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Radiology

Chapter Two

TermDefinition
Absorbed Dose (The units for measuring the absorbed dose are the gray (Gy) and the rad (radiation absorbed dose).) The amount of energy deposited in any form of matter, such as teeth, soft tissues, treatment chair, air and so forth, by any type of radiation (alpha or beta particles, x- or gamma rays, etc).
Background Radiation Ionizing radiation that is always present. Consists of cosmic rays from outer space, naturally occurring radiation from the earth, and radiation from radioactive materials.
Characteristic Radiation A form of radiation originating from an atom following removal of am electron or excitation of the atom. The wavelength of the emitted radiation is specific for the element and the particular energy levels involved.
Coherent Scattering Radiation that is scattered when a low-energy x-ray passes near an atom's outer electron. Approximately 8 percent of interactions of matter with the dental x-ray beam are the result of coherent scattering.
Compton Effect ( Compton Scattering) An attenuation (absorption) process for x- and gamma radiation in which a photon interacts with an orbital electron or an atom to form a displaced electron and a scattered photon (x-ray) of reduced energy.
Decay The radioactive disintegration of the nucleus of an unstable atom by the emission of particles, photons of energy, or both.
Dose The amount of absorbed radiation in grays or rads at any given point. Dose may refer to absorbed dose, depth of the dose, entrance dose, or surface dose.
Dose Equivalent (The units for measuring are the sievert (Sv) and the rem). Dose equivalent is defined as the product of the absorbed dose times a biological effect qualifying factor. Because the qualifying factor for x-rays is one, the absorbed dose and the dose equivalent.
Effective Dose Equivalent Aids in making more accurate comparisons between different radiographic exposures. Compensates for the differences in area exposed and the tissues that may be in the path of the x-ray beam. Measured in microsieverts (uSv)
Electromagnetic Radiation Forms of energy propelled by wave motion as photons. This is a combination of electric and magnetic energy. Has no charge, mass, or weight and travels at the speed of light. Differs in wavelength, frequency, and properties.
Exposure A measure of ionization produced in air by x- or gamma radiation. The units of exposure are coulombs per kilogram (C/kg) and the roentgen (R).
Frequency The number of crests of a wavelength passing a given point per second.
Gray (Gy) Systeme Internationale unit for measuring absorbed dose. One Gy equals 100 rads; 1,000 milligrays equals 1 Gy.
Hard Radiation Rays of high energy and extremely short wavelengths. Essential for dental radiography.
Ionizing Radiation Radiation that is capable of producing ions.
Ionization The formation of ion pairs.
Photon(x-ray photon) A quantum of energy. Both x-rays and gamma rays are photons.
Rad Traditional unit for measuring absorbed dose. 100 rads equals one gray (Gy). One rad equals 0.01 Gy. 1,000 millirads equal 1 rad.
Raidiation The emission and propagation of energy through space or through a material medium in the form or electromagnetic waves, corpuscular emissions such as alpha and beta particles, or rays of mixed and unknown types such as cosmic rays.
Radiolucent That portion of the radiograph that is dark. Structures that lack density permit the passage of x-rays with little or no resistance. These structures appear dark on the image.
Radiopaque That portion of the radiograph that appears light. Dense structures resist the passage of radiation. These structures appear light on the image.
Rem (Roentgen Equivalent In Man) Traditional unit for measuring dose equivalent. Used to compare the biological effects of the various types or radiation.
R (Roentgen) Traditional unit measurement of exposure to radiation. Measured in air. A simplified definition of the roentgen is the amount of x-radiation or gamma radiation required to ionize 1 cc of air at standard conditions or pressure and temperature.
Secondary Radiation Given off by any matter irradiated with x-rays. Created at the instant the primary beam interacts with matter and gives off some of its energy, forming new and less powerful wavelengths. Often referred to as scatter radiation.
Sv (Sievert) Used to compare the biological effects of various types of radiation. The number of sieverts is identical to the absorbed dose in grays for these radiations.
Soft Radiation Longest wavelengths of the x-rays. Removed from the polychromatic beam by filtration because soft radiation (Grenz Rays) have no value in producing dental radiographs.
Wavelength In radiography, the length in angstrom units or centimeters of the electromagnetic radiations produced in the x-ray machine. The distance from the crest, or top of one wave to the crest of the next, determines the wavelength-hence its penetration ability.
Created by: daisenmurray