Evaluation of metal artefact techniques with same contrast scale for different commercially available dual-energy computed tomography scanners.

The aim of our study is to evaluate the metal artefact reduction techniques with the same contrast scale for different vendors' dual-energy CT (DECT): kV-CT image with metal artefact reduction method and monoenergetic CT image using Canon's DECT, and monoenergetic CT image with metal artefact reduction method using GE's DECT. The kV-CT image and DECT scans were performed with the water-based polymethyl methacrylate phantom with various metal materials (brass, aluminium, copper, stainless steel, steel, lead, and titanium). Two types of metal artefact reduction (MAR) algorithm with the monoenergetic CT images were used. Smart MAR implemented by GE and the kV-CT images with MAR algorithms. Single-energy metal artefact reduction (SEMAR), implemented by Canon, was reconstructed. The artefact index was evaluated using the converted electron density values from the kV-CT and DECT images. The artefact index with all material inserts in the monoenergetic CT images were smallest at 70-90 keV for Canon and 140 keV for GE. The artefact index without SEMAR was larger than that with SEMAR for the 80 and 135-kV CT images. In the comparison of the artefact index for the converted electron density images from the 80 and 135-kV CT images with SEMAR, as well as the monoenergetic CT images with and without MAR, the monoenergetic CT image at 140 keV with MAR showed a reduction. In the comparison of the monoenergetic CT images at 140 keV and other energy ranges without and with Smart MAR, there was no statistically significant difference (P < 0.05) for all-metal inserts at more than 100 keV for Canon's DECT and 70 keV for GE's DECT. The metal artefact could be reduced by using a monoenergetic CT image at high energy with MAR algorithm. The metal artefact for the different-contrast-scale images can be compared on the same contrast scale by the electron density conversion method.