| Flap 1 |
 |
|
| Flap 2 |
|
|
| 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 |
