Digital and Film Radiology Flashcards
(90 cards)
1
Q
What is the difference in digital and film radiography?
A
- They differ in how the x-ray beam is dealt with after it has interacted with the patient e.g. how it is captured, converted into an image and stored
2
Q
Which do we use more nowadays, digital or film radiography?
A
- Digital has mostly superseded film radiography
- There are multiple benefits to film radiography
- However, film is still used by some GDP’s (some decide that the cost of making the change is not worth the benefit)
3
Q
What are the 2 different types of digital receptor?
A
- Phosphor plate
- Solid-state sensor
- (all multiple use as can disinfect and use again)
4
Q
What are the 2 different types of film receptor?
A
- Direct action film
- Indirect action film
- (all single use)
5
Q
Receptors come in a variety of sizes to suit different purposes and the exact measurements can vary between companies. Phosphor plate sizing tends to match the films, what are these? (3)
A
- Size 0 (anterior periapicals)
- Size 2 (bitewings, posterior periapicals)
- Size 4 (occlusal radiographs)
6
Q
What is an x-ray shadow?
A
- This is the pattern of attenuation you would see if you do a cross section of the x-ray beam after it has passed through an object
7
Q
Explain the conversion of an x-ray shadow into an image? (3)
A
- When the x-ray beam passes through an object some of the x-ray photons are attenuated, creating an ‘x-ray shadow’
- The x-ray shadow is basically the image ‘information’ held by the x-ray photons after an x-ray beam has passed through an object
- The image receptor detects this x-ray shadow and uses it to create an image
8
Q
How do we turn an x-ray shadow into a digital image? (go and look at this slide again)
A
- The receptor measures the x-ray intensity at defined areas (arranged in a grid)
- Each area is given a value relating to the x-ray intensity (typically from 0-255)
- Each value corresponds to a different shade of grey
- 0 = black
- 255 = white
9
Q
How is a digital image displayed?
A
- Displayed as a grid of squares called pixels
- Each pixel can only display one colour at a time
- The more pixels you have the more detailed/accurate your image can be
10
Q
What is pixilation and what is important about it?
A
- Where you have converted an image into a grid of squares
- A very important part of pixilation is how many pixels you are using to create the image - the more pixels the better image
11
Q
How many pixels do you want for a better image to be produced?
A
More pixels = better image
Less pixels = worse image
- More pixels = better detail = higher resolution
- Increasing the resolution will provide a more diagnostic image up to a limit - eventually it will not provide any meaningful clinical benefit
12
Q
Why might increasing the pixels in an image be a problem?
A
- Each digital image will require more storage space - increase cost
- Digital receptors are limited in how small they can make the pixels because of manufacturing issues
13
Q
What is the Greyscale bit depth?
A
- This is a term that essentially describes the number of shades of grey that have been used to represent the image - digital dental radiographs typically use 8 bits
- 1 binary digit is either a 1 or a 0 so gives 2 different shades - wouldn’t get a very useful image with just these 2 colours
- 8 binary digits = 2^8 = 256 = 256 shades of grey
14
Q
What is one of the biggest advantages of digital radiographs?
A
- Being able to manipulate the image
- Software can be sued to copy, resize & alter images
We can: - Change the contrast
- Invert the colours
- Magnify image
- Rotate it
15
Q
Digital images are stored using DICOM. What is this?
A
- Digital Imaging & Communications in Medicine
- International standard format for handling digital medical images
- Used to transmit, store, retrieve, print, process and display images
- Essentially an alternative to JPEG, GIF etc
16
Q
What is the biggest benefit of DICOM?
A
- Allows imaging to work between different software, machines, manufacturers, hospitals & countries without compatibility issues
- It stores other important data alongside the image e.g. patient ID, exposure settings, date of image
17
Q
We manage digital images using PACS. What is this?
A
- Picture Archiving & communication system
- A medical imaging technology which provides storage & access to images (typically in a healthcare organisation)
- Note: hospital PACS NOT connected to dental practices
18
Q
What are the main components for PACS? (4)
A
- Input by imaging modalities e.g. plain radiography, CT, MRI, US
- Requires a secure network for the transmission of patient information
- Workstations for interpreting & reviewing images
- Archives for the storage & retrieval of images & reports
19
Q
When viewing digital radiographs, what do we want the environment to be like? (2)
A
- Subdued lighting
- Avoid glare
20
Q
When viewing digital radiographs, what do we want the monitor to be like? (4)
A
- Clean
- Adequate display resolution so the image can be sharp enough
- High enough brightness level
- Suitable contrast level
21
Q
What is the SMPTE test pattern?
A
- Society of Motion Picture & Television Engineers
- IT is available online
- It can be used to assess the resolution, contrast, & brightness of your monitor/monitors
22
Q
What are the 2 types of digital (intra-oral) receptors?
A
- Solid State Sensors
- Phosphor plates
23
Q
What are 2 other names for phosphor plate sensors?
A
- Photostimulable phosphor plate
- Storage phosphor plate
24
Q
Are phosphor plate sensors connected to a computer?
A
No
25
How are phosphor plate sensors used?
- After receptor is exposed to x-rays, it must be put in a scanner & 'read' to create the final image
26
What is the process of image creation using phosphor plates (within the patient's mouth)? (2)
- Receptor exposed to x-ray beam
- Phosphor crystals in receptor excited by the x-ray energy, resulting in the creation of a latent image (which is stored on the receptor and we cannot see it)
27
What is the process of image creation using phosphor plates (within the scanner)? (3)
- Receptor scanned by a laser
- The laser energy causes the excited phosphor crystals to emit visible light
- This light is detected & creates the digital image
28
What are the 2 types of solid-state sensors?
- CCD (charge-coupled device)
| - CMOS (complimentary metal oxide semiconductor)
29
Are solid state sensors connected to the computer?
- Yes
| - They are usually wired but can be wireless
30
How do solid state sensors work?
- Latent image created & immediately read within the sensor itself
- The final image is created virtually instantly so don't have the additional steps that we have with phosphor plates where it has to go into a scanner
31
What are the components of a solid state sensor? (6)
- Back housing + cable
- Electronic substrate
- CMOS imaging chip
- Fibre-optic face plate
- Scintillator screen
- Front housing
- There are many different components and this makes them a lot more bulky and a lot more expensive to make as well
32
What is an identification dot?
- It is located in the corner of a receptor to aid orientation of image
- This helps to ensure that when you are looking at an image you know that it has not been accidentally flipped
- Only effective if the receptor was positioned correctly during exposure
33
What do we have in place to ensure cross-infection control when taking radiographs? (3)
- Intra-oral receptors have purpose-made covers to prevent saliva contamination - single-use covers
- Examples of these are:
- Adhesive sealed plastic covers (for phosphor plates)
- Long plastic sleeves (for wired solid state sensors)
- Receptor is still disinfected between uses
34
What are extra-oral phosphor plates?
- They are basically just larger versions of intra-oral ones which are doing the exact same thing
- Because they are larger we will need different scanners that take a larger receptor
35
Why must we handle receptors carefully?
- Receptors can be damaged if not handled correctly (digital and film)
- If digital, certain types of damage will impact every subsequent image obtained from that receptor (reduces their diagnostic value & may render receptor unusable)
- Hold the receptors by their edges, not by their flat surfaces
36
What are the advantages of phosphor plate sensors compared to solid-state sensors? (3)
- Thinner, lighter &(usually) flexible
- Wireless -> more stable (& more comfortable)
- Handling similar to film
37
What are the disadvantages of phosphor plate sensors compared to solid-state sensors? (2)
- Variable room-light sensitivity -> risk of impaired image if not stored properly
- Latent image needs to be processed in scanner separately so means there is an additional step
38
What are the advantages of solid-state sensors compared to phosphor plate sensors? (2)
- No issues with room-light control
| - Arguably more durable -> replaced less often
39
What are the advantages of solid-state sensors compared to phosphor plate sensors? (4)
- Bulkier and rigid
- Usually wired
- Smaller active area (for same physical area of receptor)
- More expensive
40
The intra-oral film packet is what goes into the patient's mouth when you are taking a radiograph. It has several components all of which play an important role in helping to create the image. What are the components? (5)
- Inner paper
- Dental film
- Inner paper wrap
- Lead foil backing
- Outer package
41
What is the function of the lead foil in an intra-oral film packet?
- Absorbs some excess x-ray photons
42
What is the function of the protective paper in an intra-oral film packet?
- Protects film from light exposure, damage by fingers & saliva
43
What is the function of the outer wrapper in an intra-oral film packet? (2)
- Prevents ingress of saliva
| - Indicates which side of the packet is the front
44
What is the radiographic film?
- It is the material in which the actual image is formed
| - Sensitive to both x-ray photons & visible light photons
45
How does the radiographic film work?
- Photons interact with emulsion on film to produce latent image which only becomes visible after chemical processing
46
What is the function of the transparent plastic bag in the radiographic film?
- Supports the emulsion
47
What is the function of the adhesive in the radiographic film?
- Attaches the emulsion to the plastic base
48
What is the function of the emulsion in the radiographic film?
- Layered on both sides of the plastic bag
49
What is the function of the protective coating of clear gelatin in the radiographic film?
- Shields the emulsion from mechanical damage e.g. fingerprints, scrapes and scratches
50
What is embedded in the gelatin binder of the radiographic emulsion?
- Silver halide crystals
51
What is the function of the silver halide crystals embedded in the gelatin binder?
- Crystals microscopic & are what effectively become the 'pixels' of the final image - film is generally higher resolution than digital
52
What are the silver halide crystals usually made from?
- Usually silver bromide
53
How do silver halide crystals work?
- They become sensitised upon interaction with x-ray (& visible light) photons
During processing:
- Sensitised crystals converted to particles of black metallic silver (these are the dark parts of the final image)
- Non-sensitised crystals are removed (these become the light parts of final image)
54
Where is the lead foil found?
- In the packet, lying behind the film
55
What is the function of the lead foil?
Absorbs some excess x-ray photons
- Those in the primary beam continuing past the film
- Those scattered by patient's tissues & returning back to film
56
Why does the lead foil have an embossed pattern?
- To highlight (on image) if the receptor was placed the wrong way around
57
What does film speed relate to?
- Relates to the amount of x-ray exposure required to produce an adequate image - one that is not too dark or too light
58
If you increase film speed what does this decrease?
- Decreases radiation required to achieve an image
59
What is film speed affected by?
- Affected by number and size or the silver halide crystals within the radiographic emulsion
- Larger crystals means a faster film but a poorer image quality (this is because these crystals essentially act as the pixels as well so if they are larger you are going to have a worse resolution
60
If you are changing to different film speeds, what must you do? (2)
Either:
- Convert settings on x-ray unit (by a qualified technician)
- Install a filter to absorb part of the primary x-ray beam so that you are not over-exposing the film
61
What are intensifying screens?
- They are used alongside special 'indirect action' film for extra-oral radiographs (e.g. panoramic radiographs, cephalograms)
- too bulky for intra-oral use so not suitable for putting in patient's mouth
62
What is the main benefit and main drawback of intensifying screens?
```
Benefit = reduce radiation dose
Drawback = reduces detail
```
They are becoming less common as digital receptors are becoming more common
63
How do intensifying screens work?
- 'indirect action' film placed inside cassette with an intensifying screen on either side
- Screens release release visible light upon exposure to x-rays and this visible light creates a latent image on the film and this can be converted using film processing
64
Look at the slide on why intensifying screens decrease the detail
There is an image
65
What is film processing?
- A sequence of steps which converts the invisible latent image to a visible permanent image
66
What is a must when it comes to film processing and what are the different methods of doing this?
- MUST be carried out under controlled, standardised conditions to ensure consistent image quality and not variations from radiograph to radiograph
Different methods:
- Manual
- Automated
- (self-developing films) - these are less common
67
What are the common steps to film processing? (5)
1. Developing
2. Washing
3. Fixing
4. Washing
5. Removing
68
What is involved in the developing step of film processing?
- Converts sensitised crystals to black metallic silver patches resulting in the darker areas of the image
69
What is involved in the first washing step of film processing?
- Removes residual developer solution
70
What is involved in the fixing step of film processing?
- Removes non-sensitised crystals (so you can have a lighter area on the image)
- Hardens emulsion (which contains the black metallic silver) - this makes it more hard wearing and long lasting
71
What is involved in the second washing step of film processing?
- Removes residual fixer solution
72
What is involved in the drying step of film processing?
- Removes water so that film is ready to be handled/stored
73
What is the manual (or wet) cycle?
Person dips film into different tanks of chemicals:
- At precise concentrations/temperatures
- For specific periods of time
- Washes film after each tank
74
What is a requirement for the manual/wet cycle?
- It must be carried out in a dark-room with absolute light-tightness and adequate ventilation because of all of the chemicals being used
75
What is the automated cycle?
- All necessary steps carried out within a machine
| - Exposed film goes into one end and the processed film comes out the other end
76
What is one advantage and disadvantage of the automated cycle compared to the manual cycle?
Advantage: Faster and more controlled than manual processing & avoids the need for a dark room
Disadvantage: more expensive
77
How do we open a film packet (for automated processing)? (7)
1. Disinfect the surface of the packet (& wipe off)
2. Hold the packet under the hood of the 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
(once placed the film on the shelf it usually takes several minutes for it to pass through the whole machine)
78
Are self-developing films recommended?
- No
79
What are the advantages of self-developing films? (2)
- No darkroom or processing facilities required
| - Faster (e.g. one minute)
80
What are the disadvantages of self developing films? (6)
- Poor image quality
- Image deteriorates more rapidly over time
- No lead foil
- Easily bent
- Difficult to use in positioning holders
- Relatively expensive
81
Developing involves a chemical reaction where sensitised silver halide crystals are converted into black silver. What can this reaction be affected by? (3)
- Time, temperature and solution concentration
82
What happens if developer solution oxidises in air? (2)
- It becomes less effective over time
| - It needs to be replaced regularly (irrespective of how many films have been developed)
83
What is the possible exposure issue that causes a pale image?
- Radiation exposure factors too low
84
What are the possible developing issues that can cause pale images? (3)
- Film removed from solution too early
- Solution too cold
- Solution too dilute/old
(note: opposite will result in dark image)
85
What is fixing?
- Fixing involved a chemical reaction which removes non-sensitised crystals & hardens the remaining emulsion
86
What problems can be faced if there is inadequate fixing?
- This means non-sterilised crystals are left behind
- The image can become greenish-yellow or milky
- The image becomes brown over time
87
What is the potential processing issue related to washing?
- Developed and fixer solution will continue to act if not washed off
88
What are the requirements for film storage? (3)
- Takes up room (so need a lot of it)
- Need to be easily accessible & safe from damage
- Require a reliable organisation system
- To allow images to be found easily
- And to reduce the risk of images being lost/mixed up
89
What are the advantages of digital radiography compared to film radiography? (6)
- 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
90
What are the disadvantages of digital radiography compared to film? (5)
- Worse resolution therefore risk of pixilation
- Requires diagnostic level computer monitors for optimal viewing
- Risk of data corruption/loss (solved by backing up)
- Hard copy print outs generally have lower image quality
- Image enhancement can create misleading images
