Digital Imaging Foundations #2 Flashcards
What defines the possible number of colors that a pixel can show?
Bit depth
What are examples of structures that are radiopaque?
- enamel
- dentin
- bone
- restorative materials
What does it mean an image has low contrast?
A radiograph with too many gray values
What is a stepwedge?
device used to demonstrate contrast scales and used for quality control in radiology
Why should the X-ray beam be perpendicular to the tooth and receptor?
To reproduce adjacent structures with minimal distortion.
True or false: Opacity is the overall darkness of a radiograph
False, density is the overall darkness of a radiograph
What influencing factor(s) result in an inverse effect on image density?
Object thickness and target-receptor distance
What is the only influencing factor which impacts image contrast?
Kilovoltage (illustrated on stepwedge’s contrast scale)
What factors increase a radiographic image’s sharpness?
- smaller focal spot (angled focal spot helps with this too)
- smaller pixel size
- no movement of receptor or patient during the acquisition.
What is the relationship between focal spot and sharpness?
A. directly related
B. inversely related
B. inversely related
The penumbra area which is an area of loss of sharpness is related to?
A. Density
B. Sharpness
C. Magnification
D. Contrast
C. Magnification
T/F: A lower radiation dose is an advantage of digital radiography.
True
Digital radiography’s initial cost compared to film imaging is ___ (higher/lower)
higher
The equation for intensity is:
intensity = —/—
(number of photons) x (energy of each photon) / (area) x (time)
What is the maximum voltage that makes the cathode electrons move to the anode?
kilovoltage-peak (kVp)
Which set of options have a direct relationship?
a. movement, sharpness
b. kVp, contrast
c. exposure time, image density
d. object thickness, image density
c. exposure time, density
inverse relationships: target-receptor distance and density. object thickness and density. kVp and contrast. focal spot and sharpness. pixel size and sharpness. movement and sharpness. target-receptor distance and magnification.
direct relationships: density and mA. kVp and density. exposure time and density. object-receptor distance and magnification.
An X-ray with mostly dark areas and very bright areas are said to have?
high contrast
What is the disadvantage of digital radiography?
Initial cost is higher.
Advantages include: lower radiation dose, easier image acquisition, eliminate chemical processing, possibility of using resources, easier copying and sharing, easier to store
if a structure had very little or no density, it will appear what color on the x-ray?
Black (radiolucent)
The x-rays are able to pass and reach the detector with almost no interactions
What term refers to the the overall darkness of a radiograph?
Density
Describe the difference between radiolucent and radiopaque.
Radiolucent is the area that’s dark/black; it indicates structures with little physical density and X-rays can pass through easily without interacting.
Radiopaque is the area that’s light/white; it indicates dense structures like enamel and dentin; X-rays are absorbed more and less photons reach the detector.
True or False: If the thickness of an object increases, then so does the density.
False! They are inversely related; if the object thickness increases, then the image density decreases.
Which of the following would be radiolucent?
A. air
B. enamel
C. dentin
D. bone
E. restorative materials
A. air
True or False: There is no single permanent value of optimal density.
True
Which of these factors affect density?
A. milliamperage
B. exposure time
C. Kilovoltage-peak
D. Object thickness
E. Distance from target-receptor
F. All of the above
F. All of the above
In a good quality diagnostic image, what are the 5 basic tissues that must be observed?
enamel, dentin, pulp cavity, alveolar bone and soft tissues
Which of the following is a factor that influences magnification?
A. Focal Spot Size
B. Detector Resolution
C. Object-Receptor Distance
D. Object-Receptor Alignment
C. Object-Receptor Distance
A,B are factors that influence Sharpness. D influences Distortion
What are the two main visual characteristics of a radiographic image?
Density and contrast
T/F: Contrast is defined as the overall darkness of a radiograph
False; density
Are the areas of the receptor that had higher intensity of x-ray photons reaching the sensor represented by dark (radiolucent) or light (radiopaque) images?
Dark (radiolucent) images
What is the major downside of a small focal point size?
Small, concentrated, focused (not dissipated) heat spot on Tungsten (W) target block, which may cause melting despite sharper image quality
If target-receptor distance increases, magnification _______ (increases/decreases).
Decreases
The geometric characteristics that influence the quality of the final image and, consequently, its interpretation are:
Sharpness, Distortion, Magnification
What is contrast?
The difference between the various degrees of darkening (densities) on a radiograph
What are factors that influence density?
- Miliamperage (mA)
- Exposure time
- Distance target receptor
- Kilovoltage-peak (kVp)
- Object thickness
When the distance from the focal spot is doubled __________________ .
the intensity of the beam decreases to one quarter
An x-ray with too many gray values is said to have a
low contrast
Beam intensity is:
Reference to the quality and quantity of the x-ray beam.
It has a direct influence on the density of the image.
High vs low contrast
High contrast: Radiograph with mostly very dark and very bright areas
Low contrast: Radiograph with too many gray values
What two factors influence magnification?
Target receptor distance
Object receptor distance
T or F: In the paralleling technique the X-ray beam should be parallel to the tooth and receptor to prevent distortion of the image.
FALSE (should be perpendicular to the tooth and receptor)
What two factors influence distortion?
Object-receptor alignment
X-ray beam angulation
The ideal image has the darkest areas appear ______, the lighter areas appear ______, with an intermediate ________ between them.
black, white, grayscale
Dark or black portion of a radiograph; structure with no or little density
Radiolucent
What is the area with a loss of sharpness in a radiograph called?
Penumbra
What is a variation in actual size and shape of the object of an image called?
Distortion
T/F: When the distance from the focal spot to the receptor is doubled, the intensity of the beam is also doubled.
False. The beam decreases to one quarter.
(Inverse square law)
What should the orientation of the receptor be in comparison to the object to prevent image distortion?
parallel
True/False: Radiopaque areas in radiographs illustrate denser materials.
True
Which of the following has an influence on contrast and density?
a. mA
b. object thickness
c. exposure time
d. kV
d. kV influences both contrast and density
* kV is the only factor influencing contrast where answer choices a-d all effect density
First Statement: As the target-receptor distance increases, so does the magnification.
Second Statement: At the object-receptor distance increases, so does the magnification.
A. First statement true, second statement false
B. First statement false, second statement true
C. Both statements true
D. Both statements are false
B. First statement false, second statement true
First Statement: The picture provided shows high contrast.
Second Statement: High contrast is when the images is composed mostly of very dark and very bright areas in it.
A. First statement true, second statement false
B. First statement false, second statement true
C. Both statements true
D. Both statements are false
B. First statement false, second statement true.
