Image Receptors 1 Flashcards
What are the two ways and types an x-ray image can be captured?
Film: placed in chemicals in dark conditions
- direct action
- indirect action
Digital: read and translated into an image by a computer
- solid state sensor
- photostimulable phosphor plate
How does direct action film work?
Indirect action?
Direct action - actual piece of film containing silver halide crystals whoch are sensitive to x-rays, wrapped in a packet
Indirect action - a film inside a cassette which contains intensifying screens, x-ray photons react with intensifying screens to produce light photons which expose the film to produce the image, used for extra-oral radiography
How do solid state digital sensors work?
Photo-stimulable phosphor plates?
Solid state: charged couple device (CCD) and complimentary metal oxide semiconductor (CMOS)
- convert light into electrons, info collected by a computer programme and transformed into the image
Photostimulable phosphor plates:
- images produced by interaction of x-rays with the phosphor layer on the plate, which is then scanned by a laser to produce the image
What is the difference between phosphor plates and solid state sensors?
Phosphor plate:
- can be used with existing film holders
- tolerated well by patients
- plates easily damaged
- relatively expensive
- sensitive to background radiation - must be cleared every 24hrs if not being used
Solid state sensor:
- similar to image capture in digital camera
- can only be used with its own holders
- not tolerated well by patients - can be bulky
- sensors very expensive
- easily damaged
How does the PSP work?
- phosphor layer on plate exosed to x-ray photons
- x-ray energy stored in the electrons of the phosphor crystals (latent image)
- plate inserted into scanner
- scanned by red laser
- stored energy released as blue light
- light detected by photodetector and sent to a signal digitiser (ACD convertor)
What is grey-scale?
What is the latent image?
Grey-scale - the ADC concerts light to a digital signal which corresponds to a different shade id grey which forms the image on the monitor
Latent image - x-ray energy stored in the electrons of the phosphor crystals
What are the layers of a CCD?
- front cover
- scintillator layer - converts x-ray energy to light
- silicon wafer layer - converts light into an electrical signal
- back cover - particular sensor incorporating cable to carry signal to PC
How does a CCD work?
- x-rays hit the scintillator layer within the sensor
- this gives off light which hits the phtoosensitive cells within a very thin piece of silicon, these make up pixels of image
- electrons within each cell are released and form a charge which is converted to an electrical signal which the computer software converts to an image
What advantages are there to having digital imaging?
Advantages - digital:
- no chemicals
- faster processing times
- easy archiving
- easy image transfer
- image manipulation
- dose reduction
What disadvantages are there to digital imaging?
Disadvantages - digital:
- expensive and easily damaged
- reduction in resolution due to pixel size (larger the pixel, lower the detail)
- archiving - issues accessing, powercuts, software issues, cyber terrorism
- security issues due to easy image transfer
- image manipulation - incorrect diagnoses
- dose reduction drop in resolution
How are digital images stored?
Stored in:
- dental practice
- local server
- some form of backup - CD, DVD, hard drive
DDH use PACS
