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chap 27 contrast
Imaging1.
| Question | Answer |
|---|---|
| What classifies an image as "high contrast" | differences between the adjacent densities that comprise contrast are great. (fewer shades of gray..) |
| What makes an image "low contrast' | When differences in adjacent densities are minimal. (has more shades of gray) |
| define dynamic range | the concept of contrast as it is displayed on a soft-copy monitor for digital images. |
| Scale of contrast is? | # of useful visible densities or shades of gray. |
| Short scale contrast? | image that demonstrates considerable or maximal differences between densities and has a minimal total number of densities. (short scale is high contrast) |
| Long scale contrast? | image that demonstrates slight or minimal differences between densities but has a maximal total number of densities. (long scale is low contrast) |
| Physical contrast? | total range of density values recorded by the IR. It is the maximum contrast possible and most accurate representation. |
| Visible contrast? | total range of density values that can be perceived by the human eye in a single image. |
| Radiographers manipulate the ____ contrast available into the ____ range to produce the diagnostic image. | physical, visible. |
| What is the primary method for adjusting display contrast with digital imaging systems? | with window width manipulation. |
| In what ways can you manipulate contrast? | Change in D log E curve of film Adjustment to kVp Adjustment of window width |
| Film contrast depends on what four things? | Intensifying screen Film density Slope of D log E curve Processing |
| What post-processing factors affect the final digital image receptor contrast? | Histogram and LUT (look up table) |
| What is subject contrast? | Range of differences in the intensity of the x-ray beam after it has been attenuated by the subject. |
| What is subject contrast dependent on? | Kilovoltage Amount of irradiated material Type of irradiated material |
| What is the primary controller of subject contrast? | kVp. |
| What are the two controlling factors of contrast? | kVp and pulses by the generator. |
| Increasing # of pulses by generator waveform causes contrast to what? | decrease. |
| Increasing OID causes contrast to what? | Increase. |
| Increasing filtration causes contrast to what? | Decrease. Increase filtration, increase beam energy, higher beam causes more scatter, scatter decreases contrast. |
| Increasing collimation causes contrast to what? | Increase. The smaller the IR and closer the collimation, the less photons, which is less scatter. |
| Additive pathological conditions cause contrast to what? | Decrease. |
| Increasing grid ratio causes contrast to what? | Increase. Grids absorb scatter, increasing contrast. |
| Increasing SID causes contrast to what? | SID has no effect. |
| High contrast is high or low energy? | Low energy. |
| Low contrast is high or low energy? | High energy. |
| Attenuation is what? | Reduction of # of photons in beam as it passes though the patient. ex) bone attenuates more than the lungs… has higher/more attenuation. |
| High frequency generators have what kind of ripple? | Less than 1% ripple. This is most efficient. |
| ei means? | Exposure index. |
Created by:
Zoest35
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