Basic Concept of Radiation (Final Term) PDF

BASIC CONCEPT OF RADIATION FINAL TERM  What is radiation?  Energy emitted and transferred through space is called radiation.  Visible light, is a form of electromagnetic energy, is radiated by the sun, and is electromagnetic radiation.  Electromagnetic energy is usually re...

BASIC CONCEPT OF RADIATION FINAL TERM  What is radiation?  Energy emitted and transferred through space is called radiation.  Visible light, is a form of electromagnetic energy, is radiated by the sun, and is electromagnetic radiation.  Electromagnetic energy is usually referred to as electromagnetic radiation or, simply, radiation. TYPES OF RADIATION  Ionizing Radiation – refers to any type of radiation that is capable of removing an orbital electron from the atom with which it interacts. This type of interaction between radiation and matter is called ionization. Examples: X-rays, Gamma rays, Particulate radiation (alpha and beta particles)  Ionization – removal of an electron from an atom  Non-ionizing Radiation – refers to any type of radiation that does not carry enough energy to ionize atoms or molecules – that is, to completely remove an electron from an atom or molecule. Examples: MRI, Ultrasound  1. Natural Environmental Radiation i. Cosmic Rays – are particulate and electromagnetic radiation emitted by the sun and Sources of stars. Ionizing ii. Terrestrial Radiation – results from the deposits of uranium, thorium, and other radionuclides). Radiation iii. Internally-deposited radionuclides potassium-40, are natural metabolites. – mainly iv. The largest source of natural environmental radiation is radon. A radioactive gas that is produced by the natural radioactive 2. Man-Made Radiation  Man-made Radiation  Diagnostic x-rays constitute the largest man-made source of ionizing radiation (3.2 mSv/yr.). This estimates was made in 2006 by the National Council on Radiation Protection and Measurements (NCRP). Earlier estimates by the NCRP in 1990 put this source at nearly 0.4 mSv/yr.  TYPES OF IONIZING RADIATION 1. Particulate radiation – a type of radiation consisting of protons, neutrons, and electrons if they are in motion and possess sufficient kinetic energy. At rest, the cannot cause ionization. 2 main types of particulate radiation: a. Alpha Particles equivalent to a helium nucleus. It contains two protons and two neutrons. It is emitted only from the nuclei of heavy elements. Ionization accompanies alpha radiation. The average alpha particle possesses 4 to 7 MeV of kinetic energy and ionizes approximately 40,000 atoms for every centimeter of travel through air. Because of this amount of ionization, the energy of an alpha particle is quickly lost. It has a very short range in matter. Whereas in air, alpha particles can travel approximately 5 cm; in soft tissue, the range may be less than 100 µm. TYPES OF IONIZING RADIATION b. Beta Particles Differ from alpha particles in terms of mass and charge. They are light particles with an atomic mass number of 0 and carry one unit of negative or positive charge. The only difference between electrons and negative beta particles is their origin. Beta particles originate in the nuclei of radioactive atoms. After being emitted from a radioisotope, beta particles traverse air, ionizing several hundred atoms per centimeter. The beta particle range is longer than that for the alpha particle. Depending on its energy, a beta particle may traverse 10 to 100 cm. of air and approximately 1 to 2 cm. of soft tissue.  TYPES OF IONIZING RADIATION 2. Electromagnetic Radiation X-rays and gamma rays are often called photons. Photons have no mass and no charge. They travel at the speed of light (c=3x108 m/s) and are considered energy disturbances in space. The only difference between x-rays and gamma rays is their origin. Gamma rays are emitted from the nucleus of a radioisotope and are usually associated with alpha and beta emission. X-rays are produced outside the nucleus in the electron shells. X-rays and gamma rays have unlimited range in matter. Photon radiation loses intensity with a distance but theoretically never reaches zero. THE X-RAY MACHINE X-RAY IMAGING SYSTEM There are 3 main components of an x-ray imaging system: 1. The x-ray tube 2. The operating console and; 3. The high-voltage generator. THE X-RAY TUBE The component of the x-ray imaging system rarely seen by radiologic technologists. It is contained in a protective housing and therefore inaccessible. Two primary parts: 1. cathode and 2. anode – each of these is an electrode, and any electronic tube is a special type of diode. Three external structures: 1. the support structure, 2. protective housing and, 3. the glass or metal enclosure. PROTECTIVE HOUSING X-rays that escape through the protective housing are called leakage radiation. Leakage radiation contribute nothing in in the way of diagnostic information and result in unnecessary exposure of the patient and radiologic technologist. Properly designated protective housing reduces the level of radiation to less than 1 mGy/hr at 1m when operated at maximum conditions. GLASS OR METAL ENCLOSURE It is made of Pyrex glass to enable it to withstand the tremendous heat generated. The enclosure maintains a vacuum inside the tube. This vacuum allows for more efficient x-ray production and a longer tube life. Metal enclosure tubes maintain constant electric potential between the electrons of the tube current and the enclosure.  GLASS OR METAL ENCLOSURE  The part outside the glass or metal enclosure, called the stator, consists of a series of electromagnets equally spaced around the neck of the tube.  Inside the enclosure is a shaft made of bars of copper and soft iron fabricated into one mass is called the rotor.  CATHODE Filament – it is a coil of wire similar to that in a kitchen toaster, but it is much smaller. It is approximately 2 mm in diameter and 1 or 2 cm long. Filaments are usually made of thoriated tungsten. The addition of 1-2% thorium to the tungsten filament enhances the efficiency of thermionic emission and prolongs tube life. When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are “boiled off” and ejected from the filament. This phenomenon is known as thermionic emission. Tungsten vaporization with deposition on the inside of the glass enclosure is the most common cause of tube failure. FOCUSING CUP The filament is embedded in a metal shroud called the focusing cup. It is negatively charged so that it electrostatically confine the electron beam to a small area of the anode. Since all of the electrons accelerated from cathode to anode are electrically negative, the electron beam tends to spread out owing to electrostatic repulsion. ANODE It serves 3 functions in an x-ray tube. 1) the anode is an electrical conductor. It receives electrons emitted by the cathode and conducts them through the tube to the connecting cables and back to the high voltage generator; 2) it provides mechanical support for the target and; 3) the anode also must be a good thermal dissipater. Copper, molybdenum, and graphite are the most common anode materials.  TARGET The target is the are of the anode struck by the electrons from the cathode. In stationary anode tubes, the target consists of a tungsten alloy embedded in the copper anode. In rotating anode tubes, the entire rotating disc is the target.  OPERATING CONSOLE Allows the radiologic technologist to control the x-ray tube current and voltage so that the useful x-ray beam is of proper quality and quantity. Radiation quantity refers to the number of x-rays or the intensity of the x-ray beam. The operating console usually provides for control of line compensation, kVp, mA, and exposure time. HIGH VOLTAGE GENERATOR A high voltage generator powers the x-ray tube. It is responsible for increasing the output voltage from the autotransformer to the kVp necessary for x-ray production. High voltage generators are used for x-ray because they operate on single phase and give less voltage ripples. IMAGING EQUIPMENT X-RAY TUBE  X-rays are not stored, nor do they come form radioactive materials.  The radiographer manufactures x-ray for each exposure using technical factors manipulated on the x-ray control panel.  X-rays are produced by a series of energy conversions. The primary items needed for the production of x-rays are: (1) a source of electrons, (2) a means to accelerate the electrons, and (3) a way to bring the electrons to a sudden stop. All of these items are accomplished in the x-ray tube.  DIGITAL IMAGING  Digital imaging equipment enhances images of the body.  The primary advantages of digital equipment include the ability to post-process images in a variety of ways to provide multiple views of the anatomy.  In digital radiography, the density and contrast of the image can be altered any time after the completion of the study without re-exposing the patient.  The images are stored in a computer and can be transferred to multiple locations on a network or sent via e-mail.  COMPUTED RADIOGRAPHY  In computed radiography (CR), the x- rays exit the patient and strike a cassette containing and imaging plate (IP).  The IP is coated with a substance known as photostimulable phosphor. This phosphor becomes excited as a result of the deposit of x-ray energy, and it remains so until the cassette is placed in a reader. Once inside the reader, the IP is scanned with a laser beam, releasing the x-ray energy that is then converted to a visible image by the computer. The resulting image is viewed on a high resolution monitor.  DIRECT DIGITAL RADIOGRAPHY  In direct digital radiography (DR), the cassette is eliminated and replaced by an imaging plate that remains in place inside the x-ray table or wall Bucky.  The DR image appears on the monitor almost immediately, saving time and eliminating the need to handle cassettes of any kind.  FILM-SCREEN IMAGING  After traversing the patient, the x-rays continue to a cassette that contains the intensifying screens and x-ray film,  The primary means of making a radiographic image is through the use of a film-screen system. The intensifying screen is a sheet of plastic that is embedded with crystals called phosphors. When struck by radiation, phosphors glow with visible light, this light from the phosphors exposes the x-ray film, which is sandwiched between intensifying screens in the lid and the base of the cassette.  The phosphors produce thousands of light rays for each x-ray striking them, thereby significantly reducing the amount of radiation necessary to make a good exposure.  The x-ray film is a sheet of polyester plastic that is coated with a thin layer of gelatin and silver compounds. The image contained in the film is made visible by developing the film; the finished radiograph then becomes permanent record of the examination and is considered a legal document. FLUOROSCOPY  Digital fluoroscopy provides a live-action view of the interior of the body. Waiting for the film to be developed is no longer necessary because the image is immediately displayed on a monitor.  In fluoroscopy, the x-ray tube in most installations is located inside the x-ray table. The radiation passes through the table top and the patient, and it strikes the fluoroscopic screen to produce an image of the patient’s body part.  A device known as an image intensifier electronically brightens and enhances the image and transmits it to the monitor.  If the radiologist wants to make a permanent record of the image, digital fluoroscopy allows an image to be captured, saved in a computer, and postprocessed in a variety of ways.  COMPUTED TOMOGRAPHY CT units provide cross-sectional views of the body. It greatly improve the accuracy of diagnoses and, in many cases, eliminates the need for exploratory surgery. With the patient lying on a movable couch, an x- ray tube and radiation detector rotate around the table; this rotation provides the computer with a slab information about the patient’s body. The computer reconstructs the information into an image that is viewed on a monitor and stored for later retrieval and interpretation.  MAGNETIC RESONANCE IMAGING MRI units allow cross-sectional views of the body to be made without the use of ionizing radiation. With the patient lying on the couch in the cylindrical imager, the body part in question is exposed to a magnetic field and radio wave transmission. The images are produced in the computer by reconstructing the information that was received from the interaction of radio waves and magnetism with the body part. The information and images provide the physician with data about both the anatomy and the physiologic characteristics of the body part being examined.  POSITRON EMISSION TOMOGRAPHY  PET is similar to nuclear medicine in that it uses a radiopharmaceutical agent injected into the circulatory system to image the area of interest.  However, PET is also used to evaluate the physiologic condition or function of an organ or system in the body. The radiation emanates from the body and is received by the radiation detectors. The resulting cross- sectional images indicate how the radiopharmaceutical agent was taken up and used by the body.  NUCLEAR MEDICINE In nuclear medicine, radioactive materials introduced into the body are used to produce images of major organs. The radioactive material concentrates in the are of interest and emits radiation; this radiation is then detected by a sensing device and is computed into an image.  PORTABLE RADIOGRAPHY AND FLUOROSCOPY Portable radiography and fluoroscopy can be performed if the patient cannot be moved to the radiology department. Mobile radiography units operate with battery power. The quality of images of most anatomic structures is equivalent to that obtained in the radiology department. Portable radiography is used in such areas as the surgical department (OR), post anesthesia recovery unit, intensive care unit (ICU), coronary care unit (CCU), burn unit, orthopedic unit, and morgue. Mobile fluoroscopy (C-arm) is used primarily in the OR, where the surgeon must see the images immediately.  SONOGRAPHY Sonography uses high-frequency sound waves which is a form of non-ionizing radiation, to obtain sectional images of the body. It is a useful diagnostic tool in certain areas of radiology. The sound waves bounce off interior structures of the body and return as echoes to a probe from which images can be electronically displayed on a monitor; permanent images can then be made from the screen. Cross-sectional images of the body are obtained. Evaluation of moving organs can also be made with sonography. Doppler technique is a type of sonography used to evaluate blood flow through the arteries. PICTURE ARCHIVING AND COMMUNICATIONS SYSTEM (PACS)  Computed imaging procedures such as DR, CT, NM, UTZ, and MRI can be combined into a network. The picture archiving and communication system (PACS) brings digital imaging together with hospital and radiology information systems; it allows for the total management of a patient’s case. In addition, conventional radiographs can be digitized and also entered into the system.  Digital images and patient information from a computer network that can be accessed from any workstation that is connected to the system. Data are stored on optical disks. Information can be transmitted from the computer storage device via cable throughout the hospital and vicinity or via satellite across the world.