test 2 xray physics Flashcards
What happens to contrast when lower kVp is used?
Higher contrast image is created with a shorter scale of contrast (less steps between darkest and lightest)
What type of x-ray will create an image with less contrast?
High kVp and Low mAs
or
Low kVp and High mAs
High kVp and Low mAs
How does higher kVp/lower mA affect scatter?
More scatter
Where is the grid placed?
Behind the patient and in front of the image receptor (basically between patient and image receptor)
When using a grid, how does it affect the exposure to the patient?
It will increase the exposure to the patient anywhere between 4-5 times compared to no grid
How does a grid affect image quality?
Improved diagnostic image quality
What happens to non-scattered photons as they pass through a grid?
They pass through the radiolucent part of the grid, but some do still get absorbed by the lead strips
What is grid ratio?
Height of the lead strips divided by the distance between the lead strips (h/D)
What is the grid frequency?
Number of lines per inch or other unit of measurement
lines/inch
Pertaining to grids, what is the height of the lead strips divided by the distance between the lead strips?
Grid ratio
What is grid selectivity or “Sigma”?
Amount of primary radiation transmitted divided by the scatter radiation transmitted
If the grid ratio is very high, how much scatter goes through?
Very little scatter
If the grid ratio is very low, how much scatter goes through?
Lots of scatter goes through
What is a typical grid ratio for musculoskeletal imaging?
5:1 - 12:1 ratio
What type of grid ratio has better clean up and better contrast?
Higher ratio grids
What happens to patient dose as you increase the grid ratio?
It increases
Pertaining to grid frequency, what frequency is generally less efficient? (high or low)
High frequency
Pertaining to grid frequency, what frequency is generally more efficient? (high or low)
Low frequency
Do higher frequency grids require more or less dose?
More pt. dose
Most grids range from _____-_____ lines per centimeter
25-45 lines per centimeter
How can you increase grid ratio?
Increase the height of lead strips or decrease the distance between the lead strips
Where does grid cut-off occur?
The lateral margins of the grid, especially with closer source-image distances
What is the grid that involved grid strips that are angled to accommodate the increasingly divergent angle of photons further away from the central ray?
Focused grids - these are used for general radiography
Do higher ratio grids have more or less focal range than low ratio grids?
Less focal range
What happens to focal range with a lower grid ratio?
It increases
What are crossed grids?
Grids with lead strips that run both lengthwise and side-to-side to reduce more scatter photons. (These are not usually used in general radiography)
What are some drawbacks to the air-gap technique?
There can be image magnification and distortion of the image
Higher exposure is also necessary (about 10% increase per cm of air gap)
What projection includes a natural air gap?
Lateral cervical spine x-ray
What is the term for screen film radiography?
Analog radiography
What is the exiting beam also known as?
Remnant beam, it is the x-ray beam that forms the image
What is the purpose of the film?
To create a permanent record of the x-ray exiting beam
What are the major components of film?
Base - piece of plastic for physical support
Emulsion - picture layers of the film
Adhesive lay
Supercoating - protection
Originally, glass was used as what part of the x-ray film?
Base
What type of material replaced the glass base very long ago, but was very flammable?
Cellulose nitrate
What type of material is currently used as the base of x-ray film?
Polyester
What makes up the emulsion layer of x-ray film?
A homogenous mixture of gelatin and silver halide crystals
Gelatin provides = support
Silver halide crystal = sensitive to light and X-ray
What type of formation is silver halide?
Crystal lattice formation
What are the components of the silver halide crystal that helps make up the emulsion layer of x-ray film?
Silver bromide 95%
Silver iodide 5%
Silver sulfide
What component of the silver halide crystal is extremely important in photosensitivity of film?
Silver sulfide
X-ray film is mostly exposed by light from what
Intensifying screens
Exposure of the film to light or x-ray photons causes a movement of electrons and/or atoms within the silver halide crystal is know as what? It is the invisible change in electron configuration of silver halide crystal.
Latent image formation
What is latent image?
It is the invisible change in electron configuration of silver halide crystal
What happens at the molecular level of the silver halide crystals when exposed to light/x-rays?
electrons accumulate at the silver sulfide “sensitivity specks” and reduce a very small number of the silver ions to metallic silver
Electrons accumulate at the silver sulfide “sensitivity specks” and reduce a very small number of the silver ions to _______________.
Metallic silver
What is the most common type of film used in general purpose radiography?
Screen film
What type of film is used in conjunction with intensifying screens?
screen film
What is the purpose of the intensifying screen?
To convert x-ray photon energy into visible light photons
What causes the “most” film exposure?
Visible light generated by the intensifying screen
Screen film that has emulsion on the front and back of it to increase speed is known as what?
duplex film
What effect does duplex film do when taking x-rays?
Increases speed of the system/decrease amount of radiation
What are important film characteristic that can be influenced by the kind of film that is being used?
Speed and Contrast
What color systems are used in x-ray?
Blue or Green
In what color wavelengths are x-ray films most sensitive to light?
Blue and Green spectra
If using blue sensitive film, what color light should be used?
blue
If using green sensitive film, what color light should be used?
greeeeeeeen
Which color is better for x-rays? Green or Blue?
DO NOT MATTER
What is the term for a light source that emits light in a spectra that the film has a low sensitivity to?
safe lights
are safe lights completely safe?
no, that are only safe at a limited time and intensity
Red safe light filters are safe for what color film?
blue and green
What is the maximum wattage for safe lights?
15 watts
What is the minimum distance that the safe light can be from the working surface?
5 ft.
What type of film is designed to be used without intensifying screens?
direct exposure film
What is direct exposure film used for?
Dental applications
What is the film that only has emulsion on one side?
single emulsion
How does duplicating film (film used to make a copy of x-rays) act compared to regular x-ray film?
Reacts in opposite fashion to regular x-ray film
What color do exposed areas of duplicating film become?
white
which is the opposite of x-ray film which turns black
What temperature should unexposed x-ray film should be stored?
below 68 deg.
How long will x-ray film last at room temperature?
45 days
What humidity should x-ray film be stored at?
Less than 60%
What should you avoid when handing unexposed film?
Avoid excess heat = <68 degrees
Avoid excess humidity = <60%
Avoid static electricity (occurs with <40% humidity)
Avoid light or x-ray exposure
Avoid mechanical force
If we have static electricity on an unexposed film, what can occur?
latent image can occur
Film that has been exposed to diagnostic x-ray is more sensitive to ______ or __________ than unexposed film
light; radiation fog
How do you remove lines/marks on exposed and processed x-ray films?
Denatured Alcohol, do not use water because it will make gelatin softer and can cause the image to be scratched
What do you do if your processed x-ray film is wet?
Let it dry but
Do not place next to anything because acts like glue
What is the term for converting latent image formation into visual (manifest) image?
film processing
What does film processing do at the atomic level?
It will potentiate the reaction of the ionic silver into metallic silver of the exposed crystals. (it turns black)
What are the 4 steps of film processing?
Developing
Fixing
Washing
Drying
What stage of film processing involves the latent image becoming the manifest image?
Developing stage
What makes up the developer solution?
Water and Reducing agent (reduces ionized silver into metallic silver)
What color do exposed silver halide crystals become?
Black
What is the purpose of the fixing solution?
Stop the reduction reaction of the developer solution
Removes unexposed emulsion
Preserves the image
What chemical in the fixing solution stops the action of the developer?
Acetic acid
What solution stops the reduction reaction of the developer solution, removes the unexposed emulsion, and preserves the image?
Fixing solution
What are important variables in processing images?
Time, Temperature, Chemical concentration
What happens if film is left in developer solution for too long?
It will over-develop causing the reducing agent to begin to act on unexposed silver halide crystals. It will look like an over exposed film (black)
Is time more important in the developing or fixer stage?
developing
What stage is the most temperature dependent part of processing film?
developing
Developing temperature should not vary by more than how much degrees?
+/- 1 degree Fahrenheit
Excess temperature in developer solution will make film appear like what?
Over-exposed
What temperature do most automatic processes operate at for processing film?
95 degrees Fahrenheit
Proper chemical concentration is important in what stage(s) when processing film?
Developing and fixing stages
What happens to chemical strength/potency when a film is processed?
It diminishes
What happens to chemical strength/potency when developer/fixing solution is stored over time?
it will diminish
What removes residual chemicals from the emulsion when processing film?
Washing - “Water bath”
What color will the film look like over time if fixer solution is left on the film?
Rusty-brown/orange color
You notice an old x-ray that appears to have a rusty-brown/orange tint. What caused this?
Fixer solution was left on the image and not washed off properly
A small amount of _______ solution will ruin a large amount of _______ solution.
A small amount of fixer solution will ruin a large amount of developer solution.
What is the final stage of processing film?
Drying stage - using forced hot air
What is worse? Having some developer solution contaminate fixer solution or having some fixer solution contaminate developer solution?
Having some fixer solution contaminate developer solution is much worse.
why is having some fixer solution contaminate developer solution much worse?
has to do with the flow of processing. The fixer solution come after the developer solution and will have a worse affect with only a bit getting in
