Hi. I have calculated CTDIw with a calibrated ...

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32cm body phantom on 5 Siemens CT scanners. Scan parameters was as follow: kv. mA. Total collimation. Rotation time. CTDIw. (mGy). Single slice. 120. 170.
Hi. I have calculated CTDIw with a calibrated ionization chamber with active length of 10cm and a 32cm body phantom on 5 Siemens CT scanners. Scan parameters was as follow:

Single slice Plus 4 series 6 slices 16 slices 64 slice

kv

mA 170

Total collimation 1×5= 5mm

Rotation time 1s

CTDIw (mGy) 12.23

120 120

170

4×2.5=10mm

1s

14.47

120 120 120

170 170 170

6×2=12mm 1s 16×0.6=9.6mm 1 s 24×1.2=28.8mm 1 s

13.27 13.02 10.29

My question is about different values of CTDIw. Why in constant scan parameters (kv and mA) I have different values of CTDIw? How can I justify that? Is it for total collimation or have another reason? Thank you for your help. Dary . June 18, 2015