Concepts of Radiographic Image Quality
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| Resolution | the ability to image two separate objects and visually detect one from another
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| spatial resolution | ability to image small objects that have high subject contrasts (ex. bone/tissue)
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| contrast resolution | ability to distinguish anatomic structure with similar subject contrast. (ex. kidneys/liver)
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| Recorded detail | the degree of sharpness of structural lines on a radiograph
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| visibility of detail | ability to visualize recorded detail when contrast/density are optimal.
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| Noise | undesirable fluctuation in optical density of the image
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| film graininess | randomness in distribution and size of silver-halide crystals in the emulsion
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| structure mottle | randomness in distribution and size of phosphors in the intensifying screen
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| quantum mottle | randomness with which xray photons interact with Ir.
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| things to reduce quantum mottle: | slow speed screen, high mAs, low kVp BUT this will all add to increased patient dose
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| Speed | the ability of an xray film to respond to an xray exposure
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| Fast IR has which characteristics? | high noise, low resolution, less patient dose.
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| Slow IR has which characteristics? | low noise, high resolution, high patient dose.
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| Sensitometry | the study of the relationship between xray intensity and blackness on a processed radiograph.
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| Toe side of characteristic curve | underexposed or low exposure. Appears White.
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| Shoulder portion of characteristic curve | overexposed or higher exposure. Appears Black.
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| Straight line portion of characteristic curve | diagnostic range.
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| Optical Density | degree of blackening on the image.
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| Useful range of optical density: | .25-2.5
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| Contrast | the differences in adjacent densities
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| high contrast characteristics: | large differences in OD; black and white image
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| low contrast characteristics: | small differences in OD; lots of grey shades.
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| Latitude | the range of exposures over which an IR responds.
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| Wide latitude: | more horizontal, low contrast, long scale, many shades of grey. More room for technique
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| Narrow latitude: | more vertical, high contrast, short scale, black and white. Less room for technique.
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| What will longer development/ higher development temperature do to the image? | faster speed, increased fog, lowers contrast
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| Magnification | images on radiograph are larger than the object
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| The reduce magnification we: | inc. SID; dec. OID
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| Magnification Factor Formula | Image Size/ Object Size = SID/ SOD
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| Distortion | unequal magnification of different portions of the same object.
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| Elongation | object appears longer than it really is. Caused by angling tube or IR
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| Foreshortening | object appear shorter than it really is. Caused by angling the object/part.
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| Focal Spot Blur is greatest on which side? | Cathode side
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| What 3 things contribute to FSB? | large EFS, dec. SID, inc. OID
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| Focal Spot Blur Formula | SOD/ OID = EFS/FSB
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| What can we do to decrease FSB? | inc SID, dec. OID, use small FSS.
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| What are the 5 factors that affect subject contrast? | Patient Thickness, tissue mass density, atomic number, object shape, and kVp
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| Motion Blur | caused by movement of the patient or movement of the xray tube during an exposure.
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| 4 Things to reduce motion blur | short exposure time, restraining devices, large SID, small OID
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| What are the 3 things that primarily effect scatter? | kVp, field/film size, and part/patient thickness.
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| More scatter = | more matter
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| Increasing kVp will do what to scatter, density, contrast and patient dose? | increase scatter, increase density, decrease contrast, and decrease patient dose.
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| Increase film size will do what to scatter, density, contrast and patient dose? | increase scatter, increase density, dec. contrast, and increase patient dose.
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| Increase in part thickness will do what to scatter, density, contrast and patient dose? | increase scatter, decrease density, decrease contrast and increase patient dose.
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| For every change in thickness of 4cm we must adjust mAs how? | by a factor of 2
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| What are the two main reasons we restrict the beam? | reduce patient dose and increase contrast.
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| What are the two devices that reduce the amount of scatter reaching the film? | beam restricting devices and grids
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| What is the total filtration for xray tubes operating at a kVp of <50 kVp? | .5 mm Al Eq
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| what is the total filtration for xray tubes operating at kVp of 50-70 kVp? | 1.5. mm Al Eq
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| what is the total filtration for xray tubes operating at kVp of >70 kVp? | 2.5 mm Al Eq
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| What is the purpose of a grid? | To reduce the amount of scatter reaching the IR
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| Where is the grid placed? | between the patient and the IR
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| When do we use grids? | when a body part exceeds 4 in. or if the kVp is greater than 60.
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| Grid Ratio Formula | h/D- height of grid/ thickness of interspace material or distance between lead strips.
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| A higher grid ratio will do what for scatter clean up? | Increase the scatter clean up
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| Grid Frequency | the number of lead lines or grid lines per unit of length.
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| Gride Frequency Formula | 10,000 um per cm/ (T+D)um per line pair.
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| As the lead content of the grid increases what happens to the ability of the grid to remove scatter and what happens to contrast? | Increases ability to remove scatter and makes contrast better.
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| Contrast Improvement Factor | how well the grid does at improving image contrast.
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| Contrast Improvement Factor formula: | contrast w/ grid / contrast without grid
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| Bucky Factor | how much an increase in technique will be required compared to a non-grid exposure
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| Bucky Factor formula | incident remnant radiation/ transmitted radiation forming image.
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| Increase in bucky factor will mean what for technique and patient dose? | increase in technique and increase in patient dose.
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| high the grid ratio means what for bucky factor? | higher the bucky factor
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| t/f? high ratio grids have less positioning latitude than low ratio grids? | TRUE
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| Off level grid error | cutoff across entire image. From tube being angled or grid crooked
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| Off Center grid error | cutoff across entire image. CR isn't perpendicular to the center of the grid
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| Off Focus grid error | cutoff towards the edge of the image. When the grid is used with an SID out of focal range
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| Upside Down grid error | cutoff towards the edge. When the grid is place upside down.
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| What is an alternative to grid use? | air gap technique.
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| what is the conversion factor for a 5:1 grid? | 2
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| what is the conversion factor for no grid? | 1
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| what is the conversion factor for a 16:1 grid? | 6
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| what is the conversion factor for a 10:1 grid? | 5
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| what is the conversion factor for a 12:1 grid? | 5
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| what is the conversion factor of an 8:1 grid? | 4
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| what is the conversion factor of a 6:1 grid? | 3
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| Name the 4 main parts of radiographic film | base, emulsion, adhesive layer, and overcoat
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| Base of film | foundation of xray film. Provides structure
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| Emulsion of film | heart of xray film where the xray gets created
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| Adhesive layer of film | lies between the emulsion and base
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| Overcoat of film | encloses the gelatin in the emulsion and protects the entire film from damage
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| What is the emulsion of film composed of? | mixture of gelatin and silver-halide crystals
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| What are the shapes of silver halide crystals? | tabular, cubic, octahedral, polyhedral or irregular.
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| What is film contrast affected by? | the number and size of the crystals
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| What is the film speed affected by? | the number of crystals, size of crystals and emulsion.
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| Crossover | when light is emitted by an intensifying screen and it exposes the adjacent emulsion as well as on the emulsion on the other side of the base.
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| Blue sensitive film is made of what and goes with which light? | Calcium tungstate/rare earth phosphors. Amber safelight
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| Green sensitive film is made of what and goes with which light? | rare earth and red safelight.
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| Heat and humidity will do what on the film? | increase fog; decrease contrast
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| storage temp should be what for film? | lower than 68 deg. F
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| optimal humidity for storage of film? | 40-60%
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| optimal storage for film | cool, dry, climate controlled envionment
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| shelf life of film | 30-45 days
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| Latent Image | invisible image, present after exposure.
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| Manifest image | visible image, occurs after image is processed.
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| Step 1 of latent image formation in film | The xray/light photon interacts with a halide. (Br or I)and produces a photoelectron.
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| Step 2 of latent image formation in film | The photoelectron migrates to the sensitivity center and becomes trapped.
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| Step 3 of latent image formation in film | The sensitivity center becomes negative and attracts silver ions.
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| Step 4 of latent image formation in film | The silver ions neutralize the sensitivity center
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| What are the 4 lays of intensifying screens? | protective coating, phosphor layer, reflective layer and base.
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| Where does the protective layer in an IS lie and what does it do? | layer closest to the film. It makes the screen resistant to damage from handling. Eliminates static build up and provides a durable/cleanable base.
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| Phosphor layer of an IS | active layer that emits light when stimulated by xrays. Composed of calcium tungstate and rare earth phosphors
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| Why dowe use rare earth phosphors? | less pt. dose, decreased thermal stress on tube and less shielding for xray rooms.
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| Reflective Layer of IS | intercepts light that was directed elsewhere and redirects it towards the film. Made of titanium oxide or magnesium oxide. Makes the Is more effective.
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| How is light emitted from an IS? | isotropically
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| Base of an IS | mechanical support for phosphor layer. Made from polyester.
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| Luminescence | any material that emits light in response to outside stimulation
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| What are the two types of luminescence? | fluorescence and phosphorescence
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| Fluorescence | when visible light is emitted only when a phosphor is stimulated. Desirable
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| Phosphorescence | phosphor continues to glow after stimulation. Undesirable
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| Screen Speed | relative number used to identify the efficiency of the conversion of xrays to light.
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| Intensification Factor (IF) formula | Exposure required without screen/ exposure required with screen
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| Relative Screen Speed (RSS) | value given based on the amount of light produced for a given exposure.
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| Screen Speed Formula: | RSS1/RSS2 = mAs2/mAs1
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| What factors dose noise occur most often? | fast screen speed, high kVp, low mAs. but we use these techniques because it will create lower patient dose.
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| Detective Quantum Efficiency (DQE) | the percent of xrays absorbed by the screen.
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| Conversion Efficiency (CE) | the amount of light emitted for each xray absorbed.
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| Development | the process of latent image to manifest image. Changes silver ions of exposed crystals into metallic silver.
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| Reduction | process by which an electron is give up by a chemical to neutralize a positive ion.
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| Oxidation | the reaction produces an electron to expose silver halide.
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| How many components does the developer contain? | 7
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| What do developing/producing agents do in developer | produce the electron that neutralizes the silver ion to make silver.
Hydroquinone & Phenidone
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| What does Buffering Agent/ Activator do in developer? | maintains the developer in Alkaline State. Controls the pH. Causes the emulsion to swell.
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| What does the Restrainer do in developer? | Restricts the action of the developer to act only on crystals that have been exposed.
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| What does the Preservative do in developer? | Controls oxidation of the developing agent by air.
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| What does the Hardener do in developer? | controls the swelling and softening of the emulsion. Maintains uniform thickness to assist in transport.
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| What does the Sequestering Agent do in developer? | removes metallic impurities or soluble salts that act to accelerate oxidation of hydroquinone.
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| What does the Solvent do in developer? | dissolves chemicals. Uses water.
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| Chemical fog is because of? | contaminated developer
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| Radiation fog is because of? | unintentional exposure to radiation
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| How many components are in the Fixer? | 7
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| What does the Activator do in fixer? | neutralizes the developer and stops it.
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| What does the Fixing Agent do in fixer? | removed undeveloped and unexposed silver halide crystals.
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| What does the Hardener do in fixer? | stiffens and shrinks emulsion
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| What does the Preservative do in fixer? | Maintains chemical balance of the fixer?
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| What does the Buffer do in fixer? | Maintains proper pH
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| What does the Sequestering Agent do in fixer? | removes aluminum impurities
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| What does the solvent do in fixer? | dissolves other chemicals
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| Sequence of Processing film has 5 steps what are they? | Wetting, Development, Fixing, Washing, and Drying
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| What is the developer temperature? | 95 degrees
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| What is the washer temperature? | 90 degrees
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| What 3 things make up the transport system? | feed tray, entrance rollers, microswitch
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| What 3 things make up the roller subasembly? | transport rollers, master roller, planetary roller
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| What 4 things make up the transport rack subassembly? | rack, guide shoes, turnaround assembly, cross over rack.
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| What are the primary factors used to control quantity and quality? | kVp and mAs
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| What are secondary factors that control quantity and quality? | Focal spot size, SID, filtration
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| What does kVp control? | quality and quantity
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| What does mA control? | quantity.
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| What does time control? | quantity
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| What does mAs control? | quantity
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| What does distance control? | quantity
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| When do you use a small focal spot size? | when you want more detail, and smaller anatomy, because it increases patient dose.
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| How much of total filtration is inherent? | .5 mm Al Eq
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| how much of total filtration is from the variable aperature diaphragm? | 1 mm Al Eq
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| How much of total filtration is from added filtration? | 1 mm Al Eq
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| Sthenic body habitus | average
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| Hyposthenic body habitus | thin, but healthy
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| Hypersthenic body habitus | overweight/large
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| Asthenic body habitus | small, but frail
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| What will destructive pathologies do to technique? | Decrease technique because they make the part more radiolucent.
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| What will additive pathologies do to technique? | Increase technique because they make the part more radiopaque.
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| What is the controlling factor of Optical Density? | mAs- main
distance- secondary
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| What must we do to make a perceptible change in density? | mAs changes by 30%
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| What is the controlling factor of contrast? | kVp
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| What is the 5% rule? | increase kVp by 5% must decrease mAs by 30% for a perceptible change on film.
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| What is image detail (spatial resolution) controlled by? | focal spot size
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| What is contrast resolution controlled by? | kVp and mAs
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| What does a variable kVp do? | uses a fixed mAs. Short scale, high patient dose, low exposure latitude
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| What does a fixed kVp system do? | uses variable mAs and kVp stays constant. Long scale of contrast, decrease in patient dose.
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| what are the 2 types of AEC? | ionization chamber and phototimer
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| Phototimer | lies beneath the IR
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| Ionization chamber | lies between the patient and IR
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