LO 2 Flashcards
_______ of the wave determines penetrating power of the beam
Wavelength - shorter wavelengths= more penetrating power
Quality is used to describe ______
Mean energy or penetrating power of the x-ray beam
Quality of the x-ray beam is controlled by ______
The kilovoltage
Voltage is the measure of electrical _______
Force
Describe kilovoltage peak
- Maximum peak voltage of an alternating current (Ac)
- Regulates the speed and energy of the electrons and determines penetrating ability
- Increasing results in a higher energy beam (shorter wavelengths)
When kVp is increase, what happens to x-ray quality, density, and contrast?
Quality ⬆️
Density ⬆️
Contrast ⬇️
Describe density
The overall darkness of a film - kVp increases, film will appear darker
Describe contrast
How sharply dark and light areas are differentiated on film
Low kilovoltage settings (65-70kvp) creates _______ contrast film
High
Low contrast images created by higher kVp setting are good for detecting ______
Periodontal periapical disease
Exposure time is measured in ______
Impulses
When kVp increases, exposure time should _______
Decrease
Quantity refers to _______
The number of x-rays produced in the x-ray unit (controlled by mA - 7-15)
When mA is increased, exposure time is to be decreased to maintain constant ______
Density
A higher miliamperage setting _______ the temperature of the cathode filiment
Increases - results in more electrons boiling off
All dental x-ray machines have these three exposure factor settings
- kV
- mA
- Time
When miliamperage is increased, describe quantity, density, and exposure time
Quantity ⬆️
Density ⬆️
Exposure time ⬇️
How can kilovoltage and miliamperage increase intensity of the beam?
- Kilovoltage - can increase speed of electrons travelling between anode and cathode, resulting in a beam with more energy
- Miliamperage - can increase the number of electrons produced, resulting in more x-rays being produced
How does exposure time affect the intensity of the beam?
Longer exposures allow for the creation of more x-rays, resulting in a more intense beam
How is x-ray intensity measured/calculated?
Intensity = 1/d^2
What are the 5 factors that affect intensity of the x-ray beam?
- kVp
- mA
- Exposure time
- Distance
- Filters
What are the 3 distances to consider when taking an x-ray?
- Target-surface (source to patient’s skin)
- Target-object (source to tooth)
- Target-film (source to film)
When x-rays travel from their point of origin, they diverge and spread over a larger area. What happens to the intensity of the beam?
Decreases
What is the inverse square law?
The intensity of radiation is inversely proportional to the square of the distance from the source of radiation
When the distance of the beam is doubled, the beam is ______
1/4 as intense
When the distance is halved, the beam is _______
4 time more intense
Describe the half-value layer
The thickness of a specified material that reduces the intensity by half (aluminum discs)
What is the benefit of filtering long, low-energy x-rays from the beam?
Increases mean penetrating power while reducing intensity
What are the two types of x-ray machines?
Intraoral and extraoral
______ is a device used to hold and align intraoral dental x-ray receptors in the mouth
Receptor holder
___________ is an instrument used to help position the PID relative to the tooth and receptor
Beam alignment device (XCP or BAI)
What do collimating devices do?
Can be retrofitted onto a PID to restrict the size of the beam
What part of a radiograph is most radiolucent?
Black areas - show mostly air around the tooth
What part of a radiograph is most radiopaque?
White areas - resists passage of x-ray beam
What are the visual charactersistocs of a radiograph
Density and contrast
What are the geometric characteristics of a radiograph?
Sharpness, magnification, distortion
What are the 4 influencing factors of density (or the overall darkness) of a radiograph?
- mA
- kVp
- Exposure time
- Subject thickness
The difference in degrees of blackness between adjacent areas of a radiograph is ________
Contrast
What is the only influencing factor of contrast?
kVp
Short scale contrast is ______
High contrast
Long scale contrast is
Low contrast
Short scale contrast occurs at ______ kVp
Low
Long scale contrast occurs at _____ kVp
High
Sharpness, also known as resolution or definition, is the capability of the x-ray film to ______
Reproduce distinct outlines of an object
The lack of image sharpness present in every radiograph is known as _______
Penumbra
What are the influencing factors of sharpness?
- Focal spot size - smaller focal spot = sharper image
- Film composition - smaller crystals = greater sharpness
- Movement - film or patient could move causing loss of sharpness
_______ results from the divergent paths of the x-ray beam as they radiate from the focal spot
Magnification
What are the influencing factors of magnification?
- Target-film distance - longer means less magnification
- Object-film distance - decrease means less magnification
Tooth and x-ray film should always be placed as close together as possible
________ is a variation in the true size and shape of an object being radiographed and results from unequal magnification of different parts of the same object
Distortion
What are the influencing factors of distortion?
- Object-film alignment - must be parallel
- x-ray beam angulation - beam must be perpendicular to tooth and film
