The scatter to primary ratio is a ratio of the scattered radiation to the primary unscattered radiation transmitted by the object being imaged. Hence, the scatter to primary ratio provides an indication of the degree of unwanted scattered radiation arising from a particular imaging study.
The scatter to primary ratio increases with:
field size
patient thickness
increasing applied voltage (kV)
Measures to decrease the scatter ratio:
decreasing field size
decreasing kV
using a grid
air gap
Implications on Image Quality
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Increases in the scatter to primary ratio is inversely proportional to image quality due to:
Reducing contrast
Increasing noise
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