Dual-energy CT: theoretical principles and clinical applications

  • Andrea AgostiniEmail author
  • Alessandra Borgheresi
  • Alberto Mari
  • Chiara Floridi
  • Federico Bruno
  • Marina Carotti
  • Nicolò Schicchi
  • Antonio Barile
  • Stefania Maggi
  • Andrea Giovagnoni


The physical principles of dual-energy computed tomography (DECT) are as old as computed tomography (CT) itself. To understand the strengths and the limits of this technology, a brief overview of theoretical basis of DECT will be provided. Specific attention will be focused on the interaction of X-rays with matter, on the principles of attenuation of X-rays in CT toward the intrinsic limits of conventional CT, on the material decomposition algorithms (two- and three-basis-material decomposition algorithms) and on effective Rho-Z methods. The progresses in material decomposition algorithms, in computational power of computers and in CT hardware, lead to the development of different technological solutions for DECT in clinical practice. The clinical applications of DECT are briefly reviewed in relation to the specific algorithms.

List of symbols


Cross section, or the probability of interaction photon–electron


Rayleigh scattering


Photoelectric absorption

K, L

Inner electron shells


Atomic number






Physical density


Atomic weight


Plank’s constant


Speed of photon

Proportional to


Compton scattering


Electron density






Euler’s number or Napier’s constant


CT number in Hounsfield’s units


Mass attenuation coefficient

Summation of multiple terms

Approximately equal to


Constant in Eq. 8


Constant in Eq. 8


Exponent in Eq. 8


Exponent in Eq. 8


Klein–Nishina function

ρZ and Rho-Z

Material decomposition method using effective density and atomic numbers


Spatial location of the unit volume


Physical density of the ith basis material


Area density of the ith basis material


Fractional volume of the ith basis material


Fractional mass of the ith basis material



Dual-energy CT


Computed tomography


Atomic number


Dual-source dual-energy CT


Virtual monoenergetic images


Field of view


Virtual non-contrast


Magnetic resonance imaging


Volume rendering



No funding was received for this paper.

Compliance with ethical standards

Conflict of interest

AA is a speaker for Siemens Healthineers. The other authors have no conflict of interest to declare. 


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Copyright information

© Italian Society of Medical Radiology 2019

Authors and Affiliations

  • Andrea Agostini
    • 1
    • 2
    Email author
  • Alessandra Borgheresi
    • 2
  • Alberto Mari
    • 3
  • Chiara Floridi
    • 4
  • Federico Bruno
    • 5
  • Marina Carotti
    • 2
  • Nicolò Schicchi
    • 2
  • Antonio Barile
    • 5
  • Stefania Maggi
    • 3
  • Andrea Giovagnoni
    • 1
    • 2
  1. 1.Department of Clinical, Special and Dental SciencesUniversity Politecnica delle MarcheAnconaItaly
  2. 2.Department of Radiology – Division of Special and Pediatric RadiologyUniversity Hospital “Umberto I – Lancisi – Salesi”AnconaItaly
  3. 3.Department of Radiology – Division of Medical PhysicsUniversity Hospital “Umberto I – Lancisi – Salesi”AnconaItaly
  4. 4.Department of Health Sciences, Diagnostic and Interventional RadiologyHospital “San Paolo”, University of MilanMilanItaly
  5. 5.Department of Biotechnological and Applied SciencesUniversity of L’AquilaL’AquilaItaly

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