Analyzing the Latent Radiographic Image Flashcards
What does resolution refer to?
The overall ability of the imaging system to bring out the maximum number of details in an image
What is the latent image?
The image prior to digital processing
What are the variables that affect exposure to the image receptor via direct proportional relationships?
- Milliamperage (mA)
- Exposure time (seconds)
- Total mAs
- Field size
- Scatter radiation
What does a direct proportional relationship between variable and exposure mean?
As the variable increases the exposure increase
What are the variables that affect exposure to the image receptor via inverse relationships?
- Grid use
- SID
- OID
What does a inverse relationship between variable and exposure mean?
With the increase or use of a variable the exposure goes down
What are the variables that have special relationships with exposure?
- kVp
- part thickness
- generator type
- patient condition/pathology
- anode heel effect
What is the relationship between kVp and exposure?
A 15% increase in kVp causes a 2X increase in exposure (double)
If kVp increase 7% what effect does it have on exposure?
Exposure increases by 50%
Why does an increase in kVp cause such an effect on exposure?
The higher the KV the more penetrative the beam is, and causes more scatter radiation to hit the IR and more exposure
What is the relationship between part thickness and exposure?
As part thickness increases, exposure decreases exponentially
What is the relationship between generator type and exposure?
Higher efficiency machines have lower exposure, since the photons are stronger and lower efficiency machines have a higher exposure, since the photons are weaker
What is the relationship between patient condition and exposure?
Additive conditions increase exposure
Destructive conditions decrease exposure
What is the relationship between anode heel effect and exposure?
More exposure is present on the cathode end of the tube, and less exposure on the anode end of the tube
Based on the anode heel relationship and exposure, where part of the tube should be placed toward larger anatomy?
Larger parts should be placed on the cathode end, since there is higher exposure
What are the variables that decrease subject contrast in images?
- Increased kVp
- Increased field size
- Greater part thickness
- Increased scatter
- Motion
- More efficient generators
What are the variables that increase subject contrast in images?
- The use of grids
- Increase OID
Why is it better to use a grid vs increase OID to reduce scatter?
Using OID also causes magnification which should be avoided
What is spatial resolution?
The ability to distinguish individual parts of an object or adjacent images
How does the sand analogy relate to spatial resolution?
Its the ability to count each individual grain of sand which demonstrate spatial resolution
How is spatial resolution measured?
Using a line pair tool which is measure in line-pairs per millimeter (LP/mm)
What is the measure of spatial resolution called?
Spatial frequency which is defined as the number of details that can be fit into a given space
What is the benefit of better spatial resolution?
The better spatial resolution you have the smaller the objects you can see
How is better spatial resolution seen on a line pair tool?
The more lines per mm indicate a better spatial resolution
