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142 Cards in this Set
- Front
- Back
Radiation occurs in what two forms?
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1. Particulate
2. Electromagnetic |
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Who certifies advanced programs in oral and maxillofacial radiology?
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ADA Commission on Dental Accreditation or the Commission on Dental Accreditation of Canada.
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What is the basic principle of image formation?
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Energy is absorbed by the patient – when x-ray strikes image receptor it turns it black, the “remnant” radiation is captured on an image receptor; the amt of energy absorbed depends on: density, thickness, and effective atomic number
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List three physical characteristics that determine how much radiation an object absorbs.
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1. Density
2. Thickness 3. Effective atomic number |
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A Periapical radiograph gives an image of what?
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tooth and bone structures around the tooth
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A Bitewing radiograph gives an image of what?
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crowns of teeth and alveolar bone are projected with minimal vertical distortion
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α particles
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helium nuclei: 2 protons and 2 neutrons
Double positive charge and heavy mass; densely ionize matter through which they pass; quickly give up their energy and penetrate only a few micrometer of body tissue; after stopping, pick up 2 e- and become neutral helium |
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β particles
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when a neutron in a radioactive nucleus decays; identical to e-
Not densely ionizing; able to penetrate matter to a greater depth than α particles; smaller and lighter than α particles; much lower probability of interacting with matter; used in radiation therapy for treatment of some skin cancers |
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γ decay
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– photon, a form of electromagnetic radiation; result as part of a decay chain where a massive nucleus produced by fission converts from an excited state to a lower-level ground state
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Capacity of particulate radiation to ionize atoms depends on its...
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1. mass
2. velocity 3. charge |
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What is Quantum theory?
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: electromagnetic radiation is small bundles of energy called photons (travels at the speed of light and contains a specific amount of energy)
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What are the Primary components of an X-Ray machine?
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x-ray tube and its power supply
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The supplementary components of an X-Ray Machine are?
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- tube head
- arm - control panel |
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What are the Components of an X-Ray Tube?
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cathode and anode situated in an evacuated glass envelope or tube
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Electrons stream from a filament in the ______ to the ______, where they produce x-rays
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cathode; anode
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What is the function of the Power supply?
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(1) heats the cathode filament to generate electrons
(2) establish a high-voltage potential between the anode and cathode to accelerate the electrons toward the anode |
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What is the Focal spot?
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area on the target in which the focusing cup directs; where x-rays are produced
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A Cathode consists of what?
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1. Filament – tungsten wire
2. Focusing cup – where the filament lies; negatively charged concave |
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An anode consists of what?
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tungsten target embedded in copper
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The primary functions of the Power Supply are...
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(1) provide a low-voltage current to heat the x-ray tube filament
(2) generate a high potential difference between the anode and cathode |
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The Tube voltage is adjusted with an...
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autotransformer
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What does the timer do?
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controls the duration of the x-ray exposure; controls time that high voltage is applied and thus time in which x-rays are produced
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Heat is dissipated from the X-Ray machine by...
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copper ->
surrounding oil and housing tube -> atmosphere |
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What is the Duty cycle?
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frequency with which successive exposures can be made
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Most electrons traveling from the filament to the target release their energy as...
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heat
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Most electrons traveling from the filament to the target release their energy as heat, however, some convert their kinetic energy into x-ray photons by the formation of...
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Bremsstrahlung Radiation
and characteristic radiation |
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Bremsstrahlung Radiation
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sudden stop or slowing of high-speed electrons by tungsten nuclie in the target produces bremsstrahlung photons, the primary source of radiation from an x-ray tube
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Characteristic Radiation
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occurs when an incident electron ejects and inner electron from the tungsten target; when the outer e- replaces the displaced e-, a photon is emitted with an energy equivalent to the difference in the two orbital binding energies
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Three main means of beam attenuation:
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(1) coherent scattering
(2) photoelectric absorption (3) Compton scattering …9% of primary photons pass through the patient without interaction |
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Coherent Scatering
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low-energy incident photon passes outer electron -> momentarily excited -> incident photo ceases to exist and excited photon falls back to ground state -> generates another x-ray photon
Result: direction of incident photon is altered |
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Photoelectric absorption
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incident photon -> hits electron in one of the inner shells -> incident photon dissipates -> resulting photon is ejected
Result: ionization of the atom and stopping of the photon in the tissue |
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Compton scattering
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photon -> hits e- in outer shell -> both photon and e- are redirected
Result: ionization of the absorbing atom; scattering of photons; contribute to the formation of an image, but carry no information |
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Exposure
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measure of radiation quantity, the capacity of radiation to ionize air
Measured in Grays (1 Gy = 100 rads) |
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Absorbed dose
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measure of the energy absorbed by any type of ionizing radiation per unit of mass of any type of matter
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Equivalent Dose
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used to compare the biologic effects of different types of radiation on a tissue
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Effective dose
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used to estimate the risk in humans for exposure to a part of the body
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those effects in which the severity of response is proportional to the dose. Usually cell killing and occur in all people when the dose is large enough. Have a dose threshold below which the response is not seen. Ex: oral changes after radiation therapy, skin erythema, fibrosis
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Deterministic effects
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Stochastic effects
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those for which the probability of the occurrence of a change (rather than severity) is dose-dependent. They are all or none: you either do or don’t have the condition. Believed to not have dose thresholds. Ex: cancer and genetic effects
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Direct effect
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when the energy of a photon or secondary electron ionizes biologic macromolecules
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Indirect effects
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those in which hydrogen and hydroxyl free radicals (produced by the action of radiation on the water) interact with organic molecules.
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Modifying Factors for Radiation Effects are...
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1. • Dose: amount of radiation
2. • Dose rate: rate of exposure 3. • Oxygen: radioresistance increases when irradiation is conducted with reduced oxygen. Hydrogen peroxide and hydroperoxyl free radicals form in the presence of Oxygen. |
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What are the Radiation Effects of the Oral Cavity?
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• Oral mucous membrane: contains a basal layer composed of radiosensitive vegetative and differentiating intermitotc cells. Long term effects due to this therapy
• Taste buds: sensitive to radiation. Taste can decrease • Salivary glands: parenchymal part of salivary glad is radiosensitive. Loss of salivary secretion is usually seen. Salivary changes can lead to changes in microflora and dentition. • Teeth: irradiation during development severely retards growth. Could destroy tooth bud if done before calcification. Eruptive mechanism of teeth is radiation resistant. Adult teeth are also resistant. • Radiation caries: form of dental decay that may occur in individuals who receive a course of radio-therapy that includes exposure of the salivary glands. Three types exist. Combination of the types can occur. • Bone: primary damage of the vasculature of the periosteum and cortical bone (which are normally already sparse). Osteoradionecrosis (bone death) can occur if conditions are bad. |
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Late Somatic Effects
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• Carcinogenesis: caused by modifying DNA
• Growth and development: especially found in children who have been exposed • Mental retardation: found in those exposed while in utero since the developing brain is radiosensitive • Cataracts: exposure ranges from 2Gy one time to greater than 5Gy over several exposures. |
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Doubling dose
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amount of radiation a population requires to produce in the next generation as many additional mutations as arise spontaneously. In humans, it’s ~ 2Sv
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Sources of Natural radiation
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o External sources- about 16 % of radiation exposure
- Cosmic radiation (8%) - Terrestrial radiation(8%) o Internal sources: taken up from the external environment by inhalation and ingestion. (67%) - Radon (56%) - Other internal sources: ingestion of food and water that contain radionuclides. (11%) |
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Artificial radiation contributes what percentage of annual radiation exposure?
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17%
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ALARA
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as low as reasonably achievable
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The dosage allowed for those occupationally exposed in the operation of dental x-ray equipment is...
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0.2Sv
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patient dose from dental radiography is usually reported as...
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the amount of radiation received by a target organ
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The degree of risk may be associated with exposure to ionizing radiation may be expressed in two ways:
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1. equivalent natural exposure
2. probability of stochastic effects |
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Equivalent natural exposure
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calculated as the product of the effective dose (E) resulting from a specific radiographic examination and the average daily E delivered by natural sources.
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Study shows that risk for developing cancer or some heritable effect from radiation received as a result of intraoral radiography is estimated to be at most...
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11 per every million examinations
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Intraoral image receptors are available in three speed groups:
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o D: Dose is reduced by 75%. majority of dentists use D speed film.
o E: Dose is reduced by 50%. 2x as fast as D speed and 50 times as fast as regular dental x-ray film. o F: requires 75% of exposure of E speed and 47% of D speed. can be used in routine intraoral radiographic examinations without sacrifice of diagnostic information o Faster films are desired to reduce exposure. But decrease in image quality is possibly associated with increased speed. |
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Intensifying screens decrease patient exposure by as much as 55% in _______ and _______ radiography
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panoramic ; cephalometric
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Crossover
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loss of image sharpness and resolution resulting from light emitted by one screen passing through the film to expose the emulsion on the opposite side of the double emulsion film
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Due to FDA regulations, the x-ray source-skin distance must not be less than...
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20 cm
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The use of a greater focal spot-to-film distance results in a 32% reduction in exposed tissue volume because...
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the x-ray beam is less divergent at a greater distance.
also results in a smaller apparent focal spot size and thereby theoretically increases the resolution of the radiograph |
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o Federal government requires that the x-ray beam use in intraoral radiography be collimated so that the field of radiation at the patient’s skin surface is contained in a circle having a diameter of no more than
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7 cm
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Amount of radiation scatter is proportional to...
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the area exposed.
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Purpose of filtration
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to remove these low energy photons from the x-ray beam
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Thyroid shields reduce exposure of this gland by as much as...
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92%
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_________ technique has been found to reduce the number of undiagnostic x-rays compared to the ______ technique.
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Paralleling; bisecting
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Kilovoltage range of _____ is suitable for most purposes
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70-100 kV
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This is the exposure factor that controls the energy of the x-ray beam
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kV
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the most crucial factor in influencing diagnostic quality (among tube voltage and filtration)
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Exposure time
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Patient exposure is directly related to
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mAs
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X-rays should be viewed in a...
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semidarkened room with light transmitted through the films
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The diagnostic accuracy of radiographic caries diagnosis is only about...
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70%
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Walls must be of proper density so that exposure to nonoccupational individuals is no greater than ____ per week
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100μVy
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Radiographs most appropriate for revealing caries and periodontal/periapical disease
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Periapical Radiographs
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Often used instead of periapicals in children because of smaller size
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Occlusal Radiographs – film is positioned in the occlusal plane
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If the patient has high risk factors for caries, then bitewing radiographs should be taken how frequently?
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• 6 – 12 months for children
• 6 – 18 months for adults |
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If the patient haslow risk factors for caries, then bitewing radiographs should be taken how frequently?
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• 12 -14 months for children
• 18 – 36 months for adolescents • 24 -36 months for adults |
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fetal exposure is _____ for a full mouth examination
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1 microGray
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Sharpness
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how well a boundary between two areas of differing radiodensity is revealed
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Spatial resolution
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how well a radiograph is able to reveal small objects that are close together
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Three methods for minimizing loss of clarity and improving the quality of radiographs:
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(1) Use as small an effective focal spot as practical – smaller angle has greater wearing effect on the target but results in a smaller effective focal spot, decreased unsharpness, and increased image sharpness and resolution
(2) Increase the distance between the focal spot and object by using a long, open ended cylinder – the longer focal spot-to-object distance minimizes blurring by using photons whose paths are almost parallel (3) Minimize the distance between the object and the film – result of minimizing the divergence of the x-ray photons |
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Image distortion
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result of unequal magnification of different parts of the same object; happens when not all parts of an object are in the same focal spot-to-distance
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Sharpness
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how well a boundary between two areas of differing radiodensity is revealed
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To minimize shape distortion, do the following...
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(1) Position the film parallel to the long axis of the object
- Foreshortening: object is not parallel to the film and causes the radiographic image to be shorter than the object - Elongation: film is not parallel and thus the object appears longer on the film than its actual length (2) Orient the central ray perpendicular to the object and film |
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Spatial resolution
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how well a radiograph is able to reveal small objects that are close together
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Three methods for minimizing loss of clarity and improving the quality of radiographs:
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(1) Use as small an effective focal spot as practical – smaller angle has greater wearing effect on the target but results in a smaller effective focal spot, decreased unsharpness, and increased image sharpness and resolution
(2) Increase the distance between the focal spot and object by using a long, open ended cylinder – the longer focal spot-to-object distance minimizes blurring by using photons whose paths are almost parallel (3) Minimize the distance between the object and the film – result of minimizing the divergence of the x-ray photons |
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Image distortion
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result of unequal magnification of different parts of the same object; happens when not all parts of an object are in the same focal spot-to-distance
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服务
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fúwù
servieren; bedienen |
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Bisecting-angle technique
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Film is places as close to the teeth as possible without deforming it
Technique produces distortion because film and object are not parallel By bisecting the angle between the teeth and film, the practitioner can make the length of the tooth’s image on the film corresponds to the actual length |
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Paralleling technique
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Place the film parallel to the long axis of the tooth
Minimizes image distortion Have to place the film in the middle of the mouth |
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Tube shift technique is also called...
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“buccal object rule” or “Clark’s rule”
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Peripheral Eggshell Effect
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Top photon has a tangential path through the apex and a much longer path than the lower photon, which strikes at right angles to the surface. As a result, photons travel through periphery of a curved surface are more attenuated than those travelling at right angles to the surface
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Direct exposure film
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intended to be exposed by x-rays (intraoral)
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Screen film
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sensitive to visible light, and is used with intensifying screens that emit visible light (extroral)
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plastic supporting material onto which the emulsion is coated
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Base (made of polyester polyethylene terephthalate)
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Emulsions
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sensitive to x-rays and visible light, records the radiographic image (Silver halide grains)
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What is the advantage of Double emulsions film?
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less radiation can be used to produce the image
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What is an advantage of Direct exposure film?
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provides higher resolution images
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What is the purpose of the foil in a film packet?
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Shields film from backscatter radiation (which fogs film and reduces contrast)
Reduces patient exposure by absorbing residual x-ray beams |
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If a film packet is placed in backwards, what will happen to the image?
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the film will appear light due to the foil blocking radiation
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creates and image receptors system that is 10 to 60x more sensitive to x-rays than the film alone
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Intensifying screen
Used for all extraoral radiography |
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the slower the speed of a intensifying screen, the _______ its resolving power
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greater
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Characteristic curve
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plot of the relationship between film optical density and exposure; as exposure of the film increase, optical density increases
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Exposure
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Number of photons absorbed by the film emulsion
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Subject thickness
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Thicker the subject -> increase in beam attenuation and lighter resultant image
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Radiographed Speed
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amount of radiation required to produce an image of a standard density
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The Fastest film speed is...
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F
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Film latitude
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measure of the range of exposure that can be recorded as distinguishable densities on a film
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Wide latitude
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can record a subject with a wide range of subject contrast; has a long-straight line portion and a shallow slope; useful when both the osseous structures of the skull and the soft tissues of the facial region must be recorded
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What causes quantum mottling?
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fluctuation in the number of photons per unit of the beam cross-sectional area absorbed by the intensifying screen; most evident when fast-film combinations are used
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What causes Screen structure mottling?
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caused by screen phosphors; most evident in fast screens with large crystals
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Radiographic blurring is caused by:
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1. Image receptor blurring
2. Motion blurring 3. Geometric blurring |
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Image receptor blurring
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sharpness is lost because visible light and UV radiation emitted by the screen spread out beyond the point of origin and expose a film area larger than the phosphor crystal
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Motion blurring
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Movement of film, subject, or x-ray source during exposure
Enlarges the focal spot and diminishes image sharpness |
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Geometric blurring
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photons are not emitted from a point source on the target in the x-ray tube
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What are the function of grids?
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To reduce the amount of scattered radiation exiting a subject that reaches the film and increase subject contrast
The grid is placed between the subject and film, and removes scattered radiation and spares primary photons |
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Grid ratio
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ratio of grid thickness to the width of the radiolucent spacer; higher the grid ratio the more scattered radiation is removed
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Processing Solutions:
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Did We Find West Virginia?
1.Immerse exposed film in Developer: Reduces all silver ions in the exposed crystals to metallic silver grains 2. Rinse film in Water bath: dilutes the developer 3. Immerse film in Fixer: removes underdeveloped silver halide crystals from the emulsion 4. Wash film in Water bath 5. Dry film and mount for Viewing |
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What is the disadvantage of Automatic Film Processing?
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usually more grain in final image
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These mounts are the best because they prevent stray light from the viewbox from reaching the viewer’s eyes
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OPAQUE
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“cone-cut”
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misalignment of x-ray head tube
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Advantages of Digital Imaging
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Digital imagining eliminates chemical processing and hazardous wastes
Digital intraoral receptors require less radiation thus lowering exposure to patients Electronic transfer |
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Disadvantages of Digital Imaging
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High initial expense and equipment is costly to replace
Systems can become obsolete Manufacturers go out of business Film based remains competitive because of its low cost and excellent image quality |
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The two steps to analog-to-digital conversion
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1. sampling
2. quantization |
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2 main technologies for Digital Image Receptors:
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1. Solid state- can generate digital image in the computer without any external device (in dentistry these are called sensors)
2. PSP- phosphor coated on top of a plate in which a latent image is formed after x-ray exposure. Latent image is converted to digital image by a scanning device through stimulation by laser light. |
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INDIRECT detectors
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sensitive to visible light and an intensifying screen is used to convert x-ray energy into light
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DIRECT detectors
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use photoconductor material (selenium) which permits better absorption of x-rays. Electrons are conducted in a direct line to an underlying thin film transistor (TFT). Direct detectors using selenium provide higher resolution but lower efficacy in comparison with indirect detectors
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o Absorb and store energy as x-rays and then release this energy as light (phosphorescence) when stimulated by another light of an appropriate wavelength
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Photostimulable Phosphor
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Contrast Resolution
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ability to distinguish different densities in the radiographic image.
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Spatial Resolution
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capacity for distinguishing fine detail in an image (units= linepairs/mm)
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Detector Latitude
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ability of an image receptor to capture a range of x-ray exposures
Differences in densities should be apparent (i.e. enamel vs. dentin) |
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Detector Sensitivity
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(speed of a detector) is its ability to respond to small amounts of radiation.
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Digital Subtraction Radiography
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When two images of the same object are registered and the image intensities of corresponding pixels are subtracted, a uniform difference image is produced. To be diagnostically useful, the baseline projection geometry and image intensities must be reproduced. This is a good method for getting linear, area, and density measurements.
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Anterior periapical projections:
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Using #1 Receptor:
- Mandibular centrolateral incisors: two projections - Mandibular canines: two projections |
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Posterior periapical projections:
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Using #2 Receptor:
- 2 projections for all maxillary and mandibular premolars and molars |
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Bitewing projections:
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Using #2 Receptor:
- 2 projections for premolars and molars |
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occlusal radiograph is especially useful in the following cases:
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- To locate roots and supernumerary, unerupted and impacted teeth
- To localize foreign bodies in the jaws - To evaluate the integrity of the outlines of the maxillary sinus - To examine patients with trismus (can open their mouths only a few millimeters) - To obtain information about fractures of the mandible and maxilla - To detect disease in the palate or floor of the mouth |
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Tooth hard tissue that looks like bone on a radiograph:
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Dentin
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Cervical burnout
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phenomenon caused by relative lower x-ray absorption on the mesial or distal aspect of teeth, btw the edge of the enamel and adjacent alveolar crest
Mimics root surface caries |
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Lamina Dura
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thin, radiopaque layer of dense bone that surrounds the tooth socket, adjacent to the PDL
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Tasks that should be performed DAILY to ensure quality of radiographs:
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- Compare radiographs with reference film
- Make Step-Wedge test of processing system - Enter findings into Retake Log - Replenish processing solutions - Check temperature of processing solutions. |
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Tasks that should be performed WEEKLY to ensure quality of radiographs:
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- Replace processing solutions
- Clean processing equipment - Clean viewboxes - Review retake log |
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Tasks that should be performed MONTHLY to ensure quality of radiographs:
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- Check darkroom safe lighting
- Clean intensifying screens - Rotate film stock - Check exposure charts - Inspect leaded aprons and thyroid collars |
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Tasks that should be performed YEARLY to ensure quality of radiographs:
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- Calibrate x-ray machine
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Penny test for unsafe illumination:
|
A penny is left on the exposed duplicate film from the double film pack on the working surface during the time that any film would be opened.
If the processed radiograph shows an outline of the penny, the film is being fogged by bad safelighting. |
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federal equipment standard required of X-ray machines:
|
- Timer has to be accurate within 10%
- mAS has to be linear - kVp has to match within 5 - Arm has to be stable - Dead man switch w/ an audible indicator switch - Exposure switch in MD = outside room - Light on = indicate which tube head operating + audible indicator - Added filtration (1.5 at 70 and 2.5 at 90); beam diameter: 7 cm or below at skin entrance - Skin distance 20 cm or greater - Leakage radiation = has to be measured 1 m away from source and not exceed 0.88 miligray in 1 hr when x-ray tube operated at leakage technique factor - Need serial number on unit - Need magenta and yellow sign (warning label) on control panel |