Laser/Application

In medicine
Generally, lasers are used in biomedical research, medical diagnosis, medical therapy, and treatment.

Models of laser-tissue interactions
Laser radiation interacts with biological tissue. Depending on the energy of the laser beam, exposure time and wavelength this interaction results in:

Photoablation is evaporation.

Photocoagulation uses the thermal energy of a laser. Tissues on which laser is applied shrink in mass because water is expelled from them, change colour and lose their mechanical integrity. Cells in the photo-coagulated area die and a region of dead tissue called photocoagulation burn is produced.

Photocoagulation is used to destroy tumours, while treating various eye conditions (e. g. retinal disorders caused by diabetes) or during hemostatic laser surgeries to produce almost bloodless incisions or to stop vessels from bleeding. A leaking blood vessel subjected to photocoagulation develops a pinched point due to shrinkage of proteins in its wall. The coagulation restriction helps seal off the flow, while damaged cells initiate clotting.

Photomechanical (photodisruptive) mode requires nanosecond or shorter pulses with extremely high spatial density of photons

Photochemical reactions

Advantages of laser
Less invasive method of treatment that leaves minimal scarring of the tissue and enables it to heal faster.

Precision – the incision is very thin and small,

Sterility

Vaporisation of the tissue

Disadvantages of laser
High cost

Special anaesthesia

Special training

Factors influencing laser choice
Each medical specialty requires a different laser. Choosing a suitable one for a given application (given tissue) is crucial and depends on both properties of the tissue as well as of the laser. When choosing a suitable laser we look at the the absorptive characteristics of the tissue to be destroyed, the wavelength of the emitted radiation, the temporal parameters of the delivered energy including the power density, energy density and pulse repetition (rate and duration of the exposure) and the mode of beam energy delivery to a target issue (continuous/pulsed energy and direct/no contact with the target issue).

Types of lasers
According to the wattage of the laser beam we distinguish two main types of lasers - noninvasive therapeutic lasers with wattage up to 500 mV and invasive surgical lasers with wattage of more than 1 W that are used in various surgical specialties. in the area where the laser beam is absorbed. Luminous energy is transformed into thermal and mechanical one and can even induce a chemical reaction.

Lasers with shorter wavelengths (627 - 780 nm) are used in dermatology, gynaecology and stomatology, lasers with longer ones are used mainly in rehabilitation and neurology.

Types of lasers used in surgery
Argon lasers are primarily used in ophthalmology. The blue light of argon lasers is absorbed by blood, therefore they are used for photo-coagulation of small blood vessels.

Carbon dioxide lasers are used in a number of surgical fields as laser scalpels. CO2 lasers have many advantages - they produce a very thin incision and as a result of the photo-coagulation of capillaries also minimize bleeding during the surgery.

Dye lasers are used in dermatology and gastroenterology. Laser beam of the dye laser causes a fragmentation of biliary and kidney stones. Because of the tunability of their wavelengths, dye lasers are also used in diagnostics to elicit fluorescence or phosphorescence in examined molecules.

Excimer lasers (KrF, ArF) emit UV radiation and produce an extremely neat incision. Because of that they are used during angioplasties to clear clogged blood vessels. Excimer lasers are also used in ophthalmology to correct myopia and astigmatism.

Neodyme lasers are used mainly in gastroenterology. They are inserted endoscopically into the alimentary canal to stop a bleeding or to clear the GIT of patients with inoperable conditions.

Dentistry
Usage of lasers in dentistry has many advantages, such as decreased postoperative swelling which allows for increased safety when performing surgery within the airway and increases the range of surgeries that can be safely performed.

Gum surgery, drilling, diagnostics

Dermatology
Lasers are the Port-wine stands (PWS), benign vascular birthmarks consisting of superficial and deep dilated vascular capillaries in the skin resulting in a reddish to purplish discoloration.

Surgery
Surgery uses lasers for coagulating, vaporising and cutting. However, each medical specialty has different requirements for which different types of lasers with different parameters are needed.

Visible wavelength and Nd YAG lasers are used for prophylactic hemocoagulation to prevent and control bleeding in small vessels and vascularized target tissue. This method requires a lower energy density which can be achieved either by enlarging the spot size or lowering the absolute power or exposure duration.

To remove tissue mass (primarily in tumour excisions) surgeons use vaporisation. To achieve a higher rate of tissue removal a high power density beams are used in combination with a large spot size.

Pulses are used to achieve the highest possible safety and precision by limiting an off-target beam.

Neurosurgery
The major effect of a laser on neural tissue is thermal. Neurosurgery also has a higher use of stereotactic techniques because of the smaller openings, reduces brain injury, decreases morbidity and enables a shorter recovery time post surgery.

Ophthalmology
Ophthalmology was one of the first specialties to incorporate lasers as a therapeutic and diagnostic modality and did so as early as 1961, when Leon Goldman (founder of the American Society for lasers in medicine and surgery) showed how a red beam emitted from a ruby laser could remove melanomas.

Ophthalmology uses the ability of a laser beam to enter the eye without causing an injury. Today, lasers are indispensable for effective and minimally invasive microsurgery of the eye. Oftalmology predominantly uses ArF lasers

Optical Coherence Tomography (OCT)

Reshaping the cornea of the eye to improve eyesight

Orthopaedics
Lasers can be used to treat patients with herniated discs that are unable to recover using physical therapy as they can vaporise the tissue in the disc, creating a vacuum. This causes the disc to shrink away from the pressed nerve and therefore relieves the pain.

Lasers are also used in the following shoulder conditions: rotator cuff tears, impingement syndrome (tendons of the rotator cuff muscles become irritated and inflamed as they pass through the subacromial space), instability of the shoulder caused by subluxations or dislocations or arthritis to release soft tissue, debride labral tears, perform synovectomy (removal of the joint lining), subacromial decompression (removal of the thickened bursal tissue) or Laser Assisted Capsular Shrinkage (LACS).

Urology
Lithotripsy – fragmentation of urinary (or biliary) stones. Photoacoustical/photomechanical effect (laser-induced shockwave) or photothermal effect

Treatments of benign prostatic hyperplasia (BPH) which is a noncancerous enlargement of the prostate

Diagnostic applications of lasers
Laser-induced fluorescence (LIF) spectroscopy and imaging

Optical Coherence Tomography (OCT) uses low-coherence interferometry to

Laser Doppler velocimetry (LDV) is a non-invasive method that enables the monitoring of micro-vascular blood flow

Possible future applications of laser
- Area of photomedicine (using light-sensitive chemicals in combination with lasers for patients' treatment and diagnosis)

Personalised medicine - lasers can operate on different wavelength which can be altered depending on patient's needs (e. g. skin color)

Laser tweezers as a tool for biomedical research

Laser as a replacement of a surgical scalpel

Outside of medicine
The largest application of lasers lies in optical storage devices such as CD or DVD players in which a focused beam from a semiconductor laser that is less than 1 mm wide, scans and reads the disc surface. Lasers are also widely used in fibre-optic communications, laser pointers that use inexpensive semiconductor lasers. Lasers can also be used in speed measurement.

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Depending on the type of laser, a specific course of treatment can be conducted which makes a laser an excellent treatment option in certain cases. Lasers first were applied in the fields of opthalmology and dermatology in 1. After that, the technology of using an argon laser to treat detached retinas had been developed. The main principle of this kind of treatment consists of concentrating a laser beam on the area of detached retina, and the highly localized laser power causes the retina to reattach. Nowadays, eximer lasers (ultraviolet lasers) are widely used in both opthalmology and dermatology for cosmetic surgery and cornea-reshaping operations. Cosmetic surgery has largely profitted because of lasers and its applications in removing wrinkles, birthmarks etc. Lasers are widely used as tools in imaging and diagnosis: for example, in early detection of cancer and other various diseases in patients. In fact, laser-based systems are beginning to replace x-rays as laser imaging poses less risk for the patient and proves to be more accurate. Also, Optical Coherence Tomography (OCT) is already applied in ophthalmology in order to get three-dimensional high-resolution images of the tissues - that enables the ophtalmologist to diagnose retinal disease or glaucoma, for instance. Of course, the list of laser applications in medicine is endless, but one may include in it: - Varicose treatment - In vivo miscroscopy - used for locating tumors, observing cell changes in living tissues.