Evaluation of raw-data-based and calculated electron density for contrast media with a dual-energy CT technique.

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The aim of the current study is to evaluate the accuracy and the precision of raw-data-based relative electron density (REDraw) and the calibration-based RED (REDcal) at a range of low-RED to high-RED for tissue-equivalent phantom materials by comparing them with reference RED (REDref) and to present the difference of REDraw and REDcal for the contrast medium using dual-energy CT (DECT). The REDraw images were reconstructed by raw-data-based decomposition using DECT. For evaluation of the accuracy of the REDraw, REDref was calculated for the tissue-equivalent phantom materials based on their specified density and elemental composition. The REDcal images were calculated using three models: Lung-Bone model, Lung-Ti model and Lung-Ti (SEMAR) model which used single-energy metal artifact reduction (SEMAR). The difference between REDraw and REDcal was calculated. In the titanium rod core, the deviations of REDraw and REDcal (Lung-Bone model, Lung-Ti model and Lung-Ti model with SEMAR) from REDref were 0.45%, 50.8%, 15.4% and 15.0%, respectively. The largest differences between REDraw and REDcal (Lung-Bone model, Lung-Ti model and Lung-Ti model with SEMAR) in the contrast medium phantom were 8.2%, -23.7%, and 28.7%, respectively. However, the differences between REDraw and REDcal values were within 10% at 20mg/ml. The standard deviation of the REDraw was significantly smaller than the REDcal with three models in the titanium and the materials that had low CT numbers. The REDcal values could be affected by beam hardening artifacts and the REDcal was less accurate than REDraw for high-Z materials as titanium. The raw-data-based reconstruction method could reduce the beam hardening artifact compared with image-based reconstruction and increase the accuracy for the RED estimation in high-Z materials, such as titanium and iodinated contrast medium.