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67 Cards in this Set

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What is ionizing radiation?
Radiation that can knock electroms out of their shells around atoms and break chemical bonds
What are the two mechanisms of x-ray production?
- Bremsstrahlung radiation
- Characteristic radiation
What's the most common form of producing x-rays?
Bremmstrahlung radiation
3 basic things x-rays do to turn electricity into x-rays
- Produce a cloud of electrons
- Accelerate the electrons
- Bombard a metal target
What is 'mAs'?
Number x-rays per exposure

mA * s
- Milliamperes per second
What determines the maximum energy of x-rays in exposure?
kVp
What is considered the 'technique' of radiography?
Settings of kVp and mAs
Three possible fates of x-ray photons
- Complete transmission
- Complete absorption
- Scatter
Three factors that affect amount of scatter
- Size of collimated field
- kVp
- Thickness of body part
Two things to keep in mind in regards to technique charts
- Each machine needs its own
- Changes over time
What is the Rule of 2s?
For every cm of body thickness, increase technique by 2 kVp up to 80 kVp
What is the Rule of 3s?
For every cm of body thickness, increase technique by 3 kVp up to 80 - 100 kVp
What is the Rule of 4s?
For every cm of body thickness, increase technique by 4 kVp over 100 kVp
What is the purpose of a grid?
To increase contrast of the film by reducing the amount of scatter radiation
When should you use a grid?
With a body part >10 cm thick
How should your technique be adjusted when using a grid?
Increase mAs
3 common grid ratios, and most common
5:1, 8:1, 12:1

8:1 is most common
What is the 'bucky factor'?
Amount the mAs must be increased to account for the grid
Bucky factor associated with a grid ratio of 5:1
2
Bucky factor associated with a grid ratio of 8:1
3
Bucky factor associated with a grid ratio of 12:1
4

So a 4 mAs technique would require 16 mAs with a 12:1 grid
- 4x the radiation exposure
What are intensifying screens used for?
Reduce amount of radiation teh patient is exposed to
What is radiographic film actually exposed by?
Visible light due to intensifying screens
- Not the x-rays themselves, as those are what hit the intensifying screens
Key ingredient in radiographic film emulsion
Silver halide
What is the 'speed' of a radiographic film?
Ability of film to make an image from a certain number of x-ray photons
What's the tradeoff for increased speed of a radiographic film?
Decreased detail
Two components of the speed of a system
- Film
- Screen
What is the goal of film development?
Turn latent information into a visible and permanent image
What is the major determinant of film blackness?
mAs

- Increase mAs to increase blackness
4 things that control optical density (number of photons that hit the film)
- mAs
- Focal distance
- kVp
- Density of subject
What's one way to adjust the mAs without actually adjusting the mAs setting?
Adjusting the focal distance
What is the inverse square law? (formula, use)
When halving the focal distance, it's akin to quadrupling the mAs

mAs new = (FFD [focal distance] new)^2 / (FFD original)^2
In percentage, how much should kVp be adjusted to affect film blackness?
10 - 15%
What is the major determinant of film contrast?
kVp
What is the Heel Effect and how does it manifest?
Phenomenon in which the x-ray beam is of lower intensity on the side of the beam toward the anode
- Shows up as a lighter side of the radiograph than the other
Technique for orthopedic radiographs
Low kVp
High mAs
Technique for thoracic radiographs
High kVp
Low mAs
Technique for abdominal radiographs
Mid kVp
Mid mAs
5 radiopacities in order of most black to most white
- Air
- Fat
- Soft tissue
- Mineral
- Metal
What is summation and when does it occur?
Combination of radiographic silhouettes while preserving individual margins
- When two structures overlay the same path of the x-ray beam and do not touch
What is a silhouette sign and when does it occur?
Inability to differentiate the margins of two silhouettes
- When two structures of the same radiopacity are in contact with each other

So can't differentiate a solid soft tissue structure and a fluid-filled structure on radiographs
What are two things that will occur as an object to be radiographed is progressively elevated further from the table?
- It will become progressively larger due to magnification
- It will become blurry (penumbra)
Distortion (define)
Artificial change in shape of an image due to one aspect of the object being a different distance from the cassette than another aspect
Phenomenon in which the normal representation of an image is abnormally altered by its surroundings

Ex. optical illusions he showed us in class
Mach Phenomenon
Aligning radiographs on viewer, the patients right side should be on the left side of the screen
In caudocranial and dorsopalmer views, the lateral side should be on the left side of the viewing screen
Not looking at the whole radiograph and instead stopping once you find something abnormal (term)
Satisfaction of Search error
What is a Roentgen sign?
Criteria upon which to diagnose a radiographic anomaly
6 Roentgen signs
Changes in:
- Size
- Shape
- Margination
- Number
- Opacity
- Location
4 different stages of film development
- Development
- Fixation
- Rinse
- Dry
What is the purpose of developing solution?
To reduce all silver atoms within the exposed silver halide crystals to metallic silver atoms (which are black)
What three factors affect the amount of development?
- Time
- Temperature
- Concentration of developer solution
Relationship of time required for development to temperature of solution
Higher temperature requires less time
Purpose of fixer solution?
Stop development process and remove undeveloped emulsion
- If emulsion isn't removed, it eventually turns radiograph yellow
Three types of digital detectors
- Computed radiography (CR)
- Direct digital radiography (DR)
- Charge coupled device (CCD)
Downside of Computer radiography detector
Increased amount of time before you can view radiograph
Downside of charge coupled device detector (2)
- Poor image quality
- Can't do horizontal views
Downside of direct digital radiography detector
Expense
Downside of ultrasonography
Dependent on skill of ultrasonographer
Production of ultrasound waves through electrical stimulation of a crystal (term)
Piezoelectric effect
Relative brightness or darkness of a tissue or organ on ultrasound (term)
Echogenicity
Speckle pattern (define)
'Texture' of tissue displayed in the ultrasound image
Unit for quantification of brightness or darkness on CT images (term)
Hounsfield units
Attenuation (define)
Brightness or darkness on a CT image
Window width (define)
Range of Hounsfield units displayed over the gray scale in an image
Window level (define)
Mean value of Hounsfield units displayed in an image
Soft tissue window (define)

Bone window (define)
Evaluation of soft tissue with computed tomography

Evaluation of bone with computed tomography
Primary advantage of MRI
Does not use ionizing radiation