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Exposure Final

Concepts of Radiographic Image Quality

QuestionAnswer
Resolution the ability to image two separate objects and visually detect one from another
spatial resolution ability to image small objects that have high subject contrasts (ex. bone/tissue)
contrast resolution ability to distinguish anatomic structure with similar subject contrast. (ex. kidneys/liver)
Recorded detail the degree of sharpness of structural lines on a radiograph
visibility of detail ability to visualize recorded detail when contrast/density are optimal.
Noise undesirable fluctuation in optical density of the image
film graininess randomness in distribution and size of silver-halide crystals in the emulsion
structure mottle randomness in distribution and size of phosphors in the intensifying screen
quantum mottle randomness with which xray photons interact with Ir.
things to reduce quantum mottle: slow speed screen, high mAs, low kVp BUT this will all add to increased patient dose
Speed the ability of an xray film to respond to an xray exposure
Fast IR has which characteristics? high noise, low resolution, less patient dose.
Slow IR has which characteristics? low noise, high resolution, high patient dose.
Sensitometry the study of the relationship between xray intensity and blackness on a processed radiograph.
Toe side of characteristic curve underexposed or low exposure. Appears White.
Shoulder portion of characteristic curve overexposed or higher exposure. Appears Black.
Straight line portion of characteristic curve diagnostic range.
Optical Density degree of blackening on the image.
Useful range of optical density: .25-2.5
Contrast the differences in adjacent densities
high contrast characteristics: large differences in OD; black and white image
low contrast characteristics: small differences in OD; lots of grey shades.
Latitude the range of exposures over which an IR responds.
Wide latitude: more horizontal, low contrast, long scale, many shades of grey. More room for technique
Narrow latitude: more vertical, high contrast, short scale, black and white. Less room for technique.
What will longer development/ higher development temperature do to the image? faster speed, increased fog, lowers contrast
Magnification images on radiograph are larger than the object
The reduce magnification we: inc. SID; dec. OID
Magnification Factor Formula Image Size/ Object Size = SID/ SOD
Distortion unequal magnification of different portions of the same object.
Elongation object appears longer than it really is. Caused by angling tube or IR
Foreshortening object appear shorter than it really is. Caused by angling the object/part.
Focal Spot Blur is greatest on which side? Cathode side
What 3 things contribute to FSB? large EFS, dec. SID, inc. OID
Focal Spot Blur Formula SOD/ OID = EFS/FSB
What can we do to decrease FSB? inc SID, dec. OID, use small FSS.
What are the 5 factors that affect subject contrast? Patient Thickness, tissue mass density, atomic number, object shape, and kVp
Motion Blur caused by movement of the patient or movement of the xray tube during an exposure.
4 Things to reduce motion blur short exposure time, restraining devices, large SID, small OID
What are the 3 things that primarily effect scatter? kVp, field/film size, and part/patient thickness.
More scatter = more matter
Increasing kVp will do what to scatter, density, contrast and patient dose? increase scatter, increase density, decrease contrast, and decrease patient dose.
Increase film size will do what to scatter, density, contrast and patient dose? increase scatter, increase density, dec. contrast, and increase patient dose.
Increase in part thickness will do what to scatter, density, contrast and patient dose? increase scatter, decrease density, decrease contrast and increase patient dose.
For every change in thickness of 4cm we must adjust mAs how? by a factor of 2
What are the two main reasons we restrict the beam? reduce patient dose and increase contrast.
What are the two devices that reduce the amount of scatter reaching the film? beam restricting devices and grids
What is the total filtration for xray tubes operating at a kVp of <50 kVp? .5 mm Al Eq
what is the total filtration for xray tubes operating at kVp of 50-70 kVp? 1.5. mm Al Eq
what is the total filtration for xray tubes operating at kVp of >70 kVp? 2.5 mm Al Eq
What is the purpose of a grid? To reduce the amount of scatter reaching the IR
Where is the grid placed? between the patient and the IR
When do we use grids? when a body part exceeds 4 in. or if the kVp is greater than 60.
Grid Ratio Formula h/D- height of grid/ thickness of interspace material or distance between lead strips.
A higher grid ratio will do what for scatter clean up? Increase the scatter clean up
Grid Frequency the number of lead lines or grid lines per unit of length.
Gride Frequency Formula 10,000 um per cm/ (T+D)um per line pair.
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.
Contrast Improvement Factor how well the grid does at improving image contrast.
Contrast Improvement Factor formula: contrast w/ grid / contrast without grid
Bucky Factor how much an increase in technique will be required compared to a non-grid exposure
Bucky Factor formula incident remnant radiation/ transmitted radiation forming image.
Increase in bucky factor will mean what for technique and patient dose? increase in technique and increase in patient dose.
high the grid ratio means what for bucky factor? higher the bucky factor
t/f? high ratio grids have less positioning latitude than low ratio grids? TRUE
Off level grid error cutoff across entire image. From tube being angled or grid crooked
Off Center grid error cutoff across entire image. CR isn't perpendicular to the center of the grid
Off Focus grid error cutoff towards the edge of the image. When the grid is used with an SID out of focal range
Upside Down grid error cutoff towards the edge. When the grid is place upside down.
What is an alternative to grid use? air gap technique.
what is the conversion factor for a 5:1 grid? 2
what is the conversion factor for no grid? 1
what is the conversion factor for a 16:1 grid? 6
what is the conversion factor for a 10:1 grid? 5
what is the conversion factor for a 12:1 grid? 5
what is the conversion factor of an 8:1 grid? 4
what is the conversion factor of a 6:1 grid? 3
Name the 4 main parts of radiographic film base, emulsion, adhesive layer, and overcoat
Base of film foundation of xray film. Provides structure
Emulsion of film heart of xray film where the xray gets created
Adhesive layer of film lies between the emulsion and base
Overcoat of film encloses the gelatin in the emulsion and protects the entire film from damage
What is the emulsion of film composed of? mixture of gelatin and silver-halide crystals
What are the shapes of silver halide crystals? tabular, cubic, octahedral, polyhedral or irregular.
What is film contrast affected by? the number and size of the crystals
What is the film speed affected by? the number of crystals, size of crystals and emulsion.
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.
Blue sensitive film is made of what and goes with which light? Calcium tungstate/rare earth phosphors. Amber safelight
Green sensitive film is made of what and goes with which light? rare earth and red safelight.
Heat and humidity will do what on the film? increase fog; decrease contrast
storage temp should be what for film? lower than 68 deg. F
optimal humidity for storage of film? 40-60%
optimal storage for film cool, dry, climate controlled envionment
shelf life of film 30-45 days
Latent Image invisible image, present after exposure.
Manifest image visible image, occurs after image is processed.
Step 1 of latent image formation in film The xray/light photon interacts with a halide. (Br or I)and produces a photoelectron.
Step 2 of latent image formation in film The photoelectron migrates to the sensitivity center and becomes trapped.
Step 3 of latent image formation in film The sensitivity center becomes negative and attracts silver ions.
Step 4 of latent image formation in film The silver ions neutralize the sensitivity center
What are the 4 lays of intensifying screens? protective coating, phosphor layer, reflective layer and base.
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.
Phosphor layer of an IS active layer that emits light when stimulated by xrays. Composed of calcium tungstate and rare earth phosphors
Why dowe use rare earth phosphors? less pt. dose, decreased thermal stress on tube and less shielding for xray rooms.
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.
How is light emitted from an IS? isotropically
Base of an IS mechanical support for phosphor layer. Made from polyester.
Luminescence any material that emits light in response to outside stimulation
What are the two types of luminescence? fluorescence and phosphorescence
Fluorescence when visible light is emitted only when a phosphor is stimulated. Desirable
Phosphorescence phosphor continues to glow after stimulation. Undesirable
Screen Speed relative number used to identify the efficiency of the conversion of xrays to light.
Intensification Factor (IF) formula Exposure required without screen/ exposure required with screen
Relative Screen Speed (RSS) value given based on the amount of light produced for a given exposure.
Screen Speed Formula: RSS1/RSS2 = mAs2/mAs1
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.
Detective Quantum Efficiency (DQE) the percent of xrays absorbed by the screen.
Conversion Efficiency (CE) the amount of light emitted for each xray absorbed.
Development the process of latent image to manifest image. Changes silver ions of exposed crystals into metallic silver.
Reduction process by which an electron is give up by a chemical to neutralize a positive ion.
Oxidation the reaction produces an electron to expose silver halide.
How many components does the developer contain? 7
What do developing/producing agents do in developer produce the electron that neutralizes the silver ion to make silver. Hydroquinone & Phenidone
What does Buffering Agent/ Activator do in developer? maintains the developer in Alkaline State. Controls the pH. Causes the emulsion to swell.
What does the Restrainer do in developer? Restricts the action of the developer to act only on crystals that have been exposed.
What does the Preservative do in developer? Controls oxidation of the developing agent by air.
What does the Hardener do in developer? controls the swelling and softening of the emulsion. Maintains uniform thickness to assist in transport.
What does the Sequestering Agent do in developer? removes metallic impurities or soluble salts that act to accelerate oxidation of hydroquinone.
What does the Solvent do in developer? dissolves chemicals. Uses water.
Chemical fog is because of? contaminated developer
Radiation fog is because of? unintentional exposure to radiation
How many components are in the Fixer? 7
What does the Activator do in fixer? neutralizes the developer and stops it.
What does the Fixing Agent do in fixer? removed undeveloped and unexposed silver halide crystals.
What does the Hardener do in fixer? stiffens and shrinks emulsion
What does the Preservative do in fixer? Maintains chemical balance of the fixer?
What does the Buffer do in fixer? Maintains proper pH
What does the Sequestering Agent do in fixer? removes aluminum impurities
What does the solvent do in fixer? dissolves other chemicals
Sequence of Processing film has 5 steps what are they? Wetting, Development, Fixing, Washing, and Drying
What is the developer temperature? 95 degrees
What is the washer temperature? 90 degrees
What 3 things make up the transport system? feed tray, entrance rollers, microswitch
What 3 things make up the roller subasembly? transport rollers, master roller, planetary roller
What 4 things make up the transport rack subassembly? rack, guide shoes, turnaround assembly, cross over rack.
What are the primary factors used to control quantity and quality? kVp and mAs
What are secondary factors that control quantity and quality? Focal spot size, SID, filtration
What does kVp control? quality and quantity
What does mA control? quantity.
What does time control? quantity
What does mAs control? quantity
What does distance control? quantity
When do you use a small focal spot size? when you want more detail, and smaller anatomy, because it increases patient dose.
How much of total filtration is inherent? .5 mm Al Eq
how much of total filtration is from the variable aperature diaphragm? 1 mm Al Eq
How much of total filtration is from added filtration? 1 mm Al Eq
Sthenic body habitus average
Hyposthenic body habitus thin, but healthy
Hypersthenic body habitus overweight/large
Asthenic body habitus small, but frail
What will destructive pathologies do to technique? Decrease technique because they make the part more radiolucent.
What will additive pathologies do to technique? Increase technique because they make the part more radiopaque.
What is the controlling factor of Optical Density? mAs- main distance- secondary
What must we do to make a perceptible change in density? mAs changes by 30%
What is the controlling factor of contrast? kVp
What is the 5% rule? increase kVp by 5% must decrease mAs by 30% for a perceptible change on film.
What is image detail (spatial resolution) controlled by? focal spot size
What is contrast resolution controlled by? kVp and mAs
What does a variable kVp do? uses a fixed mAs. Short scale, high patient dose, low exposure latitude
What does a fixed kVp system do? uses variable mAs and kVp stays constant. Long scale of contrast, decrease in patient dose.
what are the 2 types of AEC? ionization chamber and phototimer
Phototimer lies beneath the IR
Ionization chamber lies between the patient and IR
Created by: 671470335