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Exposure Unit 2
Film, Inten. Screens, and CR/DR
| Question | Answer |
|---|---|
| What type of film is only used for display and not used for image acquistion? | laser film |
| What type of film does not use an intensifying screen and is now obsolete? | direct exposure |
| what are the layers in film? | base, emulsion, adhesive layer, protective/t-coat/supercoat layer |
| what is the difference between single and double emulsion? | double emulsion layer has 2 emulsion layers and single only has 1. single emulsion film has glossy non-emulsion side and a dull emulsion side. |
| what is the function of the base of the film? | supports the image, tinted blue for preventing eye strain. |
| What is the base of the film made out of? | polyester |
| what is the emulsion layer made out of? | silver bromide (AgBr) or silver halide crystals dissolved in gelatin |
| T/F: a film's adhesive layer glues the protective coat to the emulsion. | False; adhesive layer glues the emulsion to the base |
| T/F: silver ions have a positive charge. | true |
| T/F: silver halide crystals are made of silver bromide and silver iodide | true |
| T/F: the emulsion side of a single emulsion film can be identified in a darkroom because it is glossy or shiny | false; the emulsion side is the dull side |
| T/F: As film/screen speed increases, recorded detail decreases. | True; recorded detail is the same thing as sharpness |
| T/F: all of the folling are examples of intensifying phosphors that are not made from rare earth elements: calcium tungstate, zinc sulfide, barium platinocyanide, and barium lead sulfide | true |
| T/F: If the tech uses the tech factors for a high speed film/screen but accidently used a slow speed film/screen, the image produced will be overexposed. | False; it will be underexposed. because high speed film/screen factors use low mAs, but if low mAs is used on slow speed film/screen will be underexposed. This is because slow speed film/screens use smaller crystals and won't produce enough density. |
| T/F: Rare earth phosphors have a greater conversion and absorption efficiency compared to calcium tungstate phosphors. | true |
| T/F: If films are not spectrally matched to the light emitted by the intensifying phosphor, the film will be excessively dark. | False; the film will be excessively light. |
| What does it mean by spectrally matching? | refers to correctly matching the color sensitivity of the film to the color emission of the intensifying screen. So example, use blue-sensitive film with blue light-emitting screens. |
| define latent image. | invisible image that is on the film after it was exposed to light. Hasn't been processed yet. |
| What is the Gurney-Mott theory? | exposure of the silver bromide crystals in the film emulsion by light or xray photons creates the latent image and initiates the conversion process from a latent to a manifest image |
| What must be present in the silver bromide crystal for the gurney-mott theory to occur? | sensitivity speck (sulfide contaminant) |
| When exposure/photons causes ionization of the AgBr crystals how is this represented in an equation? | AgBr + photon --> Br (neutral) + e- + Ag+ (postively charged) |
| When the trapped e- attracts to the Ag+ ions around the sensitivity speck how is this wrote into an equation? | e- + Ag+ --> Ag (black metallic silver) |
| What are the 2 major steps in film processing? | reduction and fixation |
| What happens in reduction? | adds more e- to exposed sensitivity specks and produces more black metallic silver. Unexposed crystals are not reduced to black metallic silver. |
| What happens in fixation? | neutralizes the developer & stops the reduction process. dissolves & removes unexposed/underdeveloped crystals |
| How is film speed increased? | increasing photon absorption in the emulsion layer |
| What are ways to increase film speed in the emulsion layer? | more AgBr crystals, thicker emulsion, double emulsion. |
| In general, as film speed is increased what happens to blur and recorded detail? | film speed increases; recorded detail decreases; blur increases |
| Intensifying screens are used to: a) decrease patient exposure b)increase recorded detail c)increase film latitude d)decrease contrast | A |
| What is the relationship between screen speed, light emission and patient dose? | the faster an intensifying screen is the more light is emitted for the same intensity of the exposure. As screen speed increases, less radiation is needed and patient dose decreases. |
| Which of the following is the latent image center for radiographic film? a)phosphor layer b)polyester base c)detector element d)sensitivity speck | D |
| The ability to emit light only when stimulated by xrays is known as what? a)phosphorescence b)sensitometry c)conversion efficiency d)fluorescence | D |
| Who invented the calcium tungstate intensifying screen? | Edison |
| In intensifying screens, what are the layers? | furthest from the film: base, reflecting OR absorbing layer, phosphor layer, and protective layer |
| How does using a reflective layer lower patient dose? | reflective layer reflects light back towards the film producing more density; therefore less mAs is needed and lowers pt. dose. |
| Would you use a reflective layer or absorbing layer for detail work exams? | absorbing layer, because it produces less density and uses a slower speed system. If a reflective layer was used there would be too much density. |
| Name some rare earth phosphors. | Gadolinium, Lanthanum, Yttrium |
| What is the difference between fluorescence and phosphorescence? | phosphorescence is undesirable because it continues to glow after exposed to light photons. Fluorescence only glows when exposed to light photons and then stops when exposure is over. |
| What color light does calcium tungstate emit? | violet-blue |
| What color light do RE materials emit? | green-blue |
| What does intensifying screen efficiency determine? | it determines the amount of light that exposes the film. |
| As screen efficiency increases what happens to film density? | film density increases |
| T/F: As screen efficiency increases pt. dose decreases. | True; as screen efficiency increases, speed increases and that means more density is produced and less radiation is used to produce density. |
| What is the Intensification Factor? | IF= exposure required without a screen/exposure with a screen |
| An abd. was taken with a 200RS screen at 75kV @ 50mAs. This results in the ESE of 200mR. A similar exam was taken w/o screens and resulted in ESE=6400mR. What is the IF of the film screen combination? | IF=6400/200= 32 |
| which speed system is normally used for detail and extremity work? | slow speed |
| which speed system is normally used for abd. and bucky procedures? | fast speed |
| When RS# increases, what happens to film density, patient dose and sharpness? | Increasing the RS# means using a fast speed system where less mAs is being used lowering patient dose, film density is increased because there is bigger crystals. Sharpness decreases because of the fast film speed. |
| The rad. dept. is upgrading its system from 100 to 500 speed system for CXR. If a 10 mAs was used previously what must the new mAs be with the 500 speed system? | (mAs1/mAs2)divided by (RS2/RS1) the new mAs would be 2. If 10mAs was used with the 500 speed system the image would be overexposed because 2 mAs was the new needed factor to maintain density. |
| When converting from film/screen system to a CR system how much should you adjust your tech factors? | adjust your tech factors as if converting to a 200RS#. |
| what 3 things do intensifying screens depend on? | absorption efficiency (DQE), conversion efficiency (CE), emission efficiency |
| what is DQE? | absorption efficiency; the ability of phosphor layer to absorb xrays. |
| What has a better DQE, rare earths or calcium tungstate? | rare earths |
Created by:
mokapis
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