Siemens Software version syngo CT 2005C manual Dose Information, Ctdiw and CTDIVol

Dose Information

CTDIW and CTDIVol

The average dose in the scan plane is best described by the CTDIW for the selected scan parameters. The CTDIW 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

32cm, the CTDIW value displayed can deviate from the dose in the scanned volume.

The CTDIW 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 CTDIW, 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:

CTDIVol = CTDIW/Pitch Factor

This dose number is displayed on the user interface for the selected scan parameters.

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