radiographic screens and digital imaging Flashcards
What is a cassette
the device that provides a light tight film holder and rigid support for film, as well as an intensifying screen
The cassette contains two intensifying screen, one on each side of the inside of the cassette. What is their purpose?
this doubles the film exposure obtained with a given x-ray exposure, thus reducing the amount of exposure to the patient
What type of film is used inside an X-ray cassette?
dual emulsion
What is the function of the padding in the pack of a cassette?
it ensures that there is a light positive pressure exerted on the film when the cassette is closed so that there is optimal film/screen contact at all points on the film
How do intensifying screens double the film exposure obtained with a given x-ray?
They are coated with phosphors, which are fluorescent crystals that give off light when exposed to x-rays
this is the property of luminescence that creates 99% of the x-ray image
The process of glowing only while being excited (such as during ionizing radiation) that will cease glowing at completion of exposure
fluorescence
luminescence that demonstrates afterglow (continues to flow for a period of time after the exposure to radiation has ceased)
phosphorescence
the emission of light from a substance bombarded by radiation
luminescence
what does the term radio parent mean?
does not have a habit of absorbing X-rays
What is radioparent in the X-ray cassette?
the cassette face
What is the reflective layer of screens in a cassette made of?
titanium oxide
What is the function of the reflective later of cassette screens?
it redirects light created during exposure back towards the film
Edison discovered calcium tungstenate to be able to glow efficiently when exposed to radiation. This material was the gold standard in X-ray technology for a long time, but has been replaced with what rare earth phosphors?
gadolinium
lanthanum
yttrium
The base layer of screens in mostly made of
polyester or cellulose triacetate, which are radioparent, chemically inert, tough and flexible
What creates “faster” screens?
thicker phosphor layers and larger crystals in the phosphor
thicker phosphor layers and larger crystals in the phosphor result in
lower detail than thinner phosphor layers and smaller crystals but greater speed of x-ray exposure
the portion of electromagnetic spectrum the film is most sensitive to?
spectral sensitivity
Spectral sensitivity should match what?
the spectral emission of the screens used in the film
What is the formula for adjusting mAs for changing screen speed
(speed1/speed2) x mAs1 = mAs2
What is spectral emission
the color of light emitted by a phosphor
What is the protective layer of the screen
a thin transparent supercoat consisting of gelatin that protects the the emulsion of the phosphor on the film
How often should screens be cleaned?
monthly if films are taken every day
quarterly if films are taken once a week
What is screen speed?
the efficiency of a screen in converting x-rays to light
greater screen efficiency =
less exposure = faster screen
A screen with a speed of 200 would be twice as fast as a 100 speed screen and require _____ as much exposure
half
What screen speed is used for general purpose radiography?
400-600
What screen speed is used for extremity or other detailed radiography?
100
big crystals in thick layer =
fast exposure, lower detail
small crystals in thin layer =
slow exposure, greater detail
How do you calculate the change in technique needed to create a film of equal density on two different system speeds?
(system speed 1/system speed 2) x mAs 1 = mAs 2
Components of a film emulsion:
- gelatin (support medium)
- silver halide micro crystals (active ingredient, 90% silver bromide and 10% silver iodide)
- silver sulfide (sensitivity center)
Why is film screen contact important?
it prevents loss of detail
film screen contact is negatively affected by:
- foreign material in the cassette or on screen
- dents due to objects dropped on screen or closed inside the cassette
- damage due to improper mounting
- deterioration of padding
- warping of screen from getting wet
What is a latent image?
the image that has been created after exposure but before development, so it cannot be seen yet
What are some causes of undesired exposure of film?
- unintended light exposure
- scattered x-rays
- heat
- chemicals or fumes
- pressure
- age
film speed is directly proportional to what?
mAs
slower film speed = _____ detail
more detail
faster film speed = _____ detail
less detail
How should film be stored?
vertically oriented in a light proof case that is kept cool, clean, dry and ventilated
The rules and best practices established by the American college of radiology (ACR) and the national electronic manufacturing association (NEMA) to ensure standard and protocols for image and communications formatting
DICOM (digital imaging and communications in medicine) standards
Sets standard for what can and cannot be disclosed without the patient’s consent to provide for confidentiality, safety, and protection of health information
HIPPA (health insurance probability and affordability act)
Establishes rules and incentives for transition to digital health record management and rules regarding digital acquisition, sharing, storage, safe keeping and privacy in the digital universe
HITECH (health information technology for economic and clinical health) act
What are the three digital imaging platforms?
- analog films converted to digital images
- computer radiography
- direct (digital) radiography
computed radiography uses a ______ instead of film
detector plate (aka photostimulateable phosphor plate, PSP)
The digital plate that is used in digital radiography is a(n) _______ consisting of millions of indexical semiconductor elements deposited onto a substrate material
active matrix liquid crystal flat panel display - AMLCD
What is PACS?
picture archival and communication system - the software that stores, organizes and allows for seamless integration of images from storage to terminal interface
All images subject to compression for storage purposes must have _____
reversible compression without loss of original data
Can imaged being exported for interpretation or review be partial studies?
no, they must be complete studies
Which is more expensive: direct or computed radiography?
direct radiography
