Effects of scattered x-rays on cone-beam 3-D CT images

Scatter to primary radiation ratios at detector position were calculated for cylindrical water phantoms in corn-beam 3D-CT scanner using the Monte Carlo simulation method. A quantity of scatter reached on detector was large and was nearly twice as much as that of primary at the center of cylindrical water phantom with radius of 10 cm, A large quantity of scatter in projection data caused a decrease in CT numbers of reconstructed images and cupping effects were obserbed. When the x-ray photons exposed unformly on phantom with bow-tie filter, the scattered radiation was decreased to half and the cupping effects were not obserbed. While CT numbers in the whole region of images were reduced and roundedoff images were reconstructed.