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32 Cards in this Set
- Front
- Back
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1) What is film?
2) What is the base material for film? 3) What is the gel emulsion for film made out of? 4) What is the most important part? |
1) Transparent material covered with photographic emulsion.
2) Cellulose acetate and plastic 3) Silver halide crystals, silver bromide (AgBr) 4) The SILVER is the most important part. |
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1) What are silver bromide crystals?
2) What 5 things are they sensitive to? 3) What are the two types of grains? Which one is better? |
1) "Grains" that are microscopic in size.
2) Sensitive to: light, x-rays/gamma rays, heat (could degrade emulsion), moisture (could make emulsion soften), age. 3) Regular and T grain. T grain better b/c more sizes, flatter to make better image for film |
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1) What is exposure?
2) When film is exposed to the x-ray, what happens to the AgBr crystal? |
1) The act of making or exposing a radiograph.
2) AgBr + xrays = Ag+ + Br. Ag is the active ingredient |
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1) What is the latent image in the film emulsion formed by? What is the significance of Br-?
2) What arranges the Ag+ in shapes of the objects x-rayed? 3) When does the latent image exist? 4) What is differential absorption? 5) What can cause you to lose quality of the film? |
1) Ag+. Br- has no significant role.
2) Different absorption. Some signals will be more intense than others. 3) AFTER the film is exposed, but BEFORE it's developed. 4) Different amount of absorption (attenuation) by different tissue types 5) Not processing the image on time |
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Describe the process of the x-ray hitting the film, tooth, and the differential absorption that results.
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1) Energy strikes silver bromide in the film
2) Remainder of the energy strikes tooth and sets up silver ions in the shape that it went through |
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1) What three things do you put the film through to develop the latent image? What is the function of each?
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1) Film processor
2) Developer - reduces free Ag+ ion to Ag, metallic silver. 3) Fixer (fixing solution) - hardens metallic silver on film (fixes image on plastic, archival properties for an indefinite amount of time), washes away all unexposed AgBr crystals |
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Why do you need to use a fixer to wash away undeveloped AgBr?
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Unexposed crystals would oxidize and be around the film, would degrade the overall quality of the image.
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Compare Ultra D to F speed film. What is the general rule with crystal size?
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Ultra D - conventional emulsion, get beautiful picture, but AgBr crystals need to be small to get a high resolution. They tend to be slower film - too much radiation dosage. AgBr crystals smaller = "pebble like grains"
F speed - changed the shape, flattened and larger AgBr crystals (T-grain). Benefit of a large crystal: doesn't require as much exposure, and uniform shape gives good resolution. 3-4x faster than ultra D Larger crystals = faster film = lower patient dose |
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What is the pixel image?
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The computer translating grains to an image. Image data is comprised of little boxes, graphic evaluation of film and digital images occur.
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Compare digital vs. analog film.
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Mountain is much more precise, has the same continuity. Analog mounts with irregularities in the film.
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What is a scintillator?
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Screen that allows x-ray beam to go through it. Reacts with the x-ray to produce additional photons, enhances the fiberoptics which leads to the charge couple device (CCD) under it. This enhances the x-ray so you can keep the dose down low.
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Why use a fiberoptic layer?
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1) Originally way to image a larger area to a smaller CCD
2) Now, it shields the CCD from the direct x-ray beam |
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What does the phosphor screen do?
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Maybe protects the electronics.
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What are the three properties of the developed radiograph that we need to look at?
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1) Radiographic density
2) Radiographic contrast 3) Radiograph detail (definition) |
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1) What is radiographic density?
2) If you see low density, what's happened? 3) If you see high density (super black), what's happened? 4) If you don't have good density or light, what exposure factors would you change? |
1) The degree of blackening on an x-ray film.
2) Underexposed 3) Overexposed 4) Usually time or mA (usually fixed). kVp does NOT increase darkness more as well. |
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What is radiographic contrast? What do you want it for? Do you want high or low contrast?
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Difference in densities between adjacent areas on the radiograph. Want high contrast so you can see caries. Contrast between enamel (white) and dentin (gray)
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Explain short scale and long scale contrast.
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Short scale = high contrast = low detail = high kVp
Long scale = low contrast = high detail = low kVp |
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Explain why a metallic restoration comes out so radioopaque, and why a lesion comes out so radiolucent.q
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It's very dense, few rays get through it, so few AgBr crystals exposed. Fixer washes away basically all of the AgBr.
All the x-rays go through the lesion, so all AgBr crystals exposed, produce radiolucent area. |
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Describe the relationship between subject density and radiographic density.
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A more dense subject (like a crown, amalgam) will have less radiographic density. It'll turn out white (less radiographic density).
A less dense subject (pulp tissue, caries, lesions) will have more radiographic density (turn out blacker). |
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What happens to film density and photon energy as you increase time? What happens to the film density when you double the number of photons?
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Increase time = increase density, but doesn't change the photon energy. Just increases the number of photons. Doubling the number of photons makes the film twice as dense.
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If the radiograph is too light (not dense enough), what do you do? What do you do if it's too dark?
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Too light - increase exposure time. Too dark - decrease exposure time.
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What is the controlling factor for radiographic contrast and why?
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kVp - higher kVp = less contrast because it penetrates everything evenly.
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What is radiographic detail? What is the best instrument for measuring radiographic detail?
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Sharpness of radiographic images, ability to observe fine structural lines. Phantom - has ~ 14 line pairs/mm.
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What are the 3 geometric characteristics affecting detail/definition?
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1) Radiographic image unsharpness
2) Magnification/enlargement of radiographic image 3) Distortion in shape X-rays are bouncing off different parts of the target. |
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What is the main influencing factors of detail/definition?
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1) Umbra - complete shadow/image
2) Penumbra - incomplete shadow/false image |
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Because of what 4 factors do images exhibit some penumbra?
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1) Motion - film, patient, x-ray tube
2) Focal spot size 3) Source-object-film distance 4) Film grain (AgBr) size |
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How do you minimize motion and increase detail/definition, reduce penumbra?
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1) Prevent movement of x-ray tube, patient
2) Use short exposure times |
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How does movement affect the image of a tooth?
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Increase penumbra and decreases detail, because both apical/incisal edges are recorded over an rea of film rather than a discrete spot.
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How does focal spot size affect detail/definition? What is the ideal focal spot size?
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Large focal spot = more penumbra
Smaller focal spot = less penumbra Ideal size <1 mm |
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What in the source-object-film-distance measurement gives you the best detail?
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Mix of object-film-distance being as small as possible, target-film-distance as long as possible
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Inverse square law relates what two factors?
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Intensity of radition is inversely proportional to the square of the distance
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How do you increase the target-film distance? What do you substitute for the intensity lost? When you increase the distance, divergent paths of x-rays increase the surface area, so what controls this increase?
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1) Longer PID - lower dose
2) Sub time for intensity 3) Lead collimation |
