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.
7. Add all squared values and divide by (n-1) to get the variance. In this case n=10.
8. Calculate the square of the variance, i.e. the standard deviation, and divide it by the
mean value of the n measurements
An acceptable value for the coefficient of variation is less than 0.05.
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