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Technology > LASER > Flashcards

LASER Flashcards

1
Q

laser safety -9

A 
Laser Safety Training
Responsibility – Laser Officer / Surgeon
Correct Laser
Correct  Fibre
Minimse no. of staff members
Eye protection
Door locks
Signange
Window covers
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2
Q

LASER acronym

A

light amplitude by stimulated emission of radiation

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3
Q

wavelength light

A

100nm and 1mm

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4
Q

MCC

A

monochromatic, coherent, collimated
same direction - allows for focusing
wavelength
phase - spatial and temporal coherence, moving in phase with eachother allows to travel long distances, all emitted photons bear a constant relationship with each other in time and space

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5
Q

laser medium energy emission

A

atoms in laser medium can emit photons when going from excited state to ground low energy state
spontaneous emission = random process
stimulated emission = when stimulated by photon, emits another coherent photon - i.e. same wavelength, frequency and phase

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6
Q

laser - incoherent light to coherent light i.e. laser

A

incoherent light i.e. red shines on laser medium
pumps laser medium putting energy into system
excites atoms in laser medium
excited atoms release photos
laser medium will also go to same excited state so will always emit same wavelength regardless of wavelength of energy source

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7
Q

how laser beam is reflected

A

formed by partially reflecting mirror at one end of laser fibre (totally reflecting mirrow other end to reflect all photons) to release photons from laser medium through aperture

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8
Q

resonating chamber

A

this is the brick which contains the laser medium of Ho YAG
light shone onto this brick generates laser which is released through aperture
YAG is crystal is doped with holmium or thulium
requires water cooling system

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9
Q

laser fibres
what made off
what reflection
sizes

A

glass fibres
total internal reflection
200, 365, 550

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10
Q

range of Ho YAG laser

A

1mm, but can be 3-4mm

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11
Q

moses
how it works
advantages

A

emits double pulse - two smaller pulses
first one opens a gas bubble which is better medium for laser
second pulse emitted
less retropulsion and cavitation
parting the waves and shooting through them
better for dusting

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12
Q

pulse width

A

laser can adjust joules or hertz
pulse width can deliver joules in short packet or long packet
short pulse like a punch - explosion
long pulse - more for dusting and less retropulsion, reduced amplitude

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13
Q

EMS laser

A

20 watt can alter short and long pulse

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14
Q

ureter setting

A

long pulse

low energy up to 10watts maximum

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15
Q

holmium vs thulium

A

wavelength
2100nm vs 1940nm
thulium better absorbed by tissue compared to water
better for tissue
no specific advantage over stone
TFL - practical considerations, smaller quieter machine

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16
Q

attenuation coefficient of laser

A

how quickly the power of a laser falls off

exponential decay mostly due to absorption in the medium resulting in heating of medium

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17
Q

heat energy from lasers

A

cooling effect from irrigation negligible vs energy from laser even with access sheath

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18
Q

laser heat damage temperature rise

A

400J will raise 10mls of water in renal collecting system by 10 degrees
heat transferred to renal parechyma and heat sink effect from vasculature
flow through scope is less than 1ml/sec
so irrigation effect minimal
operator duty cycle
do not warm up irrigation fluid - room temperature fluid

19
Q

effect of access sheath on intra renal pressure

A

halves intra renal pressure

20
Q

TFL laser

A

high power laser
contact laser
but higher risk ureteric thermal injury
more mindful of the operator duty cycle

21
Q

what is laser in princple

A

emission of photons that occurs when an atom is stimulated by an external source

22
Q

photo acoustic effect of laser

photo thermal mechnism

A

pulsed laser release electrons at surface of stone which form a plasma bubble
expansion followed by collapse plasma bubble form a shock wave
leading to frag of stone
vapourisation when temps reach above 100

23
Q

HoYAG laser

A

rod of YAG containing ions of holmium
mainly due to laser stone heating
minimal shockwave generation
zone thermal injury 0.5 to 1mm from laser tip

The depth of penetration is limited to 0.4 mm, and with a wavelength in the mid-infrared spectrum, it is avidly absorbed by water. Since human tissue is composed mainly of water, the majority of the Ho:YAG laser energy is absorbed superficially and allows for precise superficial cutting or tissue ablation, with minimal collateral tissue injury

24
Q

stimulated emission

A

energy applied to lasing medium
photon is released from an atom within the medium
and further collides with excited atoms to release more photons

25
Q

what are laser fibres made of

A

silica/ silicon dioxide i.e. glass

26
Q

Neo YAG

A

1064nm wavelength
10mm penetration
tcc ablation, prostate tissue

27
Q

KTP Nd YAG

A

532 nm

vapourise prostate tissue penetration 0.8mm

28
Q

LBO Nd YAG

A

lithium borate greenlight also for prostate tissue

29
Q

thulium

A

TmYAG 2013 wavelenght, vapourise tcc, and prostate, 0.25mm

30
Q

monochromatic light and effect on tissues

A

Monochromatic light, of a single colour, is defi ned by its wavelength.
It can specifi cally target tissues (the chromophore) that absorb that light wavelength.

31
Q

three steps required generate laser beam

A

Three steps are required to generate a laser beam:
1. Energy is infused into the lasing medium and absorbed by many of its atoms
pushing them into an excited state. These then emit energy as photons.
2. The photons collide with other excited atoms of the lasing medium causing additional photon emission.
3. The emitted photons are amplifi ed by refl ecting them between two mirrors at either end of the laser cavity causing energy build up. This energy exits through an aperture in the front mirror as an intense laser beam

32
Q

three steps required generate laser beam

A

Three steps are required to generate a laser beam:
1. Energy is infused into the lasing medium and absorbed by many of its atoms
pushing them into an excited state. These then emit energy as photons.
2. The photons collide with other excited atoms of the lasing medium causing additional
photon emission.
3. The emitted photons are amplifi ed by refl ecting them between two mirrors at
either end of the laser cavity causing energy build up. This energy exits through
an aperture in the front mirror as an intense laser beam

33
Q

factors influencing tissue effect
laser factors 4
tissue factors 2

A

Laser factors
Wavelength

Power: energy (joules) × rate (hertz) = power
(watts)

Mode of emission: pulsed vs. continuous
Distance from target: contact or near contact =
incision; close = vaporisation; more distant
= coagulation

Tissue factors
Tissue density

Water content: if the chromophore is water
then water-rich tissues (e.g., prostate,
bladder tumours) will be specifi cally
targeted by that wavelength.

34
Q

what happens when laser hits tissues

A

Tissue is affected by laser energy by absorbing light and converting it to thermal
energy.

35
Q

temperature of thermal effect and result

A

When temperatures reach 60–100°C, tissue coagulation occurs with subsequent
delayed tissue necrosis and debulking. Temperatures exceeding this will lead
to vaporisation with immediate tissue debulking

36
Q

how to lasers break up stones

A

Laser energy may break stones by
a photothermal mechanism, with direct absorption of laser energy causing vaporisation
of the stone or by a photo-acoustic effect where a pulsed laser causes formation
of a plasma bubble which expands and collapses generating a shock wave

37
Q

three laser techniques for BPH

A

vapourisation
resection
enucleation

38
Q

disadvantages laser vapourisation prostate 4

A

Vaporisation: The simplest but least effi cient method of tissue debulking.
Requires expensive single-use side-fi ring fi bres. There are concerns over durability
particularly in men with prostates >80 cc and no tissue is available for
histology.

39
Q

absorption of ho yag in water

pulsed nature and tissue relaxation time

A

The optical absorption coefficient for water at this wavelength is approximately 40 cm-1, so it is strongly absorbed by water in the superficial tissue. This property allows the laser to perform superficial cutting. Dissipating heat with a high-power laser can cause tissue vaporization. The zone of thermal injury associated with laser ablation ranges from 0.5 to 1 mm and ensures adequate hemostasis during ablation even for vessels >1 mm in diameter. The pulse duration of Ho:YAG laser is short enough so that diffusion of thermal energy of low-power lasers is minimal (thermal relaxation time for soft tissues has been estimated to be 310 msec).

39
Q

absorption of ho yag in water

pulsed nature and tissue relaxation time

A

The optical absorption coefficient for water at this wavelength is approximately 40 cm-1, so it is strongly absorbed by water in the superficial tissue. This property allows the laser to perform superficial cutting. Dissipating heat with a high-power laser can cause tissue vaporization. The zone of thermal injury associated with laser ablation ranges from 0.5 to 1 mm and ensures adequate hemostasis during ablation even for vessels >1 mm in diameter. The pulse duration of Ho:YAG laser is short enough so that diffusion of thermal energy of low-power lasers is minimal (thermal relaxation time for soft tissues has been estimated to be 310 msec).

40
Q

properties Ho Yag laser

A

The Ho:YAG laser is a pulsed laser with a wave length of
2100 nm, with a total energy emission that can vary from
0.2–6 Joules and a frequency of 6–50 Hz

41
Q

safety class of Ho YAG

A

As with most laser devices used for medical indications
and according to the American National Standards Institute
(ANSI), the Ho:YAG laser is considered a class 4 laser -highest of 1-4 meaning it may cause immediate injury to eye and skin through
direct or reflected exposure to the beam.4

42
Q

laser machine

A

Lumenis® Pulse™ 100H
Powerful Stone Dusting and HoLEP Treatments
100W of power for effective HoLEP procedures

Technology (24 decks)

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