What is dual‑energy computed tomography (DECT) and what are its benefits?

What is Dual-Energy CT and Its Benefits?

Dual-energy CT (DECT) is an advanced imaging technique that acquires CT data at two different X-ray energy spectra, enabling material characterization and tissue differentiation beyond conventional single-energy CT by exploiting the differential attenuation of materials at varying energy levels. 1, 2

Technical Principles

DECT operates by obtaining two datasets with distinct X-ray energy spectra from the same anatomic region, typically using energy levels around 80 kVp and 120 kVp. 1, 2 The fundamental physics relies on the fact that different materials exhibit energy-dependent X-ray absorption behavior based on their atomic number and electron density, not just attenuation alone. 2, 3

Available Technologies

DECT can be implemented through several hardware approaches: 1, 4

• Dual-source systems with two X-ray tubes and two detectors
• Rapid tube-voltage switching using a single source that alternates between energy levels
• Dual-layer detector CT with specialized detectors capable of separating high and low energy photons
• Photon-counting detector CT (PCD-CT), the newest technology using multiple energy bins 1

Key Clinical Benefits

Material Decomposition and Characterization

DECT enables distinction of tissues and materials with similar conventional CT attenuation by analyzing their differential behavior at different energy levels. 1, 2 This capability allows:

• Detection and quantification of specific materials including iodine, calcium, and uric acid 2, 5
• Differentiation of calcified versus non-calcified structures, which was historically used in chest radiography for improved pulmonary nodule detection 1
• Identification of bone marrow edema and urate crystal deposition in musculoskeletal imaging 1

Virtual Non-Contrast Imaging

DECT can generate virtual non-contrast images by removing iodine from contrast-enhanced acquisitions, eliminating the need for separate true non-contrast scans. 1 This provides several advantages:

• Reduced radiation exposure by avoiding duplicate acquisitions 1, 5
• Visualization of intramural hematoma in aortic imaging, where the hyperattenuating crescent is often masked on contrast-enhanced images 1
• No significant difference in diagnostic confidence between true and virtual non-contrast images for conditions like intramural hematoma 1

Virtual Monoenergetic Imaging

Virtual monoenergetic reconstructions at optimized energy levels can improve image quality by reducing beam hardening artifacts and optimizing contrast-to-noise ratios. 5, 6 This is particularly valuable:

• Around cardiac devices and prosthetic valves where metal artifacts are problematic 1
• In patients with high body mass index requiring enhanced vascular opacification 1

Iodine Mapping and Perfusion Imaging

DECT enables creation of iodine enhancement maps and perfused blood volume images without requiring dynamic imaging. 1, 6 Applications include:

• CT lung perfusion imaging showing iodine content in the distal pulmonary bed for pulmonary embolism evaluation 1
• Myocardial perfusion maps in cardiac imaging 6
• Subtraction imaging creating parenchymal enhancement maps similar to dual-source DECT 1

Improved Lesion Detection and Characterization

DECT adds value through improved lesion detection, characterization, and ease of interpretation in routine clinical scenarios. 5 Specific applications include:

• Differentiation of intracranial hemorrhage from contrast staining in stroke imaging 2
• Characterization of incidentally detected renal and adrenal lesions 2
• Identification of uric acid renal stones and diagnosis of gout 2
• Distinguishing areas of contrast enhancement from osseous matrix production in primary bone tumors 1

Radiation Dose Considerations

Radiation dose with DECT is similar to single-energy CTA acquired at 120 kV but typically higher than CTA acquired at lower kV settings. 1 However:

• PCD-CT can provide similar image quality at lower radiation doses compared to conventional DECT 1
• Virtual non-contrast imaging eliminates the need for separate non-contrast acquisitions, potentially reducing overall radiation exposure 1, 5

Workflow and Protocol Optimization

DECT requires sophisticated noise suppression algorithms to optimize final image quality, which is mainly determined by vendor-specific postprocessing rather than raw data quality. 1 For optimal implementation:

• Higher iodine concentration (350-400 mg/mL) is advised when using PCD-CT for perfused blood volume imaging 1
• Protocols must be inherently more robust to account for unexpected pathology or suboptimal contrast opacification 5

Common Pitfalls to Avoid

• Do not assume all DECT technologies perform identically—image quality variabilities exist between dual-source, rapid switching, and dual-layer detector systems 4
• Recognize that contrast-to-noise levels vary with energy separation, though final images are optimized through postprocessing 1
• Understand that dual-source systems sacrifice superior temporal resolution when operating in dual-energy mode 1