Light in Medicine 2024-2025 PDF

University of Babylon Dr.Entidhar jasim College of medicine 2024-2025 Semester 1/ 2021-2022 Medical Physics Light in medicine Topics of the Lecture ...

University of Babylon Dr.Entidhar jasim College of medicine 2024-2025 Semester 1/ 2021-2022 Medical Physics Light in medicine Topics of the Lecture  Physical properties of light.  The application of light in medicine.  The principle of using laser in medicine. Light has some interesting properties, many of which are used in medicine: 1- 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. n= c / v c: speed of light in vacuum v: speed of light in material 2- Light behaves as both a wave and a particle. As a wave, it produces interference and diffraction. As a particle, a single molecule can absorb it. When a light photon is 3- When light is absorbed, its energy generally appears as heat. This property is the basis for the use in medicine of IR 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. 4- Some time when alight photon is absorbed, a lower energy light photon is emitted. This property is known as fluorescence. 5- Light is reflected to some extent from all surfaces. There are two types of reflection a) Specular reflection: it is obtained from very smooth surface such as mirrors. b) Diffuse reflection: occurs when rough surface scatter the light in many directions MEASUREMENT OF LIGHT AND ITS UNITS The three general categories of light-UV, Visible, and IR- are defined in terms of their wavelengths. Wavelength of light used to be measured in  Microns 1 μ = 𝟏𝟎−𝟔 m  Angstroms 1 A° = 𝟏𝟎−𝟏𝟎 m  Nanometer 1 nm= 𝟏𝟎−𝟗 m  Ultraviolet light has wavelengths from 100 to 400nm 1 University of Babylon Dr.Entidhar jasim College of medicine 2024-2025 Semester 1/ 2021-2022 Medical Physics  Visible light has wavelengths 400 to 700nm  IR light has wavelengths from 700 to 104 nm. Each of these categories subdivided according to wavelength.  Ultraviolet UV-A has wave lengths from 320 – 400nm  UV-B has wavelengths from 290 -320nm.  UV-C has wavelengths from 100 – 290nm. Visible light is measured in photometric units  Illuminance the quantity of light striking a surface  Luminace the intensity of a light source. UV and IR radiation can be measured in radiometric units - Irradiance the quantity of light striking a surface. - Radiance the intensity of a light source. APPLICATIONS OF VISIBLE LIGHT IN MEDICINE 1. Endoscopy When we wish to look into a body opening, we have to get light into the opening without obstructing the view. The curved surface focuses the light at the region of interest. More sophisticated instruments, such as the  Ophthalmoscope for looking into the eyes  Otoscope for looking into the ears, use basically the same principle Endoscopes, are used for viewing internal body cavities. Their names indicates their purpose.  Cystoscopes are used to examine the bladder.  Proctoscopes are used for examining the rectum.  Enteroscopy are used to examine small intestine.  Colonoscopy used to examine large intestine.  Hysteroscopy used to examine the uterus.  Bronchoscopes are used for examining the air passages into the lungs. Some endoscopes are  rigid tubes with a light source to illuminate the area of interest. Many of them are equipped with optical attachments to magnify the tissues being studied  Flexible endoscopes that are made of fibre optics 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 the large intestine. Flexible endoscopes usually have an opening or channel that permits the physician to take samples of the tissues (biopsies) for later microscopic examination. 2 University of Babylon Dr.Entidhar jasim College of medicine Semester 1/ 2021-2022 2024-2025 Medical Physics 2. Transillumination It is the transmission of light through the tissues of the body. 1) The detection of hydrocephalus Since the skull of young infants is not fully calcified, light is able to penetrate to the inside of the skull; if there is an excess of relatively clear cerebrospinal fluid |(CSF) in the skull, light is scattered to different parts of the skull producing patterns characteristic of hydrocephalus (water-head). 2) Detection of pneumothorax (collapsed lung) in infants. The bright light penetrates the thin front chest wall of an infant and reflects off the back chest wall to indicate the degree of pneumothorax (collapsed lung). The physician can then insert a needle attached to a syringe into the area of collapse to remove the air between the lung and chest wall, causing the lung to reinflate 3) Recovering from jaundice Many premature infants have jaundice, a condition in which an excess of bilirubin is excreted by the liver into the blood. Most premature infants recover from jaundice if their bodies are exposed to visible light (phototherapy). APPLICATIONS OF UV AND IR LIGHT IN MEDICINE UV photons have energies greater than visible and IR light. Because of their higher energies, UV photons are more useful than IR photons.  UV with (λbelow about 290 nm) 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  UV. Light from the sun affects the melanin in the skin to cause tanning, solar. UV is also the major cause of skin cancer in humans because it is very well absorbed by the DNA.  In the cell’s UV light cannot be seen by the eye because it is absorbed before it reaches the retina. 3  University of Babylon Dr.Entidhar jasim College of medicine Semester 1/ 2021-2022 2024-2025 Medical Physics Fig shows the percentages of UV light of different wavelengths absorbed by the different structures of the eye  The IR rays are not usually hazardous even though they are focused by the cornea and lens of the eye onto the retina. However, looking at the sun through a filter (e.g., plastic sunglasses) that removes most of the visible light and allows most of the IR wavelengths through can cause a burn on the retina.  About half of energy from the sun is in IR. Region.  The warmth we feel from the sun is mainly due to the IR.  IR. Light penetrates further into the tissues than visible light and thus is better able to heat deep tissues.  Heat lamps that produce a large percentage of IR light with wavelengths of 1000 to 2000nm are often used for physical therapy purposes. Two types of IR photography are used in medicine: 1- Reflective IR photography, which uses wavelength of 700 to 900nm to show patterns of veins just below the skin. 2- Emissive IR photography. Which uses the long IR heat(14000-900nm) waves emitted by the body that give an indication of the body temperature, is usually called thermograph. LASER IN MEDICINE When an electron makes a transition from higher energy to lower energy state, a photon is emitted. The emission process can be one of two types, spontaneous emission or stimulated emission.  In spontaneous emission, the photon is emitted spontaneously, in a random direction, without external provocation.  In stimulated emission, an incoming photon stimulates the electron to change energy levels. 4  University of Babylon Dr.Entidhar jasim College of medicine Semester 1/ 2021-2022 2024-2025 Medical Physics  Laser production (population inversion)  The operation of lasers depends on stimulated emission. Stimulated emission has three important features. 1. One photon goes in and two photons come out. In this since, the process amplifies the number of photons. 2. The emitted photon travels in the same direction as incoming photon. 3. The emitted photon is exactly in step with or has same phase as the incoming photon. In other word, the two electromagnetic waves that these two photons represent are coherent. A laser is a unique light source that emits a narrow beam of light of single wavelength in which each wave is in phase with others near it. This is the origin the word laser which is a crony for Light Amplification by the Stimulated Emission Radiation  Laser energy that has been stored in the laser material.  A laser beam can be focused to a spot only a few microns in diameter. When the entire energy laser concentrated in such a small area, the power density (power per unit area) becomes very large. The total energy of a typical laser pulse used in medicine, which measured in milli joules (mJ), can be delivered in less than a microsecond, and resultant instantaneous power may be in megawatts. The heat produced usually measures the output of pulsed laser.  Since in medicine lasers are used primarily to deliver energy to tissue, laser energy directed at human tissue causes a rapid rise in temperature and can destroy the tissue. The amount of damage to living tissue depends on how long the tissue is at the increased temperature  For example, tissue can withstand 70C° for 1s, in general even the briefest exposure to temperatures above 100Cº results in tissue destruction.  Kinds of Laser: 1. Pulse Laser: i.e. i. Ruby laser ( =694 nm). ii. Semiconductor ( is dependent on the applied current). iii. Glass laser. 2. Continuous wave laser (cw) e.g. ,gas filled tubes laser i. Neon-helium laser (=632.8 nm) ii. Argon laser (=488-514nm). APPLICATIONS OF Laser 1. The laser used in medicine as a blood less knife for surgery. A lens to almost a mathematical point can focus it. This means that the energy per unit area in the focal spot can be made enormous, and small regions can be vaporized without harming the surroundings. 2. In medicine, one of the most spectacularly successful uses of lasers has been in ophthalmic surgery. In eye, the retina may become detached from the choroid owing to disease, injury, or degenerative changes. The laser is primarily used for photocoagulation of the retina, the heating a blood vessel to point where the blood coagulates and blocks the vessel.  It has been found that a 1ms flash of light from a laser-focused on the retina is highly efficient in welding the retina to the choroid. Further, the patient feels no pain and no anesthetic is not required. The amount of laser energy needed for Photocoagulation depends on the spot size used. In general, 5 University of Babylon Dr.Entidhar jasim College of medicine Semester 1/ 2021-2022 2024-2025 Medical Physics the ophthalmologist determines the proper dose visually at the time of the treatment.  The minimum amount of laser energy that will do observable damage to the retina is called a minimal reactive dose (MRD).  Example: The MRD for a 50𝜇m spot in the eye is about 2.4mJ delivered in 0.25 s. Typical exposure needed for photocoagulation are 10 to 50 times the MRD (i.e., 24 to 120mJ for 50𝜇m spot in 0.25s). 3. In dermatology for abnormal skin conditions: -  The surgical (CO2, laser with10600 nm) for different skin or mucosal diseases. Erbium: YAG laser (2940 nm) is used for superficial cutaneous lesions and skin refreshing.  The vascular: DYE laser (595 nm) and Nd:YAG (1064 nm or 532 nm) because their safe profiles & wide areas of use.  Aesthetic purposes, for removal of benign pigmented lesions, hair removal, tattoo removal and patient resurfacing. 6