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Dermatology Board Prep > DERM (15) Physical Treatment Modalities > Lasers > Flashcards

Lasers Flashcards

1
Q

What are the “3 C’s” of lasers?

A

Coherence, Collimation, (mono)Chromatic

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2
Q

What is Coherence, in the setting of lasers?

A

The light waves travel together in-phase in time and space

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3
Q

What is Collimation in the setting of lasers?

A

Light waves travel together in a parallel way

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4
Q

What is the monochromatic nature of lasers mean?

A

Light waves are all the same wavelength

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5
Q

What are the 3 different laser medias?

A

Gas, Liquid, and Solid

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6
Q

What are some examples of gas media lasers?

A

CO2, xenon chloride (excimer), krypton, argon, copper vapor, helium-neon

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7
Q

What are some examples of liquid media lasers?

A

Rhodamine dye (PDL)

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8
Q

What are some examples of solid media lasers?

A

2 classes: Crystal and semiconductor

  1. Crystal: Alexandrite, Er-YAG, Nd-YAG, potassium titanyl phosphate (KTP), and Ruby
  2. Semiconductor: Diode
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9
Q

What are the 3 things that modulate selective photothermolysis?

A

Selective Photothermolysis = selective destruction of a target structure

Three factors that modulate selective photothermolysis:

  • Wavelength: Targets the desired chromophore and reach an appropriate anatomic depth to destroy that tissue
  • Pulse duration: Should be ≤ TRT
  • Fluence: Must be high enough to damage target tissue, but not so high as to nonspecifically damage surrounding tissues
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10
Q

What are the 4 types of laser waveform?

A

Continuous, Pulsed, Quality Switched, Quasi-continuous

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11
Q

What is a continuous laser waveform and an example of a laser using this waveform?

A

Emits light continuously, low power lasers can do this (CO2 and argon)

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12
Q

What is a pulsed waveform lasers?

A

Light is emitted periodically - short pulse durations (millisecond range) and high power

  • Examples = PDL, ruby, alexandrite, diode, Erbium:glass, and Erbium:YAG
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13
Q

What is a quality switched laser and examples?

A

Variant of pulsed = extremely short pulse durations (nanosecond range). These have extremely high power

Examples: Any Q-switched laser

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14
Q

What things are q-switched (quality pulsed) lasers good for and why?

A

Good for pigmented lesions, tattoos, and drug deposits

  • This is because the molecules are very small and have a short thermal relaxation time
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15
Q

What are quasi-continuous lasers, and can you provide examples?

A

Emits multiple rapid bursts of low-energy light

  • It can simulate continuous wave lasers
  • Examples: KTP and copper vapor
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16
Q

What are the 4 types of interactions that target tissues/molecules can have w/ emitted laser light particles?

A

Reflection, Scattering, Transmission, and Absorption (this one is what you want!)

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17
Q

What is reflection in the setting of laser-tissue interaction?

A

This is light that bounces off

  • 4-7% of light is reflected
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18
Q

What is scattering in terms of laser-tissue interaction?

A

Light bounces off fibers within the dermis and subcutaneous space without truly interacting –> no effect

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19
Q

What is transmission in the setting of the laser-tissue interaction?

A

Light passes straight through the tissue without interacting with anything –> no effect on tissues

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20
Q

What is absorption in the setting of the laser-tissue interaction?

A

Light is absorbed by its intended target –> this is the desired interaction

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21
Q

Skin heating/epidermal damage is minimized w/ cooling, what are the 3 most common methods employed?

A

Precooling: Most aggressive and effective –> cryogen (tetrafluoroethane) spray

Parallel cooling: only effective for pulses >5ms (solid cold sapphire window pressed against skin)

Postcooling: Used to decrease pain, erythema and edema (ice-packs, cold air)

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22
Q

What is the source of intense pulsed light procedure?

A

Xenon flashlamp –> emits noncollimated, noncoherent, and polychromatic light (500-1200nm)

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23
Q

What type of light is emitted by IPL (intense pulsed light)?

A

Noncollimated, noncoherent, and polychromatic light (500-1200nm)

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24
Q

What is the purpose of filters for IPL?

A

Narrows down the range of wavelengths for targeting certain chromophores

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25
Q

How does IPL compare to laser?

A

Less powerful, less selective

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26
Q

What is the mechanism of radiofrequency?

A

Electrodes deliver alternating electric current which locally heats tissue

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27
Q

What are the properties of radiofrequency treatments?

A

Less powerful than lasers or IPL

  • Some specificity for fat, so used for cellulite and skin tightening
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28
Q

What is the unit of work or energy for a laser?

A

Joules

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29
Q

What is fluence?

A

This is J/cm2 which is the energy delivered per cm2

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30
Q

What is power in the setting of lasers?

A

Rate of energy delivery

  • Watts = Joules/second
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31
Q

What is irradiance in lasers?

A

Power delivery per cm2

  • Watts/cm2
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32
Q

What is the pulse width of a laser?

A

Duration of laser exposure (seconds)

  • Measured in seconds (or fractions of seconds)
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33
Q

What is the impact of increasing fluence?

A

Increases the energy of treatment per unit area

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34
Q

What is the impact of increasing the pulse width/duration of a laser?

A

This increases exposure to the laser so increases the energy/heat delivered to the tissue

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35
Q

How should pulse width/duration be adjusted?

A

Keeping in mind the tissue relaxation time

  • Pulse width should be less than the tissue relaxation time that you don’t want to hurt–> give bystander tissue time to release heat and not be damaged
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36
Q

What is the spot size of a laser?

A

Diameter of the laser beam hitting the skin

  • Measured in mm
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37
Q

What is the effect of increasing the spot size of a laser?

A

Decreases scatter and increases the depth of penetration

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38
Q

What are the wavelengths of UV, visible, infrared, and radiofrequency modalities?

A

UV = 10-400nm

Visible = 400-700nm

Infrared = 700nm-1mm

Radio= >1mm

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39
Q

What is the relationship between wavelength and depth of penetration?

A

Longer wavelengths penetrate deeper

  • This is true until 1300nm –> penetration decreases past this
  • Least penetrating wavelengths = low end UV and far IR
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40
Q

What is a chromophore?

A

Absorptive target tissue of laser

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41
Q

What are the 3 commonly targeted chromophores in dermatology lasers?

A

Melanin, hemoglobin (oxyhemoglobin and deoxyhemoglobin) and water

can target multiple at the same time

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42
Q

What is the thermal relaxation time?

A

Time required for heated tissue to dissipate 50% of its heat

  • Seconds (or fractions of seconds)
  • Proportional to the diameter of target squared
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43
Q

What is the relationship between the size of the target and thermal relaxation time?

A

Thermal relaxation time in seconds is proportional to the square of the target’s diameter (in mm)

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44
Q

What is a laser’s photomechanical effect?

A

Sudden heating –> thermal expansion w/ acoustic/shock waves

  • These shock waves cause cavitation which are steam bubbles
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45
Q

What is cavitation in the setting of lasers?

A

Steam bubbles produced from the shock wave from heated tissues

  • It is the primary mechanism of vessel rupture w/ PDL
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46
Q

How much of the laser’s beam is reflected by the stratum corneum and why is this a safety hazard?

A

7% of a laser is reflected by the stratum corneum

  • This reflected light can cause eye damage, blindness, and thus requires the use of specialized goggles
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47
Q

What portion of the eye can be damaged by KTP, PDL, IPL, ruby, Alexandrite, diode, and ND:YAG lasers?

A

Any laser that targets melanin or hemoglobin can lead to retinal damage b/c the retina is highly pigmented

  • Also damages the uvea and iris
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48
Q

What lasers are highest risk of retina damage?

A

Those w/ near-infrared or Q-switched lasers

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49
Q

What part of the eye is particularly susceptible to laser/light sources in the UV range?

A

Lens –> cataracts

  • Excimer laser
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50
Q

What part of the eye is susceptible to damage from the lasers targeting water (mid and far-infrared wavelengths) like ND:YAG (1320nm), erbium:glass (1550nm), and Co2 (10,600nm)

A

Corneal/scleral damage

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51
Q

What lasers have the highest risk of causing fire/burn?

A

Ablative lasers: CO2 and Erbium: YAG

52
Q

What are some measures that can help prevent fires with lasers?

A

Wet hair nearby target areas

  • Make sure any EtOH or acetone-based cleansers are dry
53
Q

How deep can the dermis be on the face before you get to fat?

A

Can be as shallow as 2-3mm (Elsewhere usually closer to 4mm)

54
Q

What depth are the superficial dermal blood vessels?

A

Around 1mm (between 1-2mm)

55
Q

At what depth do we see the deeper dermal blood vessels?

A

Between 3-4 mm (more shallow on the face… 2mm)

56
Q

What is the wavelength and depth of penetration of the excimer laser?

A

Wavelength = 308nm

Depth of penetration = epidermis

57
Q

What is the wavelength and depth of penetration of the argon laser?

A

Wavelength= 488-514

Depth: 1mm

58
Q

What is the wavelength and depth of penetration of the KTP laser?

A

532nm (green visible spectrum)

Penetrates to the dermoepidermal junction

59
Q

What is the wavelength and depth of penetration of the PDL laser?

A

Wavelength= 585-600nm

Depth= 2mm (mid dermis)

60
Q

What is the wavelength and depth of penetration of the Ruby laser?

A

Wavelength = 694

Depth = 2.5-3mm (mid dermis)

61
Q

What is the wavelength and depth of penetration of the Alexandrite laser?

A

Wavelength = 755 nm

Depth = 3mm (almost to depth of the deeper dermal vessels

62
Q

What is the wavelength and depth of penetration of the diode laser?

A

Wavelength = 800nm

Depth = 3.5mm (3-4mm) gets down to deeper dermal vessels

63
Q

What is the wavelength and depth of penetration of the Nd:YAG laser?

A

Wavelength = 1064 nm

Depth = down to subcutaneous fat (4mm +)

64
Q

What is the wavelength and depth of penetration of the Erbium:Glass laser?

A

Wavelength = 1540nm

Depth: 1-2mm (superficial dermal blood vessels)

65
Q

What is the wavelength and depth of penetration of the thulium laser?

A

Wavelength = 1927 nm

Depth = Epidermis

66
Q

What is the wavelength and depth of penetration of the Erbium:YAG laser?

A

Wavelength = 2940nm

Depth = 2 microns (just below stratum corneum) [hence ablative]

67
Q

What is the wavelength and depth of penetration of the CO2 laser?

A

Wavelength = 10,600 nm

Depth = 20microns most of the depth of the epidermis

note that the fractional versions can shoot “columns” of ablation down deeper (nearly full-thickness)

68
Q

What property of chromophores allows for selective thermolysis?

A

The heterogenous absorption spectra of the different chromophores make selective thermolysis possible.

69
Q

What lesions can be treated with a vascular laser?

A

Rosacea, spider angiomas, Poikiloderma of Civatte, hemangioma, vascular malformations, redness in striae, redness in sars, verruca vulgaris, and Kaposi sarcoma

70
Q

What is the mechanism of vascular lasers?

A

Damages blood vessels via coagulation of vessel contents which leads to vessel collapse or destruction

71
Q

What are the targets and absorptive targets (in nm) of vascular lesions?

A

Targets: oxyhemoglobin > deoxyhemoglobin > methemoglobin

Absorption peaks = 418, 542, and 577 nm respectively

72
Q

What laser is the treatment of choice for most vascular lesions?

A

PDL (585nm-600nm)

73
Q

What are some examples of vascular lesions that are amenable to therapy w/ PDL?

A

Port-wine stain, telangiectasias, erythematous scars, and hemangiomas

74
Q

What are the end-points for PDL as compared to KTP or Nd:YAG?

A

PDL = purpura (cavitation and vessel rupture)

KTP, Nd:YAG = immediate disappearance of vessel

75
Q

What are the most important side effects from vascular lesion tx?

A

Purpura –> mostly w/ PDL

Dyschromia –> Increased risk in darker skin types

Blistering –> increased risk w/ shorter pulse widths, higher fluences, and skin of color

76
Q

What part of the eye is damaged by the vascular lasers?

77
Q

Is skin cooling important w/ vascular lasers?

A

Yes!

Precooling is critical = prevents epidermal damage

  • Allows for greater pt comfort and allows us to tx w/ higher more efficacious fluences
78
Q

When should HSV prophylaxis be used for vascular lesions?

A

Perioral lesions

Larger facial lesions

79
Q

How do you do a non-purpuric protocol w/ a PDL?

A

Use pulse durations greater than 20ms

  • This causes less cavitation or vessel rupture
  • Will frequently get delayed-type purpura
80
Q

What is the treatment of choice for Poikiloderma of Civatte?

A

IPL (treats the vessels and the dyschromia)

If IPL is not an option, PDL is the next best

81
Q

What is the laser of choice for the vascular ectasias on the lower leg (venulectasias, telangiectasias, and reticular veins)?

A
  • Long-pulsed Nd:YAG (1064nm) is the laser of choice
  • Second choice would be Diode (800nm)
82
Q

What is the treatment of choice for erythematotelangiectatic rosacea?

A

IPL or long-pulsed PDL (non-purpuric protocol)

83
Q

What are the infrared lasers?

A

Nd:YAG (1064, 1320nm), Diode (1450, 1470nm), Er:glass (1540nm)

84
Q

What are the chromophore targets for laser hair removal?

A

Melanin within hair shaft, ORS and the matrix

  • Absorption peak = 300-1000nm
85
Q

What hair works best for laser hair removal?

A

Darker hair

Laser hair removal does not work for white hair

86
Q

What is the site of eye damage from hair removal lasers?

87
Q

What are the most common adverse effects of laser hair removal?

A

Post-inflammatory hyperpigmentation (more common in skin of color) [In pts w/ darker skin types, use a test spot first]

Leukotrichia

Blistering/burning (increased risk in skin of color)

88
Q

How many sessions are needed for hair removal?

A

Multiple sessions spaced 4-6 weeks apart. Goal is reduction not necessarily removal

89
Q

What things should a pt do before getting laser hair removal?

A

Shave –> shorter hairs reduce the chance of burning the skin

DO NOT: use waxes, depilatory agents, plucking etc as these remove the whole hair. Don’t do this for at least 6 weeks prior to laser

90
Q

What is the safest laser for laser hair removal in skin of color?

A

Nd:Yag (1064nm)

Safest, but slightly less effective than Diode

91
Q

What form of laser is NOT safe for skin types IV-VI?

92
Q

What 4 types of laser that can be used for laser hair removal, their wavelengths, and skin types that can be used?

A

Alexandrite (755nm), Skin types I-III

Diode (810; 940nm), skin types I-III (most effective)

Nd:YAG (1064), all skin types (safest in skin of color)

IPL (various filters), unsafe in skin types IV-VI

93
Q

What types of lesions are good for resurfacing lasers?

A

Rhytids, photoaging and actinic damage, acne scars, keloid, hypertrophic and burn scars, post-surgical scars, benign skin lesions (SKs/warts/syringomas), striae, and rhinophyma

94
Q

What is the target of the resurfacing lasers and what are the absorption peaks?

A

Target is water

Absorption peaks are: 1450, 1950, and 3000nm

95
Q

What are the two mechanisms of resurfacing?

A

Ablative: Function by removing skin via vaporization of the target tissue

Nonablative: subtle thermal effects on dermis –> stimulates a wound healing response

96
Q

What does it mean for a resurfacing laser to be “fractionated”?

A

Creates thousands of microscopic thermal zones of injury –> stimulate turnover/remodeling of the epidermis and dermis

  • Decrease downtime, decrease the duration of erythema
  • Requires more sessions and less effective
97
Q

What is the site of eye damage from resurfacing lasers?

A

Cornea, sclera (burns)

98
Q

What types of prophylaxis should be done for resurfacing lasers?

A

HSV, bacterial, or fungal

99
Q

Adverse effects of resurfacing lasers?

A

Erythema (can persist for months)

Hyperpigmentation

Relative hypopigmentation (increased risk of deeper injury; may arise months after treatment)

Secondary infections (HSV = highest risk in first week, bacteria)

Scarring

100
Q

What is the diameter, thermal relaxation time, and typical pulse duration used for tattoo ink particles?

A

Diameter = 0.1 microns

Thermal relaxation time = 10 nanoseconds

Typical pulse duration = 0.6-10 nanoseconds (needs q-swtiched lasers)

101
Q

What is the diameter, thermal relaxation time, and typical pulse duration used for melanosomes?

A

Diameter = 0.5 microns

Thermal relaxation time = 250 nanoseconds

Typical pulse duration = 10-100 nanoseconds (needs q-switched lasers)

102
Q

What is the diameter, thermal relaxation time, and typical pulse duration used for PWS?

A

Diameter = 30-100 microns

Thermal relaxation time = 1-10 milliseconds

Typical pulse duration = 0.4-20 milliseconds

103
Q

What is the diameter, thermal relaxation time, and typical pulse duration used for terminal hair follicles?

A

Diameter = 300 microns

Thermal relaxation time = 100 milliseconds

Typical pulse duration = 3-100 milliseconds

104
Q

What is the diameter, thermal relaxation time, and typical pulse duration used for leg veins?

A

Diameter = 1 mm

Thermal relaxation time = 1 second

Typical pulse duration = 0.1 seconds

105
Q

What types of lasers are needed for tattoo pigment?

A

Q-switched (very short TRT [nanoseconds])

106
Q

What is the desired endpoint for tattoo removal w/ lasers?

A

Immediate tattoo whitening (desired endpoint) is a result of cavitation

107
Q

What are the most susceptible tattoos to removal?

A

Amateur tattoos and black pigment (<5 sessions)

108
Q

What types of tattoos are more resistant to laser treatment (need as many as or more than 10 sessions)?

A

Professional tattoos and multicolored tattoos

109
Q

What 3 lasers can be used for blue, black, and brown tattoo pigments (the 3 b’s)?

A

3 lasers

  • Ruby
  • Alexandrite
  • Nd:YAG
110
Q

What laser is needed for Yellow, white, red, or violet tattoo?

111
Q

What are the only 2 lasers that can treat green tattoo pigment?

A

Ruby and alexandrite

112
Q

What tattoo pigment is the most common one to cause an allergic reaction?

A

Red (mercuric sulfide)

113
Q

Should laser be used to remove a tattoo that a patient is allergic to?

A

Very carefully!!!

Treatment can induce anaphylaxis

114
Q

What can happen if white tattoos are lasered?

A

They can darken (conversion of Ti4+–> Ti3+)

115
Q

What happens if pink or light-red tattoos are lasered?

A

May undergo immediate paradoxical darkening (brown-black) w/ laser b/c of reduction of ferric oxide to ferrous oxide

116
Q

What types of lasers would you use for a pigmented lesion (lentigo, ephelides, or nevus of ota)?

A

Same lasers as black pigment (remember RAN)

Ruby, alexandrite, and Nd:YAG

117
Q

What is the most classic laser of choice to be used for nevus of Ota?

118
Q

What lasers are used for removing minocycline-induced hyperpigmentation?

A

The “RAN” lasers (Ruby, alexandrite, Nd:YAG)

119
Q

What are the 3 types of ablative resurfacing lasers, their wavelengths, and important properties?

A

Erbium:yttrium scandium gallium garnet (Er:YSGG), wavelength = 2790, less thermal injury so poor coagulation, increased bleeding, and decreased collagen retraction

Erbium: aluminum garnet (Er:YAG), 2940nm, less thermal injury so poor coagulation, increased bleeding, and decreased collagen retraction. Targets the 3000nm peak of water more than CO2 –> decreased recovery time, decreased PIH, and erythema goes away quicker

CO2, 10,600nm, more thermal injury so good coagulation, less bleeding, increased collagen retraction

120
Q

What are the non-ablative resurfacing lasers?

A

PDL (585-600nm)

Infrared (Nd:YAG, Diode, and Er:glass), all achieve mild dermal tightening, but do not help w/ epidermal sun damage. Diode is good for acne scars

IPL (515-1200nm), leads to mild dermal tightening adn also treats epidermal photodamage

121
Q

What lasers are best for superficial pigmented lesions (lentigos)?

A

Nd:YAG 532 nm laser (probably best), others: Q-switched ruby (694), Q-switched alexandrite (755), and IPL

122
Q

What is the relationship between the thermal relaxation time and the size of the target?

A

It is related to the square of the diameter and is expressed in seconds.

an example might be a blood vessel with a diameter of 0.2mm will have a relation time of 40ms

123
Q

What is the difference in thermal relaxation time between blood vessels and melanosomes?

A

Melanosomes are much much smaller, thus the thermal relaxation time is much shorter (0.25-1microsecond) as compared to millisecond times for vessels

Takehome: Pigmented lesions need pulse durations in the nanosecond range whereas vascular lesions need pulse durations in the millisecond range

124
Q

What can minimize the risk of hyperpigmentation after laser treatment?

A

Conservative power settings, and appropriate skin cooling

125
Q

What is the clinical endpoint of the laser used for nevus of Ota?

A

Dermal whitening (similar to tattoo treatment)

126
Q

What is the clinical endpoint for a hair removal laser?

A

Perifollicular edema

DERM (15) Physical Treatment Modalities (4 decks)

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