III. Principles of Imaging Flashcards
Image characteristics
Image brightness
Brightness refers to how light or dark an image appears.
Image characteristics
Acceptable range
Determined by optimal exposure settings.
Image characteristics
Technical factors:
mAs
Affects the total quantity of X-rays.
Image characteristics
Technical factors:
kVp
Controls the energy and penetration of X-rays.
Image characteristics
Technical factors:
Distance
Source-to-image distance affects brightness.
Image characteristics
Technical factors:
Beam limitation
Reduces scatter and improves image quality.
Image characteristics
Technical factors:
Patient considerations
Body habitus and condition influence exposure requirements.
Image characteristics
Technical factors:
Contrast media
Enhances brightness and visibility of specific tissues.
Image contrast
The difference in brightness between adjacent areas in an image.
Image contrast
Types:
Long scale
Many shades of gray (low contrast).
Image contrast
Types:
Short scale
Few shades of gray (high contrast).
Image contrast
Components:
Subject
Determined by differences in tissue density.
Image contrast
Components:
Image receptor
Controlled by detector properties.
Image contrast
Technical factors:
kVp
Higher kVp reduces contrast, lower kVp increases contrast.
Image contrast
Technical factors:
Scattered radiation
Reduces contrast; minimized with collimation.
Image contrast
Technical factors:
Filtration
Removes low-energy photons, affecting contrast.
Image contrast
Technical factors:
Patient considerations
Tissue composition influences contrast.
Image contrast
Technical factors:
Distance
Increased distance reduces scatter and improves contrast.
Image contrast
Technical factors:
Contrast media
Improves contrast by enhancing specific structures.
Recorded detail
Recorded detail
The sharpness of structural lines in the image.
Recorded detail
Geometric unsharpness
a) Focal film distance
b) Object film distance
c) Focal spot
Focal film distance (FFD): Increasing FFD reduces unsharpness.
Object film distance (OFD): Decreasing OFD minimizes unsharpness.
Focal spot size: Smaller focal spots produce sharper images.
Recorded detail
Motion unsharpness
a) Voluntary
b) Involuntary
Voluntary motion: Patient movement that can be minimized with proper instructions.
Involuntary motion: Internal movements like heartbeat or breathing, managed with short exposure times.
Distortion
A misrepresentation of the size or shape of the object being imaged.
Distortion
Types:
Shape Foreshortening
Object appears shorter than it is.
Distortion
Types:
Shape Elongation
Object appears longer than it is.
Distortion
Size (magnification)
Caused by increased distance between the object and the detector.
Distortion
Factors:
Distance
Source-to-image distance (SID): Greater SID reduces magnification.
Distortion
Factors:
Tube/part (image receptor) relationships
Object-to-image receptor distance (OID): Decreasing OID minimizes distortion.
Exposure latitude
The range of exposure that produces acceptable image quality.
Exposure latitude
Factors:
kVp
Higher kVp increases exposure latitude.
Image receptor scattered/secondary radiation
Radiation that bounces off the patient or other surfaces, reducing image quality.
Image receptor scattered/secondary radiation
Interactions
Causes noise and reduces contrast in the image.
Image receptor scattered/secondary radiation
Factors:
kVpf
Higher kVp increases scatter.
Image receptor scattered/secondary radiation
Factors:
Patient considerations
Patient size and body habitus: Larger patients generate more scatter.
Image receptor scattered/secondary radiation
Factors:
Distance
Increasing distance reduces scatter.
Image receptor scattered/secondary radiation
Factors:
Contrast media
Enhances contrast but does not directly reduce scatter.
Image receptor scattered/secondary radiation
Effects:
Patient dosage
a) Adult b) Pediatric c) Body habitus
Patient size and body habitus: Larger patients generate more scatter.
Patient dose: Increases with scatter
Image receptor scattered/secondary radiation
Effects:
Image quality
Decreases due to reduced contrast.
Image receptor scattered/secondary radiation
Effects:
Occupational exposure
Increases for personnel if proper shielding is not used.
