Abstract
Purpose: The K-edge of gold (81 keV) is located within the energy range of diagnostic CT. This might be advantageous for material differentiation in dual-energy CT (DECT). The aim of this in vitro study was to compare the differentiation between iodine or gold and body tissues using DECT at different kV spectra. Methods and Materials: A water filled tank phantom containing specimens with iodine (iopamidol), gold (sodium aurothiomalate), compact bone (compact porcine bone) and porcine muscle was scanned using a dual source CT (Definition, Siemens Healthcare). Consecutive scans were performed at 80 kVp, 100 kVp, 120 kVp and 140 kVp with constant mAs settings. The mean attenuation values of the specimens were measured, and differences in calculated dual-energy ratios (DEratio) between body tissues and iodine or gold were determined for different DE spectra. Results: The attenuation of gold increased compared to 80 kVp at higher kVp-settings, while the attenuation of all other specimens decreased. The calculated DEratios at 80/100 kVp, 80/120 kVp and 80/140 kVp were 1.31, 1.62 and 1.91 for iodine, 0.89, 0.88 and 0.92 for gold, 1.20, 1.39 and 1.45 for compact bone, 1.01, 1.03 and 1.08 for muscle. The differences between the DEratios 80/100 kVp, 80/120 kVp and 80/140 kVp were 0.11, 0.23 and 0.46 for iodine and bone, 0.31, 0.51 and 0.53 for gold and bone, 0.29, 0.59 and 0.83 for iodine and muscle, 0.12, 0.15 and 0.16 for gold and muscle. Conclusion: DEratio of gold remains relatively stable along the energy spectrum of diagnostic CT and allows a reliable material differentiation between gold and bone already at contiguous low tube voltage settings (80 kV and 100 kV). Thus, gold might have a potential as a contrast agent for DECT.
Highlights
Materials can be differentiated by applying different Xray spectra and analyzing the differences in attenuation [1,2,3]
The attenuation of gold increased compared to 80 kVp at higher kVp-settings, while the attenuation of all other specimens decreased
dual-energy ratios (DEratio) of gold remains relatively stable along the energy spectrum of diagnostic CT and allows a reliable material differentiation between gold and bone already at contiguous low tube voltage settings (80 kV and 100 kV)
Summary
Materials can be differentiated by applying different Xray spectra and analyzing the differences in attenuation [1,2,3]. This works especially well in materials with large atomic numbers due to the photo effect. Iodine is commonly used in CT as a contrast material and is generally known to have stronger enhancement at low tube voltage settings [4,5]. Selective iodine imaging using dual energy CT (DECT) was proposed already by Hounsfield [6] and further investigated in the late 1970s [3,7,8]. Technical limitations of the CT scanners at that time prevented the development of routine clinical applications [9]
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