03/09/2018
Laser tattoo removal
Mechanism of laser action
Experimental observations of the effects of short-pulsed lasers on tattoos were first reported in the late 1960s by Leon Goldman and others.In 1979 an argon laser was used for tattoo removal in 28 patients, with limited success. In 1978 a carbon dioxide laser was also used, but because it targeted water, a chromophore present in all cells, this type of laser generally caused scarring after treatments.
In the early 1980s, a new clinical study began in Canniesburn Hospital's Burns and Plastic Surgery Unit, in Glasgow, Scotland, into the effects of Q-switched ruby laser energy on blue/black tattoos.Further studies into other tattoo colours were then carried out with various degrees of success.
Research at the University of Strathclyde, Glasgow also showed that there was no detectable mutagenicity in tissues following irradiation with the Q-switched ruby laser.This essentially shows that the treatment is safe, from a biological viewpoint, with no detectable risk of the development of cancerous cells.
It was not until the late 1980s that Q-switched lasers became commercially practical with the first marketed laser coming from Derma-lase Limited, Glasgow.] One of the first American published articles describing laser tattoo removal was authored by a group at Massachusetts General Hospital in 1990
Tattoos consist of thousands of particles of tattoo pigment suspended in the skin.] While normal human growth and healing processes will remove small foreign particles from the skin, tattoo pigment particles are too big to be removed automatically. Laser treatment causes tattoo pigment particles to heat up and fragment into smaller pieces. These smaller pieces are then removed by normal body processes. Q-switched lasers produce bursts of infrared light at specific frequencies that target a particular spectrum of color in the tattoo ink. The laser passes through the upper layers of the skin to target a specific pigment in the lower layers.
Laser tattoo removal is a successful application of the theory of selective photothermolysis (SPTL).] However, unlike treatments for blood vessels or hair the mechanism required to shatter tattoo particles uses the photomechanical effect. In this situation the energy is absorbed by the ink particles in a very short time, typically nanoseconds. The surface temperature of the ink particles can rise to thousands of degrees but this energy profile rapidly collapses into a shock wave. This shock wave then propagates throughout the local tissue (the dermis) causing brittle structures to fragment. Hence tissues are largely unaffected since they simply vibrate as the shock wave passes. For laser tattoo removal the selective destruction of tattoo pigments depends on four factors:
The color of the light must pe*****te sufficiently deep into the skin to reach the tattoo pigment. Pigments deeper in the skin are harder to remove than those near the surface.
The color of the laser light must be more highly absorbed by the tattoo pigment than the surrounding skin. Different tattoo pigments therefore require different laser colors. For example, red light is highly absorbed by green tattoo pigments, while yellow tends not to absorb light.
The time duration (pulse duration) of the laser energy must be very short, so that the tattoo pigment is heated to fragmentation temperature before its heat can dissipate to the surrounding skin. Otherwise, heating of the surrounding tissue can cause burns or scars. For laser tattoo removal, this duration should be on the order of nanoseconds.
Sufficient energy must be delivered during each laser pulse to heat the pigment to fragmentation. If the energy is too low, pigment will not fragment and no removal will take place.
Q-switched lasers are the only commercially available devices that can meet these requirements.
Although they occur infrequently, mucosal tattoos can be successfully treated with Q-switched lasers as well.
A novel method for laser tattoo removal using a fractionated CO2 or Erbium:YAG laser, alone or in combination with Q-switched lasers, was reported by Ibrahimi and coworkers from the Wellman Center of Photomedicine at the Massachusetts General Hospital in 2011.
This new approach to laser tattoo removal may afford the ability to remove colors such as yellow and white, which have proven to be resistant to traditional Q-switched laser therapy.
Laser parameters that affect results Edit
Several colors of laser light (quantified by the laser wavelength) are used for tattoo removal, from visible light to near-infrared radiation. Different lasers are better for different tattoo colors. Consequently, multi-color tattoo removal almost always requires the use of two or more laser wavelengths. Tattoo removal lasers are usually identified by the lasing medium used to create the wavelength (measured in nanometers (nm)):
Q-switched Frequency-doubled Nd:YAG: 532 nm. This laser creates a green light which is highly absorbed by red, yellow, and orange targets. Useful primarily for red and orange tattoo pigments, this wavelength is also highly absorbed by melanin (the chemical which gives skin color or tan) which makes the laser wavelength effective for age spot or sun spot removal. Nd:YAG lasers may cause hemoglobin absorption, leading to purpura (collection of blood under tissue in large areas), pinpoint bleeding, or whitening of the skin.
Q-switched Ruby: 694 nm. This laser creates a red light which is highly absorbed by green and dark tattoo pigments. Because it is more highly absorbed by melanin this laser may produce undesirable side effects such as pigmentary changes for patients of all but white skin.This is the best wavelength for blue ink.
Q-switched Alexandrite: 755 nm. The weakest of all the q-switched devices and somewhat similar to the Ruby laser in that the Alexandrite creates a red light which is highly absorbed by green and dark tattoo pigments. However, the alexandrite laser color is slightly less absorbed by melanin, so this laser has a slightly lower incidence of unwanted pigmentary changes than a ruby laser.This laser works well on green tattoos but because of its weaker peak power it works only moderately well on black and blue ink. It does not work at all (or very minimally) on red, orange, yellow, brown, etc. This laser wavelength is also available in a picosecond speed with anecdotal claims that it removes ink faster.
Q-switched Nd:YAG: 1064 nm. This laser creates a near-infrared light (invisible to humans) which is poorly absorbed by melanin, making this the only laser suitable for darker skin. This laser wavelength is also absorbed by all dark tattoo pigments and is the safest wavelength to use on the tissue due to the low melanin absorption and low hemoglobin absorption. This is the wavelength of choice for tattoo removal in darker skin types and for black ink.
Dye modules are available for some lasers to convert 532 nm to 650 nm or 585 nm light which allows one laser system to safely and effectively treat multi-color tattoo inks. When dye modules take 532 nm laser wavelength and change it, there is a loss of energy. Treatments with dye packs, while effective for the first few treatments, many not be able to clear these ink colors fully. The role of dye lasers in tattoo removal is discussed in detail in the literature.
Pulsewidth or pulse duration is a critical laser parameter. All Q-switched lasers have appropriate pulse durations for tattoo removal.
Spot size, or the width of the laser beam, affects treatment. Light is optically scattered in the skin, like automobile headlights in fog. Larger spot sizes slightly increase the effective pe*******on depth of the laser light, thus enabling more effective targeting of deeper tattoo pigments. Larger spot sizes also help make treatments faster.
Fluence or energy density is another important consideration. Fluence is measured in joules per square centimeter (J/cm²). It is important to be treated at high enough settings to fragment tattoo particles.
Repetition rate helps make treatments faster but is not associated with any treatment effect. Faster treatments are usually preferred because the pain ends sooner.
Number of laser tattoo removal treatment sessions needed
Complete laser tattoo removal requires numerous treatment sessions, typically spaced at least seven weeks apart.
Treating more frequently than seven weeks increases the risk of adverse effects and does not necessarily increase the rate of ink absorption. Anecdotal reports of treatments sessions at four weeks leads to more scarring and dischromia and can be a source of liability for clinicians.
At each session, some but not all of the tattoo pigment particles are effectively fragmented, and the body removes the smallest fragments over the course of several weeks or months. The result is that the tattoo is lightened over time.
Remaining large particles of tattoo pigment are then targeted at subsequent treatment sessions, causing further lightening. The number of sessions and spacing between treatments depends on various parameters, including the area of the body treated, skin color and effectiveness of the immune system. Tattoos located on the extremities, such as the ankle, generally take longest. As tattoos fade clinicians may recommend that patients wait many months between treatments to facilitate ink resolution and minimize unwanted side effects.
The amount of time required for the removal of a tattoo and the success of the removal varies with each individual and their immune system function. Factors influencing this include: skin type, location, color, amount of ink, scarring or tissue change, layers of ink, immune system function and circulation.
Factors under the individuals control are more time between treatments, nutrition, stress, sleep, exercise and fluid levels. In the past health care providers would simply guess on the number of treatments a patient needed which was rather frustrating to patients. A predictive scale, the "Kirby-Desai Scale", was developed by Dr. Will Kirby and Dr. Alpesh Desai, dermatologists with specialization in tattoo removal techniques, to assess the potential success and number of treatments necessary for laser tattoo removal, provided the medical practitioner is using a Q-switched Nd:YAG (neodymium-doped yttrium aluminium garnet) laser incorporating selective photothermolysis with six weeks between treatments
The Kirby-Desai Scale assigns numerical values to six parameters: skin type, location, color, amount of ink, scarring or tissue change, and layering. Parameter scores are then added to yield a combined score that will show the estimated number of treatments needed for successful tattoo removal. Experts recommend that the Kirby-Desai scale be used by all laser practitioners prior to starting tattoo removal treatment to help determine the number of treatments required for tattoo removal and as a predictor of the success of the laser tattoo removal treatments.Prior to 2009, clinicians had no scientific basis by which to estimate the number of treatments needed to remove a tattoo and the use of this scale is now standard practice in laser tattoo removal.
Certain colors have proved more difficult to remove than others. In particular, this occurs when treated with the wrong wavelength of laser light is used. Some have postulated that the reason for slow resolution of green ink in particular is due to its significantly smaller molecular size relative to the other colours.] Consequently, green ink tattoos may require treatment with 755 nm light but may also respond to 694 nm, 650 nm and 1064 nm. Multiple wavelengths of light may be needed to remove colored inks.
One small Greek study showed that the R20 method—four passes with the laser, twenty minutes apart—caused more breaking up of the ink than the conventional method without more scarring or adverse effects. However, this study was performed on a very small patient population (12 patients total), using the weakest of the QS lasers, the 755 nm Alexandrite laser. One of the other main problems with this study was the fact that more than half of the 18 tattoos removed were not professional and amateur tattoos are always easier to remove. Proof of concept studies are underway, but many laser experts advise against the R20 method using the more modern and powerful tattoo removal lasers available at most offices as an increase in adverse side effects including scarring and dischromia is likely. Patients should inquire about the laser being used if the R20 treatment method is offered by a facility as it is usually only offered by clinics that are using the weak 755 nm Alexandrite as opposed to the more powerful and versatile devices that are more commonly used. Moreover, dermatologists offering the R20 method should inform patients that it just one alternative to proven protocols and is not a gold standard treatment method to remove tattoos.
Factors contributing to the success of laser tattoo removal
There are a number of factors that determine how many treatments will be needed and the level of success one might experience. Age of tattoo, ink density, color and even where the tattoo is located on the body, all play an important role in how many treatments will be needed for complete removal. However, a rarely recognized factor of tattoo removal is the role of the client’s immune response.[] The normal process of tattoo removal is fragmentation followed by phagocytosis which is then drained away via the lymphatics. Consequently, it’s the inflammation resulting from the actual laser treatment and the natural stimulation of the hosts’s immune response that ultimately results in removal of tattoo ink; thus variations in results are enormous.[]
Pain management during treatment
Laser tattoo removal is uncomfortable - many patients say it is worse than getting the tattoo. The pain is often described to be similar to that of hot oil on the skin, or a "snap" from an elastic band. Depending on the patient's pain threshold, and while some patients may forgo anesthesia altogether, most patients will require some form of local anesthesia. Pre-treatment might include the application of an anesthetic cream under occlusion for 45 to 90 minutes or cooling by ice or cold air prior to the laser treatment session. A better method is complete anesthesia which can be administered locally by injections of 1% to 2% lidocaine with epinephrine.
A simple, new technique (published in March 2014) which helps to reduce the pain sensation felt by patients has been described by MJ Murphy[47] He used a standard microscope glass slide pressed against the tattooed skin and fired the laser through the glass. Results on 31 volunteers showed a significant reduction of up to 50% in pain alongside a reduction in blistering and punctate bleeding. This technique represents the simplest and most effective method to reduce the pain sensation using a non-invasive procedure.
