Siemens syngo CT 2005C - Manual (Page 28)

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Dose Information
CTDI
W
and CTDI
Vol
The average dose in the scan plane is best described by
the CTDI
W
for the selected scan parameters. The CTDI
W
is measured in the dedicated plastic phantoms – 16 cm
diameter for head and 32 cm diameter for body (as
defined in IEC 60601 –2 – 44). This dose number gives
a good estimate for the average dose applied in the
scanned volume as long as the patient size is similar to
the size of the respective dose phantoms.
Since the body size can be smaller or larger than
32 cm, the CTDI
W
value displayed can deviate from the
dose in the scanned volume.
The CTDI
W
definition and measurement is based on sin-
gle axial scan modes. For clinical scanning, i.e. scan-
ning of entire volumes in patients, the average dose
will also depend on the table feed in between axial
scans or the feed per rotation in spiral scanning. The
dose, expressed as the CTDI
W
, must therefore be cor-
rected by the Pitch Factor of the spiral scan or an axial
scan series to describe the average dose in the scanned
volume.
For this purpose the IEC defined the term “CTDIVol“ in
September 2002:
This dose number is displayed on the user interface for
the selected scan parameters.
CTDI
Vol
= CTDI
W
/Pitch Factor
C2-025.630.01.01.02_APPLICATIONGUIDE_SPIRIT.book Page 28 Friday, April 8, 2005 9:55 AM