameter at Tissue (mm) Radiant Exposure (J/cm2) 1st 3/28/ SoftLight 5 6.8 2.0 2nd 12/4/ SoftLight 5 6 2.8 Open in a new tab

Table 3. Treatment Protocol for the Tattoo Removal in Case 2 .

Session Session (M/D/Y) Equipment Repetition Rate (Hz) Spot Diameter at Tissue (mm) Radiant Exposure (J/cm2) 1st 10/06/ SoftLight 10 5 1.6 2nd 03/03/ SoftLight 10 5 2.1 3rd 06/08/ SoftLight 10 5 2.6 Open in a new tab

Table 4. Treatment Protocol for the Tattoo Removal in Case 3 .

Session Session (M/D/Y) Equipment Repetition Rate (Hz) Spot Diameter at Tissue (mm) Radiant Exposure (J/cm2) 1st 7/24/ Spectra XT 5 5 5.2 2nd 9/23/ Spectra XT 5 4 6.8 3rd 2/22/ Pico Ultra 300 2 5 1.7 4th 4/19/ SoftLight 2 5 1.8 5th 6/11/ SoftLight 2 5 2.1 6th 9/23/ SoftLight 2 5 2.8 7th 10/27/ SoftLight 2 5 2.8 8th 11/22/ SoftLight 2 5 3.2 9th 1/13/ Spectra XT 4 5 9.2 10th 2/21/ Spectra XT 2 4 9.4 11th 4/7/ Spectra XT 2 3 13 Open in a new tab

Based on the Kirby-Desai scale (KDS), the number of sessions needed for tattoo removal was estimated for each patient.12,13 This scale attributes points to the characteristics, such as the Fitzpatrick skin type, location of the tattoo, color, amount of ink, scarring, and layering of the tattoos, together with cumulative points, correlated to the estimated number of sessions. During the description of the cases, after the presentation of the parameter, the number between the parentheses was the points that were attributed to it on this aforementioned scale.

Patient 1 was a 28 years old female presenting Fitzpatrick skin type VI (6 points KDS). Her tattoo contained black ink (1 point KDS), was performed by a professional and presented complex design (3 points KDS). It measured 22 per 10 cm on the right leg in the calf region (4 points). No scars or layering were present (0 points). Only two sessions were held, starting in March , with a 21-month interval between them (Figure 1).

Figure 1.

Patient 1 - Professional Tattoo (A) Before the 1st Session, (B) 4 Months After the 1st Session, (C) Before the 2nd Session With the Laser Treatment, 20 Months After the 1st Session, and (D) Six Months After the 2nd Session.

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Patient 2 was a 28 years old male with Fitzpatrick skin type IV (4 points KDS). His tattoo was black (1 point), amateur and simple (1 point), performed on the head in the scalp region (1 point KDS) 1 year and a half before starting the removal. No scars or layering were present (0 points). A total of three sessions were held from October to November ' 25 months (Figure 2), which resulted in an average of almost one session each for eight months, with five months being the smallest interval between the sessions and fifteen months being the highest.

Figure 2.

Patient 2 - Amateur Tattoo (A) Before, (B) After a Session, 5 Months After the First Session, and (C) 15 Months After the 2nd Session.

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Patient 3 was a 19 years old male, presenting Fitzpatrick skin type V (5 points KDS). He had two black tattoos (1 point KDS) on the face (1 point KDS) performed by a professional and presenting simple design (2 points). No scars or layering were present (0 points). He underwent the removal of the two tattoos, one on each side of the face (a rose on the right side of the face and an A on the left side of the face). A total of eleven sessions were held, which started in July and ended in April ' 21 months (Figure 3). The average interval between the sessions was almost one session every two months, with one month being the smallest interval between the sessions and five months being the highest. When considering the region of the tattoos being removed, this patient was deeply anxious regarding the treatment evolution, and even with the warnings regarding the interval between the sessions, he took the risk and asked for monthly sessions.

Figure 3.

Patient 3 - Professional Tattoo (A) Before, (B) After Six Sessions, 165 Days Interval From the Beginning, (C) Results After the 11th Laser Treatment Session (an 18-Month Interval From the Beginning), and (D) Two Months After the 11th Session of the Laser Treatment (a 20-Month Interval From the Beginning).

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An independent investigator, unfamiliar with the subjects or the tattoos and not involved with the treatments, performed the assessment and the classification of tattoo ink lightness (TIL) from the serial digital photographs as presented in this study. The TIL was obtained based on the percentage of improvement in the photographs and described as 1: poor/minimal (<25%), 2: mild/moderate (25-50%), 3: good (51-75%), 4: excellent (76-95%), and 5: clear (>96%). The adverse events resulting from the laser procedure were also evaluated. These results are shown in Table 5.

Table 5. Tattoo Ink Bleaching and the Identified Adverse Events .

Patient ID Number of Predicted Number of Sessions TIL
(Before vs. After) Adverse Effects Sessions Hypopigmentation/ Hyperpigmentation Textural Changes Scarring 1 14 2 4 Trace present Absent Absent 2 7 3 3 Absent Absent Absent 3 9 11 5 Present Absent Absent Open in a new tab

Discussion

The Nd:YAG laser for tattoo removal is considered very versatile since nm is effective for dark pigments such as black and blue while using the KTP 532 nm red, orange, and yellow dyes are more prompt to respond.1 When considering individuals with darker skin types, short wavelengths are not recommended. Longer wavelengths have the potential to penetrate more deeply, reaching the dermis and acting on the dark pigments, while preserving the melanocytes and keratinocytes in the epidermis,1,11 together with a lower risk of adverse events such as hypopigmentation.2,14 In general, the nm Q-switched Nd:YAG laser is safe for darker skin types,8 and this was the choice for treating the listed cases.

In addition to the wavelength, other parameters such as radiant exposure, spot size, pulse width, the interval between the sessions, and the number of sessions are all important factors for a better tattoo removal result. Radiant exposure, measured in J/cm2, is the energy that is delivered to the tissue's superficial area. When starting the treatment, the lowest radiant exposure that can induce a whitening response was used to protect the epidermis, minimizing any laser-induced dyschromia.9 The whitening of the tattoo occurs due to the rapid heating of the pigment, which leads to the formation of gas or plasma, and that results in dermal vacuoles. This effect disappears only a few hours later. When high radiant exposure is used, the excess energy absorbed by the epidermis can result in blistering, peeling, and an increased chance of scarring.11 The radiant exposure can be increased in later sessions as the ink density decreases.1 A 7-11 J/cm2 radiant exposure range is considered optimal for ink fragmentation15; however, in ethnic skin patients, smaller values should be considered. In this study, for patients 1 and 2, SoftLight was the equipment used, and the radiant exposure was used in the range between 1.6 to 3 J/cm2, being smaller at the first session, and then it gradually increased.

Regarding the spot size, the smaller spots are usually used with higher radiant exposure in the patients with low skin phototypes (Fitzpatrick phototypes I to III), while in the patients with darker skin (phototypes IV to VI), the treatment, in general, starts with low radiant exposure and a larger spot size.1 When considering that there is a reduction in the depth of light penetration as the skin color becomes darker, the reduction of the spot size makes the energy delivery more superficial with a greater scattering degree, making it necessary to increase the radiant exposure so that there is a balance in the energy delivery and the removal of the remaining ink.1 Therefore, in the cases presented, an increase in radiant exposures was used during the sessions and was associated with the reduction of the spot size, which occurred according to the degree of remaining pigment. It is important to note that for case 1, which presented a higher skin phototype (VI), higher spot sizes were used (6.8-6), but for case 2 (phototype IV), a spot size of 5 mm was used. On the other hand, smaller radiant exposures were used in case 2 in comparison with case 1, which resulted in the worst clearance/removal (TIL 3 versus TIL 4 ' Table 5). Hence, those patients presenting higher skin phototypes need higher spot sizes and lower radiant exposures.

Additionally, the pulse width is a parameter, and this influences the results since it interferes with the extension of the photoacoustic and photothermal effects. Depending upon the particle size of the ink used, the specific thermal relaxation time (TRT) and the inertial confinement time will necessarily be used. When the pulse width is larger than the TRT, this can cause thermal damage to the surrounding tissue, reducing the bleaching effect and increasing the unwanted effects on the tissue. Smaller pulse widths might be necessary for treated tattoos since the particle size gets smaller.

When considering the devices that were used in this report, SoftLight presented the largest pulse width (17 ns), followed by Spectra XT (5 ns), and finally Pico Ultra (300 ps). At the beginning of cases 1 and 2, SoftLight was the only equipment available at the clinics, so it inevitably was the choice for these treatments. For the treatment of patient 3, the first two sessions were performed with Spectra XT since it was mentioned that the black ink pigments of TRT were around 10 ns; thus, the pulse width used was smaller than that for the TRT. With tattoo bleaching, a smaller pulse width was used with Pico Ultra. When using Pico Ultra, some technical issues were observed regarding the maintenance of the device. The treatment was then reinitiated using SoftLight when considering the low radiant exposure. Gradually, the radiant exposure was increased up to 3.2. The treatment was again changed to a smaller pulse width with Spectra XT, gradually increasing the radiant exposure and reducing the spot size.

Tattoo removal is a treatment that greatly involves the patient's emotional/psychological state. The regret or dissatisfaction with the tattoo might affect self-esteem, confidence, and both social and professional relationships. Accordingly, it is important to manage the patient´s anxiety and his/her expectation regarding the treatment. In case 3, it was possible to verify that after 11 sessions, there was slight hypopigmentation at the removal sites (see Table 5), which does not have an exact mechanism described but might be associated with cellular damage by shock waves, as well as the physical effects that are induced by thermal expansion and/or the extreme thermal gradients within the melanocytes.14 Hypopigmentation is considered a common adverse effect, where the number of sessions is considered a risk factor,16 reaching 8.1% and 2.7% when using the nm nanosecond laser and the nm picosecond laser, respectively.15 In addition, the patient in question requested a greater number of sessions during the initially combined treatment period, causing a reduction in the interval between the sessions, and insisted even after the professional alerted the patient about the possible risk of hypopigmentation. In the most recent photo that was obtained after the 11th session, it was possible to verify that despite having improved, the observed hypopigmentation was still considerable. In the other cases, there was a longer interval between the sessions, and any pigmentation changes were not observed. Furthermore, the patient's immune response was essential for the success of laser tattoo removal since, after the ink fragmentation, the tissue response directs the phagocytosis and the removal from the skin.

The optimal number of sessions varies on a case-by-case basis, but typically, 4-6 sessions were required for amateur tattoo removal and 15-20 sessions, if not more, for professional tattoos.17 When considering the KDS, 14, 7, and 9 sessions would be necessary for the tattoo clearance for patients 1, 2, and 3, respectively (Table 5). Very good results were obtained since TIL 4 (excellent) was obtained for case 1 after 2 sessions (12 sessions less than predicted), and TIL 3 (good) was achieved for case 2 after 3 laser sessions (4 sessions less than estimated), while TIL 5 (clear) was achieved for case 3 with 11 sessions (2 sessions more than estimated). Both Cases 1 and 2 could exhibit better results (TIL 5), with some additional sessions. It was important to keep in mind that a 'not so good' response in the lower limb tattoos might occur when compared with other locations, and this fact is documented.17 This problem is possibly related to the transport of the particles resulting from the photo-pyrolysis and the photoacoustic breakdown via the lymphatic system,18 which has a smaller number of lymph nodes in the lower extremities,19 making it difficult to eliminate the pigment residues from the tattoo.

From the results presented, it can be observed that case 1 was the one that presented the best result with the smallest number of sessions, demonstrating, once again, the importance of using low radiant exposures, high spot sizes, and having an adequate interval between the sessions for the decomposition of the pigments and the removal of the residues that are generated via phagocytosis, especially in those patients prone to pigmentary and textural changes, in which longer treatment intervals might be useful.13 It was also important to note that during the laser tattoo removal process, the patient should be instructed to avoid sun exposure, as well as using sunscreen during the treatment, to reduce the risk of complications.7,13 In case 1, the patient, after the second session, did not show any signs of hypopigmentation, but in the most recent photo, the patient presented this complaint significantly after the skin tanning, which is also considered a risk factor for this adverse effect.20 Last but not least, the use of cooling devices was also included since they increase comfort during the laser application, with decreased damage to the surrounding tissue.

Despite the anxiety and the expectation on the part of the patients to have the tattoo removed in the shortest possible time, this laser application when conducted several times on the same tattoo can result in fibrosis and visible textural changes, which reduce the response for the subsequent treatments.13 A minimum time of a month is required between the sessions for optimal ink removal and wound healing,1 as well as for the immunological breakdown process of the pigments, which leads to the continuous whitening of the tattoo, even after several weeks of treatment.17 The findings of this study suggest that longer intervals between the sessions might lead to more favorable results.

Conclusion

The successful laser tattoo removal, with low or absent adverse effects on ethnic skin, is related to a good evaluation of the patient (for instance, Fitzpatrick's phototype, immunosuppression, the use of medications such as oral steroids, and whether the skin is tanned), and the tattoo to be removed (color, density of the ink, region of the body, and the age of the tattoo). Regarding this analysis, the success of the clearance/removal is defined by the treatment protocol that was used when considering the laser parameters such as wavelength, pulse width, radiant exposure, spot size, the number of sessions, and the interval between them. In this work, the researchers noted that for the black tattoos in ethnic skin, the nm with a 17 ns pulse width was effective (as did the smaller ones) using radiant exposures from 2 J/cm2, with higher spot sizes (5-6.8 mm) and interval between the sessions longer than 2 months. The compliance of the patient to avoid sun exposure and to use sunscreen was essential to reduce the side effects that are related to dyschromia.

Conflict of Interests

The authors declare no conflict of interest.

Ethical Considerations

This case series report was evaluated by the Research Ethics Committee from the Universidade Nove de Julho, Brazil, and approved by No. 5,495,933 on June 28, . Informed consent was obtained from all of the human adult participants.

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Please cite this article as follows: Pincelli G, Mota Sena M, Pavani C. Nd:YAG laser tattoo removal in individuals with skin phototypes IV-VI: A Case series. J Lasers Med Sci. ;13:e79. doi:10./jlms..79.

Macroscopic laser-tissue irritation evaluation

For establishing a reference for skin irritation, healthy skin was exposed to the same laser parameters as the laser-treated areas (Figs. 2 and 3). Areas irradiated with 532 nm wavelength were more severe using the 2 mm spot size beam, that produced intense and localized erythema. Barely perceptible edema increased in severity past 75 mJ pulse energy and became moderate at 120 mJ (Fig. 2S-2). In comparison, the irradiation effect with 4 mm spot size was milder, resulting in a well-defined erythema and edema only at 120 mJ, and the erythema that was developed by the pulse energy of 75 and 120 mJ had a uniform distribution (Fig. 2S-4).

Figure 2

Dermatoscopic evaluation of untattooed skin immediately following treatment with 532 nm laser therapy.

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Figure 3

Dermatoscopic evaluation of untattooed skin immediately following treatment with  nm laser therapy.

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The laser treatment on healthy skin using the  nm wavelength displayed almost no indications of laser-induced patterns at 30 mJ, but a rapid increase in erythema was observed past 95 mJ with the 2 mm spot size, developing a severe form (Fig. 2S-2). Areas treated with the 4 mm spot size up to 95 mJ pulse energy were comparable to healthy skin. Sporadic petechia formation (<'1 mm) was observed in areas treated with 155 mJ using the 4 mm spot size (Fig. 2S-4).

The degree of tissue irritability was assessed to ascertain how various laser parameters affected different colored tattoos. The erythema and edema for all areas were overall reduced (Fig. 4B) using a 4 mm spot size at a 532 nm wavelength in comparison to the treatment using a 2 mm spot size (p'='0.054) (Fig. 4A). The severity of tattoo removal, as measured by the outcome of treatments utilizing 75 mJ (p'='0.011) and 120 mJ (p'='0.041) energy levels and matching pigment color, was found to be higher when using a 2 mm spot size compared to a 4 mm spot size.

Figure 4

Assessment of tissue irritation immediate post-laser treatment. Laser treatment parameters: (A) wavelength of 532 nm and 2 mm spot size; (B) wavelength of 532 nm and 4 mm spot size; (C) wavelength of  nm and 2 mm spot size; (D) wavelength of  nm and 4 mm spot size.

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When utilizing a 2 mm spot size, pulse energies of 75 to 120 mJ, and a 532 nm wavelength, black tattoos exhibited the most pronounced response to laser treatment, resulting in moderate to severe edema (Fig. 4A). The laser-tissue reactions elicited by 532 nm wavelength were found to be the mildest in red and green tattoos, with only moderate edema observed even at the highest pulse energy levels. The analysis of the data presented in Fig. 4B revealed that, apart from black tattoos, all laser-treated areas subjected to irradiation with 120 mJ pulse energy using a 4 mm spot size resulted in comparable or reduced irritation scores when compared to the control skin.

The skin irritation scores of the areas treated with  nm wavelength were significantly higher (p ' 0.037) after treatment with 2 mm spot size compared to 4 mm spot size (Fig. 3C, D). The use of a 2 mm spot size at both 30 mJ and 155 mJ pulse energies resulted in a significantly higher irritation score compared to the 4 mm spot size. Specifically, at 30 mJ pulse energy, the 2 mm spot size resulted in a 2.7-fold increase in irritation score, primarily due to the presence of edema. Similarly, at the highest pulse energy level of 155 mJ, the use of a 2 mm spot size led to a 1.9-fold higher irritation score (p'='0.013) compared to the 4 mm spot size, as shown in Fig. 3D.

The overall irritability of the treated areas was found to be highest in black, blue, and yellow tattoos, due to lower edema severity at pulse energies ranging from 30 to 95 mJ with a 2 mm spot size (Fig. 4). Conversely, the treatment of red and green tattoos resulted in the least irritation compared to the other colors, due to a slight reduction in edema formation.

Tattoo clearance evaluation

Different wavelengths of laser light have varying degrees of effectiveness in tattoo removal. The clearance rates demonstrated a positive correlation with pulse energy. When comparing the clearance rates achieved using different wavelengths, it is observed that the  nm wavelength produced lower clearance rates compared to the 532 nm wavelength, with the exception of black tattoo (Fig. 5).

Figure 5

Dermatoscopic view of laser-treated tattoos 30 days post third treatment. For 532 nm wavelength a pulse energy of 75 mJ was used and for  nm ' 95 mJ. Tattoo color'(A'E). Spot size (S)'2- and 4-mm. Treatment wavelength (λ)'532/ nm.

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The highest clearance rate for black tattoos was achieved using a 2 mm spot size at  nm wavelength and 155 mJ pulse energy, resulting in a rate of 76.46% (Fig. 6C). Conversely, the least effective treatment, which only achieved a clearance rate of 16.41%, was observed when using a 4 mm spot size at 532 nm wavelength and 25 mJ pulse energy (Fig. 6B).

Figure 6

Assessment of tattoo clearance 150 days post-treatment. Laser treatment parameters: (A) wavelength of 532 nm and 2 mm spot size; (B) wavelength of 532 nm and 4 mm spot size; (C) wavelength of  nm and 2 mm spot size; (D) wavelength of  nm and 4 mm spot size.

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The most effective treatment for removing blue, green, red, and yellow tattoos utilized a beam size of 2 mm, a wavelength of 532 nm, and an energy of 120 mJ (Fig. 6A). After three laser treatments, yellow and green tattoos exhibited the highest clearance rates, achieving 71.87% and 71.69%, respectively. Blue tattoos were the third most effectively treated, with a clearance rate of 65.04%, followed by red color tattoos, with a rate of 48.96%. The lowest clearance for blue, green, red, and yellow color tattoos was observed after treatment utilizing the 4 mm spot size at  nm wavelength and 30 mJ pulse energy, achieving 20.24%, 18.74%, 5.15%, and 10.20% respectively (Fig. 6D).

Microscopic tattoo removal evaluation

The histological characteristics of the epidermis in untreated and laser-treated tattoo samples were evaluated. The epidermis maintained its characteristic architecture after treatment with various laser settings. Furthermore, no extracellular ink particles were detected in the epidermis, even in the accumulations of necrotic tissue that formed in the stratum corneum of the epidermis.

The skin tissue slides stained with hematoxylin and eosin (HE) showed variations in ink color of non-laser treated areas, with black tattoos appearing black, blue tattoos displaying a range from dark blue to black with a bluish border, green tattoos exhibiting a range from dark green to black with a greenish border, red tattoos showing a range from dark red to black with a reddish border, and yellow tattoos presenting a heterogeneous black color with multiple pigment granules (Fig. 7).

Figure 7

Histological analysis of pre-treatment tattoo pigments: control samples 150 days after tattooing. HE-stained sections of pigment clusters in different colored tattoos: (A) black tattoos; (B) blue tattoos; (C) green tattoos; (D) red tattoos; (E) yellow tattoos.

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Ink particles were observed in the dermis up to a depth of 1.2 mm, with the highest concentration locating within 100'600 μm from the skin surface (Fig. 8A1'2). The majority was concentrated in clusters distributed in mononuclear infiltration, comprising mainly of macrophages surrounding dilatated blood vessels (Fig. 8). The cytoplasm of phagocytic cells contained large pigment deposits, which showed a high degree of color saturation and homogeneity, except for yellow tattoos.

Figure 8

Histological assessment of black tattoos 150 days post-laser treatment with 532 nm wavelength and 120 mJ pulse energy: (A1) control (untreated) tattoo; (A2) black pigment cluster in untreated tattoo; (B1) laser-treated tattoo (2 mm spot size); (B2) pigment particles in laser-treated tattoo (2 mm spot size); (C1) laser-treated tattoo (4 mm spot size); (C2) pigment particles in laser-treated tattoo (4 mm spot size).

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The study showed that 532 nm wavelength at the 4 mm spot size only reached up to 250 μm (Fig. 8B1'2), while the 2 mm spot size was capable of achieving pigment fragmentation up to 400 μm (Fig. 8C1'2). Reduction in overall pigment quantity and the transformation of large intracellular pigment deposits into considerably smaller particles containing granules resulted in a lightening of the treated areas. By increasing the laser pulse energy from 75 to 120 mJ, the fragmentation effect was significantly enhanced, as demonstrated by the tattoos' clearance (Figs. 5 and 6).

Laser treatment at 532 nm wavelength produced detached melanin'containing parakeratotic mounds or microscopic epidermal necrotic debris (MEND) that reside in the upper levels of the SC in sub-granular position. The laser beam spot size, pulse energy, and pigment characteristics affected the size variation of MENDs. The treatment with a 2 mm spot size resulted in the formation of MENDs in blue, green, and yellow tattoos, especially past 75 mJ pulse energy. The largest MENDs were observed in yellow tattoos, measuring up to 1.5 mm in diameter. In blue tattoos, the detached necrotic tissue was measured up to 500 μm, and in green tattoos'up to 300 μm. MENDs were not observed in black and red tattoos, and they were not observed in tattoos of any color treated with a 4 mm spot size. Vascular dilatation of superficial capillaries was observed throughout the samples treated with 532 nm wavelength and both spot sizes. Using the 2 mm spot size the dilatation was observed up to 1.5 mm in the dermis and using the 4 mm'up to 500 μm (Fig. 8).

The application of a  nm wavelength for tattoo removal was particularly effective in decreasing the amount of pigment deposits in black tattoos (Fig. 5), especially when a 2 mm spot size was used (Fig. 9B1). The total black pigment amount in the samples treated with both beam sizes were lower than in the untreated areas (Fig. 9A1'2), which positively correlated with pulse energy past 95 mJ using a 4 mm spots size and 30 mJ with 2 mm spot. Treatment up to 95 mJ with the  nm laser using a 4 mm spot size affected mostly the superficial layer of the black pigment clusters up to 300 μm, leaving the lower layers visually comparable to control tattoos (Fig. 9C1'2). Fragmentation of pigments throughout their distribution depth was observed to be successful after irradiation with a 2 mm beam width at all energy levels, and with a 4 mm beam width from 155 mJ pulse energy (Fig. 9B1'2).

Figure 9

Histological assessment of black tattoos 150 days post-laser treatment with  nm wavelength and 155 mJ pulse energy: (A1) control (untreated) tattoo; (A2) black pigment cluster in untreated tattoo; (B1) laser-treated tattoo (2 mm spot size); (B2) pigment particles in laser-treated tattoo (2 mm spot size); (C1) laser-treated tattoo (4 mm spot size); (C2) pigment particles in laser-treated tattoo (4 mm spot size).

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Our observations indicate that colored tattoos exhibited fragmentation to some degree throughout the entire range of pigment distribution. In addition, we noted a slight dilatation of superficial capillaries up to 300 μm, along with a significant infiltration of mononuclear cells in all areas containing pigment. MENDs were only observed in histological samples of blue, green, and yellow tattoos treated with 2 mm spot size. The highest MEND formation was observed in blue and yellow tattoos up to 1.5 mm in diameter past 95 mJ, while in green tattoos the detached necrotic tissue measured up to 200 μm.

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