236 MI-42-0001 Rev. 19
CT USER INFORMATION: Dosage Factors and Image Quality
CTDI Per Peak Tube
Potential
CTDI
100
at the maximum of the 4 entrance locations for different selectable CT conditions of
operation. The value at 120 kV, 192 mAs is treated as 1.00, and other
measurements are normalized
to this value. Conditions of operation selected are the
minimum, midrange and maximum values of
voltage (80, 100 and 120 kV) and tube current – time product (48, 96, 192 and 240 mAs).
CTDI Free-In-Air CTDI
free air
was measured using the 100 mm pencil ion chamber positioned at isocenter, in the
absence of the patient table or any other extraneous material. The exposures were made at 25 mA,
2 sec (50 mAs). Data is presented for 80, 100 and 120 kV, extrapolated to 192 mAs. The 120 kV,
192 mAs combination represents both typical head and body CT conditions of operation. There is
only one (fixed) collimation, with a nominal tomographic section thickness of 33.92 mm (N = 32
detectors, T = 1.06 mm).
Phantom kV mA sec mAs mGy
Normalized
mGy
Body
80 25 1.92 48 4.12 0.09
100 25 1.92 48 7.12 0.15
120 25 1.92 48 11.58 0.25
Head
80 25 1.92 48 4.42 0.10
100 25 1.92 48 7.66 0.17
120 25 1.92 48 11.39 0.25
Body
80 50 1.92 96 8.24 0.18
100 50 1.92 96 14.24 0.31
120 50 1.92 96 23.16 0.50
Head
80 50 1.92 96 8.84 0.19
100 50 1.92 96 15.33 0.34
120 50 1.92 96 22.79 0.50
Body
80 100 1.92 192 16.48 0.36
100 100 1.92 192 28.48 0.61
120 100 1.92 192 46.33 1.00
Head
80 100 1.92 192 17.68 0.39
100 100 1.92 192 30.65 0.67
120 100 1.92 192 45.58 1.00
Body
80 125 1.92 240 20.60 0.44
100 125 1.92 240 35.60 0.77
120 125 1.92 240 57.91 1.25
Head
80 125 1.92 240 22.10 0.48
100 125 1.92 240 38.32 0.84
120 125 1.92 240 56.97 1.25
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