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35. Mechanisms of action of laser radiation on biological tissues.

There are three kinds of photobiological effects:

1) photodestructive influence at which thermal, hydrodynamical, photochemical effects of light cause destruction of tissues. This kind of laser interaction is used in laser surgery.

2) photophysicaland photochemical influence, at which light absorbed by biotissues raises in them atoms and molecules, causes photochemical and photophysical reactions. This laser radiation is used as therapeutic.

3) unperturbedinfluence, when the biosubstance does not change the properties during interaction with light. These are such effects, as dispersion, reflection and penetration. This kind use for diagnostics (laser spectroscopy).

36. Aplication of laser radiation in medicine. (lilr, hilr)

Lasers have a wide and growing range of applications in medicine. Lasers for Medical Applications summarises the wealth of recent research on the principles, technologies and application of lasers in diagnostics, therapy and surgery.

Part one gives an overview of the use of lasers in medicine, key principles of lasers and radiation interactions with tissue. To understand the wide diversity and therefore the large possible choice of these devices for a specific diagnosis or treatment, the respective types of the laser (solid state, gas, dye, and semiconductor) are reviewed in part two. Part three describes diagnostic laser methods, for example optical coherence tomography, spectroscopy, optical biopsy, and time-resolved fluorescence polarization spectroscopy. Those methods help doctors to refine the scope of involvement of the particular body part or, for example, to specify the extent of a tumor. Part four concentrates on the therapeutic applications of laser radiation in particular branches of medicine, including ophthalmology, dermatology, cardiology, urology, gynecology, otorhinolaryngology (ORL), neurology, dentistry, orthopaedic surgery and cancer therapy, as well as laser coatings of implants.

Laser light does many things in the bloodstream, for example it makes red blood cells more pliable, slippery, and increases their efficiency.

• Cosmetic surgery (removing tattoos, scars, stretch marks, sunspots, wrinkles, birthmarks, and hairs): see laser hair removal. Laser types used in dermatology include ruby , alexandrite, pulsed diode array.

• Eye surgery and refractive surgery

• Soft tissue surgery:

• Laser scalpel (General surgery, gynecological, urology, laparoscopic)

• Photobiomodulation (i.e. laser therapy)

• Intelligent laser speckle classification for skin health assessments

• In dentistry for caries removal, endodontic/periodontic procedures, tooth whitening, and oral surgery

The laser beam allows surgery on parenchymatous organs. Operations using a laser beam is short, painless and give an opportunity to get thin seams. Ophthalmologists are using a laser to "welding" detached retina to the underlying choroid underneath. A laser beam may be destroyed in the treatment of dentine of teeth, dentures welded directly into the mouth, eliminating damage of the vocal cords, the removal of the cervical vertebrae.

37. Spectrophotometry.

Spectrophotometry is a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution. The basic principle is that each compound absorbs or transmits light over a certain range of wavelength. This measurement can also be used to measure the amount of a known chemical substance. Spectrophotometry is one of the most useful methods of quantitative analysis in various fields such as chemistry, physics, biochemistry, material and chemical engineering and clinical applications. A spectrophotometer is an instrument that measures the amount of photons (the intensity of light) absorbed after it passes through sample solution. With the spectrophotometer, the amount of a known chemical substance (concentrations) can also be determined by measuring the intensity of light detected. Depending on the range of wavelength of light source, it can be classified into two different types:

UV-visible spectrophotometer: uses light over the ultraviolet range (185 - 400 nm) and visible range (400 - 700 nm) of electromagnetic radiation spectrum.

IR spectrophotometer: uses light over the infrared range (700 - 15000 nm) of electromagnetic radiation spectrum.

In visible spectrophotometry, the absorption or the transmission of a certain substance can be determined by the observed color. 

A spectrophotometer, in general, consists of two devices; a spectrometer and a photometer. A spectrometer is a device that produces, typically disperses and measures light. A photometer indicates the photoelectric detector that measures the intensity of light.

Spectrometer: It produces a desired range of wavelength of light. First a collimator (lens) transmits a straight beam of light (photons) that passes through a monochromator (prism) to split it into several component wavelengths (spectrum). Then a wavelength selector (slit) transmits only the desired wavelengths.

Photometer: After the desired range of wavelength of light passes through the solution of a sample in cuvette, the photometer detects the amount of photons that is absorbed and then sends a signal to a galvanometer or a digital display.

Beer-Lambert Law (also known as Beer's Law) states that there is a linear relationship between the absorbance and the concentration of a sample. For this reason, Beer's Law can only be applied when there is a linear relationship. Beer's Law is written as:A=ϵlc

  • where A
A
 is the measure of absorbance (no units),

  • ϵ
ϵ
is the molar extinction coefficient or molar absorptivity (or absorption coefficient),

  • l
l
is the path length, and

  • c
c
 is the concentration.

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