5 - Digital and film radiography Flashcards
What are the different types of intra-oral digital receptor?
- phosphor plate
- solid-state sensor
What are the different types of film receptor?
- direct action film
- indirect action film
What are the typical sizes of film/plates used?
Size 0 = anterior PA
Size 2 = BWs, posterior PA
Size 4 = occlusals
What is an x-ray shadow?
- when x-ray photons are attenuated by the subject, they create an x-ray shadow
- the receptor picks up the shadow and creates an image
How do digital plates display an image?
- 1000s of pixels that can only display one colour at a time
- colour determined by the number of photons that interact with it
- ranges from 0-255
- black = 0
- white = 255
- grey shades = 1-254
- the more pixels there are the moral detailed the image
What format are digital images stored in?
- DICOM
- digital imaging and communications in medicine
- international standard for handling digital medical images, which allows compatibility with all HC software
- also stores patient ID, exposure settings and date
How are digital images managed?
- PACS
- picture archiving and communication system
- stores multiple imaging modalities
- secure network for transmission of patent information
- allows for reviewing images
How should you review digital radiographs?
- subdued lighting
- avoid glare
- clean monitor with adequate resolution, suitable brightness and contrast
How can you test if your screen is suitable to assess radiographs?
- SMPTE test
- society of motion picture and television engineers
- assess resolution, contrast and brightness
How do phosphor plates function?
- not connected to computer
- must be scanned to read “final” image
- phosphor crystals are excited by x-ray energy to create latent image
- receptor is scanned by a laser cause the excited crystals to emit visible light
What are the different types of solid-state sensors?
- CCD (charged-coupled device)
- CMOS (complimentary metal oxide semiconductor)
How do solid-state sensors function?
- connected to computer
- latent image created and immediately read within sensor
What is the identification dot?
Located in corner of receptor to aid orientation
How is cross-infection controlled in intra-oral digital radiology?
- single use covers
- receptor also disinfected between uses
How can you reduce damage to digital receptors?
Handle by the edges
How do phosphor plates compare to solid-state sensors physically?
- phosphor plates are thinner, lighter and more flexible
- solid-state sensors are more rigid and bulkier
- phosphor plates are wireless and therefore more comfortable and stable that solid-state sensors
How do phosphor plates compare to solid-state sensors regarding storage?
- phosphor plates are light sensitivity so should be stored in a dark box
- solid-state sensors are not light sensitive
Describe the composition of a dental film packet.
- outer package
- lead foil packaging
- inner paper wrap
- dental film
What is the function of the lead foil in an intra-oral film packet?
Absorb excess x-ray photons
What is the function of the outer wrapper in an intra-oral film packet?
- prevent ingress of saliva
- indicate which side of the packet is the front
What is the function of the protective paper wrap in an intra-oral film packet?
Protect film from light exposure, damage by fingers and saliva
How does radiographic film function?
Photons interact with emulsion on film to produce latent image which becomes visible after chemical processing
Describe the structure of radiographic film.
- protective coating of gelatin (shields emulsion from mechanical damage)
- emulsion (layered on both side of plastic base)
- adhesive (attached emulsion to plastic base)
- transparent plastic base (supports emulsion)
What is the radiographic emulsion?
- silver halide (often silver bromide) crystals embedded in gelatin binder
- crystals are microscopic and are the “pixels”
How does the emulsion capture a radiographic image?
- silver bromide crystals become sensitised upon interaction with x-ray photons (and visible light - bad)
- when processed, sensitised crystals converted to black metallic silver = dark parts of image and non-sensitised crystals are removed = light parts of image
Define film speed.
- the amount of x-ray exposure required to produce an image
- high speed = less radiation required
- speed is affected by number and size of silver halide crystals
- larger crystals = faster film = poorer image quality
What is an intensifying screen?
- screen release visible light upon exposure to x-ray which creates latent image on film
- bulky so used in extra-oral radiographs
- reduced image quality but do reduce dose
What are the stages of developing film?
- Developing
- Washing
- Fixing
- Washing
- Drying
Describe developing film.
Converts sensitised crystals to black metallic silver particles
Describe washing (1).
Removes residual developer solution
Describe washing (2).
Removes residual fixer solution
Describe fixing film.
- removes non-sensitised crystals
- hardens emulsion which still contains black metallic silver
Describe drying film.
Removes water so that film is ready to be stored
What are the advantages and disadvantages of self-developing films?
ADVANTAGES
- no dark room required or procession facilities
- faster
DSISADVANTAGES
- poor image quality
- image deteriorates after time
- no lead foil
- easily bent
- difficult to use
What can cause a pale image?
- radiation exposure factors too low
- film removed from solution too early
- solution too cold
- solution too dilute
What can cause a darker image?
- radiation exposure factors too high
- film removed from solution too late
- solution too warm
- solution too strong
What causes a milky/greenish-yellow image?
- inadequate fixing meaning non-sensitised crystals are left behind
- image browns over time
