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img crit contrast 2
image critique - contrast 2
| Question | Answer |
|---|---|
| Contrast | the difference between adjacent densities |
| Dynamic range | contrast as displayed on the monitor, the number of shades of gray which a pixel can display. |
| Window width | digital processing that controls changes in contrast |
| A high contrast x-ray exhibits ____ shades of gray? | few shades of gray |
| A high contrast x-ray exhibits ____ scale? | short scale |
| A high contrast x-ray exhibits ____ dynamic range? | short dynamic range |
| A high contrast x-ray exhibits ____ window width? | narrow window width |
| A low contrast x-ray exhibits ____ shades of gray? | many shades of gray |
| A low contrast x-ray exhibits ____ scale? | long scale |
| A low contrast x-ray exhibits ____ dynamic range? | large dynamic range |
| A low contrast x-ray exhibits ____ window width? | wide window width |
| Low contrast is associated with what kind of kVp? | high kVp |
| Low kVp yields what kind of contrast? | high |
| Alternate names for the D log E curve | H and D curve, Characteristic curve. |
| On the H and D curve, a more vertical slope demonstrates what? | short scale or high contrast |
| What minimum kVp change is needed for a noticeable change in contrast? | 4kVp |
| How do IS affect contrast? | they increase contrast or shorten the scale. |
| How does screen speed affect contrast? | it has a negligible effect |
| What is the range for desired density? | .25 – 2.5 |
| The shoulder of the H and D curve demonstrates what? | overexposure |
| The toe of the H and D curve demonstrates what? | underexposure |
| what does fog do to the toe of the H and D curve? | it raises it, decreases contrast |
| What does fog do to contrast? | it decreases it |
| What is created when a higher kVp is used? | longer scale of contrast, greater amount of scatter, greater range of exposures, greater penetrability. |
| When an image is repeated to improve contrast, how should the kVp be changed? | 8-15% increments or by 5-10 kVp |
| How are kVp and contrast related? | inversely |
| How does FSS affect contrast? | it doesn’t |
| When taking advantage of the anode heel effect, how should the patient be positioned? | with the thicker anatomy under the cathode. |
| Air gap technique: | an increase in OID increases contrast |
| An increase in the average energy of the beam affects contrast how? | it decreases it |
| An increase in beam restriction affects contrast how? | it increases contrast due to decreased scatter |
| An increase in grid ratio affects contrast how? | it increases contrast because it absorbs more scatter |
| What is the contrast improvement factor? | (K) it measures contrast with and without a grid |
Created by:
annaluz87
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