5. Measurements with the Barracuda System
Mammography
2012-10/4.3A
133
Barracuda & QABrowser Reference Manual
The displayed dose value has very little energy dependence because the dose value is
automatically compensated, using the tube voltage, which is measured simultaneously
for each exposure.
If any of the displayed values cannot be compensated or cannot be measured with full
accuracy, the symbol is displayed at the top of the screen. If the symbol is
displayed you can tap it to get more information.
You can also change the dose and dose rate units. Tap the dark part of the display
where the unit and its prefix are displayed to get the list of units. The value for the new
unit is automatically calculated and updated.
A delay of 5 ms is standard but can be changed. If you get a High kVp message you
have probably selected a set kV value higher than the actual measuring range.
Another reason may be that you have selected wrong beam quality compared to what
the generator is set to.
To be able to trust the kVp reading it is always very important to make
the Position Check to verify that the whole detector area is uniformly
irradiated. The Position Check is normally started automatically every
time you change Beam Quality, but please make sure to do a Position
Check every time the MPD is repositioned.
The kV and radiation waveform is always stored together with the RTD values and can
be displayed by tapping the Wave button. The kVp calibration for MPD is made without
the compression paddle in place.
The purpose of dose measurement is often to determine the ESAK, Entrance Surface
Air Kerma (or ESE, Entrance Skin Exposure).
It is recommended to perform dose measurements according to a mammography
protocol. One is the "European Protocol on dosimetry in mammography EUR 16263
EN from the European commission". Chapter 3 in this protocol describes in detail the
determination of AGD, Average Glandular Dose (or MGD, Mean Glandular Dose). The
AGD is derived from measurements of the HVL and of the ESAK. Make use of
tabulated conversion factors from ESAK to AGD. See Average Glandular Dose, AGD
(MGD) .
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