Digital and Film Radiography

Question 1

How do digital and film forms of radiography differ?

Answer 1

• 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

Question 2

What are the types of Digital x-ray receptors used in dentistry?

Answer 2

• Phosphor plate
• Solid state sensor
• Both multiple use

Question 3

What are the Film x-ray receptors used in dentsistry?

Answer 3

• Direct action film
• Indirect action film
• All single use

Question 4

What are different sizes of receptors?

Answer 4

• 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

Question 5

How is the x-ray converted into an image?

Answer 5

• 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

Question 6

What is the digital image?

Answer 6

• 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

Question 7

How is x-ray shadow and digital image related?

Answer 7

• 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

Question 8

What is the benefit of having more pixels?

Answer 8

• 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

Question 9

Negatives of having more pixels?

Answer 9

• Each digital image requires more storage space
• Increased costs
• Digital receptors limited in how small they can make the pixels because of manufacturing challenges

Question 10

What is the greyscale bit depth?

Answer 10

• 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

Question 11

How can you manipulate digital images?

Answer 11

• Software can be used to copy, resize and alter images
• Contrast/windowing
• Negative
• Emboss
• Magnify

Question 12

What is DICOM?

Answer 12

• Digital Imaging and Communications in Medicine
• International standard format for handling digital medical images

Question 13

What does DICOM allow a user to do?

Answer 13

• 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

Question 14

What is PACS?

Answer 14

• Picture Archiving and Communication System
• A medical imaging technology that provides storage and access to images in a healthcare organisation

Question 15

How is PACS different in Scotland and England?

Answer 15

Scotland - NHS has nationwide hospital PACS
England - Separate hospital PACS for each NHS trust
- Hospital PACS not connected to dental practices

Question 16

What are PACS main components?

Answer 16

• 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

Question 17

How is best to view digital radiographs?

Answer 17

Environment
- Subdued lighting
- Avoid glare

Monitor
- Clean
- Adequate display resolution
- High enough brightness level
- Suitable contrast level

Question 18

What are some other names for Phosphor plates?

Answer 18

• Photostimulable phosphor plate
• Storage phosphor plate

Question 19

What are phosphor plates?

Answer 19

• 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

Question 20

How do you create an image using phosphor plates?

Answer 20

• 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

Question 21

What are the different types of Solid-state sensors?

Answer 21

• CCD (charge-coupled device)
• CMOS (complimentary metal oxide semiconductor)

Question 22

What are solid-state sensors?

Answer 22

• 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

Question 23

What is the identification dot?

Answer 23

• Found in corner of receptor to aid orientation of image
• Only effective if receptor was positioned correctly during exposure!

Question 24

What cross-infection control do receptors have?

Answer 24

• 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

Question 25

Why do you need to handle receptors carefully?

Answer 25

• 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

Question 26

Phosphor plates Summary

Answer 26

• 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

Question 27

Solid state sensors summary

Answer 27

• 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

Question 28

What is the radiographic film?

Answer 28

• 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

Question 29

What do the silver halide crystals do?

Answer 29

• 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)

Question 30

What is the lead foil?

Answer 30

• 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

Question 31

What is the film speed?

Answer 31

• 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

Question 32

What do intensifying screens do?

Answer 32

• Reduced radiation dose
• Reduce detail
• Less common as digital receptors taking over

Question 33

What are intensifying screens?

Answer 33

• Used alongside special “indirect action” film for extra-oral radiographs (eg. panoramic radiographs, cephalograms)
• Too bulky for intra-oral use

Question 34

How do intensifying screens work?

Answer 34

• “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

Question 35

What is film processing?

Answer 35

• Sequence of steps which converts the invisible latent image to a
  visible permanent image

Question 36

What happens during automated cycle of film processing?

Answer 36

• All necessary steps carried out within a machine
• Exposed film goes in one end
• Processed film comes out the other

Question 37

Benefit of Automated cycle over manual processing

Answer 37

• Faster and more controlled than manual
• Avoids need for dark room
• But more expensive

Question 38

How do you open a film packet for automated processing?

Answer 38

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

Question 39

What does film storage need?

Answer 39

• 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

Question 40

Digital radiography advantages

Answer 40

• 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

Question 41

Digital radiography disadvantages

Answer 41

• 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