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What is the difference between adjacent densities within the radiographic image?
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What is the primary controlling factor for contrast?
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Stack #132647
| Question | Answer |
|---|---|
| What is the difference between adjacent densities within the radiographic image? | radiographic contrast |
| What is the primary controlling factor for contrast? | KVP |
| What are the two types of contrast seen in medical radiography? | Long scale (low contrast), Short scale (high contrast) |
| Which scale of contrast has many shades of gray? | Long scale (low contrast) |
| Which scale of contrast has few shades of gray with many black and white images? | Short scale (high contrast) |
| Which of the two types of contrast exhibit wide exposure latitude? | Long scale contrast |
| Which of the two types of contrast is a product of low KVP? | Short scale contrast |
| What factors compose radiographic contrast? | Image receptor (film) contrast and subject contrast |
| What influences image receptor (film) contrast? | Characteristics of the film and processing |
| What determines subject contrast? | size, shape, and attenuating characteristics of the material being irradiated |
| Which of the 2 contrast factors should be standardized? | Image receptor (film) contrast |
| What effect do grids have on contrast? | improves contrast by removing scatter before it reaches the film which results in a shorter scale of contrast |
| how does increasing filtration affect contrast? | Contrast is decreased slightly because filtration increases the average photon energy of the beam |
| How does tighter collimation affect contrast? | tighter collimation reduces the number of photons available, thus reducing the amount of scatter and increasing contrast (shortens the scale of contrast) |
| How does mas affect contrast? | Mas alters density of image and therefore affects contrast |
| What is different degrees of absorption in adjacent tissues that result in image contrast? | differential absorption |
| How does KVP relate to differential absorption? | Differential absorption increases as the KVP is decreased; conversely, as KVP increases, more photons pass through and differential absorption decreases |
| What change in KVP is needed to make a visible change in contrast? | 4-12% |
| When making contrast changes on a radiograph, what changes in KVP should be made? | Changes should be made in increments of 8 or 15% |
| What is the overall blackening of the film from the black metallic silver deposited in the emulsion? | radiographic density (optical density) |
| What is the ratio of light incident on the film to amount of light transmitted through the film? | radiographic density (optical density) |
| What is the controlling factor of density? | Mas |
| What factors secondarily influence density? | KVP, distance, beam restriction, anatomic part, grid, film/screen combination, processing, anode heel affect |
| How does KVP affect density? | Directly, as KVP increases density increases because penetrability increases so more photons are reaching the IR |
| Why should KVP not be used to control density? | changing KVP also changes contrast |
| How do intensifying screens affect density? | As the speed of the intensifying screen increases, density increases |
| How does increasing grid ratio affect density? | as grid ratio increases, density decreases because grids absorb scatter that would otherwise reach the image receptor |
| What effect does SID have on density? | As SID increases, density decreases and vice versa (according to the inverse square law) |
| What effect does doubling the SID have on density? | Density is reduced to 1/4 |
| What effect does halving the SID have on density? | Density is increased 4 times |
| Do filters have an effect on density? | Because filtration alters beam intensity, density decreases slightly with increases in filtration |
| What percent change in MAS makes a visible difference in density. | 30% |
| How does beam restriction affect density? | It reduces the amount of scatter radiation and therefore, reduces the overall density of the image. |
| How does tissue thickness affect density? | There is an inverse relationship; as tissue thickness, average atomic number, and/or tissue density increases, radiographic density decreases |
| Because of the anode hill effect, density is less at which end of the x-ray beam? | Anode (because of absorption of x-rays by the "heel of the anode") |
| Which formula should be used to maintain density when making distance changes? | Density maintenance formula: MAS1/MAS2=D1(D1)/D2(D2) |
| How does film processing affect density? | Density increases as developer temperature, immersion time, or replenishment rates increase: contaminated developer will decrease density |
| What is considered the useful range of optical densities? | 0.25 to 2.5 |
| What is the sharpness of the structural lines as recorded in the radiographic image? | recorded detail |
| What is the ability to image an object with accuracy? | resolution also called recorded detail |
| What are some alternate terms for resolution? | detail, sharpness, definition and resolving power |
| What term means the misrepresentation of the size or shape of a structure recorded in the radiographic image? | distortion |
| What are the two types of distortion? | size and shape |
| What is the enlargement of the recorded image as compared to the actual size of the structure? | size distortion |
| What are the two factors that control size distortion (magnification)? | SID and OID |
| How does SID affect size distortion? | As SID increases, size distortion decreases |
| How does OID affect size distortion? | As OID increases, size distortion increases |
| What is the misrepresentation (elongated or foreshortened) of the shape of the structure recorded as compared to the actual shape of the structure? | shape distortion |
| What is the enlargement of the recorded image as compared to the actual size of the structure? | magnification |
| What formula is used to calculate size distortion? | MF = SID/SOD (MF=magnification factor) |
| What is foreshortening of an object? | foreshortening projects the object so it looks shorter than it really is |
| What factor causes foreshortening of the radiographic image? | misalignment of the part |
| What is elongation of an object? | elongation projects the object so it appears to be longer than it really is |
| What factors cause elongation of an object? | misalignment of the tube or film |
| How can distortion be reduced? | By proper alignment of the tube, part and film (centering, keeping object parallel with fim and as close as possible |
| How is resolution measured? | By using a resolution grid, resolution is measured in lines per millimeter (lp/mm) |
| How does OID affect recorded detail? | OID is inversely related to recorded detail. Recorded detail improves as OID decreases |
| How does SID affect recorded detail? | SID is directly proportional to recorded detail. As SID increases, recorded detail increases and vice versa. This is because shorter SID's causes an increase in magnification, thus causing a decrease in recorded detail |
| What is the unsharpness that is an inherent part of every radiographic image due to the position and shape of anatomic structures within the body? | inherent object unsharpness |
| What is the region of the anode target where electrons interact to produce x-rays? | focal spot |
| How does the focal spot size affect recorded detail? | There is an increase in recorded detail as focal spot size decreases |
| What is the rate at which x-ray energy is transformed into light in an intensifying screen? | conversion efficiency |
| What refers to the random nature in which x-rays interact with image receptor and occurs with the use of high speed screens with very low mas and high KVP and causes a grainy appearance of the image? | quantum mottle |
| What is the loss of radiographic quality caused by movement of the patient or x-ray tube during exposure? | motion blur |
| How can a radiographer reduce motion blur? | Use the shortest possible exposure time; give proper breathing instructions; use restraining devices; use a large SID; use a small OID |
| What is most often the cause of motion blur? | patient motion; motion of the x-ray tube is not a problem |
| What is the absorption of x-rays in the heel of the anode which results in decreased x-ray intensity of the anode side of the central ray? | heel affect |
| What is the imperfect unsharp shadow caused by size of the focal spot (replaces the terms penumbra and geometric unsharpness)? | focal spot blur |
| Changing peak KVP by what percentage will have the same effect on density as doubling the MAS or halving the MAS? | 15% |
| Increasing or decreasing the contrast does what to density? | density remains the same |
| The 15% rule can be used to do what? | increase/decrease density and maintain density while increasing or decreasing contrast |
| What states that the blackening on the film remains constant as long as MAS remains the same and usage of mA and time combinations? | Reciprocity Law |
| What is the exception to the Reciprocity Law? | Extreme exposure times (more than 10s or less than 10ms with use of intensifying screen |
Created by:
quietone055
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