Chapters 5-6: Radiation Characteristics & Dental X-ray Image Characteristics Flashcards
Exposure Controls and Settings, X-ray Beam Quality and Quantity, Diagnostic Dental Images and Characteristics
How does exposure time affect the intensity of the x-ray beam?
longer exposure time produces more x-rays, which increases the intensity of the x-ray beam
What are the two influencing factors of distortion of an image?
- object-receptor alignment
- x-ray beam angulation
Define the term: distortion
- a geometric characteristic that refers to a variation in the true size and shape of the object being imaged
- influenced by object-receptor alignment and the vertical angulation of the x-ray beam
What are the two factors that influence the sharpness of an image?
- focal spot size
- movement
Define the term: focal spot
the tungsten target of the anode that converts bombarding electrons into x-ray photons, concentrating the electrons and creating an enormous amount of heat
What is the scale of contrast on an image with low kilovoltage settings?
short-scale contrast
How does increased kilovoltage affect the density of the image?
increased density, which makes the image appear darker
How does a larger focal spot size influence the sharpness of an image?
loss of sharpness
Define the term: subject contrast
the characteristics of the subject (patient) that influence contrast, including the size and thickness of the patient
Define the term: tungsten target
a portion of the anode in the x-ray tube that serves as a focal spot and converts bombarding electrons into x-ray photons
Define the term: wavelength
- the distance between the crest of one wave and the crest of the next wave
- determines the energy and penetrating power of the radiation
How does increased exposure time affect the image?
the longer the exposure time, the more x-rays are delivered, which results in a darker image
How does increased subject thickness affect the density of the image?
the image appears more dense due to absorbing more of the x-ray beam
Define the term: exposure factors
factors that influence the density of an image (ex: milliamperage, kilovoltage, exposure time)
Define the term: penumbra
the unsharpness or blurring of the edges of a structure viewed on a dental image
In order to create an x-ray beam with increased penetrating ability, how would you adjust the kilovoltage setting on the control panel?
increase the kilovoltage
Define the term: high contrast
a term describing an image with many very dark areas and very light areas and few shades of gray
How does increased kilovoltage affect the contrast of the image?
low contrast, which helps in the diagnosis of periodontal or periapical diseases
Define the term: voltage
in dental imaging, the measurement of force that refers to the potential difference between two electrical charges
Define the term: stepwedge
a device constructed of uniform-layered thickness of an x-ray absorbing material (usually aluminum) used to demonstrate densities and contrast scales
Define the term: low contrast
a term describing an image with many shades of gray and few areas of black and white
What exposure setting controls and regulates the temperate of the cathode filament in the x-ray tubehead?
milliamperage
Define the term: control panel
a part of the x-ray machine that contains an on/off switch and indicator light, an exposure button and indicator light, and control devices to regulate the x-ray beam
How does a decreased object-receptor distance affect the magnification of an image?
decreased magnification
What exposure setting determines the quantity of x-rays produced in the x-ray tubehead?
milliamperage
What determines the energy and penetrating power of radiation?
wavelength
How does a small focal spot size influence the sharpness of an image?
sharper image
Define the term: quantity of the x-ray beam
- the number of x-rays produced in the dental x-ray unit
- controlled by the milliamperage
How does decreased kilovoltage affect the density of the image?
decreased density, which makes the image appear lighter
Define the term: quality of the x-ray beam
- the mean energy or penetrating ability of the x-ray beam
- controlled by the kilovoltage
Which scale of contrast is preferred in the diagnosis of caries, and why?
- short-scale contrast
- the carious lesion will appear more radiolucent, and the areas are easily distinguishable
Define the term: angulation
the alignment of the central x-ray beam in the horizontal and vertical planes
True or false: The tooth and the image receptor should always be positioned as close together as possible during exposure.
True
Define the term: image receptor
a recording medium (ex: PSP plate, digital sensor)
If the kilovoltage setting is decreased, how should you adjust the exposure time setting to achieve a diagnostic image?
increase exposure time
How does a longer target-receptor distance affect the magnification of an image?
decreased magnification
What are the two terms used to describe the black and white areas on an image?
- radiopaque
*radiolucent
Define the term: ampere (A)
the unit of measure used to describe the number of electrons passing through a conductor * (electrical current strength)*
How should the central ray of the x-ray beam be positioned in relation to the tooth and the image receptor to decrease distortion?
the central ray should be perpendicular to the tooth and the image receptor
Define the term: milliamperage
in dental imaging, the quantity (number) of x-ray emitted from the tubehead
Define the term: diagnostic image
a dental image that allows for the identifying and monitoring of diseases or injuries
Define the term: contrast
- how sharply dark and light areas are differentiated or separated on an image
- the difference in the degrees of blackness (densities) between adjacent areas on a dental image
The detail, resolution, or definition of an image can also be described with what term?
sharpness
Define the term: amperage
- the number of electrons that pass through a conductor
- the strength of an electrical current
Define the term: cathode
- the negative electrode in the x-ray tube
- consists of a tungsten wire filament in a molybdenum cup
- supplies the electrons necessary to generate x-rays
Define the term: magnification
- a geometric characteristic that refers to an image that appears larger than the actual size of the object it represents
- influenced by target-receptor distance and object-receptor distance
Define the term: exposure
a measure of ionization produced in air by x-radiation or gamma radiation
If the milliamperage setting is increased, how should the exposure time setting be adjusted to create a diagnostic image?
decreased exposure time
How does increased milliamperage affect the density of the image?
decreased density, which makes the image appear darker
Define the term: kilovoltage
in dental imaging, the x-ray tube peak voltage used during an exposure
How does milliamperage affect the intensity of the x-ray beam?
increased milliamperage produce an x-ray beam with more energy, which increased the intensity of the x-ray beam
If a structure lacks density and allows the passage of more x-rays, how does the structure appear on an image?
radiolucent
If the kilovoltage setting is increased, how should you adjust the exposure time setting to achieve a diagnostic image?
decrease exposure time
Define the term: target-surface distance
the distance from the source of x-rays (tungsten target in the anode) to the surface of the patient’s skin
Define the term: target-receptor distance
the distance from the source of radiation (tungsten target in the anode) to the image receptor
Define the term: radiopacity / radiodensity
an area on a dental image appearing radiopaque (light/white) due to resisting the passage of the x-ray beam and limiting the amount of x-rays that reach the image receptor
Define the term: radiolucent
the portion of an image that is dark or black, due to the structure readily permitting the passage of the x-ray beam and allowing more x-rays to reach the image receptor
Define the term: scale of contrast
the range of useful densities on a dental images
How does increased object-receptor distance affect the magnification of an image?
increased magnification
What are the two terms used to describe the scale of contrast?
- short-scale contrast
- long-scale contrast
Does a higher half-value layer produce a more- or less-penetrating x-ray beam?
higher x-ray beam
Define the term: radiopaque
the portion of an image that is light or white, due to the structure resisting the passage of the x-ray beam and limiting the amount of x-rays that reach the receptor
How should the object being imaged and the image receptor be positioned to decrease distortion?
the object and image receptor should be parallel to each other
Define the term: subject thickness
the thickness of soft tissue and bone in a patient
Define the term: target-object distance
the distance from the source of x-rays (tungsten target in the anode) to the object being imaged (tooth)
What are the three measurements used to describe the intensity of the x-ray beam?
- target-surface distance
- target-object distance
- target-receptor distance
What are the two visual characteristics that determine the diagnostic quality of an image?
- density
- contrast
Define the term: density
the overall darkness or blackness of an image
What are the three geometric characteristics that affect the diagnostic quality of an image?
- sharpness
- magnification
- distortion
If a structure is dense and absorbs the x-rays passing through, how does the structure appear on and image?
radiopaque
Forshortened and elongated images are a result of what geometric factor?
distortion
How does decreased milliamperage affect the density of the image?
increased density, which makes the image appear lighter
What are the two influencing factors of the magnification of an image?
- target-receptor distance
- object-receptor distance
Define the term: inverse square law
- a rule that states that “the intensity of radiation is inversely proportional to the square of the distance from the source of radiation”
- as distance is increased, the radiation intensity at the object is decreased, and vice versa
What is placed in the x-ray tubehead to reduce the intensity of the x-ray beam by removing the low-energy, longer-wavelength x-rays?
aluminum filters
Define the term: half-value layer (HVL)
the thickness of material that, when placed in the path of the x-ray beam, reduces the exposure rate by one-half
What exposure setting controls the quality of the x-ray beam?
kilovoltage
Define the term: radiolucency
an area on a dental image appears radiolucent (dark/black) due to readily allowing the passage of the x-ray beam so that more x-rays reach the image receptor
How does decreased kilovoltage affect the contrast of the image?
high contrast, which helps in the diagnosis of caries
What is the scale of contrast on an image with high kilovoltage settings?
long-scale contrast
How does kilovoltage affect the intensity of the x-ray beam?
increased kilovoltage produces more energy and shorter wavelengths, which increases the intensity of the x-ray beam
Define the term: volt (V)
the unit of measurement for voltage
How does a shorter target-receptor distance affect the magnification of an image?
increased magnification
Define the term: sharpness
- refers to the capability of the image receptor to reproduce the distinct outlines of an object
- influenced by focal spot size and movement
How many impulses occur in one second?
60
Define the term: long-scale contrast
- a term describing an image with many densities, or many shades of gray
- results from the use of a higher kilovoltage range
Which scale of contrast is preferred in the diagnosis of periodontal disease, and why?
- long-scale contrast
- the changes in bone loss as a result of periodontal disease will appear with many shades of gray
Define the term: impulse
in dental imaging, a measure of exposure time
Define the term: anode
- the positive electrode in the x-ray tube
- consists of a wafer-thin tungsten plate embedded in a solid copper rod
- converts electrons into x-ray photons
If the milliamperage setting is decreased, how should the exposure time setting be adjusted to create a diagnostic image?
increased exposure time
Define the term: intensity
- the total energy of the x-ray beam
- the product of the quantity (number of x-ray photons) and quality (energy of each photon) per unit of area per time of exposure
