  Spectral imaging is an umbrella term for energy-resolved x-ray imaging in
medicine. The technique makes use of the energy dependence of x-ray attenuation
to either increase the contrast-to-noise ratio, or to provide quantitative
image data and reduce image artefacts by so-called material decomposition.
Spectral imaging is not new, but has gained interest in recent years because of
rapidly increasing availability of spectral and dual-energy CT and the dawn of
energy-resolved photon-counting detectors. This review examines the current
technological status of spectral and dual-energy imaging and a number of
practical applications of the technology.
