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4. Measurement Principles & Theory
HVL & Total Filtration
Piranha & QABrowser Reference Manual
2014-06/5.5C
84
To measure the HVL:
1. Use the Piranha HVL stand on the table-top.
2. Set the generator to 80 kV/25 mAs.
3. If the display is unstable; press the Reset button.
4. Use some form to record your measurements.
5. Begin with 3 exposures without any added aluminum filter to get the zero-point and to
check the consistency of the generator.
6. Add the aluminum filters, 1, 2, 3, and 4 mm, and record the readings. Make a
measurement for each thickness and use the mean value.
7. Plot the results in a semi-logarithmic graph, set the value for 0 mm of added
aluminium to 1.0.
8. Join the measured points with a curve and find the value of added filtration required
to reduce the exposure to 0.5.
9. We find from the semi-logarithmic plot that the measured half-value layer is 3.3 mm
Al.
To measure Total Filtration:
In order to measure total filtration with one exposure optimally, there are some settings
to be aware of. Since the highest accuracy is obtained between 60 and 120 kV, we
recommend to do the measurement of the total filtration in between, at 80 kV. The
Piranha is also calibrated for the total filtration at this kV. Use a high signal level, i.e.
200 mA during 200 ms to get a stable result. It does not matter if you intend to do
measurements at a higher or lower kV than this, this measurement aim to get a correct
value of the total filtration.
See the graph below for optimum choice of method.
Hence, choose 80 kV, 200 mA and 200 ms and make an exposure. The total filtration
will be displayed in a pop-up screen. Tap
Keep
and the value is stored and will be used
on all further measurements. The pop-up screen will be displayed whenever the value of
the total filtration is changed.
Manually you can do this by entering the settings screen by tapping the
icon, as
shown below. As default value the total filtration is set to
Estimate
. Measure the total
filtration and then enter the settings window again. Now choose
Set
and enter the
measured value.
Summary of Contents for Piranha
Page 1: ...Reference Manual English Version 5 5C Piranha QABrowser RTI article number 9629050 10 ...
Page 8: ...Introduction Chapter 1 ...
Page 12: ...Description of the Piranha Chapter 2 ...
Page 40: ...Description of the QABrowser Chapter 3 ...
Page 77: ...Measurement Principles Theory Chapter 4 ...
Page 91: ...Measurements with the Piranha System Chapter 5 ...
Page 151: ...Optional Accessories Chapter 6 ...
Page 155: ...Problems and Solutions Chapter 7 ...
Page 161: ...Glossary Chapter 8 ...
Page 181: ...Notes Piranha QABrowser Reference Manual 2014 06 5 5C Notes 177 ...