5. Measurements with the Piranha System
Mammography
Piranha & QABrowser Reference Manual
2014-06/5.5C
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5.5.9 Mammographic Pre-pulses
Some mammography systems (e.g. GE DMR system) use a pre-pulse to determine
what radiation quality to use for a specific patient.
The time elapsing between the pre-pulse and the real exposure is usually about one
second. Therefore the default post-delay of 250 ms will not cover both the pre-pulse and
the real exposure. To get an overview of the signal output, set the post-delay to at least
1 s and the waveform recording time to a corresponding time. It is important to cover
both signals. In this measurement setup, the Piranha will add the dose from both
pulses. This is OK if the radiation quality is not changed between the signals.
If the Mammography unit changes the radiation quality after the pre-pulse however, the
kV and dose is affected and the pulses should be treated separately. To collect data
from real exposure, set the delay (not the post-delay) to exclude the pre-pulse. When
the data has been acquired, change the radiation quality to the one chosen by the
system and the measured data is automatically corrected. For the time being, this
feature is only present in the QABrowser software. With Ocean a new exposure has to
be made with the correct radiation quality using the same delay setting.
5.5.10 Scanning Beam Mammography
When measuring on scanning beam mammographic equipment, like for instance Sectra
MDM or Fischer Senoscan, two factors are very important.
1. You should place the Piranha flat on the image receptor. Then position it as
described in section Setting Up the Piranha for Mammography .
2. Always perform a position check. This makes sure than any field imbalances are
corrected for.
3. If you use the compression paddle, make sure that you use the correct settings,
see section Corrections for the Compression Paddle .
Please also see the CT section for measurement tips on scanning beams.
For Sectra L30, see special application note on the RTI Electronics website
(www.rti.se).
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