Retrospective clinical evaluation of Q‐switched Nd:YAG laser safety and efficacy in tattoo removal: A new perspective on the Kirby–Desai scale

With nearly 50% of the population in the United States, Italy, and Sweden tattooed with at least one tattoo, the demand for its removal has risen by 32% since 2011. Traditional removal methods, such as Q‐switched (QS) laser‐based tattoo removal, can be lengthy, requiring up to 20 sessions.

or thermal techniques. 4However, these methods often caused hyperpigmentation, hypopigmentation, and scarring. 4A major paradigm shift came in 1965, with the use of a Q-switched (QS) Ruby laser for tattoo removal. 5QS lasers produce short pulses of high-energy beams that target chromophores, such as ink.In tattoos, these chromophores are mainly found in membrane-bound granules within macrophages, fibroblasts, and mast cells. 6Tattoo removal using a QS laser is based on the photoacoustic effect, in which rapid heating produces an acoustic wave that causes the rupture of these intracellular granules and pigment is then released into the intracellular space.Phagocytosis takes up the tattoo fragments, which are eliminated through the lymphatic system, [7][8][9] causing a gradual fading of the tattoo.
QS lasers can shatter tiny fragments of pigmentation or ink, increasing effectivity and stimulating collagen production to reduce scarring. 10Furthermore, because their area of contact with the skin is smaller than other lasers, thermal energy can be easily released and there is less damage to surrounding tissue and side effects. 10ly QS lasers or pico lasers can produce high enough energy to remove both dark and bright tattoos without scarring. 11However, removing a professional tattoo is lengthy and requires 12-16 sessions and even up to 20 sessions performed every 6 weeks. 12Assessment of the number of treatments needed is often difficult and inaccurate thus a few modalities were suggested to try and estimate.One of the more relevant and in-use scoring for effective removal is provided by the Kirby-Desai scale, which takes into consideration multiple factors, all relevant for the laser procedure and most likely affect its time course.Patients' Fitzpatrick skin type and scar tissue were taken into account with the tattoo properties: location, color, ink intensity, and the presence of layering tattoo. 13ong the different types of QS lasers, the Nd:YAG emitting light at 1064 nm is considered safe and effective since it is weakly absorbed by natural chromophores, such as melanin, thereby reducing side effects. 14Furthermore, Nd:YAG laser penetrates the skin deeper than other QS lasers, up to 2 mm, easily reaching the tattoo pigments. 14The QS modality delivers high laser intensity pulses and is available in various wavelengths (1064, 755, 694, 650, 585, or 532 nm), making it ideal for removing multicolored tattoos, at different depths.Here we present a retrospective clinical study showing a safe and effective treatment for tattoo removal using a 7-ns QS laser of 1064 and 532 nm.Furthermore, we were able to demonstrate that it required fewer treatments than predicted by the Kirby-Desai scale, questioning the validity of this scale given the technological improvements and highlighting the new QS laser superior efficacy.

| Patients
This is a retrospective evaluation of 11 patients (7 males, 4 females) aged 28-48 (average 39.2 years).Study was conducted in accordance to the Declaration of Helsinki and the Good Clinical Practic/ International Council of Harmonization Guidelines.Inclusion criteria were individuals over 18 years of age with professional tattoos only, in which the tattoo had been done at least 5 years previously and had never been attempted to be removed by any means and has no scar tissue.Exclusion criteria were any dermatological skin condition, the use of immunosuppressive medication in the past year, a history of skin cancer, renal failure, or keloids.

| Treatment
Patients were treated with the Alma-Q, laser device (Alma Lasers LTD, Israel) using its QS Nd:YAG mode at 1064, an 532 nm wavelengths.Subjects underwent three to eight treatments (average 5.09) every 2-3 months.The laser was applied using the focus applicator, set at a 3-6 mm spot size, 1-2 Hz in frequency, using a single or double pulse mode, at a single pass.Depending on the spot size and treatment number, the fluence ranged from 0.8 to 8.5 J/ cm 2 , with high fluence required in the more advanced treatments as the tattoo fades.Figure 1 presents the fading between sessions.

| Outcomes
Prior to begin the treatment, each tattoo was assessed for its Kirby-Desai score based on location, Fitzpatrick skin score, amount of ink, ink layering, scarring and tissue changes, and color.Patients were followed up 6 months after their last laser session (short follow-up) and again after 4-5 years (long follow-up, average 4.36 years).Two physicians blindly scored removal results on a 0%-100% scale at both follow-up appointments.Each individual's Kirby-Desai score was compared to the actual number of performed treatments using paired t-test.

| RE SULTS
Eleven patients (7 males, 4 females) aged 28-48 (average 39.2 years) were treated every 2-3 months (Table 1).Prior to treatment, each patient was scored according to Kirby-Desai to assess the number of treatments needed for tattoo removal. 13Laser settings were spot sizes of 3-6 mm, single or double pulses, 1-2 Hz frequency, and fluence of 0.8-8.5 J/cm 2 .
Each patient was followed-up after 6 months and 4-5 years (average 4.36) after the final treatment, during which two physicians blindly assessed the tattoo removal efficacy (Table 2).The improvement was found to be statistically significant in the average score in the long follow-up compared to the short follow-up both for each evaluator separately and for their overall assessment (75.5 for shortterm follow-up vs. 93.6 in long-term follow-up, p < 0.001), indicating a long process during which the ink continues to break down and be eliminated by the immune system (Figures 2 and 3).Importantly, the number of actual treatments was significantly lower than that predicted by the Kirby-Desai scale scoring and ranged from 3 to 8 (average 5.09) compared to the Kirby-Desai prediction of 3-8 (average 9.9, p < 0.001, paired t-test; Table 3, Figure 4).In addition, there were no adverse events except for one patient who developed hyperpigmentation (PIH) which was resolved by topical application of Hydroquinone 8% for 3 months (Figure 5) and ended up to be successfully removed.

| DISCUSS ION
In 2015, it was estimated that over 40% of all US citizens had at least one tattoo.However, approximately 17% regretted their decision, and 50% of those planned to have them removed. 15Indeed, services for tattoo removal have increased by 32% since 2011 and are predicted to increase by 18% each year. 16Here, we present prospective F I G U R E 1 Fading of patient #1 tattoo as recorded before treatment (A), immediately before treatment sessions 1, 3, 5, 7 and 8 (B-F), and at the short (G) and long follow-ups (H).Tattoos are produced by injecting pigments into the skin's dermal layer and absorbed into macrophages, dermal mast cells, and fibroblasts.Laser tattoo removal is based on selective photothermolysis, during which laser energy is absorbed by the target tissue and produces localized heat, causing the organelles to rupture and release the pigments. 6This causes the electrons of the targeted tissue to become excited and vibrate, thereby producing thermal energy.Since the tattoo pigment serves as the laser's target chromophore, a tattoo comprising several colors is more difficult to remove when only one wavelength is used.The QS laser has addressed this issue by delivering high laser-intensity pulses at two wavelengths; therefore, this modality is better suited for removing tattoos.
The Kirby-Desai scale is used to predict the number of treatments and is based on Fitzpatrick skin type, location, color, ink intensity, the presence of scar tissue and tissue damage, and the presence of a layering tattoo. 13Generally, and as demonstrated in medical literature, a professional tattoo requires 12-16 and up to 20 sessions. 12However, our experience demonstrates a more effective effect at tattoo removal, and the number of treatments necessary was significantly lower than that predicted by the Kirby-Desai score erythema.Compared to previous reports, which reported a very high occurrence of adverse events; light to moderate edema (98%), erythema (95%), bleeding (9%), and purpura (24%), 14 our experience following QS 1064 nm/532 nm Nd:YAG laser treatment was milder in its skin reaction.
Taken together, we can conclude that the QS Nd:YAG laser provides an effective and safe alternative for tattoo removal and may require fewer treatments than initially expected.We believe given our experimental data, a larger cohort should be evaluated to confirm our initial findings and allow physicians to be more precise in their evaluation, and even to fine-tune the Kirby-Desai scale.
cases treated with a short pulsed Nd:YAG laser featuring QS for tattoo removal to evaluate its efficacy and safety.Results indicate that this QS module is not only safe for removing tattoos, but also the number of treatments required for efficient removal is significantly lower than that predicted by the well-established Kirby-Desai scale.

5 TA B L E 2 F I G U R E 4
Physician assessment at short-term (6 months) and long-term follow-up.Two physicians scored blindly on a scale of 1%-100%.F I G U R E 2 Patient #3 tattoo before (A), at short (B) and long follow-up (C), representing the highest scored tattoo removal (100%).F I G U R E 3 Patient #6 tattoo before (A), at short (B) and long follow-up (C), presenting the lowest scored tattoo removal (77.5%), probably due to its location and the presence of yellow and orange dyes.(average of 5.09 compared to 9.9).This is attributed to the latest developments in laser technology and also to the fact that a long follow-up is most likely to assist in tattoo ink clearance.Although the sample size presented in this report is only 11 cases, only one patient had a moderate side effect, hyperpigmentation (PIH), in addition to the expected ones, being edema and TA B L E 3 Kirby-Desai scale parameters.Comparison of calculated Kirby-Desai score and the actual number of treatments needed.F I G U R E 5 Patient #2 tattoo before (A), at short (C), and long follow-up (D).Panel (B) presents the post-inflammatory hyperpigmentation after treatment number 3, the only adverse event observed.The final clearance score at the long follow-up after PIH resolution was extremely high (99.5%).