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