Figure 2.1 depicts the setup of a spectral CT x-ray attenuation measurement. The source S emits a flux of x-ray quanta at an object. The object consists of x-ray-attenuating materials that are described by their spectral attenuation coefficient μ(E, r) at position r. The detector registers the quanta passing through the object. Two independent measurements with and without the object are performed. The resulting intensities I and I0 yield the attenuation A = I=I0 ∈ [0,1], which describes the relative decrease in intensity caused by x-ray attenuation in the object. In the following, we briefly review the spectral characteristics of the source, object, and detector.
Physics of Spectral CT Measurements