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Intensifying Screens
unit 2
| Question | Answer |
|---|---|
| What is the purpose of an intensifying Screen? | Convert x-rays to light to shorten exposure time and reduce patient dose |
| What is one negative drawback in using an intensifying screen? | Image is slightly blured |
| From top to bottom what are the layers of the intensifying screen? | Protective coating,Phosphor,Reflective Layer & Base |
| What layer of the intensifying screen is closest to the radiographic film? | Protective coating |
| What layer of the intensifying screen helps to eliminate the buildup of static electricity? | Protective Coating |
| What layer of the intensifying screen makes the screen resistant to abrasion & Damage caused by handling? | Protective Coating |
| Which layer of the intensifying screen is the active layer of the intensifying screen? | Phosphor |
| What layer of the intensifying screen emits light during stimulation by x-rays? | Phosphor Layer |
| What was the active substance of most phosphors before 1980? | Crystalline Calcium Tungstate |
| What are the rare earth Elements? | Gadolinium,Lanthanum & Yttrium |
| What are some of the benefits of Rare Earth Screens? | Lower patient dose,less thermal stress on x-ray tube & reduced shielding in x-ray rooms |
| What is the reflective layer of the intensifying screen made of? | Magnesium oxide or Titanium Dioxide |
| What is the purpose of the reflecting layer? | intercept light headed in other directions & redirects it to the film |
| What do dyes in the phosphor of intensifying screens do? | absord light photons emitted at a large angle to the film |
| What do dyes in the phosphor of the intensifying screen do to screen speed? | reduces it a little |
| What is the material used for the base of the intensifying screen? | Polyester |
| What is the name of the material that emits light in response to some outside stimulation? | Luminescent Material or phosphor |
| What is the name of the visible light emmited in response to outside stimulation? | Luminescence |
| What is it called when visible light is emitted only while the phosphor is stimulated? | Fluorescence |
| What is it called when the phosphor contines to emit light after stimulation? | Phosphorescence |
| What is the name used for phorphorescence in an intensifying screen? | Screen Lag or afterglow |
| What are the three characteristics of inensifying screens that the radio tech is concerned with? | Screen Speed, Image noise & Spatial Resolution |
| What is intensification Factor? | ratio of the exposure required to produce the same optical density with a screen to the exposure required to produce an optical density without |
| What are the main factors that determine screen speed? | the relative number of xrays that interact with the phosphor & how efficiently x-ray energy is converted into visible light |
| What increases the IF factor? | X-ray tube potential (increasing Kvp),low temperatures |
| What decreases the IF Factor? | Excessive developing time for screen film & high temperatures |
| Do films used with sreens or direct exposure fils have thinner emulsion layers? | Screen Films |
| When does image noise appear? | High Kvp & Fast Screens |
| Why do rare earth intensifying screens have increased speed? | The percentage of xrays absorbed by the screens is higher & The amount of light emitted for each x-ray absorbed is higher |
| Does an increase in CE increase image noise? | Yes because only half the amount of xrays are required |
| Does an increase in DQE increase image noise? | No because the same number of xrays are absorbed |
| Since rare earth are faster than calcium tungstate does the noise increase? | No bc the gain in speed is due to DQE |
| What is the tearm used for how small an object can be imaged? | Spatial Resolution |
| What term refers to the ability to image similar tissues? | Contrast Resolution |
| How do you measure spatial resolution? | Number of line pairs per mm |
| How many lp/mm can the human eye resolve | 10 |
| How many lp/mm can a fast screen resolve? | 7 |
| How many lp/mm can a slow screen resolve? | 15 |
| How is the screen positioned in mammography? | in contact with the emulsion side of the film away from the xray source |
| What region of the spectrum is the sensitivity of conventional radiographic film highest? | Violet blue region |
| What does intensifying screen efficiency determine? | The amount of light that exposes the film |
| What does greater intensifying scrren efficiency mean? | more light,greater density,less radiation & greater speed |
| Whatdoes intensifying screen efficiency depend on? | Apsorption efficiency,Conversion efficiency & Emission efficiency |
| What does DQE stand for? | Detector Quantum Efficiency |
| What is DQE? | Ability of the phosphor layer to absorb xrays |
| What factors affect absorption? | Z#,Thickness of the phosphor,number of phosphor layers,density of phosphor layer & size of phosphor crystal |
| What is the DQE for Calcium Tungstate? | 20-40% |
| What is the DQE for Rare earth? | 50-60% |
| What is CE? | Quantity of light produced compared to radiation exposure |
| What is the Ce of Calcium Tungstate? | 5% |
| What is the CE of Rare Earth? | 20% |
| What is the ability of light to escape the phosphor layer and expose film? | Emission Efficiency |
| What effects emission efficiency? | Dyes in the phosphor & Reflective foil |
| Do dyes in the phosphor increase of decrease emission? | Decrease |
| Does a reflective foil decrease of increase emission? | increase |
| What factors in the intensifying screen contribute to image blur? | Light Diffusion,Crossover effect,larger crystals,thicker phosphors,reflective foils,poor film screen contact |
| What is crossover effect? | When light photons pass through film base and expose emulsion on the opposite side |
| What reduces crossover effect? | Adding dye to the base,only one intensifying phosphor,single emulsion film, no reflective foil, dye added to phosphor |
| What is the crossover control layer? | Dye added to the base |
| What is the Rs of Calcium Tungstate? | 1oo |
| What is the rs of Rare Earth? | 200 |
| How can you test film screen contact? | Wire mesh |
| How do you store cassettes? | Vertically on edge |
| what cassettes are used for Scoliosis? | Gradient Cassettes |
| When using a gradient cassette for scoliosis where would you position the fast end of the cassette? | Hip |
| What type of cassette is used for chest radiography? | Assymetric |
| What makes an assymetric cassette different from a regular cassette? | front screen is slower (2 emulsions) |
| Who used edisons screen for a hand radiograph in 1896? | Michael Pupin |
| What may be used instead of the reflective layer in the intensifying screen? | Light absorbing Layer |
| What type of light does Calcium Tungstate emit? | Violet Blue |
| What type of light does Rare Earth emit? | Green-blue |
| What will happen to the image if the film is not spectrally matched? | It will be light |
| What systems are used to classify screen speed? | If,Descriptive rating & Rs #s |
| What is the RS determined by? | Film & Screen speed together |
| How can speed be doubled? | Increasing screen speed or increasing film speed |
| What are the intensifying phosphors that are not made from rare earth? | Calsium tungstate,Zinc Sulfide,Barium Platinocyanide & Barium lead sulfide |
Created by:
Sukioshii