48 DHHS
MOBILETT XP Digital SPR8-230.814.30.03.02 Siemens AG
11.05 CS SD 24
Page 48 of 70
Medical Solutions
Reproducibility test 0
Requirement:
• The coefficient of variation for the radiation dose for any combination of exposure pa-
rameters does not exceed 0.045. This requires operation at the line voltage compliant
with Siemens specifications.
NOTE
In the following test, 10 sequential exposures are taken within one
hour.
The exposure parameters should be temporarily set to different
values following each measurement.
Required measuring instrument:
- Dosimeter
Procedure:
• After switching the system on, wait until its temperature has stabilized. The unit is ready
for these measurements after 15 minutes.
X
• Release the number of exposures with the specified exposure data:
- 85 kV, 1.0 mAs, 10 exposures.
• Measure the dose for each exposure.
• Reset the display prior to each new measurement.
Calculations: Coefficient of variation C
• For a series of 10 dose measurements, coefficient of variation C is determined using
the following formula:
Fig. 21:
Coefficient of variation C must be ≤ 0.045.
Example for determining coefficient of variation C:
Step 1)
• 10 exposures with recorded measured values (fictitious values).
s = Standard deviation resulting from the measurements
_
x = Average measured value of series
x
i
= i. measured value of series
n = Number of individual measurements in series
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