2. Comparing Exposure Systems
Unit V
Comparing Exposure Systems

3. Developing Exposure Charts
Chapter 34
Developing Exposure Charts

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Objectives
Compare various exposure systems
Describe advantages and disadvantages of fixed and variable kVp systems
Discuss other exposure systems that have influenced radiographic technique
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Objectives
Explain why measurement of part thickness is critical to the accurate use of technique charts
Describe function of the radiographer when using automatic exposure control systems
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Objectives
Describe how programmed exposure control systems function
State the steps necessary to establish a technique chart
Explain a basic phantom testing procedure
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Objectives
Describe process of selecting an optimal image range
Extrapolate a technique chart from a limited number of phantom test images
Describe the clinical trial and fine tuning processes
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System Selection
Forefathers of technique
1920s – Ed C. Jerman
1940s – Arthur Fuchs
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System Selection
Radiographic exposure is a very complex process
Best technique systems manipulate one variable while holding others constant
Goal of any exposure system is consistency
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System Selection
Facilities that post and maintain exposure technique charts have lower repeat rates
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11. Comparing Exposure Systems
Technologists may develop personal preference
Should use system employed by imaging facility
Students should learn all possible systems before making personal selection
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12. Fixed Kilovoltage Systems
Developed by Fuchs during WWII
Theoretical support from literature and professionals
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Fixed kVp System
Advantages:
Reduction in patient dose
Provides more information within the image
Increased consistency in density and contrast
Lengthens exposure latitude
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Fixed kVp System
Advantages:
Reduces x-ray tube wear
Allows for shorter exposure times, thus reduces patient motion
Easier to memorize
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Fixed kVp System
Disadvantages:
Higher amount of scatter results in reduced image contrast
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16. Variable Kilovoltage Systems
Developed by Jerman
First exposure “method”
Used when kVp range was limited by equipment generators
Can adjust kVp more than mA or time
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Variable kVp System
Advantages:
Allows for small changes in exposure for small changes in part thickness
Higher contrast
Can affect the perceived image resolution
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Variable kVp System
Disadvantages:
More patient dose
Higher repeat rate
Tube wear, etc.
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19. Other Exposure Systems
Log10 Systems
DuPont Bit system
XVS System
Photographic roots
Siemens point system
Supertech Calculator
Proportional anatomy system
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Part Measurement
No exposure system can work effectively without accurate measurement of part thickness
Failure to measure part correctly will result in increased exposures and patient dose
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Part Measurement
Calipers
Central ray entrance
Thickest part
Other
Approach must be followed by all department radiographers
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Phototiming Systems
Automatic Exposure Control (AEC)
Radiographer selects kVp and possibly back-up mA and time
Equipment automatically terminates exposure
Art of phototiming requires learning when to use it and when not to use it
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23. Anatomically Programmed Radiography
Computerized technique charts
Radiographer selects body part/projection
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24. Anatomically Programmed Radiography
Radiographer can override technique to customize for individual patients
If well maintained, only a mAs correction factor is necessary
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25. Establishing a Technique Chart
Align image in middle with regard to:
Part size
kVp
mAs
Ideally
10-25 cm
60-80 kVp
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