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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