Fig. 2.

Changes in CTN affected by the thickness of foam rubber. A 3-ply bismuth shield with 1-cm (black triangles) and 2-cm (gray triangles) foam rubber sheets placed over the phantom surface. Water CTN with (triangles) and without (circles) a bismuth shield for the A zone (△) and the D zone (▼) were measured in the phantom background. Measured CTN with a bismuth shield and foam rubber at four voltages were compared with those without a shield (reference scan: ●). Error bars indicate standard deviations in CTN in six continuous images.