Flashcards in radiographic screens and digital imaging Deck (49)
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?
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
luminescence that demonstrates afterglow (continues to flow for a period of time after the exposure to radiation has ceased)
the emission of light from a substance bombarded by radiation
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?
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?
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 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
What screen speed is used for general purpose radiography?
What screen speed is used for extremity or other detailed radiography?
big crystals in thick layer =
fast exposure, lower detail
small crystals in thin layer =
slow exposure, greater detail