Abstract
The dependence of CT number and image contrast on the tube voltage, namely the photon energy in diagnostic CT imaging was theoretically investigated. The linear attenuation coefficients for various elements and mixtures were obtained for three cases that 1) for the bremsstrahlung X-rays with an ideal detector, 2) for the bremsstrahlung X-rays with an assumed detector, and 3) for the monoenergetic X-rays, by using the X-ray photon spectrum and the sensitivity spectrum of the CT detector. As a result, the CT number to several materials converged to zero with an increase of tube voltage in all cases, whereas that of some materials diverged from zero. This result indicates that the image contrast of some materials in the restricted energy range such as diagnostic range may be emphasized by using high tube voltage, as opposed to common knowledge.
