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# Light in medicine

الكلية كلية طب حمورابي     القسم الكلية ذات القسم الواحد     المرحلة 1
أستاذ المادة نادية حسين صاحب طاهر       22/05/2017 04:35:11
Project: Light in Medicine
Aims: Knowledge of the properties and applications of light also laser as therapeutic techniques.

Introduction:
The speed of light when it goes from one material into another given by equation:
n= c / v -------------------- (1)
c: Speed of light in vacuum
v: Speed of light in material
n: Refractive index
Light behaves both wave and particle:
Wave = interference + diffraction
Particle; absorbed by single molecule.
Light has a number of attractive properties, many of which are used in medicine:
1- Light behaves both as a wave and a particle. As a wave it produces interference and diffraction. As a particle it can be absorbed by a single molecule.

2-When light is absorbed, its energy generally appears as heat. This property is the basis for the use IR light to heat tissues. Also the heat produced by laser beams is used to weld attached retina to the back of eyeball and to coagulate small blood vessels in retina.
3- Some time when a light photon is a absorbed, a lower light energy light photon is emitted. This property is known as fluorescence.
4-The speed of light changes when it goes from one material into another. The ratio of the speed of light in a vacuum to its speed in a given material is called the index of refraction.
5- Light is reflected to some extent from all surfaces. There are two types of reflection:
A-Diffuse reflection: occurs when rough surface scatter the light in many direction.
B- Specular reflection: it is obtained from very smooth surface such as mirrors.

Measurement of Light and Its Unit:
The three general categories of light (UV- Visible- IR) are defined in terms of their wavelengths. Wavelength of light used to be measured in:
Microns 1 ? =10-6 m
Angstroms 1 A? = 10- 10 m
Nanometer 1 nm = 10-9 m
-Ultraviolet light has wavelengths from 100 to 400 nm.
-Visible light has wavelengths from 400 to 700 nm.
-IR light has wavelengths from 700 to 104 nm.
Visible light has energy (2-4 ev).
K.E of molecule in air (0.025 ev).
Visible light is measured in photometric units:
IIIuminance; the quantity of light striking a surface
Luminace; the intensity of a light source
Irradiance; the quantity of light striking a surface

Application of Visible Light in Medicine:
1.Endoscope: a number of instruments are used for viewing internal body cavities.
2.Gyroscopes: are used to examine the bladder.
3.Bronchoscope: are used for examining the air passages into lungs. Some endoscopes are rigid tubes with a light source to illuminate area of interest. Flexible endoscopes can be used to obtain information from regions of the body that cannot be examined with rigid endoscopes, such as the small intestine and much of large intestine.
Application of UV and IR light in Medicine:
-UV photons have energies than visible and IR light.
Because of their higher energies, UV photons are more useful than IR photons.
-UV can kill germs and used to sterilize medical instruments.
-UV produces more reaction in the skin some of these reactions are beneficial, and some are harmful.
Beneficial effects of UV light from the sun is the conversion of molecular products in the skin into vitamin D.

Harmful effects of UV light can produce sunburn. Solar UV light is also cause of skin cancer in humans.
Two types of IR photography are used in medicine:
1.Reflective IR photography, which uses wavelength of 700 to 900 nm to show patterns of viens just below the skin.
2.Emissive IR photography uses the long IR heat waves emitted by the body that give an indication of the body temperature, is usually called thermo graph.

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .