Radiography Flashcards
What is scatter radiation?
The movement of radiation in different directions after it’s had contact with matter (i.e. not the primary beam!)
What can increase scatter?
High kV or high exposure factor
What are sources of high scatter radiation?
The patient’s thickness is too large
Collimator not used effectively
Too high a voltage
How can scatter be controlled?
Using a grid! (85-95% scatter reduction)
Decreasing the thickness of the patient (e.g. compression bands)
Reducing the voltage
What is the basic structure of a grid?
Alternating lead strips with radiolucent material gaps to allow the primary beam to pass through (made from aluminium or carbon plastic fibres)
What is a grid ratio?
The ratio of the height of each lead strip to the distance between the strips.
What is a grid ratio used for?
To calculate the grid factor. This is then used to calculate the correct exposure factor (mAs) (correct exposure factor with grid = exposure factor x grid factor)
Where must the centre of the X ray be focussed on a grid?
On the grid focal point
What is the Grid Focus?
The distance between the tube head and the grid
What is Grid Cut off?
An unwanted absorption of x-rays via an x-ray grid,
What does Grid Cut-off cause?
Lighter image and white lines over the unexposed areas of film.
What causes Grid cut-off?
Improper centring of X ray tube head over the grid
Titling tube laterally
Tilting the grid
Focussed grid upside down
Where can grids be placed?
On top of a cassette
Within a cassette (built in)
Under the X ray table
Name the common grid types
Parallel
Potter Bucky
Linear
What is a parallel grid?
Lead strips run parallel to each other
Cheapest, most common
Stationary grid
Gives a good result
What is a Potter Bucky grid?
Mobile grid - moves rapidly from side to side
A parallel grid that is integrated into the table
Eliminates fine lines usually visible with a stationary grid
Why does care need to be taken when handling grids?
Delicate and expensive
If dropped on its side, can damage inside permanently - lead stalks may become bent or warped
How is an X ray actually recorded? Using what?
Radiographic Film
- sensitive to both light and X rays
The X rays are converted to a latent image
Processing of the film allows the image to be visible
What are the 2 types of X ray film?
Duplitised and Single
What is the better type of film and why?
Duplitised
- layers are duplicated on either side of the polyester base (emulsion/active layer)
- increases its efficiency - more effective at producing an image than single
- results in a lower radiation dose to the patient
(the single just has one active side and a counterbalanced side to prevent curling)
How should X ray film be stored?
Within expiry Rotated stock Vertical! - prevents black lines/crescents Handle from corners with clean hands Handle in paper Keep away from chemicals On dry side of room Away form radiation and light
What does film contain?
Silver halide crystals - specifically silver bromide
these are sensitive to x rays and light
How is an image produced on the film?
There is a sensitivity speck on the film. During exposure, the silver bromide migrates to the sensitivity speck and the bromide is released.
The more silver that move, the more bromide is released and the darker the film becomes
What determines the film speed?
The size of the grain that’s within the film - the larger the grain, the faster the film
The type of film used (either screen or non-screen)
How does film speed affect image?
The faster the film speed the poorer the image generally
What are the 2 types of film?
Screen and Non-screen
Describe a screen film?
Intensifying screen used
Cheaper than non screen films
Speed is characterised by the grain size
Film speed increases with grain size but loses definition
Shorter developing time and shorter exposure time than non-screen films
Describe Non-screen film?
Light-tight envelopes
Used for high definition in areas where thick cassettes cannot be used e.g. dental x rays
Greater developing time and greater exposure time than screen films.
Greater definition than screen films
Can you use any screen with the screen films?
No- it has to be able to detect the light given off by the screen!
What are the 2 types of Film Screens?
Calcium Tungstate and Rare Earth
Describe the calcium tungstate screen
Emits blue light
Film used with it must be ‘blue-light sensitive’ or ‘monochromatic’
Describe the Rare earth screen?
Emits green light and sometimes blue
Film used with this has to be sensitive to blue and green lights or Orthochromatic
What affects the intensifying screen speed?
The size of the phosphor grain
Thickness of the intensifying screen layer
Presence or absence of the reflective layer
What is important to get a good sharp image?
Contact with the film screen
How would you clean a film screen or cassette?
Cleaned on a regular basis dependant on workload. Any dirt on it with show up as bright white specks
- brush with a soft brush to remove any debris
- Use a preparatory cleaner with a lint-free swab
- Use a circular motion from inside to out
- stand the film/ cassette vertically to dry in a dust free area
- label and date
What are the 2 types of digital radiography?
Computed Radiography and Direct Radiography
What are the main differences between digital radiography and analogue radiography
No film solution used
Quicker
Less equipment
What equipment is needed for a CR?
Imaging plate
Describe an imaging plate?
Phosphor plate
Looks like an intensifying screen
Has a large layer of crystals that can store X ray energy
Placed inside the cassette
What is the process of CR ? Simple!
After the X ray has been taken, the cassette is placed into a reader
The reader scans the plate with a red laser, causing the electrons to fluoresce and produce light. The light is converted to a digital signal and an image is sent to the computer
The image is then erased form the plate
What are the advantages of digital imaging (CR) to analogue imaging?
- More sensitive to radiation so can use lower dose
- Shorter exposure times
- Easier to use
- Less time consuming
- More forgiving than film giving better image
- Fewer need for repeat exposures
- can get objects of different thicknesses onto 1 image
- quicker processing time - no chemical development
- no chemicals or associated hazards, environmental impacts, costs of disposal
- reduced GA/sedation time
- No dark room needed - less equipment
- Immediate review/analysis of image
- Can be sent to specialist - email, burned to disc
- Editing possible
- Can store electronically - saves space
How does DR differ from CR?
Requires a special DR plate
- converts light into a digital signal directly without requiring a reader
- much more expensive!
What is a good DR plate?
Coated with amorphous silicone
What are the benefits of DR over CR?
- real time image
- highest quality digital image
- zoom facility
- maximum resolution to identify small anomalies
- can use for many helpful things .e.g. comparing 2 pictures side by side, measuring pins for orthopaedics whilst someone is X raying, calculating angles for TPLO from theatre
- Moral of staff increased as less admin
- no need for films allows for improved positioning
- data can be stored within the image
What are the limitations of DR?
Expensive!!!!!!! CPD needed for staff Staffing for the day Space? Certification programmes needed
When should radiography be used to check for in a debilitated patient?
To check for any invisible trauma e.g. diaphragmatic trauma, bladder rupture, internal bleeding etc.
A fracture also, but this can wait as its not life-threatening!
What must we consider before X raying a debilitated patient?
Is it worth it? Do the potential benefits of the scan outweigh the risk to the patient?
What must be done before an emergency patient is X rayed?
Stabilise!
o2 therapy, IVFT
Have to consider if vital signs are stable enough for GA/sedation - if not, vet may have to hold as an exceptional circumstance.
Need to ensure that the positioning and manipulation of the patient isn’t contraindicated
When should radiography be delayed?
If animal’s condition may be aggravated by radiographic procedures
The benefits do not outweigh the risks
If wont have an effect on the treatment plan
What is very important in preparing a debilitated patient for radiography??!
Debilitated patients rarely need, and often cannot tolerate, fasting and/or enemas in relation to abdominal radiology
What are the main point to remember in radiography of exotics?
Lower kV generally due to smaller size
(chelonia may require high kV due to shell)
Grids rarely used as patients rarely >10cm
Non screen films better to show finer details
Need rapid exposure of 0.008-0.016s as high respiratory rates can cause blurry images
Need chemical restraint usually
What is PACS?
Picture Archiving and Communication Systems
Makes storage and retrieval of images easy. Can store data with the image (e.g. patient details, consultation numbers etc)
Can store previous X-rays together, allowing continuity of patient care and assessment
What is kV?
Kilovoltage = energy across the tube. It determines the penetrating power of the xrays and therefore affects the contrast and density of the film.
The higher the kV, the higher the ____?
Penetrating power
What should the aim be when setting kV for an image?
Should be as low as possible sufficient enough to penetrate the part of interest
What will too high a kV result in?
Increased scatter
Lack of contrast