Radiation Characteristics Flashcards
What are 5 things that affect x-ray beam quality?
- Voltage and kilovoltage
- Kilovoltage peak (kVp)
- Density and kVp
- Contrast and kVp
- Exposure time and kVp
What determines the energy and penetrating power of radiation?
Wavelength (x-rays with shorter wavelengths have more penetrating power)
What is the term x-ray beam quality in reference to? What is the quality controlled by?
Describes the mean energy or penetrating ability of the x-ray beam. Controlled by the kilovoltage peak
What is voltage? What is it a measurement of?
The potential difference between two electrical charges. Measurement of force (speed). This force is the electrical force that causes electrons to move from the cathode to the anode.
What happens to the speed of electrons when voltage is increased?
The speed of the electrons is increased and the electrons strike the target with greater force and energy. End result is a penetrating x-ray beam with a short wavelength
What range of voltage should be used in dental radiography?
Between 65 kilovolts to 100 kilovolts (kV = 1000 volts). 65 kV is inadequate penetration and 100 kV is overpenetration
What is the kilovoltage peak?
The maximum or peak voltage, usually referring to the peak voltage of an alternating current
What is density in an image?
Overall darkness or blackness of an image
How will the image appear if the kilovoltage is increased? How will this affect the contrast?
Image will appear lighter (low-contrast - many shades of gray)
How will the image appear if the kilovoltage is decreased? How will this affect the contrast?
Image will appear lighter (high-contrast - black and white)
What is the exposure time?
Interval of time during which x-rays are produced and is measured in impulses
What should we do if we increase the kilovoltage?
Decrease the exposure time
What is x-ray beam quantity?
Number of x-rays produced in a dental x-ray unit
What is amperage?
Determines the amount of electrons passing through the cathode filament
What does increasing amperage do?
Increases the number of electrons travelling from cathode to anode and produces more x-rays
The QUANTITY of the x-rays produced are controlled by what?
Milliamperage
What is ampere?
Unit of measure used to describe the number of electrons of current flowing through the cathode filament (milliampere = 1/1000 amperes)
What does milliamperage range from in dental radiography?
7-15 mA, any more will produce excessive heat
Milliamperage also regulates what?
The temperature of the cathode filament
What does increasing milliamperage do to the image?
Makes the image darker (higher density)
What are milliampere-seconds?
mAs, the product of milliamperes and exposure time
When milliamperage is increased, exposure time must be ____
Decreased
What is x-ray beam intensity determined by? (equation)
The product of the quantity and quality per unit of area per unit of exposure time - intensity = (quantity)(quality)/(area)(exposure time)
In summary, how does a higher kilovoltage peak affect the x-ray image?
- Produce an x-ray beam with more energy + shorter wavelengths
- Increase the intensity of the x-ray beam
- Controls the amount of contrast (high kVp = low contrast)
In summary, how does a higher milliamperage affect the x-ray image?
Produces an x-ray beam with more energy, increasing the intensity of the x-ray beam which increases the density
What are the three distances to consider in x-ray imaging?
- Target-surface (source to patient’s skin)
- Target-object (source to patient’s tooth)
- Target-receptor (source to image receptor)
How does a higher distance affect the intensity of the beam?
Lower intensity
What is the inverse square law?
When the distance increases, the beam intensity is the inverse square of the distance (ie. distance is doubled, beam is 1/4 as intense)
What is the half-value layer?
The thickness of a specified material that reduces the intensity by half is termed the half-value layer
