Laser therapy .
Laser therapy is also known as Phototherapy . The word LASER is an acronym for Light Amplification of Stimulated Emission of Radiation. It refers to the production of a beam of a radiation which differs from the ordinary light in several ways. These are nowadays used in laser light shows, compact disk players, surgical incisions, in ophthalmology and gynecology etc.
In very simple words, laser is a beam of radiation, which is used for various purposes. Lasers are termed as magic rays since, they have enormous applications in different fields. For physiotherapeutic purpose, therapeutic laser is used. Therapeutic laser is also known as low intensity laser, soft laser, cold laser, medical laser, and class 3A and 3B laser .
History of Laser therapy .
Historically, Einstein was the first person who gave an account of stimulated emission. In 1953, MASER (Microwave amplification by stimulated emission of radiation) was discovered. In 1955, Dr Theodore Maiman devised a working model for the production of laser from Ruby crystal. In 1960, Bennett, Javan and Herriott discovered Helium Neon laser. In 1962, White and Ridgen produced visible red laser with 632.8 nm wavelength. In 1964, Flock and Zueng for the first time used laser for surgery. From 1980 onwards, therapeutic laser is used for physiotherapeutic applications.
Characteristics of Laser therapy .
Laser has unique characteristics, which differentiate it from other forms of light. Various characteristic features of laser are monochromaticity, coherence and collimation. (You can remember them with CMC where C stands for coherence, M for monochromaticity and C for collimation).
1. Monochromaticity .
Here, the word mono means single and chromaticity means color. On its emission, laser produces single pure color. It produces single pure color because, it has one specific wavelength. Laser light entering a prism would be identical on exit because it is monochromatic. On the other hand, white light is made up of many different colors or wavelengths and when it passes through a prism, it produces a rainbow of colors.
2. Coherence .
Laser rays are synchronous to each other. This property of synchronicity is termed as coherence. Crest and trough of individual rays match each other. Laser rays are synchronous to each other in space, i.e. they travel in the same direction and this coherence is known as spatial coherence. Laser rays are also coherent to each other in relation to time and this type of coherence is known as temporal coherence. Analogy about the coherence can be done with army soldiers when they are marching in step in the same direction and wearing the same dress.
3. Collimation .
Collimation is also termed as non-divergence. Laser rays travel parallel to each other rather than diverging from each other, this property is known as collimation. Collimation does not occur in other forms of light for example, bulb and battery. In case of bulb and battery, the rays divert since they consist of many different wavelengths and they spread out in all directions. If sunlight is called crowd scattering after explosion of tear gas, then laser light can be called disciplined military drill. It is said that the laser rays can travel up to the moon from earth in parallel to each other, with very negligible divergence.
Production of Laser .
It is recalled that the electrons of an individual atom remain as a ‘cloud’ of negative charge around the positive nucleus. According to the quantum theory, the electrons can only occupy certain energy levels or shells around the nucleus. Under normal circumstances, in the vast majority of the atoms the electrons remain at the lowest energy level, i.e. at the resting or ground state. If enough energy is added to atom, an outer electron may gain sufficient energy to free itself from the nucleus.
The atom then becomes a positively charged ion and the electron becomes a free negative charge. When the outer electrons are in one of the higher energy states, they will tend to return to a lower energy state, sometimes to the most stable or ground state. Also, the quantum energy which is expressed in electron volts is inversely proportional to the wavelength. This means the greater the quantum energy; the lesser will be the wavelength. A large number of atoms with the electrons in the excited state can lead to amplification since one photon releases a second and these two can release more and so on.
Apparatus of Laser .
A Laser device consists of three chief components such as lasing medium, energy source and mechanical structure (Remember with MEL and not MEL GIBSON).
1. Lasing medium .
It is a material, which is capable of producing laser. It may be gaseous, liquid, solid crystal or semiconductor. The material which is capable of producing laser is known as lasing medium. It can absorb energy from the external source and then gives off its excess energy as photons of light. Lasing medium could be solid crystal or semiconductor, liquid or gas. The lasing media in low intensity laser or cold laser are either helium-neon (He-Ne) or semiconductor, i.e. gallium-arsenide (Ga-As) .
2. Energy source .
An energy source is used to excite the lasing medium. This excitation is usually electrical. It is also known as flashgun.
3. Mechanical structure .
It is central chamber-like structure, which contains the lasing medium. It has two mirrors at either end. Out of these two mirrors, one is for reflection of photons of light back and across the chamber. Other mirror in addition to reflection, serves as an exit for the output of photons of light or laser .
Working of Laser .
When an energy particle or a photon is applied to the atom of lasing medium, it may be absorbed or reflected back. When the atom absorbs it then, there is a change in its electron configuration. An electron may jump from lower energy level to higher energy level. An atom with change in its electronic configuration is termed as an excited atom.
Atom cannot remain in an excited state for long time and tries to seek its original or ground state. In order to achieve its ground status, atom emits back the absorbed energy. It is emitted spontaneously and termed as spontaneous emission. If spontaneous emission is allowed to take place then, laser rays will not be emitted because the energy level necessary to achieve this may not be obtained.
Hence, when the atom is in its excited state, then an additional energy is applied so that the atom emits its excess of energy immediately. This emission is known as stimulated emission. Since the emitted energy is more than what is supplied it is known as amplification. Excess of energy is emitted in the form of photons of light. When these photons are emitted, they are likely to be collected inside the mechanical chamber and when they move from one place to another they may hit one of the mirrors.
When they hit the mirror they are reflected back. Once they are reflected back, they travel further through the lasing medium and increase the amplification process further. As a result, more and more photons are accumulated in the mechanical chamber. When the number of photons is more than what can be accommodated in the mechanical chamber, they are then emitted out of the semipermeable mirror or the mirror that has an exit. The emitted photons are in the form of laser. They are carried by fiberoptic cable to the probe for treatment purpose.
Types of Laser .
The various types of laser are available nowadays. The commonly used lasers are:
1. Ruby laser (or crystal laser) .
2. Helium-neon laser (gas laser) .
3. Diode laser (or semiconductor laser).
1. Ruby Laser (Crystal Laser) .
Ruby laser is also known as crystal laser because it contains synthetic ruby as a lasing medium. Synthetic medium (aluminium oxide and chromium) are used rather than the natural one to ensure purity of the medium which is necessary to generate physical characteristics of laser. Aluminium oxide with trace of chromium oxide forms a 10 cm long and 1 cm wide synthetic ruby rod. A helical electric discharge tube containing xenon tube is wound around the ruby rod.
Both the ends are made reflecting by silvering the surfaces with one end as 100% reflective and other slightly less. The xenon tube is used to give intense flash of white light which excites the ruby molecules and raises the electron to a higher energy level. As the excited state is unstable, the electrons return to ground state by releasing a photon. This is known as spontaneous emission. The rate of supply of energy exceeds to a greater extent which leads to a large number of atoms at higher energy levels. This is known as population inversions.
Atoms in their excited state are encountered by the photons and this leads to further stimulated emissions. The excited electron falls to its resting state and gives off a photon of exactly the same energy as that of photon which collided with it (photon of 694.3 nm wavelength). Hence, a beam of red laser with a wavelength 694.3 nm is emitted.
2. Helium-neon Laser (Gas Laser) .
Gas laser consists of a mixture of primarily helium and neon in a low pressure tube. This low pressure tube is surrounded by a flashgun which excites the atom to a higher energy level. Thus, photons released by the spontaneous emission and have a wavelength of 632.8 nm. These photons reflect to and fro to the tube and collide with the atoms of higher energy levels. This leads to stimulated emission with the release of similar photons. Intense beam of light emerges from the narrow partially transmissive which is red in color and has a wavelength of 632.8 nm.
3. Diode Laser (Semiconductor Laser) .
Gallium and arsenide are used as a diode or semiconductor to produce an infrared invisible laser with a wavelength of 904 nm. In these with an external electric potential, positively charged ‘holes’ are thrown from the p-type gallium-aluminium-arsenide layer into the active layer of gallium-arsenide. The negatively charged electrons interact with the active layer and thus photon of light is released.
The photons are reflected to and fro and emitted as a laser beam from one partially transparent end. By varying the ratio of gallium to aluminium, desired specific wavelengths are obtained. The advantage of semiconductor laser diode is that these can either emit a continuous or a pulsed output.
Techniques of Application .
The method of application of laser therapy is quite simple. Generally, the laser energy is emitted by a hand held applicator for therapeutic purposes. The gallium-arsenide laser contains the semiconductor or diode element at the tip of the applicator, whereas the helium-neon laser contains their components inside the unit and delivers the laser light to the target area via a fiberoptic tube. This causes divergence of the beam. To administer the laser for therapeutic purposes, two methods are generally used :-
1. Grid method .
2. Scanning method.
1. The grid method .
The treatment area is divided into a grid each of 1 square cm. The hand held applicator should be in light contact with the skin and directly perpendicular to the target tissue. Each square cm is stimulated for a specific period of time.
2. The scanning method .
No contact is made between the tip of the laser and the patient’s skin. The tip of the applicator is held at a distance of 5 to 10 mm. Since the divergence of beam occurs, there is a decrease in the amount of energy applied as the distance increases.
Dosage of Laser therapy .
1. Wavelength .
Wavelength depends on the lasing medium used. For superficial conditions like wounds and ulcers, visible red laser is used. For deep conditions of muscles and bones, infrared laser is used. Cluster probe laser having several diodes are used for the larger area of soft tissues.
2. Power .
The power output is measured in watts. Since the power output of laser beam used therapeutically is quite small, mW is generally used. Moreover, percentage of power output is sometimes used, i.e. 10, 20 or 30% of the total power output.
3. Energy .
The energy delivered to the treatment tissue is expressed in Joules. It is calculated by the following equation:
Energy (in Joules) = Power (in watts) × Time (in seconds) . Sometimes, when the energy required for the treatment of a particular tissue is known and the power output is available then the total treatment time can also be calculated.
4. Power density .
Power density decreases as the area between the tip of the applicator and the part to be treated increases. Power density is expressed as: Power density = Incident power/area in cm2 . Total power used therapeutically is thus calculated by the inverse square law.
5. Energy density .
Energy density can be calculated as:
Energy density = Power (W) × Time (sec) / Area (in cm2) .
The dosage in laser therapy is calculated in terms of energy density applied which is expressed in joules/cm2 .
Interaction of Laser with Body Tissues .
Low intensity lasers are used therapeutically for their nonthermal effects. Visible radiations are remarkably absorbed in the hemoglobin whereas infrared light is strongly absorbed by water. Absorption results in the transformation of energy in the body tissues. Human body consists of 70% of water and 30% of organic material.
Organic material which absorbs visible light contains chromophores. Chromophores are defined as the molecular structures which get excited by the visible spectrum due to its configuration. In human body, hemoglobin and melanin contain chromophores and thus absorbs laser energy.
Indications for Laser .
In physiotherapy, laser is used mainly for pain relief and for the acceleration of wound healing. Therapeutic laser is used in many musculoskeletal conditions for pain relief. Various conditions in which laser can be used for this purpose are
- Rheumatoid arthritis .
- Osteoarthritis .
- Bursitis .
- Periarthritis .
- Bicipital tendonitis .
- Tenosynovitis .
- Ankle sprain .
- Trigger finger .
- Carpal tunnel syndrome .
- Tennis elbow .
- Chronic low back pain .
- Sports injuries .
- wounds .
- Chronic ulcers .
- Incisions .
Dangers and Contraindications of Laser .
1. Effects on eyes .
The main danger of low power laser therapy is a risk of eye damage if the beam is applied directly into the eye. So, to avoid the exposure of eye with a beam of laser, protective goggles should be worn by the patient as well as by the physiotherapist.
2. Effects on cancerous growth .
The laser should not be applied over the area of cancerous growth. Laser acts as a photobiostimulatory agent, its exposure to cancerous tissue can lead to acceleration of its growth and metastasis.
3. Effects on pregnant uterus .
Laser should not be applied directly over the pregnant uterus as it may cause abnormal growth.
4. Effects on infected tissues .
When treated in contact with the infected tissue, the laser head needs to be cleaned thoroughly or sterilized. It should be used preferably in conjunction with ultraviolet therapy for the treatment of infected wounds.
5. Hemorrhagic areas or cardiac conditions .
Laser can cause vasodilatation and hence, care should be taken while exposing any hemorrhagic area. Patients of certain cardiac conditions are avoided the exposure of laser therapy around the cardiac region.
Physiological and Therapeutic Effects of Laser .
1. Wound healing .
Laser therapy is nowadays being effectively used for the treatment of wounds. Healing of wounds is thought to accelerate by the application of laser (Dyson & Young, 1986). It is a complex physiological process which involves chemotactic activity, vascular changes and the release of chemical mediators. Radiations particularly from the red spectrum of light are found effective in the treatment of chronic ulcers. Both untreated chronic ulcers as well as trophic ulcers can be very effectively treated by laser therapy.
Laser therapy increases tissue proliferation and thus enhances wound healing caused due to burns, surgical incisions, diabetic ulcers and pressure sores. Both direct contact or grid method as well as scanning method is effectively used for healing of wounds. Wound margins are effectively treated by direct contact technique. For doing this, the laser probe is usually applied at 1 to 2 cm from the edges.
Dosage of 4 to 10 joules/cm2 is usually sufficient. Treatment of wound bed is preferably done by noncontact method. The dosage from 1 to 5 joules/cm2 is usually sufficient for the treatment of wound bed. The low dosages are usually sufficient because the protective layer of dermis is absent in this area.
2. Tensile strength and scar tissue .
The tensile strength of the tissues treated with laser therapy is more than the normally healed ones. This tensile strength is directly related to the increased levels of collagen. Collagen synthesis and thus the tensile strength are fibroblasts mediated functions which are improved significantly by the treatment of laser. Also, the wounds exposed to laser therapy have more epithelialization and less exudate formation. Hence, they have less scar tissue formation with a better cosmetic appearance.
3. Musculoskeletal conditions .
The laser therapy is found to be very effective in various overuse tendinitis or bursitis conditions like tennis elbow, golfers elbow, supraspinatus tendinitis, etc. Also laser therapy is found effective in some acute conditions like ankle sprain as it enhances the healing process and relieves pain. Various arthritic conditions like rheumatoid arthritis, osteoarthritis, ankylosing arthritis, pyogenic arthritis, etc. are benefited by the use of laser therapy.
Laser has its effect on prostaglandin synthesis and thus it relieves inflammation. Laser is found to be very effective in the healing of the connective tissues and thus is effective in the treatment of various arthritic conditions. Laser therapy has bactericidal effects because of increased phagocytosis by leukocytes. When used in conjunction with antibiotics, laser therapy is found effective in the treatment of various inflammatory conditions.
4. Pain relief .
Laser therapy is found effective in relieving pain, both acute as well as chronic. Acute pain as in ankle sprain is relieved by the laser by reducing swelling and enhancing the healing process. Many musculoskeletal pains as in fibrositis or trigger pain are relieved by the application of laser on trigger points or acupressure points.
In postoperative conditions also, the laser is found effective in the enhancing healing process and thus reducing pain. Analgesia is achieved in certain neurogenic conditions also. Pain due to trigeminal neuralgia is found to be relieved by laser therapy. Studies on superficial median or radial nerve conduction velocity have shown a decrease in sensory nerve conduction velocity by a low intensity laser.
5. Bone and articular cartilage .
Studies on the effects of laser on bones and articular cartilage is increasing day-by-day. It has been found that the longer duration of low power laser helps in fracture healing and bone remodulation. It helps in chondral proliferation and remodeling of the articular line. It has also been found useful for the treatment of nonunion of fractures.
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