Advances in Radiography - Digital Radiography Flashcards
What is the film focus distance equation?
New exposure = old mAs x (new FFD2)
(old FFD2)
What are the two categories of digital radiography?
Computed (CR) & Digital (DR).
CR & DR can be subcategorised into….?
Direct digital & Indirect digital
What piece of equipment is used in CR that are contained within a cassette?
An imaging plate.
What are the layers of an imaging plate?
- protective layer
- phosphor layer-photostimulable
- reflective layer
- conductive layer
- colour layer
- support layer
- backing layer
How does an imaging plate work?
X-ray photons cause excitation of phosphors within the phosphor layer which trap and store energy from x-ray photons in electron traps.
What is a cassette placed into, in order for the imaging plate to be removed?
A digitizer (CR reader)
Outline the process of a digitizer.
- The imaging plate is removed from the cassette
- plate is scanned with a laser
- amount of light released is dependant on quantity of x-ray photons received by crystal.
- photons are detected and digitalised by analogue-digital converter.
Storage/Maintenance requirements of CR
- clean cassette according to manufacture guidelines
- ensure cassette edges are free of gross contamination before putting in digitizer
- plates need erasing if not used often
- radiographs need storing on digital system.
Does DR require the use of a cassette?
No. DR (Direct and Indirect) are both cassette-less
How is an image stored (DR)?
- image captured directly and can be viewed on a computer screen within seconds.
- stored on the computer
- can be more expensive
One phase process…. (Direct).
Outline the process of DR, Direct.
- flat panel detector is connected to the image processor by a cable linkage & replaces x-ray film or imaging plate.
- once x-ray strikes surface of FPD, image is produced ‘direct’ when x-ray photon light is converted to an electronic charge.
Two phase process…
Outline the process DR, Indirect.
uses indirect FPD to convert x-rays into light by a scintilator. light is converted into electrical charge by photodiode layer within FPD.
OR
info from charged couple device is process by computer, resulting in image on screen. light still being produced by scintilator and converted to digital signal by a matrix grid of electronic sensors.
