1. Dual-Energy Computed Tomography
Reza Forghani, MD, PhD, Bruno De Man, PhD, Rajiv Gupta, MD, PhD 
Neuroimaging Clinics 
Volume 27, Issue 3, Pages (August 2017)
DOI: /j.nic
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2. Fig. 1
SECT equivalent VMIs at 65 keV (A) and 70 keV (B) from a scan of a patient with a left laryngeal cancer (arrows) acquired with a fast kilovolt peak switching single source DECT scanner. As discussed in the text, VMIs at these energies are nearly equivalent to a standard 120-kVp SECT acquisition. Quantitatively, there are small differences in tissue attenuation but subjectively they are very similar.
Neuroimaging Clinics  , DOI: ( /j.nic )
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3. Fig. 2
Strong spectral properties of iodine in CT contrast agents. Spectral Hounsfield unit attenuation curves derived from ROI analysis of iodine solutions at 3 different concentrations, imaged within a phantom, are shown. Note the progressive and marked increase in attenuation at lower energies approaching the K-edge of iodine (33.2 keV). For example, note the higher attenuation at 40 keV compared with conventional SECT equivalent VMI energies at 65 or 70 keV. However, there is a tradeoff, with increasing image noise at lower energies, as represented by the error bars depicting SD of attenuation within the ROI evaluated. The scan was acquired with a fast kilovolt peak switching scanner.
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4. Fig. 3
Examples of VMIs at different energies reconstructed from a contrast-enhanced neck CT of a patient with a left oral tongue cancer (arrow). VMIs of the same scan/slice are shown at 40 (A), 50 (B), 65 (C), 80 (D), 110 (E), and 140 (F) keV. In order to emphasize the differences between different VMI energies, all images were displayed using the same window-level setting. Note how enhancing tissues such as the tumor (arrow) or vessels have increased attenuation with decreasing VMI energy, with the highest attenuation on the 40 keV VMI (A). However, there is a tradeoff as image noise increases with increasing conspicuity of enhancing tissue at lower energies, and this tradeoff is expected with most of the currently used DECT systems, as described in the text. Conversely, at high energies, the lower noise is accompanied by lower attenuation and contrast of enhancing tissues. The scan was acquired with a fast kilovolt peak switching scanner.
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5. Fig. 4
Example of low-energy VMIs obtained using a layered or sandwich detector system. (A) Conventional SECT equivalent and (B) 55-keV VMI are shown. With these systems, lower-energy VMIs may be reconstructed without increased image noise. As the ROI analysis shows, the SD, representative of image noise, is actually lower on the 55 keV image compared with the conventional CT image.
(Courtesy of Professor, David Maintz, MD, The Institute for Diagnostic and Interventional Radiology, Uniklinik, Cologne, Germany; and Philips Healthcare; with permission.)
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6. Fig. 5
Example of WA or blended image. This type of reconstruction is obtained when using dual-source CT scanners. Axial head CT obtained after administration of contrast is shown in a patient with an intracranial tumor (arrows). A linear blend consisting of 30% of the low- and 70% of the high-energy acquisitions is typically considered equivalent to the standard 120-kVp SECT acquisition. The scan was acquired with a dual-source scanner.
Neuroimaging Clinics  , DOI: ( /j.nic )
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7. Fig. 6
BMD. All tissue attenuations are fundamentally a combination of Compton scatter and photoelectric absorption (ignoring the small contribution from Rayleigh scatter). Different representations are obtained by projecting these fundamental attenuation properties onto different spaces. Graphs illustrating the principles and approach for (A) water-iodine basis-material decomposition, (B) multimaterial decomposition, and (C, D) virtual monochromatic imaging at 70 keV and 40 keV are shown. Please refer to the text for additional details and explanations.
(Courtesy of Reza Forghani, MD, PhD, Montreal, Quebec, Canada and Bruno De Man, PhD, Niskayuna, NY)
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8. Fig. 7
Examples of different BMD maps from a contrast-enhanced CT of the neck. (A) 65 keV VMI (typically considered equivalent to SECT), (B) water-iodine BMD map (one type of virtual unenhanced image), and (C, D) iodine-water BMD maps displayed in gray scale or color are shown. Note the suppression of iodine in the vessels and thyroid gland on the virtual unenhanced image (B). The iodine-water maps represent the iodine distribution and relative iodine content in different tissues (for example higher intensity in the carotid arteries compared with the internal jugular veins). ROI analysis of iodine-water maps can provide an estimate of iodine concentration within a tissue. The scan was acquired with a fast kilovolt peak switching scanner.
Neuroimaging Clinics  , DOI: ( /j.nic )
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9. Fig. 8
Example of iodine map of the brain from the same patient as shown in Fig. 5. Note increased intensity in the area of the enhancing tumor (arrows). The scan was acquired with a dual-source scanner.
Neuroimaging Clinics  , DOI: ( /j.nic )
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10. Fig. 9
Example of iodine-water material decomposition map from a contrast-enhanced CT of the neck from a patient with buccal invasion by tumor (arrows). The iodine (or iodine-water) maps represent the iodine distribution and relative iodine content in different tissues (for example note the higher “signal” in the tumor compared to surrounding tissues). ROI analysis of iodine-water maps can provide an estimate of iodine concentration within a tissue. The scan was acquired with a fast kilovolt peak switching scanner.
Neuroimaging Clinics  , DOI: ( /j.nic )
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