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101 Cards in this Set
- Front
- Back
What are the 4 Radiographic Image Properties?
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1. Density
2. Contrast 3. Resolution 4. Distortion |
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Define DENSITY.
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The overall degree of BLACKNESS on the film.
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The overall degree of BLACKNESS on the film is the definition of what radiographic image property?
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Density
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If the density is too low, how does the film look?
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underexposed, thus very light and white
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if there is high density, how does the film look?
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it is overexposed and appears darker.
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what property of a radiographic image allows one to say "this film is too light or that one is too dark?"
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Density
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what are the 2 primary controlling factors for DENSITY?
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Miliamperage (mA) and Exposure Time (sec)
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Miliamperage (mA) and Exposure Time (sec) are primary controlling factors for what radiographic property?
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DENSITY
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What is the equation for Total Exposure?
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mA x sec = mAs = Total exposure
aka miliamperage times sec = total exposure |
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mA x sec = ?
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Total Exposure
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as long as mAs is equal, what else will also be equal?
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density
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T/F: as long as mAs (= miliamerage x exposure time) is equal, film density will also be equal.
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T
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Ideal Exposure is what exposure time?
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0.5 sec
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1/2 of ideal exposure is what exposure time?
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0.25 sec
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What does LATITUDE describe?
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The Range of exposures that make a suitable radiograph.
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The Range of exposures that make a suitable radiograph describes what concept?
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Latitude
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how is density effected by kilovoltage?
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increases with kVp
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how is density effected by object size?
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decreased with thickness. if you go through something really THICK it will turn out pretty white = radiopaque
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how is density effected by developing time?
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increases with time
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how is density effected by developing temperature?
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increases with temperature.
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how is density effected by fixing time?
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decreases with overFixing
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how is density effected by TFD (tube film distance)?
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decreased with TFD
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how is density effected by film?
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increases with speed
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how is density effected by screens?
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increases vs. non-screen
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how is density effected by PSP scanner settings?
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mathematical adjustment
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name some other factors that influence density:
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kilovoltage, object size, developing time, developing temperature, fixing time, tube-film distance (TFD), film screens, PSP scanner settings
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CONTRAST is defined as?
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The difference in densities btwn adjacent areas of a radiograph or The range of densities from white to black.
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The difference in densities btwn adjacent areas of a radiograph is the definition of what property?
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CONTRAST
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The range of densities from white to black is a definition of what property?
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contrast
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what is the primary controlling factor for CONTRAST?
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kVp (kilovoltage peak)
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why is kVp the controlling factor for contrast?
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bc an x-ray beam with HIGH ENERGY (kVp) penetrates all tissues more evenly, giving LESS CONTRAST.
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what specialty LOVES high kVp? (less contrast)
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periodontists. low contrast = little steps of contrast.
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is High contrast is associated with short or long scale?
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high contrast = short scale
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Long scale is associated with what type of contrast?
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low contrast = long scale
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Detecting caries is easier with what type of contrast?
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High contrast = short scale
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T/F: Low Contrast = High kVp = Long scale contrast = Periodontists preferred.
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T
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T/F: High Contrast = Low kVp = Short scale contrast = good for detecting Caries
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T
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Overall GRAYNESS or Dull film quality is due to what qualities?
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High kVp, long scale, low contrast
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Overal CRISPNESS or Bright Quality to film is due to what quality?
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Low kVp, short scale, high contrast
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What scale has MANY shades of gray?
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Long scale (high kVp, low contrast)
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small differences exist btwn steps describes what type of contrast?
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LOW contrast (long scale, high kVp)
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what type of kVp produces low contrast bc all thicknesses are penetrated more EVENLY due to the high engery of xrays?
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High kVp
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HIGH CONTRAST has smaller or larger differences existing btwn steps?
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Larger differences
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Does high contrast of more or fewer shades of gray? and what type of scale is this?
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fewer, short scale
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T/F: a LOW kVp produces High Contrast bc the thicker steps stop all of the lower penetrating xrays produced by the lower energy
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T
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70 kVp is ideal. T/F
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T
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50 kVp is High contrast. T/F
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T
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90 kVp is High contrast. T/F
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F. Low contrast
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what is the purpose of CONTRAST?
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to bring out DETAIL
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HIGH contrast = better caries detection. T/F?
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T
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T/F: high contrast better for caries detection. low contrast better for perio desiease (bone loss) eval.
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T
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Fog affects contrast. T/F
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T
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how is contrast improved?
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by the elimiation of FOG
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eliminating FOG improves what?
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contrast
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the standard diameter xray beam to decrease FOG is what?
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2.75 inch
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compton scatter causes FOG. t/f
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T
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how do you eliminate compton scatter?
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metal grids or make the beam very small.
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for NBDE, what is the diamter of the beam to decrease FOG?
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2.75 inch diameter
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RESOLUTION is defined as what?
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the ability to distinguish btwn 2 closely spaced points.
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the ability to distinguish btwn 2 closely spaced points defines what?
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resolution
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what are the primary controlling factors of Resolution (the geometric ones)?
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1. focal spot size
2. object film distance (OFD) 3. tube film distance (TFD) |
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what are the primary controlling factors of resolution (the non-geometric one)?
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1. film grain size
2. patient/tube/film motion |
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strip + space =
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line pair
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measurement of resolution can be done by using resolution plate which is constrcuted of alternating lead strips and what?
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adjacent spaces of equal width
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what are the units of resolution?
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line pairs/ milimeter
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the human eye can only resolve ______ unmagnified in ideal situations.
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8-10 line pairs/mm
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PSP plates provide 7 line pairs which when magnified creates a building block pattern or pixelated appearance which demonstrates the limits of the imaging system. T/F
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T
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the D-speed intraoral film is how many lp?
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15 line pairs/ mm
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digital radiography image receptor is how many lp?
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10 line pairs/ mm
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the pan/ceph film (used with screens) is how many lp?
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2 line pair / mm
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what is PENUMBRA?
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the area of UNSHARPNESS in the projected shadow of an object
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the area of UNSHARPNESS in the projected shadow of an object is defined as what?
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PENUMBRA
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T/F if you have a LARGE focal spot will your penumbra be more or less?
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more
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a small focal spot = less penumbra. t/f
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t
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a 16 inch TFD is known as the Long cone technique. and creates large penumbra. t/f
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f. 16 inch TFD is the long cone technique but it creates small penumbra
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what can create a large penumbra?
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8 inch TFD = short cone technique or increased OFD (paralelling technique)
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decreased OFD (bisecting technqiue) creates what size of penumbra?
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small
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E speed film = faster speed, larger crystals, less radiation to expose. t/f?
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t
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faster speed, larger crystals, less radiation to expose describes what type of film?
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E Speed film
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D speed film = slower speed, smaller crystals, more radiation to expose. t/f?
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t
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slower speed, smaller crystals, more radiation to expose describes what type of film speed?
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D speed film
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t/f: points of information are dispersed more widely by the fluorescence of the intesifying screen crystals, resulting in unsharpness.
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t
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film is exposed by both radiation (xray) and visible and UV light (fluorescence) t/f
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t
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miscellaneous factors affecting resolution include ?
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patient motion (blurring), film movement (blurring), xray tube motion (increase the effective focal spot size & thus penumbra)
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who invented the PARALELLING technique, the breaksystem in the elevator and killed himself later?
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KELLS
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Distortion describes what?
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The image should be the same size and shape as the object
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size distortion = what?
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magnification
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size distortion = magnification. t/f
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t
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shape distortion = distortion. t/f
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t
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what are the primary controlling factors of magnification? (they also control sharpness)
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geometric factors: 1. OFD
2. TFD |
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if image size is larger than object this =
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magnification
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if you have a SMALL OFD what type of magnification will you get?
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less
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less magnification results from smaller ofd. t/f
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t
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greater magnification results from what type of OFD?
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larger ofd
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long TFD results in what type of magnification
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reduced magnification
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short TFD results in what type of magnification?
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increased magnification
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increased magnification results from what type of TFD?
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short Tube film distance and LARGE object film distance
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distortion is controlled by what primary factors?
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angular relationship btwn :
TEETH FILM BEAM |
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elongation distortion occurs when?
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insufficient beam angulation. image is LONGER than objectF
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FORESHORTENING distortion occurs when?
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when there is excessive beam angulation. image is SHORTER than object
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the 4 image properties of radiographs are?
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DENSITY
CONTRAST RESOLUTION DISTORTION |