Digital and Film Radiography Flashcards
How do digital and film forms of radiography differ?
- Different in how x-ray beam is dealt with after it has interacted with patient
- e..g how it is captured, converted to image and stored
What are the types of Digital x-ray receptors used in dentistry?
- Phosphor plate
- Solid state sensor
- Both multiple use
What are the Film x-ray receptors used in dentsistry?
- Direct action film
- Indirect action film
- All single use
What are different sizes of receptors?
- Come in variety of sizes to suit diff purposes
- Exact measurement varies between companies
- Phosphor plate sizings tend to macth films
e.g. Size 0 = Anterior periapicals
size 2 = Bitewings, posterior periapicals
Size 4 = Occlusal
How is the x-ray converted into an image?
- X-ray beam passes through object
- Some x-ray photons attenuated and create x-ray shadow
- X-ray shadow is image info held by x-ray photons after x-ray beam has passed through
- Image receptor detects x-ray shadow and uses it to create image
What is the digital image?
- Displayed as grid of squares called pixels
- Each pixel can only display one colour at a time
- More pixels there are, more detailed/ accurate image
How is x-ray shadow and digital image related?
- Receptor measures x-ray intensity at defined areas arranged in grid
- Each area given value relating to x-ray intensity (typically 0-255)
- Each value corresponds to different shade of grey
- 0=black
255 = white
What is the benefit of having more pixels?
- More pixels = better detail = higher resolution
- Increasing resolution will provide more diagnostic image up to a limit
- Eventually it will provide no more meaningful clinical benefit
Negatives of having more pixels?
- Each digital image requires more storage space
- Increased costs
- Digital receptors limited in how small they can make the pixels because of manufacturing challenges
What is the greyscale bit depth?
- Radiographs typically processed in at least 8 bits
- Refers to number of different shades of grey available
- 8 binary digits = 2^8 = 256 shades of grey
How can you manipulate digital images?
- Software can be used to copy, resize and alter images
- Contrast/windowing
- Negative
- Emboss
- Magnify
What is DICOM?
- Digital Imaging and Communications in Medicine
- International standard format for handling digital medical images
What does DICOM allow a user to do?
- Allows imaging to work between different software, machines, manufacturers, hospitals and countries without compatibility issues
- Stores other imp data alongside image e.g. patient ID, exposure settings etc
What is PACS?
- Picture Archiving and Communication System
- A medical imaging technology that provides storage and access to images in a healthcare organisation
How is PACS different in Scotland and England?
Scotland - NHS has nationwide hospital PACS
England - Separate hospital PACS for each NHS trust
- Hospital PACS not connected to dental practices
What are PACS main components?
- Input by imaging modalities eg. plain radiography, CT, MRI, US
- Secure network for the transmission of patient information
- Workstations for interpreting & reviewing images
- Archives for the storage & retrieval of images & reports
How is best to view digital radiographs?
Environment
- Subdued lighting
- Avoid glare
Monitor
- Clean
- Adequate display resolution
- High enough brightness level
- Suitable contrast level
What are some other names for Phosphor plates?
- Photostimulable phosphor plate
- Storage phosphor plate
What are phosphor plates?
- Type of digital intra-oral receptor
- Not connected to computer
- After receptor is exposed to x-rays, it must be put in a scanner &
“read” to create the final image
How do you create an image using phosphor plates?
- Within the patient’s mouth
1. Receptor exposed to x-ray beam
2. Phosphor crystals in receptor excited by the x-ray energy, resulting in
the creation of a latent image - Within the scanner
3. Receptor scanned by a laser
4. The laser energy causes the excited phosphor crystals to emit
visible light
5. This light is detected & creates the digital image
What are the different types of Solid-state sensors?
- CCD (charge-coupled device)
- CMOS (complimentary metal oxide semiconductor)
What are solid-state sensors?
- Type of digital receptor
- Connected to computer
- Usually wired but can be wireless
- Latent image created & immediately read within the sensor itself
- Final image created virtually instantly
What is the identification dot?
- Found in corner of receptor to aid orientation of image
- Only effective if receptor was positioned correctly during exposure!
What cross-infection control do receptors have?
- Intra-oral receptors have purpose-made
covers to prevent saliva contamination - Single-use covers
- Examples
- Adhesive sealed plastic covers (for PPs)
- Long plastic sleeves (for wired SSSs)
- Receptor still disinfected between uses
Why do you need to handle receptors carefully?
- Both digital and film receptors can be damaged if not handled correctly
- Certain damage impacts every image obtained after the damage
- Reduces diagnostic value and may render receptor unusable
- Hold receptors by edges not flat surfaces
Phosphor plates Summary
- Thinner, lighter & (usually) flexible
- Wireless so more stable (& more comfortable)
- Variable room-light sensitivity gives risk of impaired image
- Latent image needs to be processed in scanner separately
- Handling similar to film
Solid state sensors summary
- Bulkier & rigid
- Usually wired
- Smaller active area (for same physical area of receptor)
- No issues with room-light control
- Arguably more durable as replaced less often
- More expensive
What is the radiographic film?
- Material in which the actual image is formed
- Sensitive to both x-ray photons & visible light photons
- Photons interact with silver halide emulsion on film to produce latent image which only becomes visible after chemical processing
What do the silver halide crystals do?
- Become sensitised upon interaction with x-ray (& visible light) photons
- During processing
1. Sensitised crystals converted to particles of black metallic silver (= dark parts of final image)
2. Non-sensitised crystals removed (= light parts of final image)
What is the lead foil?
- In a packet lying behind film
- Is embossed to highlight on image if receptor placed wrong way
- Absorbs some excess x-ray photons
1. Those in primary beam continuing past film
2. Those scattered by patients tissues and returning back to film
What is the film speed?
- Relates to the amount of x-ray exposure required to produce an adequate image
- ↑ speed then ↓ radiation required to achieve an image
- Affected by number & size of the silver halide crystals
- Larger crystals = faster film but poorer image quality
What do intensifying screens do?
- Reduced radiation dose
- Reduce detail
- Less common as digital receptors taking over
What are intensifying screens?
- Used alongside special “indirect action” film for extra-oral radiographs (eg. panoramic radiographs, cephalograms)
- Too bulky for intra-oral use
How do intensifying screens work?
- “Indirect action” film placed inside cassette with an intensifying screen on either side
-Screens release visible light upon exposure to x-rays - Visible light creates latent image on film
What is film processing?
- Sequence of steps which converts the invisible latent image to a
visible permanent image
What happens during automated cycle of film processing?
- All necessary steps carried out within a machine
- Exposed film goes in one end
- Processed film comes out the other
Benefit of Automated cycle over manual processing
- Faster and more controlled than manual
- Avoids need for dark room
- But more expensive
How do you open a film packet for automated processing?
- Disinfect the surface of the packet (& wipe off)
- Hold the packet under the hood of processor unit
- Peel back flap of outer wrapper
- Fold back lead foil
- Pull back paper flap
- Hold film by edges (NB. not surfaces) & slide out
- Insert film into processor slot/shelf
What does film storage need?
- Takes up room!
- Need to be easily accessible & safe from damage
- Require a reliable organisation system
1. To allow images to be found easily
2. To reduce risk of images being lost/mixed up
Digital radiography advantages
- No need for chemical processing
- Easy storage & archiving of images
- Easy back-up of images
- Images can be integrated into patient records (if digital)
- Easy transfer/sharing of images
- Images can be manipulated
Digital radiography disadvantages
- Worse resolution and risk of pixelation
- Requires diagnostic-level computer monitors for optimal viewing
- Risk of data corruption/loss (solved by backing up)
- Hard copy print-outs generally have ↓ image quality
- Image enhancement can create misleading images
