Complementary contrast media for metal artifact reduction in Dual-Energy CT

摘要

Image artifacts generated by metal implants have been a problem associated with CT since its introduction. Recent techniques to mitigate this problem have included the utilization of certain Dual-Energy CT (DECT) features. DECT can produce virtual monochromatic spectral (VMS) images, simulating how the data would appear if scanned at a single x-ray energy (keV). High-keV VMS images can greatly reduce the severity of metal artifacts. A problem with these high-keV images is that contrast enhancement provided by all commercially-available contrast media is severely reduced. It is therefore impossible to generate VMS images with simultaneous high contrast and minimized metal artifact severity. Novel contrast agents based on higher atomic number elements can maintain contrast enhancement at the higher energy levels where artifacts are reduced. This study evaluated three such candidate elements: bismuth, tantalum, and tungsten, as well as two conventional contrast elements: iodine and barium. A water-based phantom with vials containing these five elements in solution, as well as different artifact-producing metal structures, was scanned with a DECT scanner capable of rapid operating voltage switching. In the VMS datasets, substantial reductions in the contrast were observed for iodine and barium, which suffered from contrast reduction of 97 and 91% respectively at 140 versus 40 keV. In comparison under the same conditions, the novel candidate agents demonstrated contrast enhancement reductions of only 20, 29 and 32% for tungsten, tantalum and bismuth respectively. At 140 versus 40 keV, metal artifact severity was reduced by 57-85% depending on the phantom configuration.