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RadiologyTest2

Terms ch. 3,4,5,8

QuestionAnswer
Quality Assurance Special procedures used to ensure the production of high-quality, diagnostic radiographs
quality administration The management of the quality assurance plan in the dental office
Normalizing device A commercially available device used to monitor developer strength and film density
quality control tests Specific tests designed to maintain and monitor dental x-ray equipment, supplies, and film processing
radiograph, reference A radiograph processed under ideal conditions and then used to compare the film densities of radiographs that are processed daily.
stepwedge A device constructed of uniform-layered thicknesses of an x-ray absorbing material, usually aluminum; different steps absorb varying amounts of x-rays and are used to demonstrate film densities and contrast scales
viewbox A light source used to view dental radiographs
Amperage Determines the amount of electrons passing through the cathode filament. Increasing amperage: Results in an increased number of electrons traveling from cathode to anode and production of an increased number of x-rays
Contrast how sharply dark & light areas are differentiated on an image. Low kVp settings (65-70 kVp)create high contrast film: Many black & white areas, few shades of gray. High kVp settings (≥ 90kVp) create low contrast image:Many shades of gray.
Density Density: overall darkness or blackness of a image. When the kVp is increased, the image will be darker. When the kVp is decreased, the image will be lighter.
Exposure time Exposure time affects the number of x-rays produced. A longer exposure time produces more x-rays and a more intense x-ray beam.
Half-value layer (HVL) Alum. filters placed in path of beam inside tubehead.Filters remove low-energy, less penetrating, longer wavelength x-rays. Inc. mean penetrating capability of x-ray beam while reducing intensity. HVL: thickness of specified material cuts intenisty in 1/2
Intensity The product of the quantity (number of x-ray photons) and quality (energy of each photon) per unit of area per unit of time of exposure
Inverse square law Intensity of radiation inversely proportional to the square of distance from source of radiation. When the distance is doubled, the beam is 1/4 as intense. When the distance is halved, the beam is 4 times more intense.
Kilovoltage peak (kVp) Regulates penetrating power of x-ray beam by controlling speed of electrons traveling b/w cathode and anode. Higher kVp settings: Produce x-ray beam w/ more energy & shorter wavelengths. Increases intensity of x-ray beam
Milliamperage Controls the penetrating power of the x-ray beam by controlling # of electrons produced in the x-ray tube and the number of x-rays produced. Higher milliamperage settings: Produce an x-ray beam with more energy, increasing the intensity of the x-ray beam
Milliamperage & Exposure time Milliamperage and exposure time are inversely related. When milliamperage is increased, exposure time must be decreased. When milliamperage is decreased, exposure time must be increased.
Milliampere-seconds (mAs) mAs is the product of milliamperes and exposure time. When milliamperage is increased, exposure time must be decreased to maintain constant density.
Quality (of x-ray beam) Wavelength determines the energy and penetrating power of radiation. X-rays with shorter wavelength have more penetrating power. Quality is used to describe the mean energy or penetrating ability of the x-ray beam. Quality is controlled by kilovoltage
Quantity (of x-ray beam) number of x-rays produced in the dental x-ray unit; how many
Voltage potential diff. b/w 2 electrical charges. Voltage inc.=electron speed inc. The electrons strike the target with greater force & energy. Voltage is measured in volts or kilovolts. Dental radiography requires the use of 65 to 100 kV.
Critical organ Skin Thyroid gland Lens of eye Bone marrow
cumulative effects Effects of radiation exposure are additive Unrepaired damage accumulates in tissues
Direct theory cell damage results when ionizing radiation directly hits critical areas within the cell
dose, total more damage occurs with larger quantities of radiation
dose equivalent Compares biologic effects of different kinds of radiation; Traditional unit is the rem SI equivalent is the sievert 1 Sv = 100 rems
dose rate more radiation damage takes place with a higher dose rate
dose-response curve Linear, non-threshold relationship; Relationship indicates that response of the tissues is directly proportional to the dose;Non-threshold dose-response curve suggests: no matter how small the amount of radiation received, some biologic damage occurs.
free radical Cell damage occurs primarily thru formation of free radicals. Free radicals formed when x-ray photon ionizes water.Free radical: An uncharged atom/molecule that exists with a single, unpaired electron in its outermost shell; Highly reactive & unstable
genetic cells reproductive cells
genetic effects Not seen in the person irradiated; Passed on to future generations
gray (gy) sievert
Indirect theory X-ray photons are absorbed within the cell and cause the formation of toxins, which in turn damage the cell: When x-ray photons are absorbed by water within a cell, free radical formation results.Free radicals combine to form toxins that damage cells.
injury, period of Variety of cellular injuries may result
ionization When x-rays strike pt tissue:Produced through photoelectric effect/Compton scatter; Results:formation of a +ve atom & dislodged neg. electron. Electron will interact w/ other atoms w/in absorbing tissues =ing chem.changes w/in the cell = biologic damage
latent period Amount of time that elapses between exposure to ionizing radiation and the appearance of observable clinical signs; Depends on the total dose of radiation received and the amount of time it took to receive the dose
long-term effects Small doses absorbed repeatedly over a long period of time;Effects seen after years, decades, or generations including Cancer, birth abnormalities, genetic defects
nonstochastic effects There is a threshold; Severity increases with increasing absorbed dose; Examples: erythema, loss of hair, cataracts, and decreased fertility
radiation, background Cosmic, Terrestrial
radiation absorbed dose (rad) a unit for measuring absorbed dose; the traditional unit of dose equivalent to the gray (Gy); 100 erg of energy per gram of tissue; 100 rad=1 Gy
radioresistant A cell that is resistant to radiation;Salivary glands,Kidney,Liver
radiosensitive A cell that is sensitive to radiation; Lymphoid tissue, Bone marrow, Testes, Intestines
recovery period Depending on a number of factors, cells can repair the damage caused by radiation
roentgen (R) Measures radiation by determining the amount of ionization that occurs in air. Does not describe the amount of radiation absorbed
short-term effects Associated with large doses of radiation in a short amount of time;Acute radiation syndrome (ARS) such as nausea, vomiting, diarrhea, hair loss, hemorrhage
somatic cells all cells in the body except the reproductive cells
somatic effects Seen in the person irradiated; Not seen in future generations
stochasitic effects Direct function of the dose; No dose threshold; Not dependable on the magnitude of the absorbed dose; Examples: cancer and genetic mutations
inherent filtration takes place when the primary beam passes through the glass window of the x-ray tube, the insulating oil, and the tubehead seal
added filtration An aluminum disk is placed between the collimator and the tubehead seal; Filter out longer wavelength, lower energy x-rays from the x-ray beam; Filtration results in a higher-energy and more penetrating useful beam.
total filtration sum of inherent and added filtration Regulated by state and federal law; Machines operating at or below 70 kVp require a minimum total of 1.5 mm. aluminum filtration;Machines operating above 70 kVp require a minimum total of 2.5 mm. aluminum filtration
collimation Collimation restricts the size and shape of the x-ray beam; reduces patient exposure.
Maximum permissible dose (MPD) Maximum dose that a body is permitted to receive in a specific period; MPD for occupationally exposed persons-5.0 rem/year; For non-occupationally exposed persons/pregnant occupationally exposed persons:0.1 rem/year
Maximum accumulated dose (MAD) dose accumulated over a lifetime A formula based on the worker’s age: MAD = (N – 18) X 5 rem/year MAD = (N – 18) X 0.05 Sv/year
ALARA as low as reasonably achievable. Every possible method of reducing exposure to radiation should be employed.
Distance Distance traveled by x-ray beam affects intensity of beam.3 distances:Targ-surf. (srce to pt’s skin)Targ.-obj.(srce to pt’s tooth)Targ.-rec. (srce to rec.)As x-rays travel from pnt of orgn, they diverge to cover larger s.a.; intensity of beam lessens.
Density and Milliamperage An increase in milliamperage: overall density of the radiograph. Results in a darker image
Created by: ClarkDH