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Exposure Final
Concepts of Radiographic Image Quality
| Question | Answer |
|---|---|
| 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 |
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