A Comparison of Noise and Dose in Conventional and Energy Selective Computed Tomography

We compare the noise properties of conventional and energy selective X-ray computed tomography. The images produced by the systems are not directly comparable so we discuss their relationship and show that the conventional image is a subset of the energy selective data. We describe how to form a conventional image from the energy selective images and demonstrate that, if this is done at the optimal display energy, the resulting conventional image will have the same noise as that produced by a conventional system with the same dose. But the energy selective system also extracts all the energy dependent information so it produces more information for the same dose than a conventional system.