Laser tattoo removal has been available commercially since we opened the world’s first private clinic to offer this treatment in Glasgow, Scotland in 1989 following our groundbreaking clinical research program in Canniesburn Hospital, Glasgow during the 1980s (see our 1990 publication in the British Journal of Plastic Surgery). We used the Q-switched ruby laser which predated the Nd:YAG and alexandrite lasers to successfully treat a range of multi-coloured professional and home-made, amateur tattoos.
There is a lot of information available these days on the internet which can be helpful and a hindrance. It’s a bit of a minefield with all sorts of claims, some of which are real and some which are just nonsense (even from some of the major laser suppliers!!)
This post will, hopefully, help to clarify how laser tattoo removal works.
In essence, laser tattoo removal aims to alter dermal tattoo ink, which is usually found encapsulated within macrophages/fibroblasts in the dermis. This alteration will result in thermoelastic waves which fragment ink aggregates such that the smaller particles may be removed from the site by macrophage activity into the lymph system, over subsequent weeks. There are other removal processes which I won’t go into at this time (I’m working on a new report which will go into these other processes in greater detail).
To maximise the removal efficiency a number of parameters need to be properly understood:
Energy density (or fluence / radiant exposure) – this must be set properly on a laser to ensure the desired response in the ink. If it is too low then little or no reaction will occur. If it is too high then unwanted dermal damage is likely due to excessive thermal diffusion throughout the dermis leading to damaged collagen.
However, higher energy densities are required to successfully affect deeper located ink aggregates. For this reason the output energy of the laser should be carefully increased as the number of treatment sessions increases.
Pulse duration – how long each laser pulse lasts. This determines the level of confinement of the thermal and acoustic waves on the ink aggregate/particle surfaces. Consequently, this determines whether the ink aggregates will shatter into smaller fragments. In general, the shorter pulsewidths result in a more tightly confined acoustic/pressure wave in the ink resulting in a more efficient fragmentation process. Hence, shorter pulsewidth lasers, such as picosecond systems, will cause a greater level of fragmentation than longer pulsewidths.
Wavelength – the laser wavelength determines three important outcomes –
a) penetration into the dermis is strongly affected by the incident wavelength. In the visible and near infra-red part of the spectrum, the penetration depth is dependent on the scattering and absorption coefficients of the skin constituents including blood, melanin, keratin and other chromophores. For this reason the longer wavelengths penetrate deeper into the dermis, hence 755 nm (alexandrite) will penetrate further than 694 nm (ruby) but 1064 nm (Nd:YAG fundamental) will penetrate further than both of those.
The frequency-doubled wavelength available with Nd:YAG laser emits at a wavelength of 532 nm. This wavelength cannot penetrate as far into the dermis as the above wavelengths and so has a lower efficiency compared to them.
b) the wavelength also strongly determines the ability of the ink to absorb the laser energy. In general, darker colours absorb more readily than lighter coloured inks. However, some colours may be more strongly absorbed than others. For example certain red wavelengths are well absorbed by green ink and so this can be exploited by some lasers. Likewise, black ink absorbs more efficiently at the Nd:YAG 1064 nm wavelength than by the other wavelengths listed above. Hence it is important to choose the most appropriate laser wavelength when treating certain colours.
c) the skin colour of the patient can have an important effect on treatment efficiency. Tattoo ink is located in the upper dermis in most cases, just below the epidermal melanin basal layer. Hence, the laser energy must traverse the melanin layer before reaching the tattoo ink. Absorption of light by melanin is stronger in the blue part of the spectrum compared with the red end. Hence wavelengths nearer the blue end will be more strongly absorbed by melanin than red light which may lead to u wanted side-effects. 532nm is absorbed significantly by melanin and so should not be used on darker-skinned individuals. Whereas 1064 nm light is very poorly absorbed by melanin and so is much safer to use on all skin types.
Laser spot size – the spot size is particularly important when considering the effective penetration depth of the energy. Clinical observations, laboratory tests and computer simulations all show that larger spot sizes will deliver energy more efficiently into the dermis than smaller spots. Hence, the laser user should always use the largest spot size available to them while ensuring the correct energy density (fluence).
Treatment interval – when we first tested the Q-switched ruby laser in the ’80s we found that a minimum of four weeks was required to ensure no lasting tissue damage. This was adopted as the standard, as a result of this observation. However, clinicians across the world have indicated that longer intervals appear to generate ‘better’ clinical results. Consequently, many now leave between six and eight weeks between repeat treatment session, with one centre claiming a three month interval. The reason appears to be due to the body’s ‘clearing’ efficiency. As the fragmented ink particles are removed by macrophages, it makes sense to give them more time to do their job. If a patient returns after eight weeks, instead of four, then clearly there will be more ink removed from the treatment site. I have observed a small number of patients who returned for treatments after a year’s interval. They exhibited a remarkable loss of ink in that time. I’m not advocating leaving all patients for such a long period of time but I would now recommend at least an eight week interval.
Treatment area size – there appears to be a natural limit on the area that can be effectively treated in any one treatment session. The body has a finite ability to create new macrophages in any given time. Hence, if a very large area is treated in one sitting the number of macrophages created will need to cope with a large amount of fragmented ink particles. If a smaller area is treated then there is likely to be more macrophages available for that ink, compared with the larger area. It seems sensible to limit the total area treated in any one session to allow the body to remove the ink particles more efficiently.
Capillary absorption – I recently found that using my glass slide technique on patients resulted in the reduction in pain, epidermal damage, blood spots and healing time (published in the ‘Lasers in Medical Science‘ journal). I also discovered that by applying pressure to the skin using the glass slide the blood in the capillary plexus can be ‘squeezed’ out. This has a major effect on transmission of the laser energy, particularly 532 nm, since less energy is absorbed in the blood layer. Hence, using a glass side on the skin surface during treatment with 532 nm will help to get more energy into deeper tattoo ink.
Location of the tattoo – clinical evidence suggests that certain parts of the body are easier to treat than others. I’m not aware of a proper clinical study to evaluate this but there is plenty of anecdotal evidence which backs up this claim. Distal tattoos, especially on the lower legs are definitely slower to respond, I have found. It may he better to leave slightly longer intervals between sessions on these areas.
The consequences of all of the above is that the choice of laser parameters and timings are very important in the treatment process. If you choose a 1064 nm wavelength, at 5 J/cm2 in a 5 mm spot with a pulsewidth of 10 ns, then you cannot expect the same result if you subsequently choose a 4 mm spot or 750 picoseconds or 694 nm or 8 J/cm2! Changing any one of these parameters will have an effect on the treatment efficiency. They are NOT equivalent so don’t expect the same results.
When you change a laser parameter you should ask yourself a number of questions:
- How does this affect the depth of penetration? (wavelength, spot size, energy density)
Will it affect the absorption in the ink (colour, wavelength)?
How will it affect the absorption in the melanin layer? Or the capillary plexus?
Will a higher fluence/energy density adversely affect the dermis? Or the epidermal melanin?
Laser parameters must be chosen to maximise efficiency according to the tattoo ink colour, depth and location and the patient’s skin colour.
Clearly, it is important to understand how varying one parameter affects the result. This can only be done if we understand how each individual parameter changes the outcome.
Hope this helps.