C McCollough¹*, T Flohr²*, X Duan³*, C McCollough⁴*, (1) Mayo Clinic, Byron, MN, (2) Siemens Healthcare GmbH, Forchheim, BY, DE, (3) UT Southwestern Medical Center, Dallas, TX, (4) Mayo Clinic, Byron, MN

• 
  C McCollough
• 
  T Flohr
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  X Duan

WE-AB-TRACK 2-0 (Wednesday, 7/28/2021) 10:30 AM - 12:30 PM [Eastern Time (GMT-4)]

The motivation for dual- or multi-energy CT (DECT or MECT) is that in x-ray computed tomography (CT), materials with different elemental compositions can have identical CT number values, depending on the mass density of each material and the energy of the detected x-ray beam. Differentiating and classifying different tissue types and contrast agents can thus be extremely challenging. In MECT, one or more additional attenuation measurements are obtained at a second, third or more energy. This allows the differentiation of at least two materials. Commercial DECT systems (only two energy measurements) are now available either using sequential acquisitions of low- and high-tube potential scans, fast tube-potential switching, beam filtration combined with spiral scanning, dual-source, or dual-layer detector approaches. The use of energy-resolving, photon-counting detectors is now being evaluated on research systems. Irrespective of the technological approach to data acquisition, all commercial MECT systems today provide dual-energy data. Material decomposition algorithms are then used to identify specific materials according to their effective atomic number and/or to quantitate mass density. These algorithms are applied to either projection or image data. Since 2006, a number of clinical applications have been developed for commercial release, including those that automatically 1) remove the signal from bony anatomy and/or calcified plaque; 2) create iodine concentration maps from contrast-enhanced CT data and/or quantify absolute iodine concentration; 3) create virtual non-enhanced images from contrast-enhanced scans; 4) identify perfused blood volume in lung parenchyma or the myocardium; and 5) characterize materials according to their elemental compositions, which can allow in vivo differentiation between uric-acid and non-uric-acid urinary stones or uric acid (gout) or non-uric-acid (calcium pyrophosphate) deposits in articulating joints and surrounding tissues. AAPM Report 291 provides an authoritative, open-access, peer-reviewed review of the topic of MECT for both the imaging and therapy communities. It describes the fundamental principles of MECT in an intuitive manner and with mathematical rigor, current and emerging manufacturer implementations, and current and emerging clinical applications.

Learning Objectives:
1. Understand the motivation for and fundamental principles of multi-energy CT
2. Appreciate the range of technical implementations of multi-energy CT
3. Recognize strengths and weaknesses of different technical implementation strategies
4. Identify clinical CT applications made possible by multi-energy CT

Funding Support, Disclosures, and Conflict of Interest: Cynthia McCollough receives research support from Siemens Healthcare, which is not directly related to this work.

Handouts

• 166-57650-15651646-171437-1588735846.pdf (Cynthia McCollough)
• 166-57656-15651646-171086-1576734399.pdf (Xinhui Duan)
• 166-57654-15651646-171437-652258719.pdf (Cynthia McCollough)
• 166-57655-15651646-176508.pdf (Thomas Flohr)
• 166-57657-15651646-171437-1181511432.pdf (Cynthia McCollough)

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