Program Information
Updating Tools for Radiographic Technique Charts
A Walz-Flannigan*, J Lucas, K Buchanan, B Schueler, Mayo Clinic, Rochester, MN
Presentations
SU-G-IeP3-14 (Sunday, July 31, 2016) 5:00 PM - 5:30 PM Room: ePoster Theater
Purpose:
Manual technique selection in radiography is needed for imaging situations where there is difficulty in proper positioning for AEC, prosthesis, for non-bucky imaging, or for guiding image repeats. Basic information about how to provide consistent image signal and contrast for various kV and tissue thickness is needed to create manual technique charts, and relevant for physicists involved in technique chart optimization.
Guidance on technique combinations and rules-of-thumb to provide consistent image signal still in use today are based on measurements with optical density of screen-film combinations and older generation x-ray systems. Tools such as a kV-scale chart can be useful to know how to modify mAs when kV is changed in order to maintain consistent image receptor signal level. We evaluate these tools for modern equipment for use in optimizing proper size scaled techniques.
Methods:
We used a water phantom to measure calibrated signal change for CR and DR (with grid) for various beam energies. Tube current values were calculated that would yield a consistent image signal response. Data was fit to provide sufficient granularity of detail to compose technique-scale chart. Tissue thickness approximated equivalence to 80% of water depth.
Results:
We created updated technique-scale charts, providing mAs and kV combinations to achieve consistent signal for CR and DR for various tissue equivalent thicknesses. We show how this information can be used to create properly scaled size-based manual technique charts.
Conclusion:
Relative scaling of mAs and kV for constant signal (i.e. the shape of the curve) appears substantially similar between film-screen and CR/DR. This supports the notion that image receptor related differences are minor factors for relative (not absolute) changes in mAs with varying kV. However, as demonstrated creation of these difficult to find detailed technique-scales are useful tools for manual chart optimization.
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