Figure 5.

(a) The actual filter thickness for PMMA and Al is shown as the solid line, and the computed values are shown as circles. These data are for the standard basis decomposition approach and clearly demonstrate that the thickness of Al is overestimated while the thickness of PMMA is underestimated. (b) The computed attenuation factors for the standard basis decomposition procedure are compared against the actual attenuation factors for 80 kVp (open circles), 100 kVp (squares), 120 kVp (diamonds), and 140 kVp (gray circles). For low attenuation factors corresponding to thicker objects, a pronounced difference between actual and computed attenuation factors is seen. The error at higher attenuation levels is thought to be due to beam hardening.