EVALUATION OF IODINE AND CALCIUM CT NUMBER IN DUAL-ENERGY COMPUTED TOMOGRAPHY (DECT) USING A FABRICATED IN-HOUSE PHANTOM

The aim of this study was to develop an in-house phantom with inserts of iodine and calcium materials for evaluating the accuracy of CT numbers from virtual monochromatic image (VMI) of DECT. The phantom was made from polyester resin (PESR) mixed with methyl ethyl ketone peroxide (MEKP) as catalyst in a ratio of 300:1, with a 16 cm diameter and 5 cm height. The phantom had 10 holes, each with a diameter of 1.5 cm. Each hole was filled with water, air, iodine (with various concentrations of 5, 7.5, 10, and 15 mg/ml), and calcium (with various concentrations of 200, 300, 500, and 600 mg/ml). The phantom was scanned by an Ultrafast kV Switching DECT with a tube voltage of 80/140 kV, slice thickness of 5 mm, rotation time of 0.5 s, and tube current variations (200, 250, 300, 335, and 370 mA). Images were reconstructed to a VMI at 50, 70, and 100 keV. The CT number accuracy of VMI images was measured using IndoQCT software. Absolute percentage error (APE) was calculated from measured CT numbers and standard phantom. We found that the changes in CT numbers of iodine and calcium showed the same trend. The CT numbers for both iodine and calcium slightly increased with higher tube currents. The CT number decreased by 1.5-3 times from an energy of 50 to 100 keV. For all concentrations, the APE of CT numbers of the in-house phantom were <32% and <25% compared to the standard for iodine and calcium, respectively.