Figure 3. Profiles of CT image noise from the CTa system (48 cm field of view, 256 x 256 pixel matrix) along the horizontal diameter of the 48.4 cm polyethylene phantom. Noise profiles of scans with 250 mAs, 10 mm (
) (10 Hounsfield units (HU) in the centre) and 100 mAs, 3 mm (
) (30 HU in the centre) are shown. Standard deviations (SD) were obtained from circular regions ofinterest (40 mmdiameter) and the plotted profiles were normalized to unity at the centre of the phantom. Error bars represent the maximum and minimum values of six measurements.
