Digital and Film Radiography Flashcards
1
Q
How do digital and film forms of radiography differ?
A
- 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
2
Q
What are the types of Digital x-ray receptors used in dentistry?
A
- Phosphor plate
- Solid state sensor
- Both multiple use
3
Q
What are the Film x-ray receptors used in dentsistry?
A
- Direct action film
- Indirect action film
- All single use
4
Q
What are different sizes of receptors?
A
- 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
5
Q
How is the x-ray converted into an image?
A
- 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
6
Q
What is the digital image?
A
- 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
7
Q
How is x-ray shadow and digital image related?
A
- 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
8
Q
What is the benefit of having more pixels?
A
- 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
9
Q
Negatives of having more pixels?
A
- Each digital image requires more storage space
- Increased costs
- Digital receptors limited in how small they can make the pixels because of manufacturing challenges
10
Q
What is the greyscale bit depth?
A
- 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
11
Q
How can you manipulate digital images?
A
- Software can be used to copy, resize and alter images
- Contrast/windowing
- Negative
- Emboss
- Magnify
12
Q
What is DICOM?
A
- Digital Imaging and Communications in Medicine
- International standard format for handling digital medical images
13
Q
What does DICOM allow a user to do?
A
- 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
14
Q
What is PACS?
A
- Picture Archiving and Communication System
- A medical imaging technology that provides storage and access to images in a healthcare organisation
15
Q
How is PACS different in Scotland and England?
A
Scotland - NHS has nationwide hospital PACS
England - Separate hospital PACS for each NHS trust
- Hospital PACS not connected to dental practices
16
Q
What are PACS main components?
A
- 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
17
Q
How is best to view digital radiographs?
A
Environment
- Subdued lighting
- Avoid glare
Monitor
- Clean
- Adequate display resolution
- High enough brightness level
- Suitable contrast level
18
Q
What are some other names for Phosphor plates?
A
- Photostimulable phosphor plate
- Storage phosphor plate
19
Q
What are phosphor plates?
A
- 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
20
Q
How do you create an image using phosphor plates?
A
- 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
21
Q
What are the different types of Solid-state sensors?
A
- CCD (charge-coupled device)
- CMOS (complimentary metal oxide semiconductor)
22
Q
What are solid-state sensors?
A
- 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
23
Q
What is the identification dot?
A
- Found in corner of receptor to aid orientation of image
- Only effective if receptor was positioned correctly during exposure!
24
Q
What cross-infection control do receptors have?
A
- 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
25
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
26
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
27
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
28
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
29
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)
30
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
31
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
32
What do intensifying screens do?
- Reduced radiation dose
- Reduce detail
- Less common as digital receptors taking over
33
What are intensifying screens?
- Used alongside special “indirect action” film for extra-oral radiographs (eg. panoramic radiographs, cephalograms)
- Too bulky for intra-oral use
34
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
35
What is film processing?
- Sequence of steps which converts the invisible latent image to a
visible permanent image
36
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
37
Benefit of Automated cycle over manual processing
- Faster and more controlled than manual
- Avoids need for dark room
- But more expensive
38
How do you open a film packet for automated processing?
1. Disinfect the surface of the packet (& wipe off)
2. Hold the packet under the hood of processor unit
3. Peel back flap of outer wrapper
4. Fold back lead foil
5. Pull back paper flap
6. Hold film by edges (NB. not surfaces) & slide out
7. Insert film into processor slot/shelf
39
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
40
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
41
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
