Biomedical Engineering Reference
In-Depth Information
with the alexandrite laser. A randomized controlled trial of
144 Asian subjects with Fitzpatrick skin types III-V with a long-
pulsed alexandrite laser (12.5-mm spot size, pulse duration of
40 ms, and fl uences of 16-24 J/cm
2
) found that subjects with
three treatments had a 55% hair reduction compared with sub-
jects treated two times with a 44% hair reduction and subjects
treated one time had a 32% hair reduction at 9-month follow-up
(30). A combination treatment of alexandrite and Nd:YAG
lasers provides no added benefi t over the alexandrite laser alone
(31). The commercially available long-pulsed alexandrite
devices are summarized in Table 5.1.
The long-pulsed diode (800-810 nm) laser has also been
extensively used for LHR (26,32). The diode laser can be safely
used in patients with Fitzpatrick skin phototypes I-V. Two
long-term nonrandomized controlled studies showing roughly
40% hair reduction at a mean follow-up of 20 months after one
or two treatments (9-mm spot size, pulse duration of 5-30 ms,
fl uences of 15-40 J/cm
2
) (33), and 84% hair reduction at 1-year
follow-up after four treatments (9-mm spot size, pulse dura-
tion of 5-30 ms, fl uences of 12-40 J/cm
2
) (34) demonstrate the
effi cacy of the diode laser for long-term hair removal.
The long-pulsed Nd:YAG laser has been thought to offer the
best combination of safety and effi cacy for Fitzpatrick skin
phototype VI patients. In our vast experience, we have found
the Nd:YAG to offer good effi cacy but with higher relative fl u-
ences relative to the above wavelengths. A nonrandomized
trial reported a 70-90% reduction of facial, axillary, and leg
hair growth one year after three monthly treatments with an
Nd:YAG laser (5-mm spot size, pulse duration of 50 ms, fl u-
ences of 40-50 J/cm
2
) (35). A small study of axillary LHR com-
paring long-pulsed alexandrite, diode, and Nd:YAG lasers
showed that both the alexandrite and diode lasers were signifi -
cantly more effi cacious than the Nd:YAG laser for LHR (36).
IPL is composed of polychromatic, noncoherent light ranging
from 400 to 1200 nm. Various fi lters can be used to target par-
ticular chromophores, including melanin. Long-term (>1 year)
hair removal has not been convincingly demonstrated to date.
Various reports have demonstrated some short-term effi cacy
(37,38). One study of patients treated with a single IPL session
reported 75% hair removal 1 year after treatment (39). Two stud-
ies providing a head-to-head comparison of IPL versus either the
long-pulsed alexandrite laser (40) or Nd:YAG laser (41) both
found the IPL to be inferior to laser devices for hair removal. In
contrast, a study of hirsute women, some with a diagnosis of
polycystic ovarian syndrome, who underwent a split face treat-
ment with six IPL or long pulsed diode laser (LDPL), shows sta-
tistically equivalent reductions in hair counts at 1 (77% vs. 68%,
respectively), 3 (53% vs. 60%, respectively), and 6 months (40%
vs. 34%, respectively) after the fi nal treatment (42).
Table 5.2
Pertinent History for Laser/Light Device Hair
Removal
• Presence of conditions that may cause hypertrichosis:
°
Hormonal
°
Familial
°
Drug (i.e., corticosteroids, hormones, immunosuppressives,
self or spousal use of minoxidil)
°
Tumor
• History of local or recurrent skin infection
• History of herpes simplex, especially perioral
• History of herpes genitalis, important when treating the pubic or
bikini area
• History of keloids/hypertrophic scarring
• History of koebnerizing skin disorders, such as vitiligo and
psoriasis
• Previous treatment modalities—method, frequency, and date of
last treatment, as well as response
• Recent suntan or exposure to tanning or light cabinet
• Onset of hair regrowth (recent)
• Tattoos or nevi present
• Patient's expectations
• Patient's hobbies or habits that might interfere with treatment
• Present medications:
°
Photosensitizing medications
°
Isotretinoin intake within the past year
°
Gold therapy
Device Variables
Wavelength
The chromophore for LHR is melanin. Within the hair follicle,
melanin is principally located within the hair shaft, although
the outer root sheath and matrix area also contain melanin.
Melanin is capable of functioning as a chromophore for wave-
lengths in the red and NIR portion of the electromagnetic
spectrum (14) and can be targeted by ruby, alexandrite, diode,
and neodymium-doped:yttrium-aluminum-garnet (Nd:YAG)
lasers, as well as IPL devices.
The long-pulsed ruby laser (694 nm) was the fi rst device used
to selectively target hair follicles (5), and result in long-term
(follow-up at 2 years) hair loss (6-mm spot size, 270-µs pulse
duration, and fl uences 30-60 J/cm
2
) (4). The long-pulsed ruby
laser can be safely used in Fitzpatrick skin phototypes I-III.
A large multicenter trial of nearly 200 patients showed that
the majority of patients had >75% hair loss on 6-month
follow-up after an average of four treatments (25). Table 5.1 lists
the long-pulsed ruby lasers that are commercially available.
The long-pulsed alexandrite (755 nm) laser has been shown to
be effective for hair removal in multiple studies (26). The long-
pulsed alexandrite laser can be safely used in Fitzpatrick skin
phototypes I-IV, although some experts limit the use of the long-
pulsed alexandrite laser to Fitzpatrick skin phototypes I-III.
A few studies have demonstrated the safety of the long-pulsed
alexandrite laser in a large cohort of patients with Fitzpatrick
skin phototypes IV-VI (27,28). A randomized, investigator-
blinded clinical trial (29) of subjects with Fitzpatrick skin pho-
totypes III and IV treated with a long-pulsed alexandrite laser
(12- and 18-mm spot size, 1.5-ms pulse duration, and fl uences
of 20 or 40 J/cm
2
) for four sessions at 8-week intervals showed
76-84% hair reduction 18 months after the last treatment and
provides the best evidence for long-term hair removal effi cacy
Fluence
Fluence is defi ned as the amount of energy delivered per unit
area and is expressed as J/cm
2
. Higher fl uences have been corre-
lated with greater permanent hair removal (5,43), however are
also more likely to cause untoward side effects. Recommended
treatment fl uences are often provided with each individual laser
device for nonexperienced operators. However, a more appro-
priate method of determining the optimal treatment fl uence
for a given patient is to evaluate for the desired clinical endpoint
of perifollicular erythema and edema (Fig. 5.3). The highest
