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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
Created by: RadTechTKD