31 - 208 - FUNDAMENTALS OF LASER AND LIGHT-BASED TREATMENTS Flashcards
Which laser can be used for telangiectasias?
a. Diode
b. Er:YAG
c. Ruby
d. Argon
D
For large vessels and hair removal, which laser setting is best?
a. Nd:YAG; Selective coagulation; pulsed (ms)
b. Nd:YAG; Fast heating; pulsed (ns/ps)
c. Nd:YAG; Selective coagulation; pulsed (ns/ps)
d. Nd:YAG; Fast heating; pulsed (ms)
A
What creates evenly distributed zones of microthermal injury in skin to produce columns of injury in the epidermis and dermis, leaving intervening columns of unaltered skin, thereby decreasing healing time and minimizing adverse effects?
a. Selective Thermolysis
b. Fractional Thermolysis
c. BOTH
d. NEITHER
B
Which is NOT a main parameter of Optical Radiation?
a. optical power
b. fluence
c. intensity
d. all of the above are included
D
The major chromophores in skin in order of depth of location are?
a. water-melanin-hemoglobin
b. melanin-water-hemoglobin
c. hemoglobin-water-melanin
d. hemoglobin-melanin-water
A
main parameters of optical radiation
wavelength,
optical power,
intensity,
the exposure time and
radiant exposure or fluence
The spot size and the energy of the laser beam determine the
radiant exposure (J/cm2)
most frequently modified parameter in laser treatments
radiant exposure or fluence (J/cm2)
described as the conversion of laser energy to heat when its photons strike the target chromophore
Absorption
occurs when the laser beam strikes the surface at an oblique angle and a portion of the beam bounces off the surface in a different direction
Reflection
Because of the inherent reflective property of the stratum corneum, even laser beams perfectly perpendicular to the skin undergo about _____% reflectance
5%
occurs when the light passes through the stratum corneum, but deviates once in the tissue due to contact with small molecules in the skin
Scattering of laser
This process is more likely to occur with shorter wavelengths
occurs when the beam is not absorbed by the target chromophore and is conducted to deeper structures
Transmission
This laser-tissue interaction is more likely to occur with shorter wavelengths
Scattering
This laser-tissue interaction is more likely to occur with longer wavelengths and larger spot sizes
Transmission
When laser or IPL light is absorbed by a chromophore, what types of interactions ensue
- chemical (photochemical),
- mechanical (photoacoustic or photodisruptive), or
- thermal
An example of a this effect is the use of low-level laser therapy in the treatment of hair loss, in which photons are presumed to be absorbed by mitochondria and activate the cellular respiratory chain to induce hair growth
chemical (photochemical) effect
This effect can be exemplified by the use of nanosecond or picosecond lasers in the treatment of pigmented lesions and tattoos: high-energy photons absorbed by pigment generate acoustic waves within the particles leading to their break up
mechanical (photoacoustic or photodisruptive)
the mechanism on which most lasers rely, describe the transformation of light energy into heat when absorbed by a chromophore, causing direct damage to adjacent cells, tissues, and structures
Photothermal effects
Lasers that preferentially interact with oxyhemoglobin
- neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1064 nm frequency doubled to 532 nm)
- pulsed dye lasers (585–600 nm)
These lasers are less well absorbed by oxyhemoglobin and more suitable for pigmented chromophores in benign pigmented lesions and for hair removal
- ruby lasers (694 nm),
- alexandrite lasers (755 nm),
- diode lasers (around 810 nm)
Radiation of this laser is minimally absorbed by all skin chromophores.
Nd:YAG laser (1064 nm)
Nevertheless, at high radiant exposures, this laser can be used for nonspecific coagulation of tissue as a continuous wave, or for pigmented or vascular lesions as a short or long pulse.
lasers that interact solely with water heating up tissue for vaporization or ablation.
Infrared lasers such as the erbium-doped yttrium aluminum garnet (Er:YAG) and carbon dioxide (CO2 )
These ablative lasers induce thermal damage to the epidermis and dermis to stimulate neocollagenesis, tissue rejuvenation, and skin tightening.
At temperatures ________, reversible thermal damage, local vasodilation, and inflammatory cascade activation are produced
below 50°C
At temperatures _________, tissue and its proteins undergo irreversible coagulation or denaturation
between 50°C and 100°C
At temperatures ____________, tissue vaporization occurs, generating plume containing water vapor and tissue components
greater than 100°C
defined as the time needed for the irradiated tissue to cool down to half of its heated temperature
thermal relaxation time
- The keys to this theory are twofold: laser light must be absorbed by the target by selecting a wavelength absorbed by the chromophore in the target, and the correct pulse duration is essential for spatial confinement of heat in the target.
- The pulse duration should be comparable to the thermal relaxation time (tR ), which mainly depends on the diameter of the target (D)
The major chromophores in skin in order of depth of location are
water, melanin, and hemoglobin
What lasers are absorbed by water
CO laser (10,600-nm)
Er:YAG laser (2940 nm)
Lasers that may be absorbed by both hemoglobin and melanin
- Argon-ion lasers (488 and 514 nm),
- KTP lasers (532nm), and
- pulsed dye lasers (585-595 nm)
absorbed mainly by melanin pigment although a small amount of hemoglobin absorption also occurs
Ruby lasers (694 nm)
preferentially absorbed by melanin, and therefore useful for pigmented lesions and hair.
Alexandrite lasers (755 nm)
although there is no specific chromophore, this wavelength is absorbed, albeit less than with other visible wavelengths, by hemoglobin and melanin and at higher fluences it can be used to treat pigmented or vascular lesions.
Nd:YAG laser (1064 nm)
determines the size of target that will be selectively damaged.
pulse duration
correction: Hair follicles are 0.02 to 0.2 millimeters in diameter and not micrometer
Hair follicles are 0.02 to 0.2 millimeters in diameter and are targeted by pulses in the range of _______
10 to 50 milliseconds
Melanocytes are a few µm in diameter (average 7 µm) and require pulse widths ranging from
milliseconds to nanoseconds
Melanosome diameter ranges from 1 to 1.5 µm and can be targeted by what pulse duration
nanosecond and picosecond pulses
Tattoo pigment particles are on average 100 nanometers (0.1 µm) in diameter and are targeted by what pulse durations
nanosecond and picosecond pulses
Radiation between 380 and 1400 nm is transmitted by the eye and absorbed by what structure in the eye
Retina
Light of wavelengths longer than 1000 to 1400 nm is readily absorbed by water, does not penetrate deeply, and therefore may cause corneal injury, even ablation or vaporization, by a thermal process.
Photons of wavelengths shorter than 380 nm are absorbed by organic molecules in what part of the eye
Cornea, thereby causing injury or cataract formation.
Thermal damage occurs when energy is absorbed by the chromophore, such as melanin in the retina, at a pulse ranging from
microseconds to seconds
Heat is generated faster than it can be dissipated, thereby denaturing proteins resulting in cell death and tissue necrosis.
Mechanical injury is caused when energy is rapidly absorbed at pulse durations ranging from
picoseconds to nanoseconds
Laser goggles are rated by optical density (OD) at various wavelengths, and an OD of at least _____ is considered safe.
4
part of laser that is used to bring atoms and electrons to an excited energy state, and can take the form of an electrical current, flashlamp, or even another laser
energy source
part of laser composed of a medium enclosed within a tube that contains 2 parallel mirrors, one of which is completely opaque and the other is partially transmissible
resonator
this determines the resultant wavelength and properties of the laser
medium
can be a solid, liquid, liquid crystal, or gas
pulse duration that should be used for blood vessels
ms
pulse duration that should be used for hair follicles
10 - 50 ms
pulse duration that should be used for melanocytes
ms to ns
pulse duration that should be used for melanosomes
ns to ps
pulse duration that should be used for tattoo pigment particles
ns to ps
where heat is transferred from the warm skin to the cooling agent
contact cooling
regulatory document that provides guidance for the safe use of lasers in medicine
ANSI Z136.3
laser settings that decrease the risk of injury to darker skin types
Lower fluences, longer pulse durations, and longer wavelengths or higher cutoff filters
Radiation between **380 and 1400 nm **is transmitted by the eye and absorbed by what part of the eye?
retina
- The refractive media of the eye gathers and focuses this spectrum onto the retina and increases the irradiance by a factor of more than 10,000 above the irradiance at the cornea.
- Thus, even a small amount of energy from low-power lasers can still inflict significant damage on the retina.
caused when energy is rapidly absorbed at pulse durations ranging from picoseconds to nanoseconds
Mechanical injury
- A rapid absorption of energy and therefore rapid increase in temperature strips electrons from atoms, disintegrating tissue to a pool of ions and electrons, or plasma
- Concomitant vaporization of water results in a compressive pressure pulse, or explosion, that disrupts surrounding tissue.
Photons of wavelengths shorter than 380 nm are absorbed by organic molecules in what part of the eye?
cornea
- thereby causing injury or cataract formation
- Light of wavelengths longer than 1000 to 1400 nm is readily absorbed by water, does not penetrate deeply, and therefore may cause corneal injury, even ablation or vaporization, by a thermal process
occurs when energy is absorbed by the chromophore, such as melanin in the retina, at a pulse ranging from microseconds to seconds.
Thermal damage
- Heat is generated faster than it can be dissipated, thereby denaturing proteins resulting in cell death and tissue necrosis
results from energy at relatively lower levels and longer pulse durations, more than a few seconds
Photochemical damage
- The slow delivery of energy does not deliver enough heat to induce thermal damage. However, single photons can break molecular bonds in nucleic acids and proteins.
- Retinal cells can recover from this type of damage over a period of weeks, but over a certain threshold damage can be irreversible
important parameters of the radiation sources
wavelength, pulse duration, intensity, and radiant exposure
- These parameters of a laser or IPL system determine the characteristics of the safety goggles.
