The technology behind dual-energy CT (DECT) has been around for nearly 4 decades1,2, but it was not until 2006 that the first dual-source CT scanner became available for clinical use.3 The years that followed brought about further technologic advances, including the development of additional techniques for obtaining DECT data. Modern DECT imaging can be performed with radiation doses comparable to conventional single-energy CT (SECT).4 Applications of DECT exist throughout the human body, with many important applications in neuroradiology. Familiarity with the principles, applications, and potential pitfalls of DECT will be important as the use of clinical DECT becomes increasingly common.
The relationship between the CT attenuation of different materials and photon energy forms the basis of DECT.5 The CT number of a voxel is related to its linear attenuation coefficient. The linear attenuation coefficient is not only a function of material composition, but also a function of material mass density and the photon energies interacting with the material.6 Notably, linear attenuation coefficients of elements with higher atomic numbers, such as iodine and calcium, have a greater energy dependence than those of elements with low atomic numbers, such as hydrogen, carbon, nitrogen, and oxygen, which make up the bulk of the human body.5 Under certain conditions, different materials can exhibit similar attenuation on SECT. In DECT, however, attenuation measurements are obtained at 2 different energy spectra, allowing for such materials to be distinguished from one another provided that they differ sufficiently in atomic number.5 DECT data can be postprocessed with material decomposition algorithms to generate quantitative iodine maps , virtual noncontrast (VNC) images, and virtual noncalcium (VNCa) images.7 Additionally, simulated SECT images can be generated, including weighted average images created by blending low- and high-energy data, and … more »