Florian Schwarz MD, Presenter: Nothing to Disclose

Markus Haindl BS, Abstract Co-Author: Nothing to Disclose

Felix G. Meinel MD, Abstract Co-Author: Nothing to Disclose

Teresa Goelz BS, Abstract Co-Author: Nothing to Disclose

Sven Florian Thieme MD, Abstract Co-Author: Nothing to Disclose

Thorsten R. C. Johnson MD, Abstract Co-Author: Speakers Bureau, Siemens AG Research Grant, Bayer AG

Maximilian F. Reiser MD, Abstract Co-Author: Nothing to Disclose

To determine the effect of a tin-filter at the high-energy tube on the quantification of iodine concentration and radiodensity of the virtual-non-contrast enhanced image by dual-energy Computed Tomography (DECT) in the presence of different  background solutions with low photoeffect.

A phantom containing 30 samples of iodine-containing contrast material (CM) (0, 5, 10, 15, 20 and 25 mgI/ml) was constructed. CM was diluted either in water (6 samples, 0 – 25 mgI/ml), in an aqueous carbohydrate solution with a radiodensity of 40 HU (6 samples, 0 – 25 mgI/ml), in an aqueous carbohydrate solution with a radiodensity of 15 HU (6 samples, 0 – 25 mgI/ml), in a water-lipid-emulsion with a radiodensity of -100 HU (6 samples, 0 – 25 mgI/ml) or in a water-lipid-emulsion with a radiodensity of -62 HU (6 samples, 0 – 25 mgI/ml). Besides iodine-containing contrast agent, none of the atoms / molecules in the samples had pronounced photoeffect. The phantom was embedded in a thorax-shaped water-tank and scanned on a dual-source scanner using different tube energy combinations (Sn140/80kVp, Sn140/100kVp and 140/80 kVp) with application of a tin filter when stated. Commercial software was used to calculate iodine concentrations. Agreement with true values was quantified by ICC and Bland-Altman-Plots.

For all combinations of tube energies, there was excellent correlation and agreement of measured and true iodine concentration across all background solutions and regardless of whether a tin filter was used (Sn140/100kVp: r = 0.994, ICC = 0.9931; Sn140/80kVp: r = 0.992, ICC = 0.9911, 140/80 kVp: r = 0.995, ICC = 0.998). For the quantification of VNC-radiodensity, however, the application of tin-filtering resulted in significantly higher accuracy (standard deviation of differences in Bland-Altman-Plot: 9.4 and 10.2 for Sn140/80kVp and Sn140/100kVp, but 16.8 for 140/80kVp, p < 0.05).   

Dual-Energy CT permits a highly accurate quantification of iodine concentration across a wide range of backgrounds with non-iodine-related radiodensity. Increasing spectral differentiation by adding a tin-filter to the high-energy tube particularly improves the accuracy of VNC radiodensity measurements. 

Our study confirms the high accuracy of dual-energy CT based iodine and VNC measurements, particularly when using a tin-filter. This is essential groundwork for all clinical dual-energy applications.

Schwarz, F, Haindl, M, Meinel, F, Goelz, T, Thieme, S, Johnson, T, Reiser, M, Quantification of Absolute Iodine Concentration and Virtual-Non-Contrast Radiodensity by Dual-Energy CT (DECT) in "Contrast-enhanced" Background Solutions with Low Photoeffect - Increased Accuracy with Tin-filtering of the High-Energy Tube.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043921.html