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Rad102
Contrast
| Question | Answer |
|---|---|
| What is contrast? | The differences between any two areas of density levels within a radiographic image, or in other words, the difference between shades of gray |
| Why is contrast important? | Improving and achieving a quality level of contrast maximizes the amount of information visible on a radiograph to make a diagnosis. |
| Does contrast have an affect on recorded detail? | Yes, optimum contrast enhances recorded detail. |
| Scale of contrast | Represents the number of the shades of gray or the number of the differing densities on a radiograph |
| Long scale contrast | increased number of densities where only slight differnces between them exist. This is achieved by the use of high kV and results in low contrast. |
| Short scale contrast | Decreased number of densities where large differences between them exist. This is achieved by use of low kV and results in high contrast |
| Medium scale contrast | sufficient differences among the densities produced in all areas of a radiograph that make details visible |
| Factors influence contrast | 1. Any change that results in increased beam energy will decrease contrast. 2. Any change that results in decreased scatter radiation reaching the IR will increase or improve contrast. |
| Film Contrast (intrinsic) | contrast resulting from properties inherent in the itemsused to produce an image such as film, intensifying screens,and processing. |
| Subject contrast | contrast resulting from the absorption characteristics of tissue and kVp levels utilized |
| Factors affecting subject contrast | 1. Kilovoltage peak (kVp) is the major controlling factor for contrast. -As kVp increases, contrast decreases (increase beam energy) 2.Generator type: 3 phase generator will produce a higher energy beam than single phase therefore reducing contrast |
| Factors affecting subject contrast | 3. Target material: increase the atomic number of the material used in the target, will decrease the contrast (increase beam energy) 4. Filtration: an increase in filtration will decrease contrast (increase beam energy) |
| Factors affecting subject contrast | 5. Collimation/field size: limits scatter radiation production and increases contrast (decrease scatter) 6. Grid or air-gap: reduces scatter reaching the IR and increases contrast (decreases scatter) |
| Factors affecting subject contrast | 7. Compression of part: decreases part thickness and reduces scatter which will increase contrast (decreases scatter) 8. Patient thickness: the thicker the part to be imaged, more scatter is produced and a reduction in contrast |
| Factors affecting film contrast | 1. Film/screen combinations: decrease film latitude (low latitude), increase in contrast and vice versa. 2. Fog: any factor that increases fog, decreases contrast |
| Factors affecting film contrast | 3. Film processing: any suboptimal processing factor (over or under development), decreases contrast 4. Characteristic curve: toe-decrease contrast, staight line-increase contrast, shoulder-decrease contrast q |
Created by:
danielle89
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