Light in medicine.pdf

6 Light in medicine By: Dr. Abdullah Munqith Light in medicine Max Planck suggested that light could behave both as a wave and as particle. He drives an equation to explain the relationship between light energy and the frequency. E = hf Where E = photon energy f = frequency of light H = Planck's con...

6 Light in medicine By: Dr. Abdullah Munqith Light in medicine Max Planck suggested that light could behave both as a wave and as particle. He drives an equation to explain the relationship between light energy and the frequency. E = hf Where E = photon energy f = frequency of light H = Planck's constant Light in medicine f = c /λ Where f = frequency c = light velocity λ = the wave length So light with long wavelength range has a small energy , while light with short wave length range has a higher energy. Light in medicine There are three operations occurs when light strikes any surface: Reflection ( R ), Refraction ( r), Absorption ( A ) R + r + A = 1 = 100% Even though man is now very efficient at making artificial light, the sun is still the major source of light in the world The sun is both beneficial and hazardous to our health. Light in medicine ✓ Light has some interesting properties, many of which are used in medicine: 1. The speed of light changes when it goes from 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. If a light beam meets a new material at an angle other than perpendicular, it bends, or is refracted. Light in medicine 2. Light behaves both as a wave and as a particle. As a wave it produces interference and diffraction. As a particle it can be absorbed by a single molecule. When a light photon is absorbed its energy is used in various ways. It can cause a chemical change in the molecule that in turn can cause an electrical change. This is basically what happens when a light photon-is, absorbed in one of the sensitive cells of the retina. The chemical change in a particular point of the retina triggers an electrical signal to the brain to inform it that a light photon has been absorbed at that point. Light in medicine 3. When light is absorbed, its energy generally appears as heat. This property is the basic for the use in medicine of lR light to heat tissues. Also, the heat produced by laser beams is used to "weld" a detached retina to the back of the eyeball and to coagulate small blood vessels in the retina. Light in medicine 4. Sometimes when photon is absorbed, a lower energy light photon is emitted. This property is known as fluorescence, it is the basis of the fluorescent light bulb. The amount of fluorescence and the color of the emitted light depend on the chemical composition of the material that is fluorescing. Fluorescence is used in fluorescent microscopes as very important medical application. Light in medicine 5. Light is reflected to some extent from all surfaces. There are two types of reflection. Diffuse reflection occurs when rough surfaces scatter the light in many directions. Specular reflection is more useful types of reflection; it is obtained from very smooth shiny surfaces such as mirrors where the light is reflected at an angle that is equal to the angle at which it strikes the surface. Mirrors are used in many medical instruments. Light in medicine Visible light has an important therapeutic use. Since light is a form of energy and is selectively absorbed in certain molecules, it should not be surprising that it can cause important physiological effects. Many premature infants have jaundice, a condition in which an excess of bilirubin is excreted by the liver into the blood. Relatively recently (1958) it was discovered that most premature infants recover from jaundice if their bodies are exposed to visible light (phototherapy). Light in medicine ✓ Applications of ultraviolet and infrared rays in medicine The wavelengths adjacent to the visible spectrum also have important uses in medicine. Ultraviolet photons have energies greater than visible photons, while IR photons have lower energies, because of their higher energies, UV photons are more useful than IR photons. Light in medicine Ultraviolet light with wavelengths below about 290 nm is germicidal-that is, it can kill germs-and it is sometimes used to sterilize medical instruments. Ultraviolet light also produces more reactions in the skin than visible light. Some of these reactions are beneficial, and some are harmful. One of the major beneficial effects of UV light from the sun is the conversion of molecular products in the skin into vitamin D. Light in medicine Ultraviolet light from the sun affects the melanin in the skin to cause tanning. However, UV can produce sunburn as well as tan the skin. The wavelengths that produce sunburn are around 300 nm. The amount of 300 nm light in the sun's spectrum depends on the amount of field that the sunlight must pass through. Ordinary window glass permits some near UV to be transmitted but absorbs the sunburn component. Light in medicine Solar UV light is also the major cause of skin cancer in humans. The high incidence of skin cancer among people, who have been exposed to the sun a great deal, such as fishermen and agricultural workers, may be related to the fact that the UV wavelengths that produce sunburn are also very well absorbed by the DNA in the cells. Skin cancer usually appears on those portions of the body that have received the most sunlight, such as the tip of the nose, the tops of the ears, and the back of the neck. Light in medicine About half of the energy from the sun is in the IR region. The warmth we feel from the sun is mainly due to the IR component. Heat lamps that produce a large percentage of IR light with wavelengths of 1000 to 2000 nm are often used for physical therapy purposes. Infrared light penetrates further into the tissues than visible light and thus is better able to heat deep tissues.