Principles and applications of multienergy CT: Report of AAPM Task Group 291

Area of Science:

• Medical Imaging
• Radiology
• Physics

Background:

• Standard X-ray computed tomography (CT) struggles to differentiate materials with similar attenuation properties.
• Material differentiation in CT is challenging due to density and X-ray beam energy dependencies.
• Multi-energy CT acquires data at multiple energy levels to overcome these limitations.

Purpose of the Study:

• To review the physical principles and technical approaches of multi-energy CT.
• To describe current and evolving clinical applications of multi-energy CT.
• To summarize the impact of multi-energy CT on patient radiation dose.

Main Methods:

• Multi-energy CT systems acquire attenuation measurements at multiple X-ray energy levels.
• Commercial systems utilize various approaches: sequential scans, fast switching, filtration, dual-source, or dual-layer detectors.
• Energy-resolving, photon-counting detectors are under evaluation.
• Material decomposition algorithms analyze projection or image data using effective atomic number and mass density.

Main Results:

• Multi-energy CT allows differentiation of materials that appear identical in single-energy CT.
• Clinical applications include calcium removal, iodine quantification, virtual non-contrast imaging, perfused blood volume assessment, and material characterization (e.g., kidney stones, gout).
• Various technological approaches exist for data acquisition, with photon-counting detectors emerging.

Conclusions:

• Multi-energy CT significantly enhances material differentiation capabilities compared to conventional CT.
• The technology supports a growing range of clinical applications for improved diagnostic accuracy.
• Understanding the physical principles and technical variations is crucial for effective implementation and dose management.