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An image with few densities but many differences between them has ___ Contrast?
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An image with many Blacks and Whites, with few grays?
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RDTC 118 Unit 4
Contrast, Detail, Distortion
| WTF is this? | No Shit Sherlock |
|---|---|
| An image with few densities but many differences between them has ___ Contrast? | High Contrast (Short Scale) |
| An image with many Blacks and Whites, with few grays? | High Contrast |
| An image with many densities but little difference between them has ___ Contrast? | Low Contrast (Long Scale) |
| An image with many shades of Gray? | Low Contrast |
| #1 Controlling Factor of Contrast? | kVp |
| How is Digital Contrast controlled? | kVp, but altered by Computer |
| ↑ kVp = __ Transmission | ↑ Transmission |
| ↑ kVp = __ Compton Interactions | ↑ Scatter |
| ↑ kVp = __ Photoelectric Effect | ↓ Absorption |
| ↑ kVp = __ Fog | ↑ Fog |
| ↑ kVp = __ Contrast | ↑ kvp = ↓ Contrast |
| Low kVp has more of what type of Interactions? | Low kVp = ↑ Photoelectric Absorption |
| Contrast Influencing Factors | Grids, Collimation, OID, Anatomic Part, Filtration |
| ↑ kVp = __ Scatter | ↑ kVp = ↑ Scatter |
| ↑ Grid Ratio = __ Scatter = __ Contrast | ↑ Grid = ↓ Scatter = ↑ Contrast |
| ↑ Collimation = __ Tissue Exposure = __ Contrast | ↑ Collimation = ↓ Tissue Exposure = ↑ Contrast |
| ↑ OID = __ Scatter = __ Contrast | ↑ OID = ↓ Scatter = ↑ Contrast |
| Do we adjust OID for contrast? Why or why not? | No, ↑ Contrast but also ↑ Distortion |
| How does increasing OID increase Contrast? | "air gap" of OID allows Scatter to Miss the IR (↓ Scatter = ↑ Contrast) |
| ↑ Tissue Thickness = __ Scatter = __ Contrast | ↑ Tissue = ↑ Scatter = ↓ Contrast |
| ↑ Tube Filtration = __ Scatter = __ Contrast | ↑ Filtration = ↑ Scatter = ↓ Contrast |
| How does Tube Filtration decrease Contrast? | Filtration absorbs low energy photons that increase beam intensity and in turn Scatter (↑ Scatter = ↓ Contrast) |
| Result of kvp and absorption characteristics of anatomic tissue? | Subject Contrast |
| Result of manufacturing properties and processing conditions? | Film Contrast |
| _____ changes Absorption Characteristics of tissue by ↑ or ↓ Beam ____ ? | Contrast Medium, Attenuation |
| (-/+) Contrast Agents increase beam attenuation and produce less film density? | + Contrast Agent = More Absorption/Increased Brightness |
| (-/+) Contrast Agents increase transmission? | Negative Contrast Agents (Air) |
| (+/-) Contrast Agents require increase in exposure factors? | Positive Contrast Agents (Barium) |
| Film Processing temperatures outside Normal will ↑ or ↓ Contrast? | ↓ Contrast |
| kVp changes for ages below 6? | -15% kVp |
| Minimum kVp for Premies | 50 kVp |
| Minimum kVp for Infants | 55 kVp |
| Minimum kVp for Child | 60 kVp |
| mAs adjustment for ages 0-5? | 25% (75% less) |
| mAs adjustment for ages 6-12? | 50% mAs of adult |
| What types of casts do not require technique changes? | Fiberglass |
| Dry vs Wet theory for technique adjustment with Plaster Cast? | Dry = 2x mAs Wet = 3x mAs |
| Alternate theory for technique adjustment with Plaster Cast? | Treat cast as increase in Part Thickness |
| ____ Diseases increase absorption characteristics of part, making it more difficult to penetrate? | Additive Diseases |
| Examples of Additive Diseases | Ascites, Cirrhosis, CHF, Pleural Effusion |
| ____ Diseases decrease absorption characteristics of part, making penetration easier? | Subtractive Diseases |
| Examples of Subtractive Diseases | Bowel Obstruction, Free Air, Emphysema |
| Which type of diseases may need an increase in kVp? | Additive Diseases |
| When would you visualize soft tissue on an image? | Foreign body, Croup, Obstruction |
| Which exposure factor do you change when soft tissue needs less Density to visualize the area of interest? | ↓ mAs = ↓ Density |
| Which exposure factor do you change when soft tissue needs a change in Contrast to visualize the area of interest? | ↑ or ↓ kVp |
| Geometric Properties control ____ ? | Sharpness |
| ____ is the distinctness or sharpness of the structural lines that make up the recorded image? | Recorded Detail |
| 3 Factors of Geometric Unsharpness | OID, SID, Focal Spot Size |
| Another term for Geometric Unsharpness | Penumbra |
| Penumbra | Area of unsharpness or blurred margin |
| Focal Spot Size only affects ____ ? | Recorded Detail |
| Small focal spot size | .5-.6 mm |
| Large focal spot size | 1-1.2 mm |
| ↑ SID = __ Unsharpness = __ Recorded Detail | ↑ SID = ↓ Unsharpness = ↑ Recorded Detail |
| How does increasing SID increase Recorded Detail? | Xray photons more perpendicular to IR/Object with greater SID |
| ↑ OID = __ Unsharpness = __ Recorded Detail | ↑ OID = ↑ Unsharpness = ↓ Recorded Detail |
| Factor with #1 impact on Unsharpness? | OID |
| Optimal recorded detail when OID is ___ ? | zero |
| How do you compensate for unavoidable OID? | ↑ SID sligthly |
| Calculating Distance Formula | SID = OID + SOD |
| Geometric Unsharpness Formula | Geometric Unsharpness = (Focal Spot Size x OID)/SOD |
| Better recorded detail with (High/Low) Unsharpness value? | Lowest # is Better Detail |
| ↑ Film Speed = __ Recorded Detail = __ Unsharpness | ↑ Film Speed = ↓ Recorded Detail = ↑ Unsharpnes |
| High film speed reduces radiation required but at the expense of __ ? | Less dose but Lower Recorded Detail |
| Unsharpness caused by patient motion? | Motion Unsharpness (Blur) |
| Ways to control motion... | 1. Short exposure 2. Clear Communication 3. Immobilize |
| ____ is the imaging system's ability to distinguish btwn two adjacent structures? | Resolution |
| ____ is the smallest detail detected on the image? | Spatial Resolution |
| ____ is the imaging system's ability to distinguish btwn small objects with similar subject contrast? | Contrast Resolution |
| Resolution is expressed in what unit of measure? | Line pairs per millimeter (Lp/mm) |
| Define Line Pair | One metal line + space = Line Pair |
| ___ is the misrepresentation of size or shape? | Distortion |
| Shape Distortion where the part is misaligned? | Foreshortening |
| Shape Distortion where the CR or IR is misaligned? | Elongation |
| Another term for Size Distortion? | Magnification |
| ___ has the greatest effect on Size Distortion? | OID |
| ↑ OID = __ Size Distortion | ↑ OID = ↑ Magnification |
| Parts Closest to the IR will have more size distortion (T/F)? | False - Further Away more Distortion |
| ↑ SID = __ Size Distortion | ↑SID = ↓ Mag/Size Distortion |
| ___ indicates how much Size Distortion is on an image? | Magnification Factor |
| Magnification Factor Formula (Size) | MF = Image Size / Object Size |
| Magnification Factor Formula (Distance) | MF = SID / SOD |
| % of Magnification Formula | % Mag = {(Image Size-Object Size)/Object Size} x100 |
| To calculate Image/Object Size, 1st Calculate ___ ? | Magnification Factor (MF) |
| Image/Object Size Formula | Object Size = Image Size/MF |
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RadTechTKD
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