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Contrast
Ch. 29
| Question | Answer |
|---|---|
| ______ is the difference between adjacent densities. | contrast |
| The term ___________ describes the concept of contrast as it is displayed on a soft-copy monitor for digital images. | dynamic range |
| The term __________ accurately describes the digital processing that produces changes in the range of density/brightness. | window width |
| Any change in overall ____ will affect contrast. | density |
| _____ contrast provides more diagnostic information, if it is still in visible range. | Low |
| High contrast is also known as: | Few shades of gray Increased contrast Low kVp Short scale contrast Short dynamic range/window width |
| Low contrast is also known as: | Many shades of gray Decreased contrast High kVp Long scale contrast Large dynamic range/window width |
| ___________ is the number of useful visible densities or shades of gray. | Scale of contrast |
| _____ is the total range of density values recorded by the image receptor. | Physical contrast |
| ______ is the total range of density values that can be perceived by the human eye. | Visible contrast |
| Compression or expansion of densities can be accomplished by the following: | change in the film's Dlog E curve, adjustments in kVp or by the use of window width. |
| ___________ is the range of densities that the film is capable of recording. | Film contrast |
| Film contrast depends on four factors: | intensifying screens film density D log E curve Processing |
| Intensifying screens create an inherently _________ image. | higher contrast |
| Film contrast also changes with changes in ______. | film density |
| Excessive or inadequate film density will _____ contrast. (especially true in the toe and shoulder regions of the D log E curve) | decrease |
| Where on the D log E curve is contrast maximized? | straight line portion |
| As the slope of the curve becomes steeper, contrast is _______. | increased |
| Increased developer temperature, time, and replenishment cause increased fog and _________. | decreased contrast |
| __________ is the range of differences in the intensity of the x-ray beam after it has been attenuated by the subject. | subject contrast |
| ______ is the primary controller of subject contrast. | Kilovoltage (kVp) |
| An increase in kVp will lead to a wider range of exposures on the IR, which results in an overall _____ contrast. | lower |
| As long as the kVp is adequate to penetrate the part being examined, low kVp will produce _____ subject contrast. | high |
| High kVp produces a _______ range of relative exposures, while low kVp will produce an _______ range of relative exposures. | compressed; expanded |
| As kVp increases, the percentage of _________ increases. | Compton interactions |
| As a result of the increase in the amount of scatter reaching the IR, contrast is _________. | decreased |
| Fog can be caused by subjecting film to: | heat low level ionizing radiation chemical fumes |
| Any factor that results in an increase in fog will cause a _______ in contrast. | decrease |
| When the difference between adjacent thicknesses is great, subject contrast is ______; when little difference exists in the thickness of adjacent body parts, subject contrast is _____. | increased; decreased |
| When the amount of overall thickness of a body part increases = ____ scatter and ____ subject contrast. | increased; decreased |
| A decrease in overall body part thickness/field size = _______ subject contrast | increased |
| Materials with a higher Z# absorbs a _______% of the x-ray beam than low Z# materials. | greater |
| The presence of more electrons will enable _____ interactions to occur. | more |
| When the difference between the average Z# of adjacent tissues is great, subject contrast is ________. (and vice versa) | increased |
| Contrast media _______ subject contrast by introducing greater differences in Z# variations than those that exist naturally. | increase |
| When the difference between the densities of adjacent tissues is great, subject contrast is _______.(and vice versa) | increased |
| The major consideration in evaluating visible contrast is verification that a proper range of ______ is visible in the area of interest. | densities |
| A _______ is tool to help focus on the contrast in a certain area. | contrast mask |
| A visible change in contrast will not be perceived until kVp is changed by _______ | 4-12%. |
| There is no reason to repeat an exposure for contrast reasons unless a _______ change is made. | 4-5% |
| The rule for contrast changes is to make adjustments of _________ percent. | 15 or 8 |
| Contrast evaluation can be made only when sufficient ______ exists to permit the range of contrast to be seen. | density |
| Photoelectric effect interactions ______ as kVp decreases. | increases |
| A given kVp for a 3 phase generator will produce a _____ contrast than a single pase unit. | lower |
| kVp affects contrast and has the most _____ effect on the image. | direct |
| Influencing factors has a ______ effect on the image. | less direct |
| _____ is the controlling factor of contrast. | kVp |
| As kVp increases, contrast _____. (and vice versa) | decreases |
| kVp increases amount of radiation fog, which will in result _____ contrast. | decrease |
| When a film is either over or underexposed, the contrast is _______. | decreased |
| What effect do focal spot size and anode heel effect have on contrast? | none |
| Removing scatter from the image will _____ contrast. | increase |
| An increase in filtration will ______ contrast. | decrease |
| Beam restriction will reduce the amount of scatter and therefore ______ contrast. | increase |
| As the anatomical part size increases, the amount of scatter created by the part also increases, which will result in a _____ in contrast. | decrease |
| High Z#'s will cause more photoelectric absorption, resulting in _______ contrast. | increased |
| Grids improve _____ by removing scatter before it reaches the IR. | contrast |
| Higher ratio grids remove more scatter - and will result in a ____ contrast image. | higher |
| _____ is the amount of shades of gray a pixel can record. | Bit depth |
| The larger the bit depth the ____ shades of gray the can be recorded. | more |
| Decreasing film development time, temp, or replenishmen rate from the optimal range will ____ contrast. | decrease |
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