Radiology - Digital vs Film Flashcards
what types of intra-oral image receptor are used in digital radiography?
phosphor plates
solid state sensor
what types of intra-oral image receptors are used in film radiography?
direct action film
indirect action film
when is a size 0 image receptor used?
anterior periapicals
when is a size 2 image receptor used?
bitewings
posterior periapicals
when is a size 4 image receptor used?
occlusals
in digital radiography, what colour does the grid square go when few photons are reaching the receptor?
white - value 255
what type of image receptor (film or digital) used grid squares/pixels?
digital
what is the benefit of a digital radiograph having more grid squares/pixels?
better detail as it has higher resolution
resolution has a limit in terms of being beneficial cliniccally
what are the disadvantages using digital receptors?
each image requires storage space which is expensive
how many bits (binary digits) do digital radiographs typically use to create an image?
8 bits (binary digits)
= higher the number of bits the more accurate
what is the total number of shades of grey used in digital radiographs?
256 shades of grey
what is the format for digital images?
DICOM - digital imaging and communications in medicine
what software manages digital images?
PACS - picture archiving communications system
what is the limitation of PACS?
Hospital PACS is not linked to practices - have to ask for them separately
how do we view digital radiographs?
subdued lighting without glare
clean, bright monitor with adequate resolution and contrast
describe how digital phosphor plates work.
not connected to a computer
after use the plate is put in a scanner and read to create the final image.
describe how the phosphor plate used in digital radiographs create the visible image.
Receptor is exposed to the x-ray beam
Phosphor crystals in receptor are excited by the x-ray energy = latent image
The receptor is taken out of the mouth, taken out of the packet and disinfected
Then it is placed in the scanner
The laser from the scanner excited the phosphor crystals and they emit visible light
= digital image
list the types of digital solid state sensors.
CCD
CMOS
describe how solid state digital sensors work.
usually wired to a computer (some aren’t)
Latent image is created within the receptor and then also immediately read within the sensor to create an image instantly.
how is cross contamination minimised when using intra-oral receptors?
covering them with a single use cover
i.e. adhesive sealed plastic covers or long plastic sleeves for receptors with wires.
receptors disinfected between uses
Compare digital phosphor plates to solid state sensors.
PP are thinner and flexible where as SS are bulkier and rigid
PP are wireless whereas SS are usually wired to a computer
PP are sensitive to daylight and have to be kept in a dark container whereas SS dont have any problems with room light control
PP have to be processed in a scanner whereas SS are processed immediately.
PP are delicate whereas SS are more durable and have to be replaced less often.
SS more expensive
what are the advantages of digital receptors? (6)
- No need for chemical processing
- Images can be manipulated
- Easy storage and archiving of images
- Easy back-up of images
- Radiographs can be integrated into patients records
- Easy sharing and transfer
what are the disadvantages of digital receptors? (5)
- Risk of pixelation = worse resolution compared to film as you can only have a certain number or pixels in a digital radiograph.
- Requires computer monitors for optimal viewing
- Risk of loss /corruption (however this can be overcome by backing the radiographs up)
- If you print these images = poor quality image
- Image enhancement can create misleading images.
what is radiographic emulsion (film)?
Silver halide crystals embedded in a gelatin binder
The crystals act as the pixels (that is present in the digital radiograph receptors)
what type of image receptor (film or digital) has higher resolution and why?
film is generally higher resolution than digital as the silver bromide crystals are smaller (than pixels)
How do the silver halide crystals create the latent image in film radiology?
Become sensitised upon interaction with x-rays (& visible light)
- Sensitised crystals are converted to black metallic silver = dark parts of the image
- Non-sensitised crystals are removed = light parts of the image
What is the role of the lead foil in a film packet?
absorbs excess x-ray photons
what is the purpose of the embossed pattern of the lead foil in a film packet?
so that you can detect if the film packet has been placed the wrong way around in the mouth
- if it has, the pattern will be superimposed on to the radiograph and it will be pale
when are intensifying screens used in film radiology?
extra-orals - too bulky to be used in the mouth
what are intensifying screens used in film radiology for?
reduce the radiation dose
define film processing
Converts invisible latent image in the emulsion to a visible permanent image
list the methods of film processing (3)
Manual
Automated
Self developing films (less common)
list the stages in film processing.
- Developing - Converts sensitised silver bromide crystals to black metallic silver particles
- Washing - removes residual developer solution
- Fixing - removes non-sensitised crystals (allows lighter areas to be seen) and hardens emulsion
- Washing - removes residual fixer solution
- Drying - removes water so that film can be handled and stored
describe what occurs in wet developing.
Person dips film into different chemicals at precise concentrations and temperatures for specific periods of time. The film is washed after each tank.
- This must be carried out in a dark room with red lights and ventilation
what are the advantages of automated film processing ? (4)
Faster
More controlled
Avoids the need for a dark-room
Sponge rollers squeeze the solution out of the film instead of washing
describe how you prepare the film packet for automated processing.
- Disinfect the surface of the packet
- Hold the packet under the hood of the processor unit (to prevent interaction with the daylight)
All of these steps one within the automated unit;
- Peel back the flap out of the outer wrapper
- Fold back the lead foil
- Pull back the paper flap
- Hold the film by the edges
- Insert film into the processor shelf and it passes through the cycle.
what are the advantages of self developing film processing (not recommended)?
- No darkroom or processing facilities required
- Faster
what are the disadvantages of self developing film processing (not recommended)? (6)
- poorer image quality
- Image deteriorates more rapidly over time
- No lead foil
- Easily bent
- Difficult to use in positioning holders
- Expensive
what issues can arise during the film developing stage?
film not put in the solution for long enough = pale
developer solution is too cold = pale
developer solution is too dilute = pale
developer solution can oxidise and become less effective = pale
what issues can arise during the film fixing stage?
• Inadequate fixing = non-sensitised crystals are left behind and the image appears greenish/yellow/milky and becomes brown over time which makes the image harder to see and less diagnostically useful.
what issues can arise during the film washing stage?
Developer and fixer solution continues to act if not washed off properly
