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Dual-energy computed tomography (CT) has the potential to improve detection of abnormalities and increase diagnostic confidence in the evaluation of a variety of neurologic conditions.
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Virtual monochromatic imaging (VMI) can be used as an additional tool to help differentiate materials and may be useful to determine optimal VMI energy level for visualization of brain lesions.
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Three-material decomposition techniques can be readily performed to create calcium maps, virtual noncalcium images, and
Miscellaneous and Emerging Applications of Dual-Energy Computed Tomography for the Evaluation of Intracranial Pathology
Section snippets
Key points
Technical consideration for dual-energy computed tomography
In practice, 2 CT images taken at different tube voltages, typically 80 and 140 kV, are sufficient to classify many tissues. Processing dual-energy data to generate material selective or virtual monochromatic images can be performed either in the raw data space or in the image data space. Then, low-energy and high-energy images are reconstructed as a first step, and the dual-energy processing is applied to these images. Raw data-based evaluation is often considered superior to image data-based
Virtual monochromatic imaging
CT exposures, including dual-energy mode acquisitions, consist of photons within a broad spectrum of energies (polychromatic). The data from the 2 polychromatic exposures of a dual-energy scan can be reconstructed into a single data set that reflects the properties of a scan with a monochromatic x-ray beam, which is called “virtual monochromatic or monoenergetic imaging.” VMI represents one of the most widely applicable attributes of dual-energy CT and has the potential to optimize the image
Material separation using dual-energy computed tomography
One of the most versatile techniques made possible by dual-energy CT is material separation. Different vendors have adopted different algorithms for material decomposition with dual-energy CT. With a dual-source dual-energy CT (SOMATOM Definition Flash; Siemens Healthcare, Forchheim, Germany), a 3-material decomposition (default set: iodine, soft tissue, and fat) algorithm has been developed to process the data in the image-data space. With a 2-rotation kilovolt-milliampere switching system
Emerging applications of dual-energy computed tomography: future developments and challenges
Recently, dual-energy CT postprocessing techniques with raw data-based analysis have been used to create a real-time interactive display of VMI, the Zeff, and electron density, which can be readily displayed on an advanced workstation (Fig. 15). Zeff and the characteristics of the spectral HU curves may help to distinguish different lesions and have been investigated in many clinical settings, including classification of benign and malignant thyroid nodules17 and differentiation between benign
Summary
With rising clinical interest and widely available scanner technology, it is likely that dual-energy CT will increasingly be incorporated into the clinical routine as radiologists further integrate this technology into their daily practice. Various postprocessing software for dual-energy CT, although vendor dependent, are available, enable additional analysis, and provide effective tools for more accurate interpretation of clinical images. Preliminary studies have shown their additional
Acknowledgments
The authors greatly appreciate the participation of So Tsushima, MSc, Toshiba Medical Systems Corporation, Tokyo, Japan, for technical advice on dual-energy CT.
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