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67 Cards in this Set
- Front
- Back
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What is ionizing radiation?
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Radiation that can knock electroms out of their shells around atoms and break chemical bonds
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What are the two mechanisms of x-ray production?
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- Bremsstrahlung radiation
- Characteristic radiation |
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What's the most common form of producing x-rays?
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Bremmstrahlung radiation
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3 basic things x-rays do to turn electricity into x-rays
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- Produce a cloud of electrons
- Accelerate the electrons - Bombard a metal target |
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What is 'mAs'?
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Number x-rays per exposure
mA * s - Milliamperes per second |
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What determines the maximum energy of x-rays in exposure?
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kVp
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What is considered the 'technique' of radiography?
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Settings of kVp and mAs
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Three possible fates of x-ray photons
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- Complete transmission
- Complete absorption - Scatter |
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Three factors that affect amount of scatter
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- Size of collimated field
- kVp - Thickness of body part |
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Two things to keep in mind in regards to technique charts
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- Each machine needs its own
- Changes over time |
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What is the Rule of 2s?
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For every cm of body thickness, increase technique by 2 kVp up to 80 kVp
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What is the Rule of 3s?
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For every cm of body thickness, increase technique by 3 kVp up to 80 - 100 kVp
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What is the Rule of 4s?
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For every cm of body thickness, increase technique by 4 kVp over 100 kVp
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What is the purpose of a grid?
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To increase contrast of the film by reducing the amount of scatter radiation
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When should you use a grid?
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With a body part >10 cm thick
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How should your technique be adjusted when using a grid?
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Increase mAs
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3 common grid ratios, and most common
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5:1, 8:1, 12:1
8:1 is most common |
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What is the 'bucky factor'?
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Amount the mAs must be increased to account for the grid
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Bucky factor associated with a grid ratio of 5:1
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2
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Bucky factor associated with a grid ratio of 8:1
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3
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Bucky factor associated with a grid ratio of 12:1
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4
So a 4 mAs technique would require 16 mAs with a 12:1 grid - 4x the radiation exposure |
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What are intensifying screens used for?
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Reduce amount of radiation teh patient is exposed to
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What is radiographic film actually exposed by?
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Visible light due to intensifying screens
- Not the x-rays themselves, as those are what hit the intensifying screens |
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Key ingredient in radiographic film emulsion
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Silver halide
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What is the 'speed' of a radiographic film?
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Ability of film to make an image from a certain number of x-ray photons
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What's the tradeoff for increased speed of a radiographic film?
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Decreased detail
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Two components of the speed of a system
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- Film
- Screen |
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What is the goal of film development?
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Turn latent information into a visible and permanent image
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What is the major determinant of film blackness?
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mAs
- Increase mAs to increase blackness |
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4 things that control optical density (number of photons that hit the film)
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- mAs
- Focal distance - kVp - Density of subject |
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What's one way to adjust the mAs without actually adjusting the mAs setting?
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Adjusting the focal distance
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What is the inverse square law? (formula, use)
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When halving the focal distance, it's akin to quadrupling the mAs
mAs new = (FFD [focal distance] new)^2 / (FFD original)^2 |
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In percentage, how much should kVp be adjusted to affect film blackness?
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10 - 15%
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What is the major determinant of film contrast?
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kVp
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What is the Heel Effect and how does it manifest?
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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 |
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Technique for orthopedic radiographs
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Low kVp
High mAs |
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Technique for thoracic radiographs
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High kVp
Low mAs |
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Technique for abdominal radiographs
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Mid kVp
Mid mAs |
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5 radiopacities in order of most black to most white
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- Air
- Fat - Soft tissue - Mineral - Metal |
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What is summation and when does it occur?
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Combination of radiographic silhouettes while preserving individual margins
- When two structures overlay the same path of the x-ray beam and do not touch |
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What is a silhouette sign and when does it occur?
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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 |
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What are two things that will occur as an object to be radiographed is progressively elevated further from the table?
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- It will become progressively larger due to magnification
- It will become blurry (penumbra) |
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Distortion (define)
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Artificial change in shape of an image due to one aspect of the object being a different distance from the cassette than another aspect
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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
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Aligning radiographs on viewer, the patients right side should be on the left side of the screen
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In caudocranial and dorsopalmer views, the lateral side should be on the left side of the viewing screen
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Not looking at the whole radiograph and instead stopping once you find something abnormal (term)
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Satisfaction of Search error
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What is a Roentgen sign?
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Criteria upon which to diagnose a radiographic anomaly
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6 Roentgen signs
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Changes in:
- Size - Shape - Margination - Number - Opacity - Location |
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4 different stages of film development
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- Development
- Fixation - Rinse - Dry |
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What is the purpose of developing solution?
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To reduce all silver atoms within the exposed silver halide crystals to metallic silver atoms (which are black)
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What three factors affect the amount of development?
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- Time
- Temperature - Concentration of developer solution |
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Relationship of time required for development to temperature of solution
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Higher temperature requires less time
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Purpose of fixer solution?
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Stop development process and remove undeveloped emulsion
- If emulsion isn't removed, it eventually turns radiograph yellow |
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Three types of digital detectors
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- Computed radiography (CR)
- Direct digital radiography (DR) - Charge coupled device (CCD) |
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Downside of Computer radiography detector
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Increased amount of time before you can view radiograph
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Downside of charge coupled device detector (2)
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- Poor image quality
- Can't do horizontal views |
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Downside of direct digital radiography detector
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Expense
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Downside of ultrasonography
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Dependent on skill of ultrasonographer
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Production of ultrasound waves through electrical stimulation of a crystal (term)
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Piezoelectric effect
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Relative brightness or darkness of a tissue or organ on ultrasound (term)
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Echogenicity
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Speckle pattern (define)
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'Texture' of tissue displayed in the ultrasound image
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Unit for quantification of brightness or darkness on CT images (term)
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Hounsfield units
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Attenuation (define)
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Brightness or darkness on a CT image
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Window width (define)
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Range of Hounsfield units displayed over the gray scale in an image
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Window level (define)
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Mean value of Hounsfield units displayed in an image
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Soft tissue window (define)
Bone window (define) |
Evaluation of soft tissue with computed tomography
Evaluation of bone with computed tomography |
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Primary advantage of MRI
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Does not use ionizing radiation
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