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Stack #132647

QuestionAnswer
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 on 2008-05-03



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