RTI Piranha, Справочное руководство, Страница: 125 / 181

5. Measurements with the Piranha System
Mammography
2014-06/5.5C
121
Piranha & QABrowser Reference Manual
1. First readings from an exposure, where
the distance from the X-ray tube to the
breast support where the Piranha is placed
is 650 mm.
2. If the Piranha is placed on the breast
support, the sensitive detector surface of
the Piranha is situated 16.1 mm above the
breast support, which makes the distance
from the tube to the detector 633.9 mm.
ESAK is measured 45 mm above the
breast support and taking the detector
placement into consideration, the distance
from tube to the wanted measuring position
is then 605 mm.
3. When the normalizing function is used it
is indicated with a blue "N", as indicated in
the last figure. The dose and dose rate
values are then normalized to this virtual
position (at 605 mm SDD).
A practical consequence of usage of the normalizing function and scatter factor is that
the Piranha can be kept at the same position on the breast support all the time when
data is collected for AGD.
For an ion chamber it is not quite as easy because of the scatter contribution that is not
allowed during HVL measurement. The ion chamber and/or the compression paddle
must be moved to support good geometry.
More info about the correction and normalization function can be found in Application
Note 1-AN-52020-2 from RTI Electronics AB.