APPLICATION OF LASERS USED FOR HEALTH, THE MEDICAL FIELD AND SURGERY:

    • Before we dive into the LASER aspect of this page, let’s start by defining a few other words first: Medicine is defined as, “The science or practice of the diagnosis, treatment, and prevention of disease (in the technical use often taken to exclude surgery)” –hence the seemingly synonymous title of this page. Even when one looks up the definition of Medical, the following definition is found, “relating to conditions requiring medical but not surgical treatment.” Health is defined as, “The state of being free from illness or injury.” Understanding the technical definition of these terms, one understands that Surgery is not actually technically under either one, hence the addition of “Surgery” as a separate field in the title of this page. In today’s world people equate “medical” to of course include “surgery” but technically this is not the case, but of course the topic of Surgery is very much relevant to this page.
    • Ok, NOW we can begin!
    • To understand on a simple level the types of LASERs used in these fields, the easiest way to explain is that there are two very broad categories:
  • Surgical LASERs
    • SIMPLE definition:
      • INvasive laser which cuts or burns, therefore destroying cells for various purposes.
    • Examples of situations where surgical lasers are used:
      • Cut or destroy tissue that is abnormal or diseased without harming healthy, normal tissue
      • Shrink or destroy tumors and lesions
      • Close off nerve endings to block reception of pain
      • Cauterize (seal) blood vessels to reduce blood loss
      • Seal lymph vessels to minimize swelling and decrease spread of tumor cells
      • Remove moles, warts, and tattoos
      • Decrease the appearance of skin wrinkles
      • LASIK eye surgery
  • Therapeutic LASERs
    • SIMPLE definition:
      • NON-invasive laser which regenerates and rejuvenates all types of cells, stimulating and supporting the natural healing of the body.
    • Examples of situations where therapeutic lasers are used:
      • Laser Therapy can be used to support the healing of an extremely wide variety of conditions, such as wound healing, chronic pain, adrenal function, kidney disease, neurological conditions, skin conditions and more. This is possible as it essentially delivers energy to the body for the body to heal itself. More on how this works is explained on LASER THERAPY. To see a more complete list of conditions, visit HERE.
      • Laser therapy is also used by various acupuncturists, both in addition to and in replacement of needles
      • Infra-red saunas exist in some major cities
      • There are even laser therapy mattresses for a high price

Understanding the difference between Laser SURGERY and Laser THERAPY:

  • Delivery:
    • The biggest difference between surgical lasers and ones used for laser therapy is the delivery. A way to visualize the difference between a surgical laser and a therapeutic laser is to relate it to water. Water is a great analogy, as humans (and more) require water to sustain life, but water can also be extremely destructive, all dependent on the delivery.
      • The delivery of surgical lasers is similar to that of water through a pressure cleaner-a pressure cleaner is a high-pressured delivery of water, pushing a high volume of water through a small opening. This method of delivery of water makes it strong enough to cut off a barefoot toe.
      • Therapeutic lasers would be likened to the delivery of water through a watering can. This method of delivery involves a wide distribution of water delivered at a slower pace. This means there is much lower pressure, making it gentle enough to not disturb delicate petals on a flower.
    • This site explains a surgical laser this way:
      • “Most applications of [surgical] lasers, whether industrial cutting or medical surgery, require some degree of focusing the beam. The reason being that what actually does the cutting for you is not the raw power in the beam, i.e. 50 Watts, but it is the power density, i.e. how many Watts per unit area…
      • Let us say you have a 50 Watt laser. Let us also say that the 50 Watt beam of this laser, measured at about one (1) meter away from the laser head, has a beam diameter of 6 mm = ¼ inch. The area of a 6 mm circle is 28 sq mm. Hence your beam at that position has a power density (called intensity) of 50/28 = 1.8 Watt per sq mm (or an intensity of 180 Watt/sq cm).
      • If there was something you could cut with this intensity, say some kind of thin plastic, then (a) the width of the cut would be 6 mm (one diameter) wide, which would not be a precision cut, and (b) you would have to go rather slow, which would then allow heat of the beam to propagate and set things on fire and that would not be good either! It is like slicing bread with a very wide and dull knife.
      • Let us say you could turn a knob and increase the power of your laser to 500 Watts! Then we know that you spent upwards of $50,000 on this laser and both (a) and (b) above are still problems.
      • Maybe it would be easier, cheaper and wiser to reduce the area of the beam. That of course is done by using a lens in front of the beam. If you get a lens that can reduce the beam diameter from 6 mm to 0.6 mm (i.e. 10 times smaller) the area would become 100 times smaller and therefore the power density (intensity) would be 100 times larger or 18,000 Watts per sq cm or 180 Watts per sq mm!” (3)
  • Power, Frequencies, etc.
    • Surgical Lasers
      • SUMMARY:  
      • SOURCED QUOTES:
        • “There are fundamental laws of physics (bottle necks) that limit the size to which a beam of light (laser or otherwise) can be focused to. In our application, the first bottle neck says; even if all your tools (lasers and lenses) were perfect you can not focus a beam to a size smaller than its wavelength. The wavelength of CO2 laser is 10 micron (0.01 mm) therefore this is the smallest diameter of the circle it can be focused to.” (3)
        • “From the practicality point of view, you need to have some ‘working distance’ from the output of the lens to the surface you are working on. If, to get a small spot, you choose this distance to be very short (say ½ inch = 12 mm) then all the junk you are cutting will splash back into your lens and destroy it in no time (and these lenses are not cheap!). Furthermore, a very short focal length lens does not have any ‘depth of focus’. This means your ‘cone’ of light opens up too quickly and you can not cut anything that has much thickness… The smallest theoretical diameter can not be achieved practically and we would be extremely happy if we can come to a factor of 10 of that limit… Real life situations demand long ‘working distances’ and long depth of focus. That means another factor of 5 or so lager spot size diameter.” (3)
        • “The power behind a laser used in surgical procedures is typically around 300 Watts or at least 600 times more powerful than the low-level or cols laser therapy.” (2)
        • This table depicts examples of the power density and process rate used to cut various materials: (3)
          • Cutting thin plastic (3 to 5 mil = .07 to .13 mm)
            • Power density of 30-70 W/sq mm
            • Process rate of 15 to 30 in/min, 380 to 760 mm/min
          • Decorative engraving of hard wood
            • Power density of 70-110 W/sq mm
            • Process rate of 4 in/min for 1/8 to 1/6 deep
            • Process rate of 100 mm/min for 1.5 to 3 mm deep
          • Hole punching in soft wood
            • Power density of 40-100 W/sq mm
            • Process rate of 0.075 inch per 0.1 second
          • Tissue removal
            • Power density of 10-100 W/sq mm
          • Cautery
            • Power density of 5-10 W/sq mm
    • Therapeutic Lasers:
      • SUMMARY:
        • Wavelengths for lasers used in Laser Therapy can range anywhere between 390 and 1,100 nm, they can be continuous wave or pulsed, and are generally below 100 mW/cm2 in power density, or 5-500mW. Lasers used in Laser Therapy clinics are almost always Class III or Class IV. Typical maximum wattage for Class IV lasers range from 15-20Watts.
      • SOURCED QUOTES:
        • “Laser radiation or non-coherent light has a wavelength and radiant exposure dependent capability to alter cellular behavior in the absence of significant heating. Phototherapy employs light with wavelengths between 390-1,100nm and can be continuous wave or pulsed. In normal circumstances, it uses relatively low fluences (0.04-50 J/cm2) and power densities (<100 mW/cm2). Wavelengths in the range of 390nm to 600 nm are used to treat superficial tissue, and longer wavelengths in the range of 600 nm to 1,100 nm, which penetrate further, are used to treat deeper seated tissues. Wavelengths in the range 700 nm to 750 nm have been found to have limited biochemical activity and are therefore not often used. Various light sources used in LLLT include inert gas lasers and semiconductor laser diodes such as helium neon (HeNe; 633 nm), ruby (694 nm), argon (488 and 514 nm), krypton (521, 530, 568, 647 nm), gallium arsenide (GaAs; >760 nm, with a common example of 904 nm), and gallium aluminum arsenide (GaAlAs; 612-870 nm). A wide range of LED semiconductors are available at lower wavelengths, whose medium contains the elements of indium, phosphide and nitride. One question that has not yet been conclusively answered is whether there is any advantage to using coherent laser light over non-coherent LED light. While some medical practitioners treat deep tissue lesions using focused lasers in “points”, in dermatology the use of LEDs is becoming increasingly common due to the relatively large areas of tissue that require irradiation.” (1)
        • “Low-level lasers, also known as “cold lasers” or non-thermal lasers, are used as a repetitive therapy for pain and soft tissue injuries. It refers to the use of a “red-beam” that is similar to infrared lasers with a wavelength between 600 and 1000 nanometers and powered by wattage ranging from 5 to 500 milli-watts.” (2)

Common Terms used to refer to LASERs in surgical and therapeutic fields:

Terms referring to types of laser treatments:

  • Cold Laser
    • A general reference to a Therapeutic Laser (7)
    • Note, some “cold lasers” do still have a heat element dependent on which class they are in (i.e. Class II will have no heat, Class III might have low heat, Class IV will have high heat) (Class I has no heat either, but admin is unaware of any Class I lasers being used for therapeutic uses)
    • (Hot Laser defined below)
  • Class III Laser Therapy
    • See LLLT
    • For definition of Classifications, see CLASSIFICATIONS page
  • Class IV Laser Therapy 
    • See HPLT
    • For definition of Classifications, see CLASSIFICATIONS page
  • Hot Laser
    • A general reference to a SURGICAL Laser
    • “Hot lasers can cut, burn and vaporize tissue” (7)
  • HPLT: High Powered Laser Therapy
    • Class IV lasers used for therapeutic purposes (9) (10)
  • Infrared Radiation (IR)
    • This is invisible radiation of wavelengths from 700nm – 1mm. this part of the electromagnetic spectrum is broken down into 3 bands: near infrared (IR-A) 700nm – 1400nm, mid infrared (IR-B) 1400nm – 3,000nm, and far infrared (IR-C) 3,000nm – 1mm.” (6)
  • IPL: Intense Pulsed Light
    • “Where peak optical power per pulse is up to 20,000 watts achieved within capacitor banks. All bright light sources are not called IPL, they are just light sources. Wavelengths emitted range usually from 400 nm to 1200 nm and the lower wavelengths can be eliminated by various cut off filters which usually range from 515 to 755 nm.” (4)
  • LEDT: Light Emitting Diode Therapy
    • LED therapy
    • For LED explanation, see LASER THERAPY page
  • LILT: Low Intensity Laser Therapy
    • See LLLT
  • LLLT: Low Level Laser Therapy
    • Class III and Class II lasers used for therapeutic purposes (9) (10)
    • Sometimes referred to as Low Level Light Therapy
    • Admin is unaware of any Class I lasers being used for therapeutic purposes, but if they were to exist, they would be under this category as well
  • LPLT: Low Power Laser Therapy
    • See LLLT
  • MIRE: Monochromatic Infrared Light Energy
    • Uses infrared light at 880 nm, often delivered through pads placed directly on the skin (11)
    • This is a specific frequency coined by a company called Anodyne. It does NOT actually refer to a category of any type.
  • Ultraviolet Radiation (UV): 
    • “Invisible radiation that has wavelengths from 180nm – 400nm.UV radiation is broken down into 3 regions; near ultraviolet (UV- A)-315nm – 400nm, mid ultraviolet (UV-B)-280nm – 315nm, and far ultraviolet (UV-C)-100nm – 280nm.” (6)
  • Visible Radiation: 
    • Is radiation that is visible to the human eye. The wavelengths are from 400nm – 700nm. At these wavelengths the eye can focus the light onto the retina increasing the radiant exposure by 100,000 times.” (6)

Characteristics and measurements of LASERs:

  • Ablation:
    • (SURGICAL TERM) Removal of a segment of tissue using thermal energy; also termed vaporization or thermal decomposition. (5)
  • Absorption:
    • The transfer of radiant energy into the target tissue resulting in a change in that tissue. (5)
  • Active Medium:
    • Any material within the optical cavity of a laser that, when energized, emits photons (radiant energy). (5)
  • Attenuation:
    • The decline in the energy or power as a beam passes through an absorbing or scattering medium. (5)
  • Average Power:
    • An expression of the average power emission over time expressed in Watts; total amount of laser energy delivered divided by the duration of the laser exposure. For a pulsed laser, the product of the energy per pulse (Joule) and the pulse frequency (Hertz). (5)
  • Beam:
    • Radiant electromagnetic rays that may be divergent, convergent, or collimated (parallel). (5)
  • Brilliancy:
    • “The light beam emitted is extremely intense and angularly well centered. The brightness or intensity is one of the important properties and can be enhanced by techniques like pulsing and Q-switching where extremely high peak power can be delivered in nanoseconds.” (4)
  • Chopped Pulse:
    • See Grated Pulse Mode. (5)
  • Chromophore:
    • A substance or molecule exhibiting selective light-absorbing qualities, often to specific wavelengths. (5)
  • Coagulation:
    • (SURGICAL TERM) An observed denaturation of soft tissue proteins that occurs at 60˚C (5)
  • Coherency:
    • “All the photons emitted vibrate in phase agreement both in space and time. Coherence is a measure of precision of the waveform. Highly coherent laser beam can be more precisely focused.” (4)
    • “The photons within a laser beam are extremely well organized and directional. This means that all of the photons (energy) have waves that travel in unison – they are highly parallel with a specific wavelength. True laser systems focus all of their energy in one direction in a very concentrated line. A super-luminous diode, on the other hand, diffuses its energy in all directions with only a small percentage of the energy travelling in the direction of the treatment. A true laser system will deliver 90% more power to the treatment area than a super-luminous diode system of exactly the same power rating.” (6)
  • Collimation:
    • “A property of light commonly associated with lasers and accomplished with focusing lenses where all the photons are traveling in the same direction” (6)
  • Continuous Wave (or Continuous Mode):
    • “A manner of applying the laser energy in an uninterrupted (nonpulsed) fashion, in which beam power density remains constant over time; also termed continuous wave, and abbreviated as ‘CW’. Contrast with ‘Pulsed Mode’.” (5)
    • “A laser with a  continuous output of laser radiation for a duration that is greater than or equal to 0.25 seconds.” (6)
  • Directionality:
    • All the photons travel in Uni direction. Directionality of the laser correlates with the emission of an extremely narrow beam of light that spreads slowly. Within the laser apparatus, efficient collimation of photons into a narrow path results in a divergence factor of approximately 1 mm for every metre travelled. Directionality allows the laser beam to be focused on a very small spot size.” (4)
  • Energy:
    • “Each phton carries a ‘quantum’ of energy €, whereby : E=hV (h-Plank’s constant) Therefore:
      • Short wavelength = high frequency = high energy photons
      • Long wavelength = low frequency = low energy photons” (4)
    • “Energy is measured in Joules (J) and is proportional to the number of photons” (4)
  • Energy Density:
    • The measurement of energy per area of spot size, usually expressed as Joules per square centimeter; also known as fluence. (5)
  • Fluence
    • “The energy delivered per unit area. It is measured in J/cm2” (4)
    • “A measure of instantaneous power output from the laser typically measured in Watts” (6)
  • Free-Running Pulse Mode:
    • (SURGICAL TERM) A laser operating mode where the emission is truly pulsed and not gated. A flashlamp is used as the external energy source so that very short pulse durations and peak powers of thousands of Watts are possible. A laser operated in continuous wave (5)
  • Frequency:
    • “(V or f)   (1/wavelength (Hz)) Therefore shorter the wavelength, higher is the frequency and longer the wavelength, lower is the frequency” (4)
    • “The frequency of light is inversely proportional to its wavelength, and is dependent upon the energy value of the individual photons being emitted. The higher the frequency, the higher the energy, and the shorter the wavelength.” (6)
  • Gated Pulse Mode:
    • A laser operating mode where the emission is a repetitive on-andoff cycle. The laser beam is actually emitted continuously, but a mechanical shutter or electronic control ‘chops’ the laser beam into pulses. This term is synonymous with chopped pulse mode. (5)
  • Hertz (Hz):
    • “A unit of frequency equal to one cycle per second” (4)
  • Irradiance:
    • “Irradiance is the power per unit area. It is measured in W/cm2 ” (4)
  • Laser Diode: 
    • “A semiconducting device which emits monochromatic non-ionizing radiation by a process of stimulated emission. a laser beam has a number of unique properties, such as coherence, polarization and directionality. Beams emitted by laser diodes are not, as is often stated, ‘straight’ and/or ‘parallel’. Unless manipulated with additional optical devices such as lenses, a laser diode’s beam is broadly divergent along one plane and narrowly divergent along the perpendicular plane, producing an elliptical cross-section.” (6)
  • Maximum Permissible Exposure (MPE): 
    • “The maximum level of laser radiation to which a human can be exposed without harmful effects to the eye or skin.” (6)
  • Monochromatic
    • “The luminous waves emitted come out with the same wavelength and energy. A single wavelength or a narrow band of wavelengths emitted allows precise targeting within tissue, while sparing adjacent structures.” (4)
    • Contains one specific wavelength of light (one specific color). It is an exclusive property of laser light, setting them apart from all other light sources. Because the wavelength of laser light determines its effect on tissue, the monochromatic property of laser light allows energy to be delivered to specific tissues in specific ways.” (6)
  • Parameters:
    • “Parameters are the values of wavelength, fluence, number of pulses, pulse duration, pulse delay, repetition rate and spot size which are set on laser or IPL systems to treat a particular condition.” (4)
  • Peak Power:
    • The highest power in each pulse. (5)
  • Photobiomodulation (PBM):
    • The use of light radiation to elicit biological responses in living cells. (5)
    • When biomodulation occurs from a photon transferring its energy to a chromophore it is referred to as photobiomodulation.” (6)
  • Photon:
    • “Photon is an elementary particle responsible for electromagnetic phenomena. It is the carrier of electromagnetic radiation of all wavelengths, including in decreasing order of energy, gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. The photon differs from many other elementary particles, such as the electron and the quark, in that it has zero rest mass; therefore, it travels (in a vacuum) at the speed of light.” (4)
  • Power:
    • “Power is the rate of delivery of the energy. It is measured in watts (W) where 1 W = 1 J/second” (4)
  • Power Density:
    • The measurement of power per area of spot size, usually expressed as Watts per square centimeter; also known as intensity, irradiance, and radiance. (5)
  • Power Output:
    • (In reference to Laser Therapy:) Determines the depth and treatment time. The higher the power, the deeper the penetration and the shorter treatment time that is needed. (8)
  • Pulse Duration:
    • A measurement of the total amount of time that a pulse is emitted; also known as pulse width. Pulse Width: See Pulse Duration. (5)
  • Pulsed Mode:
    • Laser radiation that is emitted intermittently as short bursts or pulses of energy rather than in a continuous fashion. Contrast with ‘Continuous Mode’. (5)
  • Reflection:
    • “Reflection occurs at all interfaces of media through which the laser beam is travelling, such as optical glass or sapphire tip, air, water jelly and skin surface. For example, the stratum corneum reflects approximately 4% to 7% of visible light that encounters the skin surface… In case of focused and collimated beams, reflection can be minimized by holding the hand piece exactly perpendicular to the skin surface.” (4)
  • Repetition Rate:
    • Number of pulses per second, also known as pulse rate; usually expressed in Hertz (Hz) or pulses per second (PPS). (5)
  • Scattering:
    • An interaction as the laser beam disperses in a non-uniform manner throughout the tissue” (5)
    • “Scattering is due to lack of homogeneity in the skin’s structures, such as molecules, organelles, cells or larger tissue structures. In the dermis, scattering has been shown to occur predominantly from inhomogeneitis in structures whose size is of the order of the wavelength or slightly larger e.g. collagen fibers. It, therefore, appears to act as a turbid matrix in which scattering is an approximately inverse function of wavelength (shorter wavelength, greater scattering). The greater the scattering, less will be the depth of penetration, and more possibility of absorption.” (4)
  • Superpulse:
    • A variation of gated pulsed mode in which the pulse durations are very short, producing high peak power; also termed very short pulse. (5)
  • Wavelength:
    • “The distance between two subsequent peaks or troughs of a light wave. Usually it is expressed in nm (nanometer i.e. 10-9 meters)” (4)
    • “Length between two identical points on subsequent electromagnetic waves. The wavelength of a laser determines its color and absorption properties” (6)

 

 

For more terms, see this link: http://americanboardoflasersurgery.org/documents/LaserRelatedTerms.pdf

 

 

SOURCES:

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4126803/
  2. https://www.mycarpaltunnel.com/content/carpal-tunnel-laser-surgery.shtml
  3. http://www.parallax-tech.com/faq.htm
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2825126/
  5. http://www.teanecklaserdentist.com/assets/docs/LaserDefinitions.pdf
  6. http://www.rltvet.com/terminology.html
  7. https://discoverlasers.com/blog/cold-lasers-or-hot-lasers-what-difference
  8. http://www.promotionphysio.com/laser/39-laser/108-high-power-laser-therapy-vs-cold-laser-therapy
  9. http://www.posturepress.com/High-Power-Laser-Therapy/
  10. http://www.promotionphysio.com/laser/39-laser/105-history-of-laser-therapy-it-started-with-albert
  11. https://www.bcidaho.com/providers/medical_policies/dme/mp_10122.asp