0
Laser and its medical
applications
S.SELVAKUMAR
ASSISTANT PROFESSOR
THAMIRABHARANI ENGINEERING
COLLEGE
TIRUNELVELI
9042474...
A wide application of laser in medicine and beauty therapy
 Surgical laser: removing tumors, making incisions.
 Cosmetic...
Laser
repairing retina
Laser removal of port-wine stain
Laser skin rejuvenation
What is a laser?
Laser = Light Amplification by Stimulated Emission of Radiation

•The physics of laser
•The interaction o...
Outline of the unit 11
•Simple atomic structure
•Light emission
•Characteristic of laser
•Laser power and intensity
•Mecha...
1. Summary about atom
Atom is the smallest
building block of matters,
including body tissue and
fluids,
•it is electrically neutral, it contains...
2. Light emission
•electron orbits displayed as an energy level diagram
• energy is plotted vertically with the lowest (n=1) , or
ground sta...
(a) The electron can absorb energy and jump to a higher level, the
process is called excitation.
(b) A photon is emitted w...
Atom will absorb and emit light photons at particular
wavelength corresponding to the energy differences
between orbits. T...
3. How laser works
Spontaneous emission and stimulated emission

An excited electron may gives off a photon and decay to the
ground state by ...
Optical pumping
many electrons must be previously excited and held in an
excited state without massive spontaneous emissio...
Optical pumping

Only those perpendicular to the mirrors will be reflected
back to the active medium, They travel together...
Characteristics of laser
• The second photon has the same energy, i.e.
the same wavelength and color as the first
– laser ...
Characteristics of laser
Pure color

Directionality
Temporal coherence
The power and intensity of a laser
The power P is a measure of energy transfer rate;
Total energy output (J)
Power(W) =
ex...
laser versus ordinary lights:

The directionality of laser beam offers a great advantage over
ordinary lights since it can...
Sample problem: we compare the intensity of the light of a
bulb of 10 W and that of a laser with output power of 1mW
(10-3...
Fluence, F is defined as the total energy delivered by a
laser on an unit area during an expose time TE,
F(J/cm2)=I(watts/...
continuous wave (CW) lasers versus pulsed lasers
• CW lasers has a constant power output during whole operation
time.
• pu...
• The tw may vary from milliseconds (1ms=10-3 s) to
femtoseconds (1fs=10-15s), but typically at nanoseconds
(1ns=10-9s).
•...
Example
A pulsed laser emits 1 milliJoule (mJ) energy that lasts for 1
nanoseconds (ns), if the repetition rate R is 5 Hz,...
4. Mechanisms of laser
interaction with human tissues
When a laser beam projected to tissue
Five phenomena:
•reflection,
•transmission,
•scattering,
•re-emission,
•absorption.
...
Photocoagulation
What is a coagulation?
• A slow heating of muscle and other tissues is like a
cooking of meat in everyday...
Consequence of photocoagulation
When lasers are used to photocoagulate tissues during
surgery, tissues essentially becomes...
Applications of photocoagulation
• destroy tumors
• treating various eye conditions like retinal disorders
caused by diabe...
Photo-vaporization
With very high power densities, instead of cooking, lasers
will quickly heat the tissues to above 100o ...
Conditions for photo-vaporization
1.the tissue must be heated quickly to above the
boiling point of the water, this requir...
Intensity requirement
Intensity (W/cm2)
Low (<10)
Moderate (10 – 100)
High (>100)

Resulting processes
General heating
Pho...
Photochemical ablation
When using high power lasers of ultraviolet wavelength,
some chemical bonds can be broken without c...
5. Selective absorption of laser
light by human tissues
Selective absorption
Selective absorption occurs when a given color of light is
strongly absorbed by one type of tissue, w...
Selective absorption
6. Applications of lasers
Lasers in beauty therapy
Lasers application in beauty therapy are based on:
• selective absorption of absorbing components...
Laser skin rejuvenation

IR lasers are used to remove extremely thin layer of skin
(<0.1 mm). In the absence of pigment in...
Laser hair removal

selective absorption : absorbing component being melanin
pigment in hair and follicle, it is best work...
Laser removal of port-wine stain
Yellow laser
is absorbed
by the
presence of
hemoglobin
in blood
vessels.
Laser removal of tattoo
tattoo can be removed with
variety of laser depending
on the presence of inks in
the tattoo.
Lasers in ophthalmology
For retina operation, visible laser can be used. Visible light is
transparent to the cornea and cr...
Lasers in ophthalmology
For cornea and lens, UV light emitted by the excimer laser is
strongly absorbed by water and prote...
7. Laser hazards and protections
Absorption of the eye
Hazards to the eye
The retina
The directionality of a laser beam permits the ray to be focused
to an extremely small spot ...
Hazards to the eye
The cornea and lens
•Cornea is accessible to danger of UV and most of IR lasers,
•UV-A, UV-B (between 2...
Protection to the eye
Eye protection
Eyewear (goggles) is the most common laser protective
measure, especially for open la...
Laser and its medical applications
Laser and its medical applications
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  • The level of oxygen in the blood can be determined by measuring the absorption spectrumof hemoglobin in the blood at several wavelengths. Its absorption spectra can be used to compare with those of oxyhemoglobin and deoxyhemoglobin can be determined and used to compute the oxygen level by a device called an oxumeter.
  • The ruby laser was the first laser invented in 1960. Ruby is an aluminum oxide
    crystal in which some of the aluminum atoms have been replaced with
    chromium atoms. Chromium gives ruby its characteristic red color and
    is responsible for the lasing behavior of the crystal. Chromium atoms absorb
    green and blue light and emit only red light.
    For a ruby laser, a crystal of ruby is formed into a cylinder. A fully reflecting
    mirror is placed on one end and a partially reflecting mirror on the other.
    A high-intensity flash lamp is spiraled around the ruby cylinder to provide
    energy that triggers the laser action. The green and blue wavelengths in the
    flash excite electrons in the chromium atoms to a higher energy level.
  • Another advantage of the directionality of a laser is that laser light can be focused down to a extremely small spot with a lens, this is because that a perfect parallel beam can be focused into a single point at the focal point. So, extremely high intensity can be obtained with a laser beam. Then away from the focal point, the laser light diverges and spreads out and corresponding intensity decreases. This property can be used to vary the intensity of a laser by 100~10000 times.
  • In most cases, the photons energy of laser light is transferred to blood, tissues or bone in the form of heat. In other cases laser can also transfer photon energy to chemical bond energy of the molecules in human body, such as DNA. This risks the modification of genetic information. There are generally three interaction mechanisms involved.
  • Proteins are body’s most important structural and functional chemicals. They form the muscles, connecting tissues and blood vessels, they transport oxygen necessary for the metabolism. When temperature is much higher than the body temperature, proteins are destabilized: their complex structures begin to uncoil and losing their natural order and forming dense tangled network.
  • Transcript of "Laser and its medical applications"

    1. 1. Laser and its medical applications S.SELVAKUMAR ASSISTANT PROFESSOR THAMIRABHARANI ENGINEERING COLLEGE TIRUNELVELI 9042474329(MOBILE) kumartvl88@gmail.com(E-MAIL)
    2. 2. A wide application of laser in medicine and beauty therapy  Surgical laser: removing tumors, making incisions.  Cosmetic treatments: resurfacing, removal of birth mark, age spots, spider veins, hair, tattoos,  Ophthalmology: inner eye surgery in removing cataract, repairing retina, correct nearsightedness.
    3. 3. Laser repairing retina
    4. 4. Laser removal of port-wine stain
    5. 5. Laser skin rejuvenation
    6. 6. What is a laser? Laser = Light Amplification by Stimulated Emission of Radiation •The physics of laser •The interaction of laser light with human tissue
    7. 7. Outline of the unit 11 •Simple atomic structure •Light emission •Characteristic of laser •Laser power and intensity •Mechanisms of laser interaction with human tissues •Selective absorption of laser light by human tissues •Applications of lasers in healthcare and beauty therapy
    8. 8. 1. Summary about atom
    9. 9. Atom is the smallest building block of matters, including body tissue and fluids, •it is electrically neutral, it contains three elementary particles: the electron , the proton, and the neutron. •electrons make circular motion around the nucleus (containing proton and neutron) in different level of orbits, called stationary orbits, they correspond to different energy levels. •the number of electrons is equals to the number of protons in an atom, •a nucleus counts for vast majority of the atomic mass. •The so-called atomic number (Z number) is the proton number (also electron number) in an atom. Ions are formed when atoms obtained extra electrons or loose electrons.
    10. 10. 2. Light emission
    11. 11. •electron orbits displayed as an energy level diagram • energy is plotted vertically with the lowest (n=1) , or ground stat, and with exited states (n=2, 3,4,…) above. • n is called orbit number and can be only positive integer.
    12. 12. (a) The electron can absorb energy and jump to a higher level, the process is called excitation. (b) A photon is emitted when an electron change from a higher orbit to a lower orbit with a characteristic emission spectrum. This process is called de-excitation. (c) If an atom absorbs a photon, an electron jumps from a lower orbit to a higher orbit with a characteristic absorption spectrum.
    13. 13. Atom will absorb and emit light photons at particular wavelength corresponding to the energy differences between orbits. The wavelength λ of emitted or absorbed photon can be obtained by the formula: hc ∆E = = hf λ where ∆E is the change in energy between the initial and final orbits. A variety of biological molecules have notable absorption spectra in the visible, IR, and UV. This has many clinical application. e.g. Oximeter.
    14. 14. 3. How laser works
    15. 15. Spontaneous emission and stimulated emission An excited electron may gives off a photon and decay to the ground state by two processes: •spontaneous emission: neon light, light bulb •stimulated emission : the excited atoms interact with a preexisting photon that passes by. If the incoming photon has the right energy, it induces the electron to decay and gives off a new photon. Ex. Laser.
    16. 16. Optical pumping many electrons must be previously excited and held in an excited state without massive spontaneous emission: this is called population inversion. The process is called optical pumping. Example of Ruby laser.
    17. 17. Optical pumping Only those perpendicular to the mirrors will be reflected back to the active medium, They travel together with incoming photons in the same direction, this is the directionality of the laser.
    18. 18. Characteristics of laser • The second photon has the same energy, i.e. the same wavelength and color as the first – laser has a pure color • It travels in the same direction and exactly in the same step with the first photon – laser has temporal coherence Comparing to the conventional light, a laser is differentiated by three characteristics. They are: Directionality, pure color, temporal coherence.
    19. 19. Characteristics of laser Pure color Directionality Temporal coherence
    20. 20. The power and intensity of a laser The power P is a measure of energy transfer rate; Total energy output (J) Power(W) = exposurte time (s) where the unit of power is Joules/s or W. The energy encountered by a particular spot area in a unit time is measured by the intensity (or power density): Power (W) Intensity (W/cm ) = spot area (cm 2 ) 2
    21. 21. laser versus ordinary lights: The directionality of laser beam offers a great advantage over ordinary lights since it can be concentrate its energy onto a very small spot area. This is because the laser rays can be considered as almost parallel and confined to a well-defined circular spot on a distant object.
    22. 22. Sample problem: we compare the intensity of the light of a bulb of 10 W and that of a laser with output power of 1mW (10-3 W). For calculation, we consider an imagery sphere of radius R of 1m for the light spreading of the bulb, laser beams illuminate a spot of circular area with a radius r = 1mm. I bulb Pbulb 10W 10W = = = = 8 × 10−5W / cm2 2 2 A 4πR 4π (100cm) I laser Plaser 10−3W 10−3W = = = = 3 × 10 − 2W / cm 2 A πr 2 π (0.1cm) 2 I laser 3 × 10−2W / cm 2 = ≈ 400 −5 2 I bulb 8 × 10 W / cm
    23. 23. Fluence, F is defined as the total energy delivered by a laser on an unit area during an expose time TE, F(J/cm2)=I(watts/cm2) x TE(s) The advantage of directionality of a laser : we can focus or defocus a laser beam using a lens. This can be used to vary the intensity of the laser. f Incoming parallel ray Focused spot Diverged beam
    24. 24. continuous wave (CW) lasers versus pulsed lasers • CW lasers has a constant power output during whole operation time. • pulsed lasers emits light in strong bursts periodically with no light between pulses usually T>>Tw
    25. 25. • The tw may vary from milliseconds (1ms=10-3 s) to femtoseconds (1fs=10-15s), but typically at nanoseconds (1ns=10-9s). • energy is stored up and emitted during a brief time tw, • this results in a very high instantaneous power Pi • the average power Pave delivered by a pulsed laser is low. Instantaneous power Pi Pi = E pulse tw Average power Pave Pave = E pulse T = E pulse ⋅ R Where R is the repetition rate
    26. 26. Example A pulsed laser emits 1 milliJoule (mJ) energy that lasts for 1 nanoseconds (ns), if the repetition rate R is 5 Hz, comparing their instantaneous power and average power. (The repetition rate is the number of pulses per second, so the repetition rate is related to the time interval by R=1/T). Pi = E pulse Pave = tw 1mlliJoule 10−3 J = = − 9 = 106W 1ns 10 s E pulse T = E pulse ( J ) × R( Hz ) = 10− 3 J × 5Hz = 5 × 10− 3W
    27. 27. 4. Mechanisms of laser interaction with human tissues
    28. 28. When a laser beam projected to tissue Five phenomena: •reflection, •transmission, •scattering, •re-emission, •absorption. Laser light interacts with tissue and transfers energy of photons to tissue because absorption occurs.
    29. 29. Photocoagulation What is a coagulation? • A slow heating of muscle and other tissues is like a cooking of meat in everyday life. • The heating induced the destabilization of the proteins, enzymes. • This is also called coagulation. • Like egg whites coagulate when cooked, red meat turns gray because coagulation during cooking. A Laser heating of tissues above 50 oC but below 100oC induces disordering of proteins and other bio-molecules, this process is called photocoagulation.
    30. 30. Consequence of photocoagulation When lasers are used to photocoagulate tissues during surgery, tissues essentially becomes cooked: • they shrink in mass because water is expelled, • the heated region change color and loses its mechanical integrity • cells in the photocoagulated region die and a region of dead tissue called photocoagulation burn develops • can be removed or pull out,
    31. 31. Applications of photocoagulation • destroy tumors • treating various eye conditions like retinal disorders caused by diabetes • hemostatic laser surgery - bloodless incision, excision: due to its ability to stop bleeding during surgery. A blood vessel subjected to photocoagulation develops a pinched point due to shrinkage of proteins in the vessel’s wall. The coagulation restriction helps seal off the flow, while damaged cells initiate clotting.
    32. 32. Photo-vaporization With very high power densities, instead of cooking, lasers will quickly heat the tissues to above 100o C , water within the tissues boils and evaporates. Since 70% of the body tissue is water, the boiling change the tissue into a gas. This phenomenon is called photo-vaporization. Photo- vaporization results in complete removal of the tissue, making possible for : • hemostatic incision,or excision. • complete removal of thin layer of tissue. Skin rejuvenation, resurfacing
    33. 33. Conditions for photo-vaporization 1.the tissue must be heated quickly to above the boiling point of the water, this require very high intensity lasers, 2.a very short exposure time TE, so no time for heat to flow away while delivering enough energy, highly spatial coherence (directionality) of lasers over other light sources is responsible for providing higher intensities
    34. 34. Intensity requirement Intensity (W/cm2) Low (<10) Moderate (10 – 100) High (>100) Resulting processes General heating Photocoagulation Photo-vaporization
    35. 35. Photochemical ablation When using high power lasers of ultraviolet wavelength, some chemical bonds can be broken without causing local heating; this process is called photo-chemical ablation. The photo-chemical ablation results in clean-cut incision. The thermal component is relatively small and the zone of thermal interaction is limited in the incision wall.
    36. 36. 5. Selective absorption of laser light by human tissues
    37. 37. Selective absorption Selective absorption occurs when a given color of light is strongly absorbed by one type of tissue, while transmitted by another. Lasers’ pure color is responsible for selective absorption. The main absorbing components of tissues are: • Oxyhemoglobin (in blood): the blood’s oxygen carrying protein, absorption of UV and blue and green light, • Melanin (a pigment in skin, hair, moles, etc): absorption in visible and near IR light (400nm – 1000nm), • Water (in tissues): transparent to visible light but strong absorption of UV light below 300nm and IR over 1300nm
    38. 38. Selective absorption
    39. 39. 6. Applications of lasers
    40. 40. Lasers in beauty therapy Lasers application in beauty therapy are based on: • selective absorption of absorbing components. • photo-vaporization process for removal of the treated components. • pulsed lasers are used.
    41. 41. Laser skin rejuvenation IR lasers are used to remove extremely thin layer of skin (<0.1 mm). In the absence of pigment in general, they take advantage of the presence of water in the skin to provide an ability to remove skin and body tissue.
    42. 42. Laser hair removal selective absorption : absorbing component being melanin pigment in hair and follicle, it is best worked with a red light ruby laser. White hair can not be treated with any laser due to the lack of absorbing component.
    43. 43. Laser removal of port-wine stain Yellow laser is absorbed by the presence of hemoglobin in blood vessels.
    44. 44. Laser removal of tattoo tattoo can be removed with variety of laser depending on the presence of inks in the tattoo.
    45. 45. Lasers in ophthalmology For retina operation, visible laser can be used. Visible light is transparent to the cornea and crystalline lens, and can be focused with eye’s lens on the retina. The most popular visible laser is the green argon laser. • Treatment of glaucoma: Argon laser is focused externally on iris to make incision, creating drainage holes for excess aqueous humors to release pressure, • Retina tear: photocoagulation burn to repair retina tears due to trauma to the head. • Diabetic retinopathy: inadequate blood supply to the retina due to diabetes. Small photocoagulation burn by green argon laser to repair the retina due to vessels
    46. 46. Lasers in ophthalmology For cornea and lens, UV light emitted by the excimer laser is strongly absorbed by water and proteins, so their energy can be absorbed by transparent cornea and lens, permitting laser surgery on these areas. • Cataracts: a milky structure in the lens of the eye. Photo-vaporization by using UV laser to remove the obaque regions. • Correction of myopia: over focusing of the lens. Excimer laser removal of surface of cornea to make it flatten.
    47. 47. 7. Laser hazards and protections
    48. 48. Absorption of the eye
    49. 49. Hazards to the eye The retina The directionality of a laser beam permits the ray to be focused to an extremely small spot on the retina. A collimated laser will be concentrated by a factor of 100,000 when passing from cornea to retina. Visible or near IR lasers (400 nm to 1400nm) are particularly dangerous to the retina and always requires eye-protection when working with these kind of lasers.
    50. 50. Hazards to the eye The cornea and lens •Cornea is accessible to danger of UV and most of IR lasers, •UV-A, UV-B (between 295nm and 320 nm) and IR-A (between 1 to 2 mm) are dangerous for lens, •308-nm (UV-B) excimer XeCl laser is particular dangerous because of it can simultaneously damage the lens, the cornea and the retina.
    51. 51. Protection to the eye Eye protection Eyewear (goggles) is the most common laser protective measure, especially for open laser beams. It should be good design with all around shielding and adequate visible light transmission. Identification of the eyewear : All laser protective eyewear shall be clearly labelled with information adequate to ensure the proper choice of eyewear with particular lasers.
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