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122 Cards in this Set
- Front
- Back
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Electron interactions occur where?
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X-Ray tube
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Photon interactions occur where?
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Tube to infinity
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Projectile electrons are expelled from where?
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Cathode
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Focusing cup pushes electrons towards what?
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Anode
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What pushes electrons towards the anode?
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Focusing cup
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Amount of electrons hitting the target is proportional to what?
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mAs (quantity)
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(3) Products of Transfer of Kinetic Energy
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1. Heat (> 99%) - formation of x-rays
2. Bremsstrahlung radiation 3. Characteristic radiation |
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Majority of radiation beam is what?
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Bremsstrahlung radiation
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Maximum photon energy is equal to what?
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kVp setting
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What must the kVp be for tungsten characteristic radiation?
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69 kVp
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15% increase in kVp is equal to what?
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DOUBLING the mAs
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Which setting is based on part TYPE?
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kVp
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Which setting is based on part THICKNESS?
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mAs
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Why is aluminum added to the beam?
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- Remove weaker/lower energy photons
- Hardening |
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What is the purpose of filtration?
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To remove lower energy photons
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What is the Half Value Layer?
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Amount of aluminum that decreases the number of photons by half
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Which kind of scatter is insignificant in the diagnosis range due to filtration?
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Coherent (Classic, Thompson) Scatter
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Coherent (Classic) Scatter
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- No ionization occurs
- No loss of photon energy |
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(2) Products of Photoelectric Effect
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1) Photoelectron, which can go on to interact with matter and create another photon
2) Characteristic photon |
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Characteristic Photon
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- Produced by the tissue hit
- Can go in any direction - Typically only weak photons are produced and will be absorbed before hitting the film |
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Probability of photoelectric effect is directly proportional to what?
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Atomic number cubed
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Differential Absorption: (3) Important Interactions
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1. Transmitted x-rays
2. Photoelectric effect 3. Compton scatter |
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Transmitted X-rays results in what?
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Results in the dark (radiolucent) areas
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Photoelectric effect results in what?
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- Light, radiopaque areas
- Absorbed photons |
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Compton effect results in what?
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General noise, decreases image quality
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Probability of photoelectric and Compton reactions are directly proportional to what?
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Mass density of the object
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Less than 5 - 10 patients a day, what kind of imaging?
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Plain film
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10+ patients a day, what kind of imaging?
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Digital imaging
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What protects the film?
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Cassettes
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What contains the intensifying screen?
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Cassettes
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What exposes the film?
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The SCREEN, not the x-ray
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Pros of Intensifying Screens
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- Decrease patient dose
- Decrease exposure time which decreases patient motion artifact |
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Cons of Intensifying Screens
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- Image is blurred by using the screens
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Front cover of the cassette should have what kind of anatomic number?
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LOW
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Back cover of the cassette should have what kind of anatomic number?
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HIGH
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Why should the back cover of the cassette have a high anatomic number?
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To prevent backscatter
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Any material that emits light in response to an outside stimulus
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Phosphor
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Visible light emitted only when the phosphor is stimulated
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Flourescence
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Phosphor continues to emit light after the stimulus
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Phosphorescence
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Base layer of screen is composed of what?
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Polyester, must be very durable
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Purpose of the phosphor layer of the screen?
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- Responsible for emitted light (photon hits phosphor)
- Decreases patient dose, tube load - Reduces shielding requirements |
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Potential Problem of Reflective Layer of the screen? Solution?
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Isotropic light formation
- Dyes in phosphor layer absorb photons with steeply angled path (removes stray light) |
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What measures screen speed?
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Intensification factor
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Image noise is also called what? What appearance does it create?
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- Quantum mottle
- Grainy appearance |
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What is spatial resolution? How is it measured?
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- Amount of detail available on the film
- Line pairs per millimeter |
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System speed is directly proportional to what?
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Noise
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System speed is inversely proportional to what?
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-Resolution
- Patient dose |
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Do screens wear out from radiation exposure?
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No
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Why do we use polyester with our x-rays?
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- Provides rigid structure for the emulsion
- Flexible, water and damage resistant |
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Emulsion is composed of what?
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Gelatin base with silver halide crystals
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Describes conversion of halide crystal into metallic silver
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Gurney-Mott hypothesis
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Allows Ag and Br ion movement
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Frankel Defect
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Sulfur based small imperfection in silver halide crystal
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Sensitivity speck
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What draws in Ag+ ions
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Negatively charged sensitivity speck
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Does unexposed film appear identical to the film with a latent image?
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Yes!
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Is direct exposure film fast or slow? High or low patient dose?
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- Slow
- MASSIVE patient dose |
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What kind of film do we use?
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Screen film
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Which film is solarized?
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Duplication (copy) film
- Single emulsion film for copying originals |
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Most common speed of film?
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200
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What (3) things can vary the speed of the film?
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1. Number of silver halide crystals
2. Size and shape of crystals 3. Thickness of emulsion |
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High contrast/narrow latitude will produce what? What are the crystals like?
What kind of slope? |
- Sharp black and whites
- Smaller, uniform crystals - Steep slope |
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Low contrast/wide latitude will produce what? What are the crystals like?
What kind of slope? |
- Lots of grays
- Larger, non-uniform crystals - Low slope |
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What is the difference between black and white?
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Contrast
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Crossover is what? What does it create?
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- Light crosses over from one emlusion to another
- Creates blurriness |
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What layer prevents light from transmitting through the film?
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Crossover control layer
* Removed during processing |
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Films are sensitive to what colors?
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Blue or green
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Which color is orthochromatic?
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Green
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What is spectral mismatch? What does it do to the patient dose?
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- Mixing film and cassette colors
- Increases patient dose by up to 4x |
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What does the safelight do?
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Emit light frequency that the film is not sensitive to
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Which safelight should you always buy?
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Red!
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Processing is what?
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Chemical process that converts the latent image to a visible image
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What converts ionic silver to metallic silver?
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Developing
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The developer acts as what?
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A wetting agent
- Softens gelatin - Allows chemical penetration |
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What kind of agent is the developer?
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Reducing agent, it contributes electrons
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What allows for penetration of the developing agents?
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The neutral area that the exposed crystals have at the sensitivity speck
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Unexposed crystals have what kind of surface?
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Strongly negative surface
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Exposed crystals have what kind of surface?
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A neutral area at the sensitivity speck
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Which crystals are reduced to metallic silver?
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Ag ions
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Developer: Hydroquinone
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Produces blacks
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Developer: Phenidone/Metol
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Produces greys
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Developer: Activator
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Sodium carbonate
- Swells gelatin - Controls pH |
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Developer: Restrainer
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Potassium bromide
- Prevents development of unexposed crystals - Buffering agent |
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Developer: Preservative
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Sodium sulfite
- Controls oxidation of developer |
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Developer: Hardener
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Gluteraldehyde
- Controls gelatin swelling |
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Developer: Sequestering agent
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- Chelates
- Removes impurities |
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Developer: Solvent
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Water
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Developing is affected by what (3) factors?
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1. Time (controlled by the fixed processor speed)
2. Temperature* this is the main factor! 3. Concentration (controlled by the operator) |
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Fixer: Activator
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Acetic acid
- Neutralizes basic developer |
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Fixer: Fixing Agent
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Ammonium thiosulfate
- Removes unexposed AgBr |
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Fixer: Hardener
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Potassium Alum
- Stiffens and shrinks gelatin |
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Fixer: Preservative
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Sodium sulfite
- Maintains chemical balance |
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Fixer: Buffer
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Acetate
- pH balance |
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Fixer: Sequestering Agent
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Boric acids/salts
- Remove aluminum ions (impurities) |
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Fixer: Solvent
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Water
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What turns the emulsion yellow?
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Fixer retention
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What is the main reason for a film to come out wet?
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Expired gluteraldehyde in the developer
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PI lines are in what orientation?
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Perpendicular to the direction of feed
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Crossover marks are in what orientation?
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Parallel to direction of feed
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Amount of light getting through to your x-ray
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Optical density
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High optical density = over or under exposed?
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OVERexpsoed
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Low optical density = over or under exposed?
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UNDERexposed
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What factor primarily controls optical density?
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mAs (QUANTITY)
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Body parts with inherent contrast
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Extremities and chest
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Body parts with poor inherent contrast
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Thoracic and lumbar spine
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The shadow of the object
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Umbra
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Negative consequence of a non-point source of radiation; creates fuzzy margins
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Penumbra
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What factors of OID and SID will allow for better visualization?
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LOW OID
HIGH SID |
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What can you do to decrease magnification?
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INCREASE SID
DECREASE OI |
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What is the main reason for minimal diagnostic series?
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Distortion
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Focal spot blur is greater on which side? Why?
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(Radiographic term for penumbra)
- Greater on CATHODE side due to Anode Angle |
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Scatter is influenced by what (3) factors?
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1. kVp
2. Field size 3. Patient thickness |
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Amount of tissue irradiated
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Field size
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Best way to restrict the beam?
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Variable aperature collimator
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What can be eliminated with grids?
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Photons with high deviation angles
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Quality grids can clean how much of scatter radiation?
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80 - 90%
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Number of grid strips (lines) per inch or per cm
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Grid frequency
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Non-moving grids can result with what?
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Lines on the x-rays
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Grids increase contrast by doing what?
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Decreasing scatter
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Grid will increase what (2) factors?
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- Quality
- Patient dose |
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Represents the amount of increase in factors to produce the same optical density as without a grid
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Bucky factor (grid factor)
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Which grid has no cut off?
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Focused grid
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Best grid distance?
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40 - 72"
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