Phantom Laboratory Catphan 503 - Page 22

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Measure spatial uniformity by scanning the uniformity section. Observe the trends
above and below the central mean value of a CT number prole for one or several rows or
columns of pixels as shown above.
Select a prole which runs from one side of the uniformity module to the opposite side.
Due to scanner boundary effects, typical proles start 2cm from the edge of the test
module.
Integral uniformity may be measured by determining the minimum and maximum CT
values along the prole and by using the following equation :
Integral Non-Uniformity = CTmax - CTmin
CTmax + CTmin
The phenomenon of “cupping” or “capping” of the CT number may indicate the need for
recalibration.