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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
How does IPL compare to laser?
Less powerful, less selective
26
What is the mechanism of radiofrequency?
Electrodes deliver alternating electric current which locally heats tissue
27
What are the properties of radiofrequency treatments?
Less powerful than lasers or IPL - Some specificity for fat, so used for cellulite and skin tightening
28
What is the unit of work or energy for a laser?
Joules
29
What is fluence?
This is J/cm2 which is the energy delivered per cm2
30
What is power in the setting of lasers?
Rate of energy delivery - Watts = Joules/second
31
What is irradiance in lasers?
Power delivery per cm2 - Watts/cm2
32
What is the pulse width of a laser?
Duration of laser exposure (seconds) - Measured in seconds (or fractions of seconds)
33
What is the impact of increasing fluence?
Increases the energy of treatment per unit area
34
What is the impact of increasing the pulse width/duration of a laser?
This increases exposure to the laser so increases the energy/heat delivered to the tissue
35
How should pulse width/duration be adjusted?
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
36
What is the spot size of a laser?
Diameter of the laser beam hitting the skin - Measured in mm
37
What is the effect of increasing the spot size of a laser?
Decreases scatter and **increases the depth of penetration**
38
What are the wavelengths of UV, visible, infrared, and radiofrequency modalities?
UV = 10-400nm Visible = 400-700nm Infrared = 700nm-1mm Radio= \>1mm
39
What is the relationship between wavelength and depth of penetration?
Longer wavelengths penetrate deeper - This is true until 1300nm --\> penetration decreases past this - Least penetrating wavelengths = low end UV and far IR
40
What is a chromophore?
Absorptive target tissue of laser
41
What are the 3 commonly targeted chromophores in dermatology lasers?
Melanin, hemoglobin (oxyhemoglobin and deoxyhemoglobin) and water ## Footnote *can target multiple at the same time*
42
What is the thermal relaxation time?
Time required for heated tissue to dissipate 50% of its heat - Seconds (or fractions of seconds) - Proportional to the diameter of target squared
43
What is the relationship between the size of the target and thermal relaxation time?
Thermal relaxation time in seconds is proportional to the square of the target's diameter (in mm)
44
What is a laser's photomechanical effect?
Sudden heating --\> thermal expansion w/ acoustic/shock waves - These shock waves cause cavitation which are steam bubbles
45
What is cavitation in the setting of lasers?
Steam bubbles produced from the shock wave from heated tissues - **It is the primary mechanism of vessel rupture w/ PDL**
46
How much of the laser's beam is reflected by the stratum corneum and why is this a safety hazard?
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
47
What portion of the eye can be damaged by KTP, PDL, IPL, ruby, Alexandrite, diode, and ND:YAG lasers?
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
48
What lasers are highest risk of retina damage?
Those w/ near-infrared or Q-switched lasers
49
What part of the eye is particularly susceptible to laser/light sources in the UV range?
Lens --\> cataracts - Excimer laser
50
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)
Corneal/scleral damage
51
What lasers have the highest risk of causing fire/burn?
Ablative lasers: CO2 and Erbium: YAG
52
What are some measures that can help prevent fires with lasers?
Wet hair nearby target areas - Make sure any EtOH or acetone-based cleansers are dry
53
How deep can the dermis be on the face before you get to fat?
Can be as shallow as 2-3mm (Elsewhere usually closer to 4mm)
54
What depth are the superficial dermal blood vessels?
Around 1mm (between 1-2mm)
55
At what depth do we see the deeper dermal blood vessels?
Between 3-4 mm (more shallow on the face... 2mm)
56
What is the wavelength and depth of penetration of the excimer laser?
Wavelength = 308nm Depth of penetration = epidermis
57
What is the wavelength and depth of penetration of the argon laser?
Wavelength= 488-514 Depth: 1mm
58
What is the wavelength and depth of penetration of the KTP laser?
532nm (green visible spectrum) Penetrates to the dermoepidermal junction
59
What is the wavelength and depth of penetration of the PDL laser?
Wavelength= 585-600nm Depth= 2mm (mid dermis)
60
What is the wavelength and depth of penetration of the Ruby laser?
Wavelength = 694 Depth = 2.5-3mm (mid dermis)
61
What is the wavelength and depth of penetration of the Alexandrite laser?
Wavelength = 755 nm Depth = 3mm (almost to depth of the deeper dermal vessels
62
What is the wavelength and depth of penetration of the diode laser?
Wavelength = 800nm Depth = 3.5mm (3-4mm) gets down to deeper dermal vessels
63
What is the wavelength and depth of penetration of the Nd:YAG laser?
Wavelength = 1064 nm Depth = down to subcutaneous fat (4mm +)
64
What is the wavelength and depth of penetration of the Erbium:Glass laser?
Wavelength = 1540nm Depth: 1-2mm (superficial dermal blood vessels)
65
What is the wavelength and depth of penetration of the thulium laser?
Wavelength = 1927 nm Depth = Epidermis
66
What is the wavelength and depth of penetration of the Erbium:YAG laser?
Wavelength = 2940nm Depth = 2 microns (just below stratum corneum) [hence ablative]
67
What is the wavelength and depth of penetration of the CO2 laser?
Wavelength = 10,600 nm Depth = 20microns most of the depth of the epidermis ## Footnote *note that the fractional versions can shoot "columns" of ablation down deeper (nearly full-thickness)*
68
What property of chromophores allows for selective thermolysis?
The heterogenous absorption spectra of the different chromophores make selective thermolysis possible.
69
What lesions can be treated with a vascular laser?
Rosacea, spider angiomas, Poikiloderma of Civatte, hemangioma, vascular malformations, redness in striae, redness in sars, verruca vulgaris, and Kaposi sarcoma
70
What is the mechanism of vascular lasers?
Damages blood vessels via coagulation of vessel contents which leads to vessel collapse or destruction
71
What are the targets and absorptive targets (in nm) of vascular lesions?
Targets: oxyhemoglobin \> deoxyhemoglobin \> methemoglobin Absorption peaks = 418, 542, and 577 nm respectively
72
What laser is the treatment of choice for most vascular lesions?
PDL (585nm-600nm)
73
What are some examples of vascular lesions that are amenable to therapy w/ PDL?
Port-wine stain, telangiectasias, erythematous scars, and hemangiomas
74
What are the end-points for PDL as compared to KTP or Nd:YAG?
PDL = purpura (cavitation and vessel rupture) KTP, Nd:YAG = immediate disappearance of vessel
75
What are the most important side effects from vascular lesion tx?
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
What part of the eye is damaged by the vascular lasers?
Retina!
77
Is skin cooling important w/ vascular lasers?
Yes! Precooling is critical = prevents epidermal damage - Allows for greater pt comfort and allows us to tx w/ higher more efficacious fluences
78
When should HSV prophylaxis be used for vascular lesions?
Perioral lesions Larger facial lesions
79
How do you do a non-purpuric protocol w/ a PDL?
Use pulse durations greater than 20ms - This causes less cavitation or vessel rupture - Will frequently get delayed-type purpura
80
What is the treatment of choice for Poikiloderma of Civatte?
IPL (treats the vessels and the dyschromia) If IPL is not an option, PDL is the next best
81
What is the laser of choice for the vascular ectasias on the lower leg (venulectasias, telangiectasias, and reticular veins)?
- Long-pulsed Nd:YAG (1064nm) is the laser of choice - Second choice would be Diode (800nm)
82
What is the treatment of choice for erythematotelangiectatic rosacea?
IPL or long-pulsed PDL (non-purpuric protocol)
83
What are the infrared lasers?
Nd:YAG (1064, 1320nm), Diode (1450, 1470nm), Er:glass (1540nm)
84
What are the chromophore targets for laser hair removal?
Melanin within hair shaft, ORS and the matrix - Absorption peak = 300-1000nm
85
What hair works best for laser hair removal?
Darker hair ## Footnote *Laser hair removal does not work for white hair*
86
What is the site of eye damage from hair removal lasers?
Retina
87
What are the most common adverse effects of laser hair removal?
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
How many sessions are needed for hair removal?
Multiple sessions spaced 4-6 weeks apart. Goal is reduction not necessarily removal
89
What things should a pt do before getting laser hair removal?
Shave --\> shorter hairs reduce the chance of burning the skin ## Footnote *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
What is the safest laser for laser hair removal in skin of color?
Nd:Yag (1064nm) ## Footnote *Safest, but slightly less effective than Diode*
91
What form of laser is NOT safe for skin types IV-VI?
IPL
92
What 4 types of laser that can be used for laser hair removal, their wavelengths, and skin types that can be used?
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
What types of lesions are good for resurfacing lasers?
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
What is the target of the resurfacing lasers and what are the absorption peaks?
Target is water Absorption peaks are: 1450, 1950, and 3000nm
95
What are the two mechanisms of resurfacing?
Ablative: Function by removing skin via vaporization of the target tissue Nonablative: subtle thermal effects on dermis --\> stimulates a wound healing response
96
What does it mean for a resurfacing laser to be "fractionated"?
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
What is the site of eye damage from resurfacing lasers?
Cornea, sclera (burns)
98
What types of prophylaxis should be done for resurfacing lasers?
HSV, bacterial, or fungal
99
Adverse effects of resurfacing lasers?
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
What is the diameter, thermal relaxation time, and typical pulse duration used for tattoo ink particles?
Diameter = 0.1 microns Thermal relaxation time = 10 nanoseconds Typical pulse duration = 0.6-10 nanoseconds (needs q-swtiched lasers)
101
What is the diameter, thermal relaxation time, and typical pulse duration used for melanosomes?
Diameter = 0.5 microns Thermal relaxation time = 250 nanoseconds Typical pulse duration = 10-100 nanoseconds (needs q-switched lasers)
102
What is the diameter, thermal relaxation time, and typical pulse duration used for PWS?
Diameter = 30-100 microns Thermal relaxation time = 1-10 milliseconds Typical pulse duration = 0.4-20 milliseconds
103
What is the diameter, thermal relaxation time, and typical pulse duration used for terminal hair follicles?
Diameter = 300 microns Thermal relaxation time = 100 milliseconds Typical pulse duration = 3-100 milliseconds
104
What is the diameter, thermal relaxation time, and typical pulse duration used for leg veins?
Diameter = 1 mm Thermal relaxation time = 1 second Typical pulse duration = 0.1 seconds
105
What types of lasers are needed for tattoo pigment?
Q-switched (very short TRT [nanoseconds])
106
What is the desired endpoint for tattoo removal w/ lasers?
Immediate tattoo whitening (desired endpoint) is a result of cavitation
107
What are the most susceptible tattoos to removal?
Amateur tattoos and black pigment (\<5 sessions)
108
What types of tattoos are more resistant to laser treatment (need as many as or more than 10 sessions)?
Professional tattoos and multicolored tattoos
109
What 3 lasers can be used for blue, black, and brown tattoo pigments (the 3 b's)?
3 lasers - Ruby - Alexandrite - Nd:YAG
110
What laser is needed for Yellow, white, red, or violet tattoo?
Nd:YAG
111
What are the only 2 lasers that can treat green tattoo pigment?
Ruby and alexandrite
112
What tattoo pigment is the most common one to cause an allergic reaction?
Red (mercuric sulfide)
113
Should laser be used to remove a tattoo that a patient is allergic to?
Very carefully!!! Treatment can induce anaphylaxis
114
What can happen if white tattoos are lasered?
They can darken (conversion of Ti4+--\> Ti3+)
115
What happens if pink or light-red tattoos are lasered?
May undergo immediate paradoxical darkening (brown-black) w/ laser b/c of reduction of ferric oxide to ferrous oxide
116
What types of lasers would you use for a pigmented lesion (lentigo, ephelides, or nevus of ota)?
Same lasers as black pigment (remember RAN) Ruby, alexandrite, and Nd:YAG
117
What is the most classic laser of choice to be used for nevus of Ota?
Ruby
118
What lasers are used for removing minocycline-induced hyperpigmentation?
The "RAN" lasers (Ruby, alexandrite, Nd:YAG)
119
What are the 3 types of ablative resurfacing lasers, their wavelengths, and important properties?
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
What are the non-ablative resurfacing lasers?
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
What lasers are best for superficial pigmented lesions (lentigos)?
Nd:YAG 532 nm laser (probably best), others: Q-switched ruby (694), Q-switched alexandrite (755), and IPL
122
What is the relationship between the thermal relaxation time and the size of the target?
It is related to the square of the diameter and is expressed in seconds. ## Footnote *an example might be a blood vessel with a diameter of 0.2mm will have a relation time of 40ms*
123
What is the difference in thermal relaxation time between blood vessels and melanosomes?
Melanosomes are much much smaller, thus the thermal relaxation time is much shorter (0.25-1microsecond) as compared to millisecond times for vessels ## Footnote *Takehome: Pigmented lesions need pulse durations in the nanosecond range whereas vascular lesions need pulse durations in the millisecond range*
124
What can minimize the risk of hyperpigmentation after laser treatment?
Conservative power settings, and appropriate skin cooling
125
What is the clinical endpoint of the laser used for nevus of Ota?
Dermal whitening (similar to tattoo treatment)
126
What is the clinical endpoint for a hair removal laser?
Perifollicular edema

DERM (15) Physical Treatment Modalities (4 decks)

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