Radiology 4 Flashcards
Image receptor
the technical term for the item the x-ray image is formed on, so it could be a film, plate or digital sensor.
Fogging
Photons that don’t have enough energy to make a useful interaction with the receptor and this scatter can degrade the image.
2 ways to capture an x-ray image
film and digital
Two types of film
direct action film
indirect action film
Two types of digital
solid state sensors
photo-stimulable phosphor
Direct film
dental intra-oral. x-rays act directly on silver halide crystals in film emulsion. is an actual piece of film which is sensitive to x-rays that is wrapped in a packet. You still may come across direct action film in some general dentist practices.
indirect film
extra-oral. light from intensifying screens act on silver halide crystals in film emulsion. a film inside a cassette which contains intensifying screens. The x-ray photons react with the intensifying screens to produce light photons, which expose the film to produce the image.
digital solid state: two types
- solid state CCD (charge-coupled device)
- CMOS (complimentary metal-oxide semiconductor) sensors
digital solid state sensors: how do they work?
These sensors work by converting light into electrons. The information is then collected by a computer programme and transformed into the image.
digital PSP (photo-stimulable phosphor)
Images are produced by the interaction of x-rays with the phosphor layer on the plate, which is then scanned by a laser to produce the image. The extra-oral cassettes in the department are also PSP plates.
Film image processing
processor with bottles of chemicals
Digital image processing: solid state
OPT machine
Digital image processing: PSP plates
vista scan towers
What is this?
Solid state sensors for intra-oral use (two silver plates on black cables).
What is this?
Large floor standing processor for the cassettes we use for extra-oral radiography
Main differences between PSP and solid state? (3)
- Solid state requires use of a specific holder, PSP can be used with existing film holders.
- Solid state is not tolerated well by patients (bulky), PSP is tolerated well by patients.
- Solid state shows better image resolution that phosphor plates.
What side is this of the phosphor plate?
phosphor coating (barium fluoride) - this is the side on which the image is formed.
What side is this of the phosphor plate?
Shows the size of the film and the orientation dot. This is the back of the plate.
What is this?
Protective bag for phosphor plate (you should be able to the see the black side of the plate through the window of the bag).
PSP image processing stages (3)
- Imaging plate + x-ray = stable excited state
- Stable excited state + red laser (vista scan unit) = unexcitable state.
- Unstable excited state + blue light emitted = converted to an image.
Stable excited state
When the imaging plate is placed into the patient’s mouth and the phosphor coating is exposed to x-rays which causes a reaction within the phosphor.
Latent image
The phosphor layer on the plate is exposed to x-ray photons. The phosphors then store the radiation in local electron energies.
What happens during the scanning with red laser?
the phosphor layer is scanned by a red laser which causes the electrons to drop to lower energy levels by emitting blue light.
How is the emitted blue light (after the red laser) processed to an image?
This light is then detected by a photodetector and sent to a signal digitiser. This is called an Analogue to digital convertor or ADC.