Biomedical Engineering Reference
In-Depth Information
q-switched neodymium-doped
yttrium-aluminum-garnet laser
The Q-switched neodymium-doped:yttrium-aluminum-
garnet (Nd:YAG) laser uses a YAG crystal in which Nd has
been dispersed. The invisible near-IR beam of light emitted
has a 1064-nm wavelength but some devices also have an
option to use harmonic doubling to generate a wavelength of
532 nm. This device was explored in anticipation that its lon-
ger wavelength of 1064 nm would increase dermal penetration
and decrease melanin absorption, improving the response of
ruby laser-resistant tattoos and avoiding pigmentary changes.
An initial report of 20 professional and 3 amateur tattoos in
four treatment sessions showed the Nd:YAG laser to be equal
to the ruby laser in removal of blue-black tattoos at 6 J/cm 2 . In
this report, hypopigmentation and skin texture change were
more common with the ruby laser. Green and red pigments
were not removed with the Nd:YAG laser, whereas some green
pigment was removed with the ruby laser (209).
The ability of the Q-switched Nd:YAG laser (1064 nm, 10 ns,
5 Hz) to remove pigment in ruby laser-resistant tattoos
was assessed in the treatment of 28 tattoos (23 professional,
5 amateur) using fluences of 6-12 J/cm 2 with a 2.5-mm-
diameter spot size. In most cases, greater than 50% lightening
of residual tattoo ink was noted with the first treatment, with
the greatest improvement seen with higher fluences (210).
Unfortunately, the higher fluences (12 J/cm 2 ) and shorter
pulses (10 ns) resulted in more tissue debris and bleeding,
necessitating the use of a plastic shield or transparent mem-
brane to promote laser operator safety (211).
Kilmer et al. (212) investigated both ruby laser-resistant and
untreated tattoos in a prospective, blinded, dose-response
study using the Q-switched Nd:YAG laser (2.5-mm spot size).
Twenty-five professional tattoos and 14 amateur tattoos
were treated in quadrants using 6, 8, 10, and 12 J/cm 2 . Four
treatment sessions were performed at 3- to 4-week intervals.
Greater than 75% ink removal was seen in 77% of black tat-
toos and over 95% ink removal in 28% of tattoos (11 of 39)
treated at 10-12 J/cm 2 . There was no significant difference in
the response of previously untreated tattoos and ruby laser-
resistant tattoos. Treatment at the highest fluence (12 J/cm 2 )
proved to be signifi cantly more effective ( P < 0.01) at remov-
ing black tattoo ink than the lower doses of 6 and 8 J/cm 2 .
Green, yellow, white, and red inks were virtually resistant to
treatment and cleared 25% or less after four treatment ses-
sions. Purple and orange inks responded minimally. Although
textural changes were noted during the course of treatment,
these cleared with time, and only two of 39 tattoos were graded
as having trace textural changes. No hypopigmentation and a
single case of hyperpigmentation were noted. These results
were similar to those reported by Ferguson and August (213).
Biopsy of treated tattoos revealed fragmentation of black ink
particles up to 1.5 mm below the surface. This may prove
advantageous for the treatment of deeply implanted traumatic
tattoos (214-216). There was little if any fibrosis in the
superficial dermis. In addition, biopsies demonstrated that
even with clinical clearing of the tattoo, ink remained in the
dermis, as reported with the Q-switched ruby laser (157).
Kilmer et al. (212) noted that the lack of scarring both clini-
cally and histologically, despite the increased bleeding and
particle size and fragmentation of pigment-containing cells
probably result from rapid thermal expansion, shock waves,
and potentially localized cavitation. Fluence-dependent ther-
mal damage to collagen immediately surrounding the irradi-
ated tattoo pigment also occurs. Computer simulation models
confirm that the breakup of tattoo particles is photoacoustic,
and the optimal pulse duration for photoacoustic destruction
of tattoo particles with minimal nonspecific damage to the
surrounding tissue would be in the 10- to100-ps range (200).
Newer ruby lasers with a shorter pulse duration (approxi-
mately 25 ns), higher fluences (8-10 J/cm 2 ), and better beam
quality more rapidly cleared tattoos (201,202). Lowe et al. (203)
reported similar results using 10 J/cm 2 at 6- to 8-week intervals
and after five treatment sessions reported 22 of 28 professional
tattoos as having excellent results (greater than 75% improve-
ment). A preliminary report by Levins and coworker was
similar, with excellent results and minimal side effects (204).
In addition to amateur and professional tattoos, cosmetic,
iatrogenic, traumatic, and amalgam tattoos were removed
without scarring using Q-switched ruby lasers (78,205-207).
Kilmer and Anderson (208) initiated treatment at a fluence of
6-8 J/cm 2 with a 40- to 80-ns pulse width and reported black
and green ink to be most responsive, with other colors requir-
ing significantly more treatments. Amateur tattoos usually
required four to six treatment sessions and professional tattoos
six to ten sessions, but in some instances up to 20 treatment
sessions were needed. The authors noted several trends: profes-
sional, distally located, recently placed, or deeply placed tattoos
may be difficult to remove, requiring more treatment sessions
to eradicate them completely. Acceptable clearing varied greatly
from patient to patient, with some individuals more accepting
of vague residual pigment.
Transient hyperpigmentation is also common with the
Q-switched ruby laser and seems to be related more to skin
type than laser settings. Scarring and textural changes occur
more rarely. The risk of adverse tissue response and speed of
clearing both appear to be related to fluence and pulse width,
with higher fluences and shorter pulses being more effective
but causing more nonspecific tissue damage as well. These
high-energy short pulses cause a pressure shock wave that rup-
tures blood vessels and aerosolizes tissue with potentially
infectious particles, requiring the use of a protective barrier or
a plastic tube to protect the operator from tissue and blood
contact. The use of lower fluences eliminates this problem to a
large degree but results in the need for more treatment ses-
sions. The occurrence of scarring or tissue textural changes
has also been attributed to hot spots within the beam and
pulse-to-pulse variability. The ruby laser is very effective for
removing black, blue-black, and green ink; green ink can be
difficult, although reflectance spectra predict that it should
respond to a 694-nm wavelength. Other colors are poorly
responsive. Bleeding and tissue splatter can be cumbersome
and may increase the incidence of unwanted side effects, but
use of cone devices protects the operator from exposure.
In summary, the Q-switched ruby laser is effective in remov-
ing black, blue, and green tattoos with minimal scarring
although hypopigmentation is common (more than 50% of
patients), and although usually transient, it may result in per-
manent depigmentation (153).
 
Search WWH ::




Custom Search