Object size determination at computed tomography

To investigate whether large differences in attenuation between an object and its background at CT examination alter the apparent size of the object on the image compared with the conditions with a small attenuation difference, phantom experiments were performed. At the same time the influence of large attenuation differences on the geometric resolution was examined. The results show that neither the size reproduction of the object nor the geometric resolution is altered by variations in attenuation differences. Especially with large differences in attenuation between the object and background, however, the window centre setting was of greatest importance for correct reproduction of the object.