RADIOGRAPHIC IS Flashcards
What is the purpose of a radiographic intensifying screen?
It amplifies the effect of image-forming x-rays that reach the screen-film cassette.
What does the phosphor in an intensifying screen do?
Converts the x-ray beam into light.
Radiation emitted with equal intensity in all directions.
isotropic emission
Name one advantage of using an intensifying screen.
Lower patient dose.
Name one disadvantage of using an intensifying screen.
Slightly blurred image.
How many layers does an intensifying screen have?
Four: protective coating, phosphor, reflective layer, and base.
What is the purpose of the protective coating in an intensifying screen?
Makes the screen resistant to abrasion and allows for routine cleaning.
What is the thickness range of the protective coating?
10-20 μm.
Which layer is closest to the film in an intensifying screen?
Protective coating.
What material was used historically for the phosphor in intensifying screens?
Calcium Tungstate (CaWO4).
What materials are now used in the phosphor layer?
Rare earth elements:
Gadolinium (Gd)
Lanthanum (La)
Yttrium (Y).
Why are rare earth elements preferred over calcium tungstate in intensifying screens?
They reduce patient dose and provide other benefits like less thermal stress on the x-ray tube.
Name two properties that are favorable in a phosphor material.
High atomic number
high detective quantum efficiency (DQE).
The percentage of x-rays absorbed by the image receptor.
detective quantum efficiency (DQE)
The rate at which x-ray energy is transformed into light in an intensifying screen.
conversion efficiency (CE).
What is afterglow in the context of intensifying screens?
The continuing emission of light after exposure to x-rays.
Who developed calcium tungstate for use in radiographic screens?
Thomas Edison.
What is the role of the reflective layer in an intensifying screen?
Redirects light to the film, increasing screen efficiency.
What is a disadvantage of adding dye to the reflective layer?
reduces screen speed.
What is the purpose of the base layer in an intensifying screen?
Provides mechanical support for the phosphor layer.
What material is the base layer typically made of?
Polyester.
Define luminescence.
emission of visible light in response to outside stimulation.
Name the two types of luminescence.
Fluorescence and phosphorescence.
What is fluorescence?
emission of visible light only during stimulation.
What is phosphorescence?
The emission of visible light during and after stimulation.
What are the three primary characteristics of a radiographic intensifying screen?
Screen speed
image noise
spatial resolution.
How does screen speed relate to patient dose?
Increased screen speed reduces patient dose.
A speckled appearance on images caused by factors like fast screens.
image noise
A measure of the screen’s speed, comparing exposure with and without a screen.
intensification factor
What does spatial resolution describe?
The ability to produce a clear image with defined details.
In what unit is spatial resolution typically expressed?
Line pairs per millimeter (lp/mm).
What is the speed range for intensifying screens?
100 (slow) to 1200 (very fast).
What color emission does a calcium tungstate screen produce?
blue
What is the typical speed range for a calcium tungstate screen?
50-200
How is rare earth screen speed typically classified?
80-1200, with high DQE.
Name a property that a radiologic technologist cannot control regarding an intensifying screen.
Phosphor composition.
What effect does a thicker phosphor layer have on screen characteristics?
Increases detective quantum efficiency (DQE) but decreases spatial resolution.
What is the purpose of adding dye to the screen?
To control light spread and improve spatial resolution.
What effect do larger phosphor crystals have?
Produce more light per x-ray interaction, increasing speed but decreasing detail.
How does increased kVp affect screen speed?
Increases intensification factor (IF).
A type of image noise resulting from high conversion efficiency.
quantum mottle
Define conversion efficiency (CE) in a formula.
CE = (emitted light / x-rays absorbed) x 100.
What is spatial resolution influenced by in intensifying screens?
Phosphor thickness and crystal size.
The ability to distinguish between similar tissues in an image.
contrast resolution
What are the benefits of proper screen-film combinations?
Decreased patient dose and occupational exposure, and flexibility in kVp selection.
Holds the film and intensifying screen securely.
cassette
Why is the front cover of a cassette made of low atomic number material?
To reduce x-ray attenuation.
What material is typically used for the back cover of a cassette?
Heavy metal, to reduce backscatter.
X-rays deflected backward after interacting with an object.
backscatter radiation
What is the main cause of backscatter radiation?
High kVp techniques.
How does carbon fiber in cassettes benefit radiography?
Reduces patient exposure and extends x-ray tube life.
Compare direct film exposure to screen-film exposure in terms of x-rays absorbed.
Screen-film absorbs fewer x-rays, but produces more light photons.
What is the advantage of rare earth screens?
Faster speed with lower patient dose.
Name a disadvantage of rare earth screens.
Increased quantum mottle (noise).
Name a rare earth element commonly used in screens.
terbium
What is the purpose of spectral matching in screen-film combinations?
Ensures compatibility between the screen emission color and film sensitivity.
What color light does calcium tungstate emit?
blue
What color light does rare earth phosphors like gadolinium emit?
green
Why is a red safelight used in darkrooms with rare earth screens?
It does not affect green-sensitive film.
What element in the periodic table is a common rare earth material in screens?
lanthanum
What is the atomic number of gadolinium?
64
What is the primary use of asymmetric screens?
Chest, pediatric, and mobile radiography.
What is the benefit of using a finer screen for mammography?
Higher spatial resolution.
What is a major component of image noise?
quantum mottle
Name a common cause of poor screen-film contact.
Worn or damaged cassette components.
How often should screens be cleaned?
Periodically, using mild soap and water.
Name a substance used in commercial screen cleaning materials.
Antistatic compounds.
What is the effect of a bent hinge on screen-film contact?
Causes poor contact, affecting image quality.
Why is it recommended to avoid leaving cassettes open?
Prevents dust and debris from damaging screens.
What is the main purpose of the compression device in a cassette?
Ensures close contact between screen and film.
What happens when kVp is too high in imaging?
Increases image noise due to backscatter.
How is the spatial resolution of direct exposure film compared to intensifying screens?
Direct exposure film has higher spatial resolution.
Why should films not be slid into cassettes?
To prevent scratching and damaging the screen.
What material is preferred for cassette front covers in fluoroscopy?
Carbon fiber.
How should film be removed from a cassette?
By rocking the cassette on its hinge.
What is the K-shell binding energy of tungsten?
69 keV.
What material can be used to reduce patient exposure in CT tables?
Carbon fiber.
Why is yttrium used in radiographic intensifying screens?
It has a high atomic number, enhancing x-ray absorption.
Matching film sensitivity to the color of light emitted by the screen.
spectral matching
What effect does high-speed screen have on image quality?
Increases noise and reduces spatial resolution.
How should screens be cleaned?
With mild soap and water, avoiding abrasives.
What is the consequence of a warped cassette?
Poor screen-film contact and image quality loss.
What material in screens emits yellow-green light?
Zinc cadmium sulfide.
What is the benefit of using thulium-activated phosphors?
Blue light emission.
Why is gadolinium commonly used in screens?
High atomic number and efficient light emission.
What is the primary purpose of radiographic intensifying screens?
What is the primary purpose of radiographic intensifying screens?
What is the advantage of rare earth screens over calcium tungstate?
Higher conversion efficiency.
What is the advantage of rare earth screens over calcium tungstate?
Higher conversion efficiency.
How does a thicker phosphor layer affect screen speed?
Increases screen speed.
What property of screens is generally unaltered by temperature?
Detective quantum efficiency.
How does high temperature affect intensifying screens?
Decreases intensification factor (IF).
What phosphor layer thickness is used for fine-detail screens?
Thin layers for higher spatial resolution.
What is quantum mottle influenced by?
Higher conversion efficiency and fast screens.
What is the purpose of a cassette back cover’s high atomic number?
Reduces backscatter.
How does a thicker reflective layer affect screen performance?
Increases efficiency but blurs images.
What effect does large crystal size have on resolution?
Decreases spatial resolution.
Why are lanthanum and gadolinium used in intensifying screens?
High atomic numbers for better x-ray absorption.
What is the typical spatial resolution of a very fast screen?
Around 7 lp/mm.
How is image detail related to screen speed?
Higher screen speed reduces detail.
What is the relationship between intensification factor and spatial resolution?
Higher IF generally reduces spatial resolution.
