Digital x-ray Flashcards
what is beneficial about using digital x-rays?
increased safety since they allow for a decreased number of repeat exposures and removal of toxic processing chemicals, software programs can also correct most exposure problems
what are the two types of digital x-rays?
computerized/ computed radiography (CR), or digital radiography (DR)
what factors impact the quality on a digital x-ray?
resolution, image noise, pixel size/ number, and field of view
how do digital x-rays record images?
as a combination of rows and columns called a matrix
voxel
an area within a 3D volume of tissue which is shown by a pixel
what determines how many shades of gray there are in a digital x-ray?
grayscale bit depth
how is resolution related to pixels?
directly related
increased matrix size = increased number of small pixels
image noise
unwanted random variations in shades of gray produced on a radiograph
inversely related to image contrast
how does electronic noise interfere with digital x-rays?
it interferes with the passage of electrons and photons throughout the process of obtaining, processing, and displaying an image
what causes quantum noise?
it is caused by a random distribution of electrons striking the image receptor
how can you minimize quantum noise?
by increasing mAs or kVp
dose creep
increase in exposure factors made in an attempt to decrease the amount of image noise
what are some characteristics of CR imaging?
requires a cassette with intensifying screen
screen composed of photostimulable phosphors referred to as the photostimulable storage phosphor imaging plate (PSP)
what layers make up the imaging plates needed for CR imaging?
from outermost to innermost:
1. protective layer
2. phosphor layer (contains stimulable phosphors)
3. conductor layer (helps minimize electrostatic interference with image formation)
4. light-shielding layer (protects plate from light damage)
how is an image formulated in digital x-rays?
electrons in the IP become excited when they interact with the x-rays
some electrons are elevated into a high energy state that leaves gaps in the phosphate layer, these gaps produce the latent image
how is the imaging plate processed for CR imaging?
by loading the cassette into the image reader
how long after exposure should the imaging plate be processed in CR imagining?
must be processed shortly after exposure because the electrons are only latent for a few hours
how does the image reader work in CR imaging?
- it uses a red focused laser beam to release high-energy electrons which causes an additional release of light
- released light is directed to a photodetector that converts visible light into an electronic signal which is then converted to a digital signal
- the plate is exposed to a bright flash of white light that returns electrons to their stable state, fully erasing the image and making the IP ready to reuse
what are the IP plates most prone to?
wear and ghosting (prior image can’t be fully erased)
how does DR imaging work?
the image receptor is built into the x-ray table so it doesn’t require the use of cassettes and separate imagining processing units
what are the different system types for DR imaging?
direct detector systems and indirect detector systems
detective quantum efficiency (DQE)
describes sensitivity and accuracy of system
expressed as a % of the x-ray energy that strikes the detector and is converted to the final image, most digital systems have a DQE of 80% with the other 20% being filled in by the computer
how does the direct detector system work?
it utilizes a thin film transistor (TFT) device to detect and display image
the imaging plate contains amorphous selenium which releases electrons when they interact with the x-ray beam
TFT collects electrons and directly converts that electronic signal to digital image
what are the different types of indirect detector systems?
one uses TFT detector and the other uses a charge-coupled device (CCD)
both types use a scintillator (material that fluoresces when exposed to the x-ray beam)
