Dual- and Multi-Energy CT: Principles, Technical Approaches, and Clinical Applications

Abstract

In x-ray computed tomography (CT), materials having different elemental compositions can be represented by identical pixel values in a CT image (i.e. CT number values), depending on the materials’ mass density. Thus, the differentiation and classification of different tissue types and contrast agents can be extremely challenging. In dual-energy CT (DECT), an additional attenuation measurement is obtained with a second x-ray spectrum (i.e. a second “energy”), allowing the differentiation of multiple materials. Alternatively, this allows quantification of the mass density of two or three materials in a mixture with known elemental composition. Recent advances in the use of energy-resolving, photon-counting detectors for CT imaging suggest the ability to acquire data in multiple energy bins, which is expected to further improve the signal-to-noise ratio for material-specific imaging. In this work, the underlying motivation and physical principles of dual- or multi-energy CT are reviewed and each of the current technical approaches described. In addition, current and evolving clinical applications are introduced.

Iodine concentration as a perfusion surrogate marker in oncology: Further elucidation of the underlying mechanisms using Volume Perfusion CT with 80 kVp

“…This effect enhances the x-ray absorption by iodine due to increased photoelectric interactions and decreased Compton scattering [20]. Then CT number pairs at low energy and high energy of different materials are mapped onto a calibration diagram [29]. The material or percentage composition of a material of interest can then be estimated depending on the position in the diagram [29].…”

“…Then CT number pairs at low energy and high energy of different materials are mapped onto a calibration diagram [29]. The material or percentage composition of a material of interest can then be estimated depending on the position in the diagram [29]. When performing iodine quantification using single energy techniques, conversion factors between the kVp setting and CT enhancement are calculated for various iodine concentrations.…”

Selecting a CT scanner for cardiac imaging: the heart of the matter

“…30 Another emerging area is the application of dual-energy CT in cardiac investigations. 31 In these areas, manufacturers have again used different approaches to achieve the same aim, and different aspects of scanner technology need to be considered if the efficacy of these applications is to be compared.…”

Diagnostic Imaging for Solid Renal Tumors: A Pictorial Review

“…Contrast-enhanced dual-energy CT, in which 2 CT data sets are acquired with different x-ray spectra allowing the differentiation of the 2 materials, showed improved specificity for characterization of small renal tumors compared with conventional CT imaging [47][48][49]. However, this technique is not widely available.…”