RTI Barracuda - 4.9 Reproducibility

4. Measurement Principles & Theory
Linearity
Barracuda & QABrowser Reference Manual
2012-10/4.3A
106
A short example:
measurement 1 : X
1
= 13 µGy/mAs
measurement 2 : X
2
= 14.6 µGy/mAs
measurement 3 : X
3
= 12.8 µGy/mAs
Then:
and:
Of which both is below the 0.10 limit.
Reproducibility4.9
Reproducibility is checked to find out how constant the output is when an X-ray
exposure is repeated many times. One method is to check the coefficient of variation.
The coefficient of variation is defined as:
where
x
i
= Individual exposure readings
n = Number of readings
= Mean value of readings
To check the output reproducibility:
1. Place the dose detector on the table-top (the patient-equivalent phantom is not
necessary since this measurement can be made as a relative measurement).
2. Set the X-ray generator to technique factors commonly used clinically.
3. If the display is unstable, press the Reset button.
4. Use some form to record your measurements.
5. Make 5 to 10 exposures and record the reading for each exposure.
6. Calculate the mean value, difference from mean value and square of differences.