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Intensifying Screens

Chap 15 Bushong - Study Guide

QuestionAnswer
Identify the layers of the screens Base; Reflective layer; phosphor; protective coating
Explain the function of Phosphor Active layer
Explain the function the base layer Foundation that is radiolucent
Explain the function of the reflective layer Redirects light
Explain the function of the protective layer Protects from abrasions in handling
What is the function of the phosphor? Active layer; emitts light during x-ray; converts x-ray beam to light
Name the 4 characteristics of a phosphor 1. High atomic number (DQE); 2) Conversion efficiency; 3) Spectral matching; 4) Afterglow needs to be minimal
What is Quantum Detection Efficiency? Absorbtion
Define Spectral Matching Blue - Blue; Green - Green
List the material commonly used as screen phosphors Historically Calcuim Tunstate (blue light)
List the rare earth elements Gadolinuim; lanthanum; yttrium (green light)
Identify the substance that illumines in the photographic plates uses by Roentgen Barium platinocyanide
Define luminescence Any material that emits light in response to outside stimulation (x-ray or fast moving electrons)
Compare a screen with a reflective layer to one with out this layer Reflective layer increases speed and sensitivity
Identify which electrons are involved in luminescence Outer shell
What is the difference between FLUORESCENCE and PHOSPHORESCENCE? Fluorescence is light emitting only during stimulation; Phosphorescence is after glow
State the formula used to find the intensification factor IF = Exposure required without screens OVER exposure required with screens. Always > 1
Explain the intensification factor Magnitude of dose reduction
Give the approximate numerical speed values assigned to screens Rare earth screens are 2 times as fast as calcium tungstate
Explain the relationship of screen speed to radiographic density Fast screen speed increases optical density
Explain the term RESOLUTION Spatial and Contrast - Spatial - you can see small structures clearly; Contrast - able to differenciate between similar tissues
Explain the test done for resolution Line pair test pattern - direct exposure to screen
Describe the colors emitted by screen crystals Calcium Tunstate - blue; Rare Earth is green
Explain the relationship of screens and film Spectral Matching; Screen film compatability (blue-blue; green- green)
Define CASSETTE Rigid, light tight film holder
Explain how backscatter is prevented in a cassette Back side has higher atomic number
Compare DIRECT exposure to SCREEN-FILM exposure Direct - sharp resolution; more patient dose; Screen Film - Less sharp in resolution but less patient dose
What is the principal advantage of rare earth screens to patient exposure, dose and x-ray tube life? Less patient dose; increases x-ray tube life because less technique can be used
Compare the K-shell absorption levels and light emissions for calcium tungstate and rare earth screens Rare earth absorbs 5 times that of tungston
Compare the converstion efficiencies of calcium tungstate and rare earth screens Rare earth is 4 times better
Created by: ClassyLady on 2007-08-27



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