Radiographic Image Characteristics Flashcards
Will you always get an image? Why?
- Yes
- Receptors are designed to respond to radiation
What is the goal of an image?
Optimum diagnostic quality with minimal patient radiation exposure
What is a good radiographic image?
A radiograph that reproduces anatomical structures/tissue
Image characteristics
- Density
- Contrast
- Noise
This degree and pattern of darkness depends on…
- Energy and intensity of x-ray photons
- Subject composition
Characteristic radiation
Interacts primarily valence electrons
Breaking radiation
Produces electrons that primarily interact with the nucleus
Radiographic density definition
Overall degree of darkening of the image or exposed image receptor
Low density
Underexposed, too light
High density
Over exposure, too dark
Primary controlling factor of density
Milliamperage, mA
Contributing factors for density
- Exposure time, seconds
- Distance
Will density be equal if mA is equal when comparing?
Yes
Do you change kVp to change density?
No
mAs directly control…
The number of x-ray photons produced
If mAs increase, then density…
Increases
What is the ideal exposure time when mA is constant?
0.5 seconds
Effects of distance in radiographs include…
- Intensity of x-ray beam reduces as focal spot to object distance increases
- Inverse square law
Primary factor in density?
mA
kVp is the primary factor for…
Contrast
As you increase the kVp, do you increase or decrease penetrability of the x-ray?
Increase
As thickness increases, the more photons…
Absorbed
As thickness decreases, the more photons
Hit the sensor
Is enamel high or low in atomic number?
High
Is enamel radiolucent or radiopaque?
Radiopaque
Attenuated definition
Absorbed
The thicker the subject or object is, the more the beam is attenuated, and…
The light becomes the resultant image
Range of kVp in dental clinics are…
60-70 kVp
In order to achieve optimum density, kVp or time should be adjusted when…
Subject thickness varies
Image contrast is…
The degree of difference in the shades of the gray on the radiograph
High contrast
- Few shades of gray
- Low kVp
- Short scale contrast
Low contrast
- Many shades of gray
- High kVp
- Long scale of gray, more colors
Children require more or less radiation compared to adults?
Less
Noise
- Spurious information about an object
- Degrades images
- Makes difficult to differentiate between structure
Noise is the appearance of uneven _______ in a digital sensor
Density
As mA increase, density
Increases
As mA decreases, density
Decreases
As kV increases, density
Increases
As kV decreases, density
Decreases
As time increases, density
Increases
As time decreases, density
Decreases
As thickness increases, density
Decreases
Increased kV leads to ___ - scale contrast
Low -scale contrast, low contrast
Decreased kV leads to ___ - scale contrast
Short-scale contrast, high contrast
Image sharpness
Measurement of how well a boundary between two areas of differing radiodensity is revealed
Spatial resolution
Measures how well a radiograph is able to reveal small objects that are close
Smaller the focal spot..
The sharper the image
Can you control the focal spot size?
No
If you move sensor away from tooth, the image will…
Not be sharp
If you increase distance from focal spot, you will avoid…
Magnification error, including foreshortening and elongating
Radiographic sharpness
Ability of radiographic to define an edge precisely
Radiographic resolution
Ability of the radiograph to record separate structures that are close together
An increase in the mA, kVp, or exposure time will increase…
The overall density of the image
mAs directly control what?
Number of x-ray photons produced
What does kVp control?
Energy and penetrability/quality of x-ray
High kVp is specifically used in what kind of objects?
Thick objects
As subject/object thickness increases, what happens to X-ray absorption and density?
Absorption increases, density decreases
What is image contrast?
Degree of difference in the shades of gray on the radiograph
Why is contrast important?
Various structures and pathologies will pop up if contrast is good
What are other factors that contribute to image contrast?
Subject thickness, density, and atomic number
Does an increasing kVp increase or decrease the subject contrast?
Decreases
