Digital and Film Radiology Flashcards
What is the difference in digital and film radiography?
- 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
Which do we use more nowadays, digital or film radiography?
- Digital has mostly superseded film radiography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)
What are the 2 different types of digital receptor?
- Phosphor plate
- Solid-state sensor
- (all multiple use as can disinfect and use again)
What are the 2 different types of film receptor?
- Direct action film
- Indirect action film
- (all single use)
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)
- Size 0 (anterior periapicals)
- Size 2 (bitewings, posterior periapicals)
- Size 4 (occlusal radiographs)
What is an x-ray shadow?
- 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
Explain the conversion of an x-ray shadow into an image? (3)
- 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
How do we turn an x-ray shadow into a digital image? (go and look at this slide again)
- 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
How is a digital image displayed?
- 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
What is pixilation and what is important about it?
- 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
How many pixels do you want for a better image to be produced?
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
Why might increasing the pixels in an image be a problem?
- 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
What is the Greyscale bit depth?
- 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
What is one of the biggest advantages of digital radiographs?
- 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
Digital images are stored using DICOM. What is this?
- 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
What is the biggest benefit of DICOM?
- 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
We manage digital images using PACS. What is this?
- 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
What are the main components for PACS? (4)
- 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
When viewing digital radiographs, what do we want the environment to be like? (2)
- Subdued lighting
- Avoid glare
When viewing digital radiographs, what do we want the monitor to be like? (4)
- Clean
- Adequate display resolution so the image can be sharp enough
- High enough brightness level
- Suitable contrast level
What is the SMPTE test pattern?
- Society of Motion Picture & Television Engineers
- IT is available online
- It can be used to assess the resolution, contrast, & brightness of your monitor/monitors
What are the 2 types of digital (intra-oral) receptors?
- Solid State Sensors
- Phosphor plates
What are 2 other names for phosphor plate sensors?
- Photostimulable phosphor plate
- Storage phosphor plate
Are phosphor plate sensors connected to a computer?
No
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
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)
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
What are the 2 types of solid-state sensors?
- CCD (charge-coupled device)
- CMOS (complimentary metal oxide semiconductor)
Are solid state sensors connected to the computer?
- Yes
- They are usually wired but can be wireless
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
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
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
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
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
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
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